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National Center for Health Statistics, Hyattsville, MD 20782 and * National Cancer Institute, Bethesda, MD 20892
2To whom correspondence should be addressed. E-mail: Kflegal{at}cdc.gov.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONTHE EVOLUTION AND CURRENT...PARTICULAR ISSUES RELATED TO...MONITORING PROGRESSISSUES IN ASSESSMENTSTRATEGIES FOR IMPROVEMENTSUMMARY AND CONCLUSIONSREFERENCES |
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KEY WORDS: • body weight • dietary guidelines • health and nutrition surveys • obesity • overweight
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONTHE EVOLUTION AND CURRENT...PARTICULAR ISSUES RELATED TO...MONITORING PROGRESSISSUES IN ASSESSMENTSTRATEGIES FOR IMPROVEMENTSUMMARY AND CONCLUSIONSREFERENCES |
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. The apparent
simplicity of the weight guideline statements, in both this and
previous editions of the Dietary Guidelines
(2
3
4
5)
, masks the density and complexity of this
guideline. The topics covered in this single guideline include weight
standards, body composition and fat distribution, recommendations for
who should lose weight, recommended methods for weight loss, health
risks associated with weight, thinness, eating disorders, weight
maintenance and weight in childhood. Some of these topics remain
controversial. The content and emphasis of this guideline have changed
in a variety of ways over time. The purposes of this paper are to
describe the evolution and current status of the weight guideline in
the Dietary Guidelines, to present some issues related to
this guideline and to discuss methods of monitoring and evaluating
progress on this guideline. |
THE EVOLUTION AND CURRENT STATUS OF THE GUIDELINE STATEMENT |
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TOPABSTRACTINTRODUCTIONTHE EVOLUTION AND CURRENT...PARTICULAR ISSUES RELATED TO...MONITORING PROGRESSISSUES IN ASSESSMENTSTRATEGIES FOR IMPROVEMENTSUMMARY AND CONCLUSIONSREFERENCES |
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7
8
9)
, are advisory to the
Department of Agriculture and the Department of Health and Human
Services. Further changes, both editorial and substantive, may be made
before the final Dietary Guidelines are released jointly by
the two Departments. In this section, we describe the changes over time and the reasons given for major changes, when specified. Not all of the changes have been discussed in the reports of the Dietary Guidelines Advisory Committees; some changes may have been made in the governmental review process subsequent to the committee reports. Many of the changes in the weight guideline over time are changes in wording or emphasis, not changes resulting from new scientific knowledge per se.
The guideline statement has changed over time from "Maintain ideal weight" (in 1980) to "Maintain desirable weight" (in 1985) to "Maintain healthy weight" (in 1990) to "Balance the food you eat with physical activity—maintain or improve your weight" (in 1995) to "Aim for a healthy weight" in 2000. In the 2000 edition of the Dietary Guidelines, the weight guideline is now the first rather than the second guideline, as in earlier editions. Most of the material on physical activity included in previous weight guidelines has been moved to a new physical activity guideline ("Be physically active each day") that now follows the weight guideline.
Beyond the changes resulting from the new physical activity guideline, the 2000 weight guideline differs from previous versions in other respects. It uses different terminology and cut-off points than previous editions. Compared with previous guidelines, it appears to focus more on weight loss and less on weight maintenance and avoiding weight gain, dropping the word "maintain" from the title of the guideline for the first time. More dietary and behavioral advice related to weight loss is provided, recommendations for weight loss are more clinical, directive and specific, and some cautions related to weight loss in previous editions have been removed. These and other changes are described in more detail below.
Terminology.
Discussions of weight and overweight are plagued by minor but continuing variations in terminology and definitions. The ongoing confusion is reflected in the changes in the Dietary Guidelines over time. All versions present some kind of tabulation or graphic showing ranges of weights for each inch of height. These ranges are referred to as "ideal" weight (in 1980), also called "normal," "suggested" and "acceptable" weights; as "desirable" weights (in 1985); as "suggested" weights (in 1990); and as "healthy" weights (in 1995 and 2000). Before 1995, the term "overweight" was not used. The 1995 Dietary Guidelines introduced the terms, "moderate overweight" and "severe overweight." The 2000 Dietary Guidelines use the terms "healthy weight," "overweight" and "obesity."
Recommended weight ranges.
The proposed range of weights, variously referred to as ideal,
desirable, suggested or healthy, differs slightly in each edition of
the Dietary Guidelines. Examples are presented in
Table 1
of the recommended weight ranges for a man 5'9'' tall and for a woman
5'4'' tall. The differences are generally minor, although it is notable
that the lower end of the range [body mass index
(BMI)318.5) is lower in 2000 than in any previous edition, and the difference
for men is a fairly sizeable one.
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, which in turn were adapted from the 1959
Metropolitan Life Insurance Company (MLIC) table of "desirable"
weights for men and women 
25 y of age (11)
.
The 1985 weight ranges, in contrast, were taken directly from the 1959
MLIC table of desirable weights.
In contrast to preceding editions, the 1990 edition presented a table
of "suggested" weights for two age groups. This was a single table
for adult men and women combined, although a footnote indicated that
the higher weights in the range were more applicable for men, "who
tend to have more muscle and bone," and the lower for women, "who
have less muscle and bone." Also in contrast to preceding editions,
although these tables are presented as ranges of weight for specified
heights, they were actually constructed using a uniform range of values
of BMI. These BMI ranges were modified from those recommended in a 1989
report from the National Research Council (NRC), National Academy of
Sciences, (12)
. The upper end of the range in the
Dietary Guidelines is lower than the range in the NRC
report. The recommendations in the NRC report were based on data of
Andres (13)
and Waaler (14)
, which suggested
that the lowest mortality occurs at progressively increasing body
weight as age increases. The rationale for lowering the upper end of
the range states, "The BMI for the upper limit for the older group is
set at 27, the upper limit for acceptable weight in the Canadian
standards. The NRC report’s highest BMI of 29 was not used because of
age categories presented and of new research that indicates that men
may be less able than women to gain weight as they grow older without
risk to health" (7)
. No reference was cited for the new
research described, however.
