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Original Research Communication |
1 From the Research Department of Human Nutrition, Center for Food Research, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark, and the Department of Medical Physiology, The Panum Institute, the University of Copenhagen.
2 Supported by the Danish Research and Development Programme for Food Technology 19901994, Danisco Sugar, and the Danish Medical Research Council (grant no. 12-9537-3). MasterFoods and Toms Chokolade A/S generously provided foods for the study.
3 Address reprint requests to A Raben, Research Department of Human Nutrition, Center for Food Research, The Royal Veterinary and Agricultural University, 30 Rolighedsvej, DK-1958 Frederiksberg, Copenhagen, Denmark. E-mail: ar{at}kvl.dk.
| ABSTRACT |
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Objective: We investigated the effects of 2 low-fat diets (high-sucrose and high-starch) and a high-fat diet on glycemia, lipidemia, and hormonal responses in never-obese and postobese women.
Design: Eighteen normal-weight women (8 postobese and 10 never-obese) consumed 3 ad libitum diets (high-fat, high-starch, and high-sucrose) for 14 d each. On day 15, we measured fasting and postprandial glucose, lactate, insulin, triacylglycerol, nonesterified fatty acids (NEFA), glycerol, glucagon, glucose-dependent insulinotropic polypeptide, and glucagon-like peptide 1.
Results: The high-sucrose diet induced significantly lower total areas under the curve (AUCs) for glucose and NEFA and a significantly higher lactate AUC than did the high-fat and high-starch diets; there were no significant differences in the insulin AUCs. The triacylglycerol AUC was greater with the high-fat and high-sucrose diets than with the high-starch diet. Gastrointestinal hormone concentrations differed between diets, but not between the 2 subject groups. Comparisons between subject groups for all diets combined showed lower relative insulin resistance and lower AUCs for glucose, insulin, and triacylglycerol in the postobese group.
Conclusions: High-starch and high-sucrose diets had no adverse effects on postprandial glycemia, insulinemia, or lipidemia compared with a high-fat diet. A sucrose-rich diet may improve glucose metabolism, but may have an adverse effect on lipidemia, compared with a starch-rich diet. Postobese women seemed to be more insulin-sensitive and more efficient at storing triacylglycerol than were never-obese women, regardless of dietary composition.
Key Words: Obesity homeostasis model assessment resistance insulin resistance women carbohydrate metabolism diabetes cardiovascular disease glycemia lipidemia
| INTRODUCTION |
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It was believed previously that sucrose consumption resulted in rapid, large increases in plasma glucose and insulin concentrations; therefore, restrictions were recommended for diabetic individuals. However, studies conducted in the 1980s and 1990s showed that sucrose produces lower postprandial glycemic and insulinemic responses than do many types of starch (5, 6). Although recommendations about sucrose intake are therefore less restrictive now, uncertainties persist among both scientists and laypersons as to whether sucrose has detrimental effects on glucose control and insulin sensitivity in healthy and diabetic individuals when sucrose is consumed for longer periods.
Another issue that has been of major concern for >30 y is the possible adverse effect of sucrose (and fructose) on blood lipids and other risk factors for coronary heart disease (7). Some believe that a high-starch, high-fiber diet, which was recommended previously, also has these adverse effects. It was therefore suggested that the dietary recommendations be revised accordingly to recommend less carbohydrate in the diet (8, 9). This is, however, still controversial (10, 11).
Obesity is a growing health problem all over the world. The increased prevalence is probably a result of both a sedentary lifestyle and consumption of high-fat, energy-dense foods (12). Studies on subjects with genetic susceptibility to obesity showed that their lipid metabolism in particular was abnormal compared with subjects who were not predisposed to obesity (1317). However, these results were obtained after only 03 d of dietary intervention and the subjects' habitual dietstypically more carbohydrate-rich in successful postobese subjects (18)may have influenced the results. To our knowledge, the metabolic profiles of postobese subjects have not been studied after more prolonged dietary interventions.
The purpose of the present study was 2-fold. The first objective was to compare the effects of 3 diets (a low-fat, high-sucrose diet; a low-fat, high-starch diet; and a high-fat diet) on fasting and postprandial glycemia, lipidemia, and hormonal changes when the diets were consumed for 14 d ad libitum. The second objective was to compare the responses to the diets of normal-weight never-obese women with those of normal-weight postobese women.
| SUBJECTS AND METHODS |
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± SEM: 38 ± 9%) (19), and had been weight-stable for
2 mo. None had undergone surgical procedures to reach their normal weight. The study was approved by the Municipal Ethical Committee of Copenhagen and Frederiksberg and was found to be in accordance with the Helsinki II Declaration. All subjects gave their written consent after the experimental procedure was explained to them.
