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Amgen, Incorporated, Thousand Oaks, CA 91320-1799
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
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KEY WORDS: • fiber • food intake • satiety • obesity • viscosity • cholecystokinin
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
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, Pi-Sunyer 1993
).
Consequently, research efforts have focused on identifying the key
factors contributing to the development of obesity with the goal of
devising reasonable strategies that will successfully prevent further
weight gain and perhaps induce weight loss.
Among the many areas in obesity research, one area has focused on the
possible ways in which the composition of the diet may affect food
intake regulation and energy balance. Numerous studies have examined
the role of dietary fat, protein and carbohydrate on energy intake
control, whereas fewer studies have focused on the role of dietary
fiber (Barkeling et al. 1990
, Burton-Freeman et al. 1997
and 1998
, Foltin et al. 1992
,
Hill and Blundell 1986
, Rolls 1995a
). The
purpose of this paper is to discuss the importance of fiber in the diet
as it relates to energy regulation in humans.
|
Fiber: background |
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TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
|---|
). In the diets of humans, fiber sources include
fruits, vegetables, grain products, legumes, nuts and concentrated
plant sources such as oat and wheat bran. The benefits of consuming
foods rich in fiber are numerous, ranging from improved large bowel
function to slowed digestion and absorption of carbohydrate and fat and
reduced risk for certain diseases (Ali et al. 1982
,
Schneeman and Tietyen 1994
). The recommended daily
intake of fiber for healthy adults is between 20 and 35 g/d; however,
much lower intakes of fiber have been reported (Pilch 1987
). The significance of this lower intake of fiber to
obesity development is suggested by epidemiologic and
cross-sectional studies, indicating that diets low in dietary fiber
are associated with increased risk for obesity (Alfieri et al. 1995
, Burkitt and Trowell 1975
, Van Itallie 1978
). |
Fiber and obesity development: food intake control |
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TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
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). Because obesity
represents the long-term result of an imbalance between energy
intake and energy expenditure, the most obvious link between dietary
fiber and obesity development is through its effects on energy intake
control mechanisms. The ingestion of fiber has been hypothesized to
suppress energy intake by inducing satiation and satiety
(Blundell and Burley 1987
). Satiation is defined as the
satisfaction of appetite that develops during the course of eating and
eventually results in the cessation of eating. Satiation can be
quantified by the duration of a meal and/or the size of the meal. In
contrast, satiety is the state in which further eating is inhibited and
occurs as a consequence of having eaten. The intensity of the satiety
response to a meal/food(s) is measured by the duration of time between
meals/eating occasions and/or the amount of food consumed at the next
meal (Blundell et al. 1996
). Together, satiation and
satiety are integral processes controlling food intake and feeding
behavior. The means by which dietary fibers influence satiation and
satiety are related to their inherent chemical and physical properties,
particularly their bulking and viscosity-producing capabilities.
Adding fiber to the diet adds bulk, which in turn alters energy density
and palatability. The addition of fibers that form viscous colloidal
dispersions when hydrated affects multiple aspects of gastrointestinal
(GI) function, such as gastric emptying, small bowel transit time, and
the digestion and absorption of nutrients, particularly fat and
carbohydrate (Schneeman and Tietyen 1994
, Vahouny et al. 1988
). Hence, dietary fiber has the ability to modify
cephalic-, gastric- and intestinal-phase processes of ingestion,
digestion and absorption, providing it numerous opportunities to
influence satiation and satiety. |
Fiber, energy density and palatability: means for enhanced satiation |
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TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
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). Briefly, energy
density is defined as the number of kilojoules per unit weight of food.
The energy density of foods can range from 0 to 37 kJ/g of food. Water,
fat and fiber are the main food constituents contributing to energy
density, whereas sugar and protein take on a lesser role, except in
some reduced- or modified-fat food products. In general,
fiber-rich diets, whether achieved through fiber supplementation or
incorporation of high fiber foods into meals, have a reduced energy
density compared with high fat diets. This is related to fiber’s
ability to add bulk and weight to the diet. Therefore, for a given
weight or volume of food, fiber can displace the energy of other
nutrients. If people consume a constant weight of food rather than a
constant quantity of energy, as some studies have suggested
(Rolls et al. 1998
, Seagle et al. 1997
),
then addition/incorporation of fiber into the diet is one strategy for
inducing fullness or satiation while consuming less energy. The
underlying hypothesis is that gastric capacity along with sensitive
mechanoreceptors to gastric distention is key in the regulation of food
intake.
Fiber’s effect on palatability, as well as other sensory qualities of
the diet, may affect energy intake (Drewnowski 1998
,
Rolls 1995b
). Bulky, low energy-dense foods/diets
are, for the most part, less appealing than more energy-dense foods
or diets because energy density and palatability have been shown to be
correlated (Holt et al. 1995
, Meiselman et al. 1974 as shown in Drewnowski 1998
).
Therefore, the energy-diluting effects of dietary fiber may reduce
energy intake by lowering the overall palatability of the diet. The
effect of dietary fiber on other qualities of food(s), such as texture
may also reduce energy intake. Textural qualities of some fibrous foods
may increase the work effort and time required for mastication. This
increase in chewing effort and time may result in a variety of
cephalic- and gastric-phase responses and signals, leading to early
satiation and reduced food intake (Duncan et al. 1983
,
Heaton 1980
, Sakata 1995
).
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Fiber affects gastrointestinal function: means for enhanced satiety |
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TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
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). Therefore, prolonging the
intestinal phase of nutrient processing and absorption is likely to
intensify satiety and aid in food intake control.