The 1995 guidelines included a chart of "healthy" weights for
heights for men and women combined that was based on the BMI range from
19 through 25. The upper bound was based on several considerations. The
committee noted that although the prevalence of diabetes appeared to
increase well below a BMI of 25, mortality increased significantly
above a BMI of 25 (9)
. The committee was reluctant to use
a cut-off point below 25 because that would label well over half of
the population obese. Thus they felt that a BMI of 25 was the most
reasonable definition. In addition, levels of moderate and severe
overweight were shown in a shaded figure in which severe overweight was
defined as a BMI 
28–29 or greater; [according to the committee
report (9)
, an exact BMI value was deliberately not
indicated because there was no consensus on a precise threshold]. The
lower bound of 19 is described as the 15th percentile, but further
information is not provided on the selection of the lower bound. This
committee also stated that there was lack of a clear cut-off point
or consensus to distinguish categories of weight associated with risk
for morbidity or mortality. The committee felt that weight standards
should be age-neutral, stating that several large published studies
failed to show an increase with age in the BMI associated with the
lowest mortality. Curiously, one of the three references cited for this
statement is the same reference (14)
used in the original
NRC report to justify standards that increased with age.
In the 2000 guidelines, BMI values were chosen to be consistent with
the recommendations of the 1997 WHO Consultation on Obesity
(15)
and the 1998 National Heart, Lung, and Blood
Institute (NHLBI) Clinical Guidelines for the Treatment of Overweight
and Obesity (16)
. The 1997 WHO Consultation on Obesity
(15)
recommended terminology and definitions as follows:
"The Consultation noted that a coherent system for classifying
overweight and obesity in adults is now available and should be adopted
internationally. This is based on the Body Mass Index
(BMI) ... with BMI 25 denoting ‘overweight’ and BMI
30 denoting ‘obesity.’" The WHO consultation also
classified BMI values lower than 18.5 as "underweight." In the
Dietary Guidelines, the healthy weight range has been
modified slightly at the lower end to encompass a range of BMI values
from 18.5 up to but not including 25. However, the term underweight is
not used to categorize BMI values < 18.5. Obesity is defined as a
BMI 30. Overweight is defined as a BMI of "25 up to 30,"
but the guideline notes that obese people are also overweight. Thus,
this could be considered consistent with the definition of overweight
as a BMI 25 put forward by the WHO consultation. The
terminology and definitions in the Dietary Guidelines are
also consistent with those used for the Healthy People 2010 objectives
discussed below (17)
.
What is a healthy weight?
In 1980 and 1985, the guideline begins "If you are too fat ... " However it goes on to state that there is no absolute answer to what the ideal weight is for you. The range of weights for heights was described as an "acceptable" range for most adults and the term "healthy weight" was not used.
In 1990, the concept of "healthy weight" was introduced. This concept combined weight, body composition, fat distribution and weight-related medical conditions. The 1990 guideline states that whether your weight is healthy depends on how much of your weight is fat, where in your body the fat is located, and whether you have weight-related medical problems or a family history of such problems. The specific weight ranges in the tables are described as "suggested" weights, not as "healthy" weights. The higher ranges in the tables, which for the first time are not gender specific, are described as suggested for men, and the lower as suggested for women. Body shape is mentioned and excess fat in the abdomen is described as being of possibly greater health risk than fat in the hips and thighs. Directions are given for measuring your waist and hip circumferences and calculating the waist-to-hip ratio.
Although the 1995 guideline uses the term healthy weight, it does not use the definition of healthy weight put forth in the 1990 guideline. In 1995 the term "healthy weight" simply refers to the weight ranges shown in the figure, without regard to the factors of body composition, fat distribution and medical history used to define healthy weight in 1990. However the text mentions risks associated with excess abdominal fat and recommends that readers compare their waist measurements with measurements of their hips or buttocks "to see if your abdomen is larger."
In 2000, the range is also labeled as "healthy weight." However, the text points out that this is not exact and notes, somewhat confusingly, that weights above or below the healthy weight range may actually be healthy and that weights inside the healthy weight range may not be healthy. These comments implicitly associate body composition with healthy weight: "Not all adults who have a BMI in the range labeled ‘healthy’ are at their most healthy weight ... some may have lots of fat and little muscle"; "a BMI above the healthy range is less healthy for most people but it may be fine if you have lots of muscle and little fat"; "BMIs slightly below the healthy range may still be healthy unless they result from illness." The 2000 guidelines also recommended that readers measure their waist circumferences and advised that waist measurements > 35 inches for women or 40 inches for men are associated with increased health risks. The guidance on waist measurements in the 2000 guidelines did not include a range or any adjustment for body size.
Who should and shouldn’t lose weight?
The 1980 and 1985 guidelines both recommend that adults maintain "ideal" or "desirable" weight; however, no explicit recommendations are made regarding weight loss decisions. In 1990, the guideline was somewhat more specific but took a conservative approach, suggesting consultation with your doctor: "If your weight is within the range in the table, if your waist-to-hip ratio does not place you at risk, and if you have no medical problem for which your doctor advises you to gain or lose weight, there appears to be no health advantage to changing your weight. If you do not meet all these conditions, or if you are not sure, you may want to talk to your doctor about how your weight might affect your health and what you should do about it."
