![]() |
|
|
3 Department of Human Biology, School for Nutrition, Toxicology and Metabolism, Maastricht University, 6229 ER Maastricht, The Netherlands; 4 Laboratory of Experimental Vascular Medicine, Academic Medical Center, 1105 AZ Amsterdam, The Netherlands; 5 Department of Physiology and Nutrition, University of Navarra, 31008 Pamplona, Spain; 6 Department of Nutrition, Hôtel-Dieu Hospital, University Pierre-et-Marie Curie (Paris 6), 75004 Paris, France; 7 Department of Sports Medicine, Centre of Preventive Medicine, Third Faculty of Medicine, Charles University, 10000 Prague, Czech Republic; 8 Department of Human Nutrition, Faculty of Life Sciences, University of Copenhagen, 1958 Frederiksberg, Denmark; 9 Department of Medicine, Karolinska Institute, Huddinge University Hospital, 14186 Stockholm, Sweden; 10 Institute of Preventive Medicine, Copenhagen University Hospital, Centre for Health and Society, 1357 Copenhagen, Denmark
* To whom correspondence should be addressed. E-mail: anneke.vanhees{at}hb.unimaas.nl.
| ABSTRACT |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
Several studies have been performed to determine which factors may play a role in RLP metabolism and show associations with insulin resistance, BMI, upper body obesity, other blood lipids, gender, and age (7–15). However, most of these studies were performed in a relatively small number of participants so that multiple factors could not be taken into account. Moreover, data on the influence of lifestyle factors such as diet and physical activity are limited.
Results of a study investigating the effect of dietary composition on plasma RLP-C suggest that a 2-wk high-carbohydrate diet [60 energy % (en%) carbohydrate] increased plasma TG and decreased plasma HDL-C concentrations but also led to increased fasting and postprandial RLP-C concentrations compared with a 2-wk low-carbohydrate diet (40en% carbohydrate) (16). On the other hand, it has been shown that reducing the total fat content of the diet causes weight loss and better weight maintenance, which can also have a favorable effect on the blood lipid profile (17). Nevertheless, little information is available on the relative effects of weight loss and dietary fat modification on plasma RLP-C concentrations.
The objective of this part of the European multicenter trial Nutrient-Gene Interactions in Human Obesity–Implications for Dietary Guidelines (NUGENOB) was to take the drawbacks of earlier studies into account and investigate the factors that affect plasma RLP-C concentrations in a large cohort of lean and obese participants with a detailed phenotype, both in the fasting state and postprandially after the consumption of a high-fat meal. Second, we investigated determinants of change in fasting RLP-C concentration after a 10-wk hypo-energetic diet with either a high- or low-fat content in the obese participants who participated in the NUGENOB trial.
| Materials and Methods |
|---|
|
|
|---|
Participants.
In total, 740 Caucasian participants (552 women) were included in the NUGENOB study. Inclusion criteria were age 20–50 y, BMI between 18.5 and 25 kg/m2 for lean participants and BMI
30.0 kg/m2 for obese participants. After baseline measurements, only the obese participants were allowed to enter the weight loss program. Details on participant recruitment and exclusion criteria are described elsewhere (18).
All participants were informed about the nature of the study and gave written informed consent prior to study participation. The study protocol was approved by the ethical committee at each of the participating centers.
Experimental design. All participants underwent a 1-d clinical investigation protocol. Participants arrived at the research center after a 12-h overnight fast and a preceding 3-d dietary run-in period, during which they were to keep their habitual diet and avoid excessive physical activity and alcohol consumption. After the participants voided their bladders, they underwent anthropometric and body composition assessments [as described in Petersen et al. (18)]. Thereafter, participants stayed on a bed for 3.5 h, during which circulating hormones and metabolites were determined before and after a high-fat test meal. At least 30 min before the start of the resting measurement, a catheter was inserted in an antecubital forearm vein for blood sampling. Blood was drawn in the fasting state and every 60 min following the test meal for the next 3 h. Plasma concentrations of glucose, insulin, FFA, TG, total cholesterol, HDL-C, and RLP-C were determined pre- and postprandially. Furthermore, postprandial RLP-C was also measured 6 h postprandially in a subgroup of 113 participants to compare 3-h and 6-h RLP-C concentrations. During the whole experiment, the room was kept thermoneutral at 25°C.