Incorporation of viscous fibers into a mixed meal at sufficient levels
increases the viscosity of GI contents. Increasing viscosity of
intestinal contents slows gastric emptying and small bowel transit,
interferes with the mixing of food stuffs and digestive enzymes,
disrupts micelle formation, and alters diffusion and interaction of
nutrients with mucosal surface (Schneeman and Tietjen 1994
, Vahouny et al. 1988
). The combination of
these events results in slowed fat and carbohydrate absorption, which
prolongs the period in which these nutrients can interact with
preabsorptive mechanisms of satiety. Because the small intestine is the
primary site for fat-induced satiety, delaying fat absorption and
increasing intestinal exposure to fat should intensify its effect on
satiety. Indeed, infusing equivalent amounts of fat into the duodenum
of rats at a slow rate (extended exposure) compared with a faster rate
(time-reduced exposure), resulted in reduced average daily energy
intake, altered patterns of feeding and reduced body weight gain
(Burton-Freeman and Schneeman 1996
). The concept that
intraluminal fat exposure is related to satiety and food intake control
may illuminate the reason(s) why diets that are low in fat (often those
prescribed for the management of diseases such as obesity,
cardiovascular and diabetes) are difficult to adhere to long term
(Anderson and Gustafson 1989
). Diets low in fat and
energy are associated with chronic sensations of hunger, which may be
due in part to less fat in the intestine available for stimulation of
mechanisms of satiety. Therefore, slowing dietary fat absorption to
enhance satiety, especially when fat levels are low, may have a
significant effect on the overall therapeutic benefit of low fat diets
because adherence may be maintained long term. If inclusion of viscous
type fibers in low fat diets will effectively slow fat absorption and
impart a greater sense of satiety, this would be a reasonable dietary
approach to aid in successful adoption of low fat diets. We recently
investigated this potential interaction of fat and fiber in meals to
influence postmeal satiety. The data indicated that in women,
incorporation of foods rich in viscous fibers into mixed low fat meals
(20% energy from fat) resulted in suppressed sensations of hunger and
enhanced postmeal satiety compared with an equally energetic and
palatable low fat, low fiber meal. Moreover, the satiety response to
the low fat, high fiber meal was similar to that of a high fat (38%
energy from fat), low fiber meal with similar energy content. Analysis
of plasma cholecystokinin (CCK) concentrations in response to these
meals showed a similar pattern, in that elevated and sustained CCK
concentrations were observed with both the low fat, high fiber meal and
the high fat, low fiber meal. Others have shown a similar sustained CCK
response above baseline CCK concentrations when viscous fibers were
included in a low fat meal (Bourden et al. 1999
).
Because CCK release is sensitive to fat in the small intestine and is a
proposed mediator of fat-induced satiety, the results from these
studies are consistent with the idea that delaying fat absorption from
the intestine can improve satiety of meals lower in fat.
|
Fiber, satiation, satiety and energy intake: a look at the data |
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TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
|---|
and 1993
, Burton-Freeman, personal communication,
Cybulski et al. 1992
, Di Lorenzo et al. 1988
, French and Read 1994
, Gustafsson et al. 1995
, Leathwood and Pollet 1988
,
Rigaud et al. 1997
, Tomlin 1995
). The
subsequent effect on food intake has been more variable because in some
cases, food intake at a test meal was reduced, in other cases, it was
not. Although much of the discrepancy in results may be ascribed to
differences among studies, different responses related to gender and
body weight status (i.e., obese vs. normal weight) may also be
responsible. With regard to gender, work in our laboratory indicates
that women may be more sensitive to dietary manipulation with fiber
than men, which is consistent with a previous report by Burley et al. (1993)
. Moreover, we have found that the subjective
satiety response to dietary manipulation in men and women is supported
by differences in the CCK response, suggesting that signals for satiety
differ between genders (Burton-Freeman et al. 1998 and personal communication
). The relationship of body weight status and
fiber effect on energy intake suggests that obese individuals may be
more likely to reduce food intake (Evans and Miller 1975
, Porikos and Hagamen 1986
) with dietary
fiber inclusion. However, many more studies will be required to
establish this relationship firmly by comparing directly the effects of
fiber between normal weight and obese subjects. Nonetheless, the data
highlight the importance of understanding how fiber or the different
types of fiber may influence food consumption behavior in different
groups of people. This information is valuable for developing and
successfully implementing dietary strategies aimed at food intake and
body weight control. |
Fiber and weight loss |
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|
TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
|---|
, Heini et al. 1998
, Mickelson et al. 1979
, Pasman et al. 1997
, Ryttig et al. 1985
). With the exception of Heini et al. (1998)
, the major conclusion drawn from these trials was that
subjects found it easier to adhere to the weight loss diets when fiber
was part of the dietary regimen. The lack of effect reported in the
study by Heini and co-workers may have resulted from the use of
hydrolyzed guar gum, which would have removed the viscosity effect of
the fiber, an important component of fiber-related satiety. The
usefulness of long-term fiber supplementation to induce or maintain
weight loss under unrestricted conditions is not clear (Evans and Miller 1975
, Hylander and Rossner 1983
). |
SUMMARY |
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TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
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|
FOOTNOTES |
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|
REFERENCES |
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TOPABSTRACTINTRODUCTIONFiber: backgroundFiber and obesity development:...Fiber, energy density and...Fiber affects gastrointestinal...Fiber, satiation, satiety and...Fiber and weight lossSUMMARYREFERENCES |
|---|
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