In 1995, the guideline was somewhat more directive than in 1990, although it still recommended consulting a health care provider, stating that "If you are overweight and have one of these problems [high blood pressure, heart disease, stroke, diabetes, certain types of cancer, arthritis, breathing problems] you should try to lose weight. If you are uncertain about your risk of developing a problem associated with overweight, you should consult a health professional." This edition also instructed people that they did not need to lose weight "if your weight is already within the healthy range ..., if you have gained < 10 pounds since you reached your adult height, and if you are otherwise healthy." However, "If you are overweight and have excess abdominal fat, a weight-related medical problem, or a family history of such problems, you need to lose weight." Specific advice was not given for people who did not fall into either of these two categories (e.g., a person whose weight is within the healthy range but who has gained 10 pounds in adulthood).
Unlike the 1990 and 1995 editions, the 2000 edition does not describe explicitly a category of people who probably do not need to lose weight. The "Advice for Today" in the 2000 edition is more directive about weight loss than were previous editions, stating that people who are overweight should "lose weight to improve your health." The text is less definite elsewhere, stating that if your BMI is above the healthy range you "may" benefit from weight loss, that "like younger adults, overweight and obese older adults may improve their health by losing weight," and that "if you are overweight, loss of 5 to 15% of your body weight may improve your health ..." In the 2000 edition, readers are provided for the first time with a box entitled "Find out your other risk factors for chronic disease." Readers are advised that "the more of these risk factors you have, the more you are likely to benefit from weight loss if you are overweight or obese." The list of chronic disease risk factors includes factors that are often, but not always, affected by weight, such as high blood pressure, abnormal lipids and diabetes; factors that are not affected by weight, such as age and smoking; and factors that may or may not be affected by weight such as a sedentary lifestyle and a personal or family history of heart disease. Consulting with a health care provider for weight loss guidance is recommended, especially for obese children and for older adults.
How to lose weight.
In 1980 the guidelines advised readers that to lose weight, they must either select foods containing fewer calories or increase activity or both. A gradual increase of everyday physical activities was recommended as helpful. Readers were advised to lose weight gradually, and a steady loss of 1–2 lb/wk was described as relatively safe. Readers were advised to eat less fat and fatty foods, less sugar and sweets and to avoid too much alcohol. Some cautions about weight loss were expressed: do not try to lose weight too rapidly; avoid crash diets that are restricted in food variety; diets containing < 800 kcal may be hazardous; do not attempt to reduce your weight below the acceptable range; if you lose weight suddenly or for unknown reasons, see a physician.
In 1985, dietary recommendations for weight loss became more specific, also including advice to eat a variety of foods low in calories and high in nutrients and to eat more fruits, vegetables and whole grains. Additional cautions were included against trying to lose weight by vomiting or using laxatives, and readers were advised to avoid other extreme means of losing weight.
In 1990, several changes were made. Readers were advised that
long-term success in weight loss usually depends upon new and
better lifelong habits of both exercise and eating. Weight loss was
recommended at the somewhat lower rate of 0.5–1 lb/wk. A statement was
added about the difficulty of sustaining a nutritious diet at energy
levels 
1200 kcal. Dietary advice became yet more specific, with
readers being advised to eat more fruits, vegetables, and breads and
cereals "without fats and sugars added in preparation and at the
table." Readers were also advised to drink little or no alcoholic
beverages, to eat smaller portions and to limit second helpings.
Additional cautions about extreme methods of weight loss were added,
including cautions against using certain drugs such as laxatives,
amphetamines and diuretics. Concerns about extreme dieting among
adolescents were also noted. The "Advice for today" was "Check to
see if you are at a healthy weight. If not, set reasonable weight goals
and try for long-term success through better habits of eating and
exercise."
In 1995, the statement was added that weight losses of 5–10% of body weight may improve many of the problems associated with overweight, such as high blood pressure and diabetes. Dietary advice for weight loss was similar to that in previous editions although slightly more detailed. The explicit statement about not trying to reduce your weight below the range was not included, but expressed as advice that readers should take steps to keep weight within the healthy range (neither too high nor too low). The "Advice for today" states that "If your weight is not in the healthy range, try to reduce health risks through better eating and exercise habits."
In the 2000 edition, readers are advised that if they are overweight,
loss of 5–15% of body weight may improve function and health. Readers
are advised that weight loss should be gradual and that they should aim
to lose 10% of body weight over 6 mo, with loss of 0.5–2 lb/wk
usually being safe. Dietary advice is more detailed and specific and
includes several new concepts. For instance, readers are advised that
low fat foods are not necessarily low calorie and may sometimes be very
high in calories because of extra sugars. Readers are advised about
selecting snacks and meals eaten away from home, to ask for small
portions of foods when eating out and to request that fish, poultry or
lean meat be grilled rather than fried. More detailed portion size
information is provided. Readers are referred to the guideline "Let
the Pyramid guide your food choices" for sizes and numbers of
servings. Readers are also advised that "to maintain a healthy weight
after weight loss, adults will likely need to do > 30 min of
moderate physical activity daily."
The 2000 advisory committee recommended emphasizing low
energy-density foods as a means to weight control and included an
extensive discussion of the scientific literature to support this
position (8)
. The final version of the guideline, however,
does not emphasize low energy-density foods per se, recommending
that readers choose a healthful assortment of foods that includes
vegetables, fruits and grains, but also skim milk and fish, lean meat,
poultry or beans.