The obese participants who participated in the weight loss program also underwent a second clinical investigation; at the end of the 10-wk dietary intervention, anthropometric measurements and body composition assessments were repeated and a venous blood sample was obtained after an overnight fast.
Test meal. The fluid test meal (double cream with 40% fat/100 g adjusted with butter in 2 centers) consisted of 95 en% (percent of total energy content fat load) fat, 60% of which was saturated fat, 3 en% carbohydrate, and 2 en% protein. Based on the predicted metabolic rate, the energy content was fixed at 50% of the predicted basal metabolic rate (19) and ranged from 1697 to 6590 kJ. Participants were asked to drink the test meal within 10 min.
Dietary intervention. Stratified block randomization was used with center, gender, and 3 age groups (20–29, 30–39, and 40–50 y) as strata and a block size of 12 to assign obese participants to either a low-fat diet or a high-fat diet. The target macronutrient composition of the low-fat diet was 20–25% of total energy from fat, 15% from protein, and 60–65% from carbohydrate. The target macronutrient composition of the high-fat diet was 40–45% of total energy from fat, 15% from protein, and 40–45% from carbohydrate. Both diets were designed to provide 2510 kJ/d less than the individually estimated energy requirement based on an initial resting metabolic rate multiplied by 1.3. Information about how the diet was controlled is given in detail elsewhere (18).
Biochemical analyses. All blood analyses were performed in the laboratory of one of the centers. Plasma glucose concentrations (ABX diagnostics), TG (Sigma; ABX diagnostics), and total cholesterol (cholesterol 100; ABX diagnostics) were measured on a COBAS MIRA automated spectrophotometric analyzer (Roche Diagnostica). Plasma FFA (NEFA C kit; Wako Chemicals) and HDL-C (HDL-C Roche) were measured on a COBAS FARAH centrifugal spectrophotometer (Roche Diagnostica). Standard samples with known concentrations were included in each analysis for quality control. Plasma insulin concentrations were measured with a double antibody RIA (Insulin RIA 100; Kabi-Pharmacia). RLP-C concentrations were measured in plasma using an immunoseparation technique developed by Nakajima et al. (20). The RLP fraction was prepared by mixing 5 µL of plasma with 300 µL immunoseparation gel suspension, containing a mixture of 2 monoclonal antibodies, i.e. anti-human apolipoprotein A-I (H-12) and anti-human apolipoprotein-B-100 (JI-H). The reaction mixture was gently shaken for 2 h at room temperature on a special mixer (RLP-mixer J100-A, Photal, Otsuka Electronics). After incubation, 200 µL of supernatant was used for the measurements of cholesterol (RLP-C) on a COBAS MIRA S auto-analyzer (ABX diagnostics).
Calculations. The homeostasis model assessment for insulin resistance (HOMAIR) was calculated from fasting glucose and fasting insulin according to the equation of Matthews et al. (21). An estimate of total habitual physical activity was obtained by means of the Baecke questionnaire using the sum of work, sport, and leisure scores of the questionnaire (22,23). For comparing postprandial responses, we calculated the incremental area under the curve (iAUC) according to the trapezium rule. Postprandial RLP-C is expressed as the plasma concentration of RLP-C at t = 180 min, because only baseline and 3-h values of RLP-C were available.
Statistical methods. Statistical analyses were performed using SPSS 14.0 for Windows (SPSS Inc.). All variables were checked for normal distribution and non-normally distributed data were ln-transformed to satisfy conditions of normality. Student's t test for unpaired samples was used to compare participant characteristics at baseline (lean vs. obese, low- vs. high-fat diet group) and repeated-measures ANOVA was used to test for differences in time between groups.
Multiple regression analysis was performed to evaluate which factors were associated with plasma RLP-C concentrations, both in the fasting state and postprandially after a high-fat meal. The dependent variable in each multiple regression model was ln-transformed to satisfy conditions of normality. Independent variables were included in the analyses in 2 steps; gender, BMI, age, HOMAIR, waist:hip ratio (WHR), baseline dietary fat intake, total physical activity, and/or fasting plasma RLP-C were included in model 1 and plasma concentrations of TG, FFA, and HDL-C (fasting or as iAUC in the postprandial model) were included in model 2.