The text of the 2000 edition no longer contains cautions about crash
diets and extremely low calorie diets, nor cautions about not reducing
below the "healthy weight" range, avoiding extreme methods of
weight loss or avoiding the use of certain drugs. However, the 2000
edition includes for the first time a statement that weight loss is not
advisable for pregnant women. The evolving cautions about weight loss
are summarized in Table 2
. In the 2000 edition, the "Advice for today" states that "If you
are already overweight ... lose weight to improve your health"
but does not specify, as did the "Advice for today" in previous
editions, to do this through better exercise and eating habits.
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Some previous Dietary Guideline editions expressed concern about thinness or underweight as a health risk factor. In 1980 and 1985, there were no comments about weights below the range of weights provided. In 1990 additional comments about being "too thin" were made, including a link of thinness with osteoporosis in women and with greater risk of early death for both men and women. In 1995, these comments were expanded into a paragraph headed "Problems with excessive thinness," which also discussed excessive concern about weight. In 2000, the comment regarding weights below the range of weights states only that "BMIs slightly below the healthy range may still be healthy unless they result from illness." Several possible health risks that might result from thinness, including menstrual irregularity, infertility and osteoporosis, are mentioned. A paragraph about eating disorders was added.
Weight maintenance—avoiding weight gain.
The 1980 and 1985 guidelines recommend that readers maintain ideal
weight but the only specific recommendation on avoiding weight gain is
the comment that adults should not weigh much more than when they were
younger, i.e., 25 y old. In 1990, some weight gain with age is, if
not explicitly recommended, at least condoned because the weight ranges
are higher for people >34 y of age and the comment is made that
"recent research suggests that people can be a little heavier as they
grow older without added risk to health."
In the 1980, 1985 and 1990 editions, the advice to maintain weight was
targeted to people already within the range of recommended weights.
However, the 1995 committee suggested some substantive changes in the
weight guidelines to also encourage people who were already overweight
not to gain further weight (9)
. That committee placed less
emphasis on weight loss and more on weight maintenance. The stated
rationale was that the goal of achieving a healthy weight (that is, a
weight in the suggested range) might be impossible for the large
numbers of overweight persons in the U.S. According to the committee,
"Maintenance of a healthy weight is still a major goal but is now
secondary to weight maintenance at any level."
The 2000 committee noted that there was general agreement about the
health risks of obesity but less agreement about the management of
obesity, particularly concerning whether the emphasis should be on
weight maintenance or weight loss (8)
. To some extent, the
2000 committee reversed the focus of the 1995 committee on preventing
weight gain among overweight people and returned to encouraging weight
loss. The rationale given for this was that weight cycling had not been
shown to be harmful, even though this was not the issue that had
concerned the 1995 committee. In the 2000 guideline, although there is
more emphasis on weight loss, adults are also encouraged to avoid
weight gain. The introduction to the 2000 guideline states: "To be at
their best, adults need to avoid gaining weight, and many need to lose
weight." Readers are told that if either their weight or their waist
measurement increases, they should at least try to avoid further weight
gain even if their BMI is in the "healthy" range. In the 1995
edition, the first section heading was "How to maintain your
weight"; in the 2000 edition, the first section heading is
"Evaluate your weight," followed by a section on "Manage your
weight," which discusses ways to maintain or lose weight by making
long-term changes in physical activity and eating behavior.
Children.
In the 1980 and 1985 guidelines, there was no guidance related to children’s weights. The 1990 edition included a brief paragraph on children, stating that weight-reducing diets are usually not recommended for children and that overweight children may need help in choosing enjoyable physical activities and nutritious diets with adequate but not excessive calories. In addition, readers were advised to have children’s heights and weights checked regularly by a doctor.
More guidance related to children was provided in the 1995 edition. Detailed suggestions were provided about teaching children to eat specific foods, such as grains, fruits, vegetables and low fat or lean calcium-rich and protein-rich foods, to participate in vigorous activity and to limit television time. Even though the Dietary Guidelines are directed to persons >2 y of age, it was noted that fat intake should not be restricted for children <2 y of age. It was stated that although modest restrictions in dietary fat were not hazardous, major efforts to change a child’s diet should be accompanied by regular monitoring of the child’s growth by a health professional.
Similar advice about weight loss was provided in 2000. "Since children still need to grow, weight loss is not recommended unless guided by a health care professional." However, the 1995 statement about the need for caution when helping overweight children reduce weight while growing normally was removed, as was the proscription on fat restriction for children <2 y of age. Perhaps reflecting concern about the recent increase in overweight prevalence among youth noted in the report, guidance about weight in children was slightly modified and further expanded. The 1995 edition focused on teaching children what to eat and how to be active, whereas the 2000 guideline includes more direct advice to encourage these healthy behaviors by example and by the foods offered. "Set a good example for children by practicing healthy eating habits and enjoying regular physical activities together." Readers are advised to let children decide how much food to eat, but limiting foods high in fat or added sugars is suggested. Small changes are recommended to help children develop healthy eating habits.
Like previous editions, the 2000 guideline does not specify weight standards for children. Readers are advised to talk to their health care provider if they have concerns about their child’s body size. The text recommends the guidance of a health care provider "especially for obese children" but does not define obesity in children.
The elderly.
The 1980 and 1985 guidelines both comment that adults should not weigh
much more than when they were younger, i.e., 25 y old. The first
specific statements regarding older people appeared in the 1995
guideline, which stated that weight maintenance was important for older
people who begin to lose weight as they age. The guideline went on to
say that some of this weight loss was muscle and that regular activity
to maintain muscle was advisable. This edition also advised that the
health risks due to overweight appear to be the same for older as for
younger adults.
In 2000, age (>45 y of age for men or postmenopausal age for women) is listed as one of the health risk factors that indicates you are more likely to benefit from weight loss. The text states "The more of these risk factors you have, the more you are likely to benefit from weight loss if you are overweight or obese." Interpreted literally, this states that an older person (>45 y for men or postmenopausal women) is more likely to benefit from weight loss than an otherwise identical younger person. The guideline also states that "like younger adults, overweight and obese older adults can improve their health by losing weight" and recommends the guidance of a health care provider "especially" for older adults, although older is not specifically defined.
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PARTICULAR ISSUES RELATED TO THIS GUIDELINE |
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The NHLBI convened a large panel of experts to carry out a
systematic review of published scientific evidence and produce
evidence-based guidelines for clinicians on the treatment of
overweight and obesity that were published in 1998 (16)
.
The report of the Scientific Advisory Committee for the 2000
Dietary Guidelines comments that their recommendations are
"consistent with" the NHLBI report. (8)
. The
recommendations for weight loss in the 2000 Dietary
Guidelines appear to go beyond the NHLBI expert panel’s clinical
recommendation. The reasons for doing so, however, are not discussed in
the Scientific Rationale in the Dietary Guidelines Advisory Committee
document.
The principal difference lies in the recommendations for people who are
overweight (BMI 25–29.9). Since 1960, the weight range defining
overweight has included a high proportion of the U.S. population,
almost 40% of adult men and almost 25% of adult women, as indicated
in Table 4
(18)
. Therefore, recommendations for
people in this weight range apply to a large proportion of the
population. According to the NHLBI guidelines, "treatment of
overweight [BMI 25 to 29.9] is recommended only when patients have
two or more risk factors or a high waist circumference." The 2000
Dietary Guidelines, however, imply that weight loss is
recommended for everyone with a BMI in the overweight (25–29.9) range,
even those with one or no risk factors.
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. There are some differences between the two lists. The NHLBI report
mentions a family history of "premature" heart disease, whereas the
Dietary Guidelines mention only a family history of heart
disease, without the word "premature." The NHLBI report specifies
type 2 diabetes, whereas the Dietary Guidelines mention only
diabetes, without reference to type. Some conditions are included in
the NHLBI clinical guidelines that are not included in the
Dietary Guidelines list, including other atherosclerotic
conditions, sleep apnea and impaired fasting glucose.
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The Dietary Guidelines abstract this clinical guidance in a somewhat oversimplified form. The effect is that the weight guidance in the Dietary Guidelines, which is intended as advice for the general public, includes clinical recommendations on health and medical treatments. The general public is presented with a truncated list of risk factors designed for clinical decision making. The only use of the risk factors in the Dietary Guidelines is to indicate the need for weight loss; the message from the NHLBI guidelines that these factors also indicate the need for treatment and "deserve the same emphasis as weight loss therapy" is lost. Some conditions that would lead to a weight loss recommendation, however, are not listed in the Dietary Guidelines.
The list of health risk factors differs, but the recommendations also differ. According to the NHLBI report, BMI category alone should not be considered diagnostic. Additional risk factors should be assessed, including the presence of abdominal obesity, based on a measure of waist circumference, and the presence of concomitant risk factors or comorbidities such as hypercholesterolemia or diabetes. For some persons, especially those with BMI values of 25.0–29.9 in the overweight but not obese category who do not have two or more risk factors or a high waist circumference, the NHLBI Clinical Guidelines suggest weight maintenance as a more appropriate clinical goal than weight loss. In addition, a person with other risk factors should be treated for those risk factors, not just for overweight and obesity. For example, overweight smokers should be advised to quit smoking, not just to lose weight. Similarly, the recommendation for sedentary behavior should be to engage in physical activity, not simply to lose weight.
The health risk factors tabulated in the Dietary Guidelines are presented as reinforcing the recommendations for weight loss, stating that "the more of these risk factors you have, the more you are likely to benefit from weight loss if you are overweight or obese." The listed risk factors are indeed risk factors for chronic disease. However, it is not completely clear why weight loss is considered more beneficial for someone with more of these risk factors than for someone with fewer risk factors. For example, smoking is listed as a risk factor. The formulation in the Dietary Guidelines thus implies that an overweight smoker will benefit more from weight loss than an otherwise identical overweight nonsmoker because the smoker has one more risk factor than the nonsmoker. Age is also listed as a risk factor. This similarly implies that an overweight man >45 y old will benefit more from weight loss than will an otherwise identical man <45 y old because the older man has one more risk factor than the younger man. Thus, these recommendations imply that, all else being equal, weight loss will benefit smokers more than nonsmokers and older people more than younger people. The scientific basis for this differentiation in benefit from weight loss is not obvious in either the Dietary Guidelines or the Advisory Committee Reports. The NHLBI Clinical Guidelines do not make such assertions.
Behavior or condition?
The weight guideline is unique among the dietary guidelines in that its outcome is not so much a behavior as a condition. Other guidelines exhort the reader to make particular choices or otherwise engage in specified behaviors, without specifying additional outcomes. For example, the 8th guideline encourages the reader to "choose a diet that is low in saturated fat and cholesterol and moderate in total fat." Although the text links these choices to blood cholesterol levels, the reader is not being told to aim to achieve a normal blood cholesterol level, but rather to make particular dietary choices. However, in the weight guideline, the reader is being told to aim to achieve a "healthy" weight, not to make particular dietary choices.