Determinants of change (
) in fasting RLP-C were also evaluated in 2 models, with the independent variables gender, diet, age,
weight,
HOMAIR, and
WHR in model 1 and change in fasting plasma TG, FFA, and HDL-C in model 2. The
was calculated as (10 wk – 0 wk) and the models were corrected for the mean values of each
variable (10 wk + 0 wk/2). Furthermore, all models as described above were corrected for center (dummy variables) and, in the postprandial model, for the energy content of the high-fat test meal. To avoid multicollinearity, predictors with a correlation > 0.80 were not included in the model simultaneously. The relative impact of the predictors is demonstrated as the standardized β-coefficient and its significance value. The adjusted R2 (adj. R2) of each model is indicated in the tables. Significance was set at P < 0.05.
| Results |
|---|
|
|
|---|
|
|
|
|
|
|
|
|
| Discussion |
|---|
|
|
|---|
Men had significantly higher fasting RLP-C concentrations than women and RLP-C concentrations increased with age, which is consistent with previous findings (14,26). In the postprandial response to the high-fat meal, however, the gender effects on plasma RLP-C were explained by the effect of body fat distribution; WHR was significantly associated with postprandial RLP-C, independent of gender, BMI, the degree of insulin resistance, and postprandial circulating TG concentrations, suggesting that body fat distribution is directly linked to RLP-C in the postprandial phase. Abdominal obesity plays an important role in postprandial TRL metabolism in both men and women (13,27). Based on our results, the association between WHR and postprandial RLP-C seems to be stronger than the association with gender.
The postprandial response after the high-fat meal was measured over a 3-h period, which is a relatively short time for studying postprandial lipid profiles. Therefore, we analyzed RLP-C concentrations 6 h postprandially in a subgroup of the total cohort and showed that RLP-C concentrations at 3 h were highly correlated with 6-h values. Although this indicates that our postprandial model reflects conditions after a 6-h postprandial period, it remains a limitation of this study that we could not measure RLP-C accumulation over the total postprandial period.
To detect disturbances in lipid metabolism, a pure high-fat load was administered as a metabolic stressor. We acknowledge that the very slight insulin response after this high-fat load may have induced slightly different postprandial lipid responses in this study compared with, e.g., a high-fat mixed meal. Despite this, we observed similar associations between plasma RLP-C and HOMAIR, WHR, and plasma TG concentrations to those shown previously (10,11).
We observed a small positive association between habitual physical activity and fasting RLP-C, which is not consistent with earlier findings about the relationship between total physical activity and plasma lipoprotein concentrations (12,28,29). The underlying mechanisms for this association remain to be elucidated.
Weight loss improved fasting RLP-C concentrations, even after correction for age, gender, and changes in HOMAIR and WHR, showing that weight loss per se can be an appropriate tool to improve fasting and postprandial RLP concentrations (30). Furthermore, weight loss was comparable after both diets, indicating that it was not the macronutrient composition of the diet that influenced a reduction in body weight but the total energy intake, because both diets were designed to provide 2510 kJ/d less than the individually estimated daily energy requirement (18). Therefore, it is interesting that despite a similar weight loss, a high-fat diet leads to a better improvement in both fasting RLP-C concentrations and fasting TG concentrations than a low-fat diet in obese participants. This observation extends the results of Abbasi et al. (16), showing that in healthy participants, both fasting and postprandial RLP-C concentrations are significantly lower after a high-fat diet than after a low-fat diet and may be explained by the higher carbohydrate content of the low-fat diet compared with the high-fat diet. It has been described previously for the total NUGENOB cohort that the beneficial effects of the dietary intervention on plasma TG, LDL-C, and total cholesterol were mainly the result of weight loss per se, with additional effects of diet composition (18).
Furthermore, improvements in insulin resistance were also significantly related to a decrease in fasting RLP-C, independent of weight loss. Again, after inclusion of fasting TG in the model, these effects disappeared and only weight loss and a decrease in fasting TG were associated with decreased plasma RLP-C, emphasizing the outcomes of the baseline fasting and postprandial models.
In summary, this multicenter study demonstrates that plasma RLP-C concentrations are related to body fat distribution (WHR) and the degree of insulin resistance (HOMAIR), both fasting and 3 h postprandial after a high-fat load. However, taking other plasma lipid concentrations into account, plasma TG appeared to be a strong determinant of plasma RLP-C.