The cholesterol analogy illustrates some possible difficulties that this difference raises. If the goal were to achieve a normal blood cholesterol level, this might require medical intervention and pharmacologic treatment rather than or in addition to choosing a diet low in saturated fat and cholesterol. On the other hand, some people may have low blood cholesterol levels even though their diets are not low in saturated fat and cholesterol. Thus, using blood cholesterol level as the outcome would directly or indirectly raise issues such as medical treatment and genetic predispositions that go beyond dietary behaviors and thus might be outside the scope of the Dietary Guidelines.
In the weight guideline, the goal is not to engage in a specified dietary behavior but rather to reach, maintain or at least aim for a specified condition, namely, a particular body weight. In principle, this could be accomplished through sensible dietary intake and physical activity as described in the guideline. However, individuals might choose less healthy ways to reach or maintain a weight in the healthy range; these include excessively restrictive diets, smoking initiation or continuation, vomiting or inappropriate use of some drugs. More intensive medical interventions that are not themselves without risk, such as surgery, adjunct pharmacologic treatment or a medically supervised very low calorie diet, might be required to accomplish this goal.
The guideline itself does not mention or recommend such approaches to weight loss or maintenance. However, the stress on weight itself as the key outcome, rather than on encouraging specific healthful dietary behaviors, does implicitly raise the question of the value and the role of other means to accomplish weight loss and maintenance. If the goal is to reach, or at least aim for, a healthy weight, as defined by the Guidelines, how important is the means used to accomplish that goal? What means might readers feel were justified? What is the role of currently available or future pharmacologic treatments in reaching the goal? This is particularly relevant because the majority of the U.S. adult population weighs more than the healthy weight range in the guideline. In the 1990 and 1995 guidelines, the "Advice for today" was explicit that weight loss should be accomplished "through better eating and exercise habits." Although the 2000 guideline describes behavioral approaches related to diet and physical activity, the "Advice for today" does not include the explicit statement that weight loss should be accomplished through diet and exercise.
"Medicalization"
In the past, a number of the other Dietary Guidelines have included specific medical criteria. For example, in the 1990 guidelines, readers were advised to "Have your blood cholesterol level checked, preferably by a doctor. If it is high follow the doctor’s advice about diet and, if necessary, medication." And also "Have your blood pressure checked. If it is high, consult a doctor about diet and medication." The 1990 guidelines also included specific desirable levels of blood cholesterol and of blood pressure.
However, following the recommendations of the 1995 advisory committee
(9)
, such references to medical criteria and to
medications were not included in the 1995 edition of the Dietary
Guidelines. In terms of general issues, the 1995 committee suggested
"that the text of the Guidelines relate specifically to dietary
issues and omit specific guidelines for such medical advice as
desirable levels of blood cholesterol, blood pressure and blood
glucose." When discussing the guidelines on fat and cholesterol
intake, the committee stated that "The guideline is not intended to
deal with individual heart disease risk, which includes many other
factors. The document does not now deal with those factors (such as
family history of premature cardiovascular disease, low HDL
cholesterol, hypertension, tobacco use and diabetes) because to do so
would diffuse the message about diet and tend to ’medicalize’ the
guideline." Similarly, regarding the guideline on salt and sodium
intake, the committee stated "A key objective of this revision is to
shift the tenor of this guideline toward dietary advice and away from
primary focus on hypertension."
The other guidelines have become less "medicalized" than earlier
ones, but the weight guideline has become somewhat more so. The 2000
weight guideline includes a list of risk factors for chronic disease
that are not necessarily related to diet, including age, smoking,
hypertension and diabetes. Readers in the "overweight" category are
encouraged to lose weight even though the NHLBI clinical guidelines
recommend weight maintenance as a goal for this category in the absence
of other risk factors. Previous editions of the Dietary
Guidelines simply referred readers to a health care provider for
any discussions on the need to lose weight. The 2000 committee noted
that there was general agreement about the health risks of obesity but
"less agreement about the management of obesity" (8)
.
The issue of appropriate management of obesity goes beyond dietary
advice to the public.
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.
Data from these surveys are shown in Table 4
. The prevalence of BMI values 25 among adults has been high at least
since 1960, when >43% of the population exceeded this threshold. The
prevalence of overweight, defined as a BMI of 25.0–29.9, has been
almost constant from 1960 to 1994, varying by 1–2% in either
direction. However, the prevalence of obesity, defined as a BMI 30, increased by 8% between 1980 and 1991.
Healthy People 2010 included two objectives related to adult weight
status under the heading of Weight Status and Growth (17)
.
These objectives use the same healthy weight range and definition of
obesity as those in the Dietary Guidelines. For these and
many other Healthy People 2010 objectives, target setting was done by
looking at the prevalence of the condition in subgroups defined by
factors such as gender, age, race-ethnicity, income or health
conditions (17)
. The target was selected to be equal or
greater than the prevalence of the outcome in the "best" group. For
the weight objectives, the "best" group in both cases was the
youngest group. One objective was to increase the prevalence of healthy
weight (BMI 18.5 and <25.0) to 60% [Objective 19.1]; the
highest prevalence of healthy weight (55%) was among women ages 20–39
y (48% for men of the same age). The second adult weight objective was
to decrease the prevalence of adults categorized as obese (BMI 30.0) to 15% [Objective 19.2]; the lowest prevalence of obesity
(15%) was among men ages 20–39 y. No specific objective was proposed
for adults categorized as overweight but not obese (BMI 25.0
and <30.0), but prevalence in this BMI category would be affected by
those moving into and out of the bordering categories. These objectives
could be viewed as indirectly calling for no increases in weight with
age, more than calling for weight loss. The youngest group has nearly
achieved the desired objective; thus, if there were no further weight
gain with age, considerable progress toward the objective would be
achieved without weight loss. Research among older men suggests that
high levels of physical activity prevent age-related increases in
total body fat and waist circumference (19
,20)
. However,
the more common pattern in the population is for physical activity to
decline with age (21)
.