The present mode of dietary intervention shows that, independent of weight loss, a high-fat diet is more effective in lowering fasting plasma RLP-C concentrations in obesity than a low-fat diet.
| FOOTNOTES |
|---|
2 Author disclosures: A. van Hees, W. Saris, G. Dallinga-Thie, G. Hul, J. Martinez, J-M. Oppert, V. Stich, A. Astrup, P. Arner, T. Sørensen, and E. Blaak, no conflicts of interest. ![]()
11 Abbreviations used: adj. R2, adjusted R2; en%, energy %; HDL-C, HDL-cholesterol; HOMAIR, homeostasis model assessment index for insulin resistance; iAUC, incremental area under the curve; LDL-C, LDL cholesterol; NUGENOB, Nutrient-Gene Interactions in Human Obesity–Implications for Dietary Guidelines; RLP, remnant-like lipoprotein particle; RLP-C, remnant-like particle cholesterol; TG, triglyceride; TRL, triglyceride-rich lipoprotein; WHR, waist:hip ratio. ![]()
Manuscript received 12 June 2008. Initial review completed 29 July 2008. Revision accepted 5 October 2008.
| LITERATURE CITED |
|---|
|
|
|---|
1. Ginsberg HN. Insulin resistance and cardiovascular disease. J Clin Invest. 2000;106:453–8.[Medline]
2. Twickler TB, Dallinga-Thie GM, Cohn JS, Chapman MJ. Elevated remnant-like particle cholesterol concentration: a characteristic feature of the atherogenic lipoprotein phenotype. Circulation. 2004;109:1918–25.
3. Zilversmit DB. Atherogenic nature of triglycerides, postprandial lipidemia, and triglyceride-rich remnant lipoproteins. Clin Chem. 1995;41:153–8.
4. McNamara JR, Shah PK, Nakajima K, Cupples LA, Wilson PW, Ordovas JM, Schaefer EJ. Remnant-like particle (RLP) cholesterol is an independent cardiovascular disease risk factor in women: results from the Framingham Heart Study. Atherosclerosis. 2001;154:229–36.[Medline]
5. Karpe F, Boquist S, Tang R, Bond GM, de Faire U, Hamsten A. Remnant lipoproteins are related to intima-media thickness of the carotid artery independently of LDL cholesterol and plasma triglycerides. J Lipid Res. 2001;42:17–21.
6. Nordestgaard BG, Benn M, Schnohr P, Tybjaerg-Hansen A. Nonfasting triglycerides and risk of myocardial infarction, ischemic heart disease, and death in men and women. JAMA. 2007;298:299–308.
7. Choi YJ, Jo YE, Kim YK, Ahn SM, Jung SH, Kim HJ, Chung YS, Lee KW, Kim DJ. High plasma concentration of remnant lipoprotein cholesterol in obese children and adolescents. Diabetes Care. 2006;29:2305–10.
8. Watanabe N, Taniguchi T, Taketoh H, Kitagawa Y, Namura H, Yoneda N, Kurimoto Y, Yamada S, Ishikawa Y. Elevated remnant-like lipoprotein particles in impaired glucose tolerance and type 2 diabetic patients. Diabetes Care. 1999;22:152–6.
9. Ohnishi H, Saitoh S, Takagi S, Ohata J, Isobe T, Kikuchi Y, Takeuchi H, Shimamoto K. Relationship between insulin-resistance and remnant-like particle cholesterol. Atherosclerosis. 2002;164:167–70.[Medline]
10. Chan DC, Watts GF, Barrett PH, Mamo JC, Redgrave TG. Markers of triglyceride-rich lipoprotein remnant metabolism in visceral obesity. Clin Chem. 2002;48:278–83.
11. Funada J, Sekiya M, Otani T, Watanabe K, Sato M, Akutsu H. The close relationship between postprandial remnant metabolism and insulin resistance. Atherosclerosis. 2004;172:151–4.[Medline]
12. Imke C, Rodriguez BL, Grove JS, McNamara JR, Waslien C, Katz AR, Willcox B, Yano K, Curb JD. Are remnant-like particles independent predictors of coronary heart disease incidence? The Honolulu Heart study. Arterioscler Thromb Vasc Biol. 2005;25:1718–22.
13. Mekki N, Christofilis MA, Charbonnier M, Atlan-Gepner C, Defoort C, Juhel C, Borel P, Portugal H, Pauli AM, et al. Influence of obesity and body fat distribution on postprandial lipemia and triglyceride-rich lipoproteins in adult women. J Clin Endocrinol Metab. 1999;84:184–91.