NHANES data provide prevalence estimates for subpopulations defined by
gender, age, race and ethnicity, family income, disability status and
selected disease conditions (17)
. However, state- or
local-level data cannot generally be obtained from NHANES. The
Behavioral Risk Factor Surveillance System provides state-level
data on weight status, but the basis is self-reported, rather than
measured height and weight. Self-reports of height and weight, and
thus the derived BMI, are subject to both random and systematic error
that decrease their utility for monitoring (22)
.
Good data exist for monitoring weight status in the United States, but the healthy weight Dietary Guideline is not limited to weight status classification. The weight guideline also contains advice about waist circumference and weight change. Although not included in any Healthy People 2010 objectives, NHANES III and the current NHANES include standardized measurement of waist circumferences. However, weight change is more difficult to track, and deciding whether the weight change recommendations were being followed would be difficult. For instance, avoidance of weight gain in adult life is encouraged, even within the healthy weight range. In addition, if one is already overweight, weight loss of 10–15% is recommended. This loss, if achieved, may still not put an individual within the healthy weight range, although the person had complied with the recommendations. Longitudinally measured data or detailed valid retrospective reports of past weight history would be required to assess the weight change–related recommendation; such data are not presently available at the national level and currently there are no plans to collect such data in the future.
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The other dietary guidelines address behaviors that can be monitored with varying degrees of success, whereas the weight guideline focuses on an outcome that results from the relationships among a complex set of factors. Unlike other guidelines, which focus on behaviors such as food choices, the weight guideline introduces the concept of healthy weight, not as an adjunct but as the goal of the guideline itself.
If healthy weight is simply a weight corresponding to the height-weight tables, then it is easily assessed. However, the concept of healthy weight is used in a variety of ways, with meanings less clearly defined, throughout the weight guideline. The assessment then becomes a more complex issue. As noted above, the concept of healthy weight includes elements of body composition and other health outcomes. This introduces the issue of how a healthy weight should be defined or assessed.
Body composition rather than weight?
As noted in Healthy People 2010, "Simple, health-oriented
definitions of overweight and obesity should be based on the amount of
excess body fat at which health risks to individuals begin to increase.
No such definitions currently exist" (17)
. Weight status
as measured by BMI is often considered an easily measured proxy for
adiposity, which is probably metabolically more closely related to
health risk than weight. Waist circumference is used as an adjunct to
weight status to address one shortfall of BMI, the lack of information
about body fat distribution, which is a predictor of health risk
independent of BMI (23
,24)
.
Measures of adiposity and its complement, muscularity, might provide
indicators of health risk more closely related to the metabolic
derangements associated with overweight and obesity. Until recently,
such measures were not available for use in large epidemiologic surveys
and the criteria based on these measures still do not exist. However,
progress is being made. The current NHANES includes measurements of
body composition by dual X-ray absorptiometry (DXA) and by
bioelectrical impedance analysis (BIA) (25
,26)
. DXA
provides estimates of bone content, fat-free mass, fat mass, and by
calculation, the percentage of body fat. Inclusion of DXA in NHANES
will provide population reference data for these body composition
measures. DXA is being used in increasing numbers of research studies,
which will increase knowledge of the relationships between body
composition and health outcomes. BIA also provides a measure of lean
body mass, as well as fat mass and the percentage of body fat by
calculation that is based on the intracellular and extracellular fluid
content of the person being measured. Although not as direct a measure
of body composition as DXA, BIA instruments are less expensive and more
portable. If BIA can be calibrated successfully with more direct
measures of body composition, it may provide a useful adjunct
measurement of body composition.
The proportion of body weight that is muscle has been theorized to be both an important indicator of the health risk of overweight and obesity and potentially a predictor of the maintenance of a healthy weight. However, little attention has been paid to developing discrete measures of muscularity, or its lack, for surveillance of body composition. The focus of research efforts has been on developing measures of fat mass or adiposity.
Additional health outcomes as well as weight?
Laboratory measures of disease risk, such as serum cholesterol as a
risk factor for coronary heart disease, are often an accurate,
efficient and inexpensive way to screen for a condition at a population
level. At present, there are no comparable standardized or accurate
blood measures of adiposity or body composition. Levels of leptin, a
hormone that plays an important role in energy homeostasis and the
regulation of food intake, rise when fat stores are high, and this rise
in leptin may influence food intake. In the future, leptin might play a
role in public health monitoring of adiposity (27)
.
As noted in the Dietary Guidelines, the health consequences
of overweight and obesity are related in part to associated adverse
health conditions such as diabetes, coronary heart disease and
hypertension. Screening for risk of several of these diseases is done
with laboratory measures such as fasting blood glucose for diabetes
mellitus and serum cholesterol levels for coronary heart disease. Such
screening might provide additional definition of whether an individual
is at a healthy weight. The prevalences of some conditions associated
with obesity such as hypertension and hypercholesterolemia appear to
have decreased over time in both the overweight and nonoverweight
populations (28
,29)
. Additional research on the
comorbidities associated with overweight and obesity and on trends in
those comorbidities among overweight and obese subgroups of the
population can also help to refine the concept of healthy weight.
Limitations of these approaches. Although a more sophisticated and precise definition of healthy weight for a given individual is an important research goal to achieve, this goes beyond the original purpose of the Dietary Guidelines of providing dietary advice to the general public and setting federal nutrition policy, for example, for federal food service programs. For the Dietary Guidelines, the reader should be provided with advice that can be readily understood and that does not require access to sophisticated clinical measures of body composition and health status.
If the reader is to aim at a healthy weight, the guidelines should make the target clear to the reader. It is relatively simple for the reader to check weight in relation to height using the figure provided in the guidelines. But clearly the concept of healthy weight as presented in the guidelines in some way encompasses the issues of body composition, fat distribution and weight-related health conditions, and goes beyond simple measurements of height and weight. Other more sophisticated measures, such as DXA to estimate body composition and blood samples for assessing health conditions such as hypercholesterolemia or glucose tolerance have been incorporated into national surveillance and can be evaluated in physicians’ offices. However, these elements of evaluating whether weight for an individual is healthy cannot be readily accomplished by the lay public and extend the concept of a healthy weight guideline beyond the original intent of the Dietary Guidelines of providing dietary guidance to the public.
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,30)
. Progress is being made on
the biomedical measures related to weight status, but there is also a
need for better understanding and monitoring of the determinants of
overweight and obesity. Obesity prevalence varies considerably across
groups described by gender, race and ethnicity and socioeconomic status
(17)
.
On an individual level, behavioral changes related to reducing dietary
intake and increasing physical activity are necessary to control
weight. In a broader societal context, the United States and other
developed countries today seem to provide what has been called a
"toxic environment" (31)
in which it is difficult to
control weight. Overweight and obesity appear to be highly prevalent
and increasing conditions not only in the U.S. but in many other parts
of the world. The causes of these increases are not clear. However,
major factors presumably include a decrease in activity required in our
increasingly industrialized societies and a change in eating habits
that appears to be detrimental to weight control. Little research has
been done on the prevention of obesity, which appears to be a
formidable task requiring some innovative public health strategies
(32
,33)
. When attempts have been made, interventions at
the community or workforce level have not prevented increases
(34)
.
The question concerning the nature of the risk factors leading to
obesity may be restated as the more general question: what factors
determine body weight and body composition in the absence of major
environmental constraints? These factors are complex, and many aspects
are not well understood (35
,36)
. From the point of view of
energy balance, the initial development of overweight is due to energy
intake that exceeds energy expenditure. However, the interrelationships
among energy expenditure, adipose tissue and energy intake suggest some
degree of physiologic regulation of body weight or body fat content
(35)
. Recent advances, such as the identification of
leptin, the product of the ob gene, may lead to a better
understanding of these interrelationships (27)
.
The ready availability of food, coupled with technological advances that require relatively little physical activity, appears to make it difficult to constrain weights to lower levels. A public health challenge is to find ways in which the environment can be modified to encourage weight maintenance and weight control. Another public health challenge is to find ways to maintain and improve health in an environment conducive to higher weights and higher levels of overweight and obesity. The social costs of obesity are high, and the social costs of attempts to prevent or to treat obesity are high as well. The prevalence of overweight and obesity is increasing in many parts of the world and may continue to increase in the future. The health risks associated with these increases and the risks and benefits of prevention and treatment strategies, including long-term use of pharmacologic treatment, must be evaluated objectively.
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. Although the terminology has changed over time, the general concept of providing a range of recommended, suggested or healthy weights has been constant over all editions of the Dietary Guidelines. The range of weights itself has also changed very little over time, defining healthy weights generally as those below a BMI of 25. The recommended range of healthy weights in the Dietary Guidelines is such that more than half of the adult population is above that range today. In fact, close to half or more of the adult population, in particular half of adult males, has been above that range at least since 1960.
Although the weight standards recommended by the Dietary Guidelines have changed little over time, the guidance regarding weight loss has become more complex and directive, introducing elements of clinical decision making into the most recent guideline. The current guideline’s weight loss recommendations to the general public for the category of BMI 25–29.9 are stronger than the recommendations of the NHLBI expert committee’s guidelines for clinicians. Many cautions relating to weight loss have been removed. Thus, the most recent edition appears to emphasize weight loss more strongly than previous editions. Even the evolving title of the guideline over time suggests the change in emphasis. All previous editions from 1980 through 1995 included the word "maintain" in the title, but the 2000 guideline does not.
It may be difficult for the public or even for health care providers to understand or interpret some statements in the Dietary Guidelines. For example, the statement is made that some people within the healthy weight range may not be at their most healthy weight, but further comments or recommendations are not provided. A sophisticated list of risk factors for chronic disease is offered with relatively little guidance. The extent to which the public understands the current, somewhat complex, clinical decision-making recommendations within the Dietary Guidelines should be evaluated with targeted research on how the public interprets this guidance. Such research may help to refine further the type and detail of guidance on weight that should be included in future Dietary Guidelines.
The weight guideline has become more medically oriented over time, now including lists of other health risk factors for chronic disease and making more detailed and sweeping weight loss recommendations. In contrast, other guidelines have moved away from inclusion of specific medical issues over time. Issues related to the appropriate management of weight for an individual can be complex and may require a health care provider as a resource for interpretation. Rather than try to incorporate further clinical decision-making and weight loss guidance within the weight guideline, it may be more appropriate on this issue to refer the reader to a health care provider for guidance, as was done in previous editions.
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FOOTNOTES |
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3 Abbreviations used: BIA, bioelectrical impedance
analysis; BMI, body mass index; DXA, dual X-ray absorptiometry;
MLIC, Metropolitan Life Insurance Company; NHANES, National Health and
Nutrition Examination Surveys; NHLBI, National Heart, Lung, and Blood
Institute; NRC, National Research Council.
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REFERENCES |
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