14. McNamara JR, Shah PK, Nakajima K, Cupples LA, Wilson PW, Ordovas JM, Schaefer EJ. Remnant lipoprotein cholesterol and triglyceride reference ranges from the Framingham Heart Study. Clin Chem. 1998;44:1224–32.
15. Ai M, Tanaka A, Ogita K, Sekinc M, Numano F, Numano F, Reaven GM. Relationship between plasma insulin concentration and plasma remnant lipoprotein response to an oral fat load in patients with type 2 diabetes. J Am Coll Cardiol. 2001;38:1628–32.
16. Abbasi F, McLaughlin T, Lamendola C, Kim HS, Tanaka A, Wang T, Nakajima K, Reaven GM. High carbohydrate diets, triglyceride-rich lipoproteins, and coronary heart disease risk. Am J Cardiol. 2000;85:45–8.[Medline]
17. Astrup A, Grunwald GK, Melanson EL, Saris WH, Hill JO. The role of low-fat diets in body weight control: a meta-analysis of ad libitum dietary intervention studies. Int J Obes Relat Metab Disord. 2000;24:1545–52.[Medline]
18. Petersen M, Taylor MA, Saris WH, Verdich C, Toubro S, Macdonald I, Rossner S, Stich V, Guy-Grand B, et al. Randomized, multi-center trial of two hypo-energetic diets in obese subjects: high- versus low-fat content. Int J Obes (Lond). 2006;30:552–60.[Medline]
19. Energy and protein requirements. Report of a joint FAO/WHO/UNU Expert Consultation. World Health Organ Tech Rep Ser. 1985;724:1–206.[Medline]
20. Nakajima K, Saito T, Tamura A, Suzuki M, Nakano T, Adachi M, Tanaka A, Tada N, Nakamura H, et al. Cholesterol in remnant-like lipoproteins in human serum using monoclonal anti apo B-100 and anti apo A-I immunoaffinity mixed gels. Clin Chim Acta. 1993;223:53–71.[Medline]
21. Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia. 1985;28:412–9.[Medline]
22. Philippaerts RM, Westerterp KR, Lefevre J. Doubly labelled water validation of three physical activity questionnaires. Int J Sports Med. 1999;20:284–9.[Medline]
23. Montoye HJ, Kemper HCG, Saris WHM, Washburn RA. Measuring physical activity and energy expenditure. Champaign (IL): Human Kinetics; 1996.
24. Satoh A, Adachi H, Tsuruta M, Hirai Y, Hiratsuka A, Enomoto M, Furuki K, Hino A, Takeuchi T, et al. High plasma level of remnant-like particle cholesterol in the metabolic syndrome. Diabetes Care. 2005;28:2514–8.
25. Abbasi F, McLaughlin T, Lamendola C, Yeni-Komshian H, Tanaka A, Wang T, Nakajima K, Reaven GM. Fasting remnant lipoprotein cholesterol and triglyceride concentrations are elevated in nondiabetic, insulin-resistant, female volunteers. J Clin Endocrinol Metab. 1999;84:3903–6.
26. Schaefer EJ, McNamara JR, Shah PK, Nakajima K, Cupples LA, Ordovas JM, Wilson PW. Elevated remnant-like particle cholesterol and triglyceride levels in diabetic men and women in the Framingham Offspring Study. Diabetes Care. 2002;25:989–94.
27. Couillard C, Bergeron N, Pascot A, Almeras N, Bergeron J, Tremblay A, Prud'homme D, Despres JP. Evidence for impaired lipolysis in abdominally obese men: postprandial study of apolipoprotein B-48- and B-100-containing lipoproteins. Am J Clin Nutr. 2002;76:311–8.
28. Kraus WE, Houmard JA, Duscha BD, Knetzger KJ, Wharton MB, McCartney JS, Bales CW, Henes S, Samsa GP, et al. Effects of the amount and intensity of exercise on plasma lipoproteins. N Engl J Med. 2002;347:1483–92.
29. O'Donovan G, Owen A, Kearney EM, Jones DW, Nevill AM, Woolf-May K, Bird SR. Cardiovascular disease risk factors in habitual exercisers, lean sedentary men and abdominally obese sedentary men. Int J Obes (Lond). 2005;29:1063–9.[Medline]
30. Dallongeville J, Gruson E, Dallinga-Thie G, Pigeyre M, Gomila S, Romon M. Effect of weight loss on the postprandial response to high-fat and high-carbohydrate meals in obese women. Eur J Clin Nutr. 2007;61:711–8.[Medline]
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||