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2 wk but
6 wk. The subjects were instructed to make no changes in their physical activity pattern during or between the 3 experimental diets. Data on ad libitum macronutrient and energy intakes, body weight and composition, 24-h energy expenditure, substrate oxidation, appetite sensations, habitual food intake, plasma catecholamines, blood cholesterol, and coagulation and fibrinolysis factors were published previously (18, 20).
Diets
The standardized weight-maintenance diet provided to subjects before each dietary period contained 13% of energy as protein, 37% as fat, 50% as carbohydrate (9% as sucrose), and 2.9 g dietary fiber/MJ and had a polyunsaturated-to-saturated fatty acid ratio (P:S) of 0.4. The diet was prepared according to each subjects' individual energy needs, adjusted to the nearest 0.5 MJ (21).
The average macronutrient intakes (as percentages of energy intake) were as planned: 59% carbohydrate (23% sucrose), 28% fat, and 13% protein with the high-sucrose diet; 46% fat, 41% carbohydrate (2% sucrose), and 13% protein with the high-fat diet; and 59% carbohydrate (2% sucrose), 28% fat, and 13% protein with the high-starch diet. Dietary fiber amounted to 22, 32, and 20 g/d with the high-fat, high-starch, and high-sucrose diets, respectively. The P:S was 0.4 with the high-fat diet and 0.7 with both the high-sucrose and high-starch diets. The amounts of saturated, monounsaturated, and polyunsaturated fatty acids, respectively, as percentages of total fat were as follows: 45%, 37%, and 18% with the high-fat diet; 38%, 37%, and 26% with the high-sucrose diet; and 35%, 40%, and 25% with the high-starch diet. The distribution of macronutrients was similar in all meals during the day (breakfast, lunch, dinner, and snack). The 14-d ad libitum energy intake was significantly lower during the high-starch diet (9.1 ± 0.4 MJ/d) than during both the high-sucrose (10.3 ± 0.5 MJ/d) and high-fat (10.3 ± 0.4 MJ/d) diets (P < 0.05). Postobese subjects consumed significantly more energy than never-obese subjects during the high-fat diet (11.0 ± 0.7 and 9.7 ± 0.4 MJ/d, respectively; P < 0.001) and during the high-sucrose diet (11.4 ± 0.7 and 9.5 ± 0.5 MJ/d, respectively; P < 0.0001).
The types and amounts of foods provided to subjects for breakfast and lunch on day 15 were similar to the ad libitum amounts consumed on day 14 in the chamber (Tables 2 and 3![]()
). Coffee, tea, and water consumption and smoking (by 2 postobese subjects and 1 never-obese subject) were allowed, but the amounts and times were duplicated from the first dietary period. On average, both groups consumed more energy during the high-fat and high-sucrose diets at breakfast, whereas there were no significant differences at lunch (Table 3
). Total energy intake at both breakfast and lunch was significantly lower during the high-starch diet than during the high-fat and high-sucrose diets (P < 0.01). There were no group differences in energy intake over the day (Table 3
). The computer database of foods from the National Food Agency of Denmark (DANKOST version 2.0) was used to calculate the energy and nutrient intakes (22).
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Blood sampling
On day 15, the subjects left the respiration chamber at 0900. After voiding and being weighed, each subject lay down on a bed in the supine position and a Venflon catheter (Viggo, Gothenborg, Sweden) was inserted into an antecubital arm vein. After 10 min, a fasting blood sample was obtained. Subjects ate breakfast at 1000 and lunch at 1400. Blood samples were obtained 15, 30, 60, 120, and 240 min after the beginning of both breakfast and lunch, ie, blood was sampled over an 8-h time span. Subjects rested in the supine position for 10 min before each blood sample was obtained. During the day, they could sit, walk quietly, or go to the toilet. The type of activity each subject engaged in during day 15 of the first dietary period was noted and repeated on day 15 in the remaining 2 dietary periods.
Laboratory analyses
Blood was sampled without stasis through an indwelling antecubital cannula and was centrifuged at 3000 x g for 10 min at 4°C. Iced syringes were used to store samples for glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon analyses.
Blood for glucose and lactate analyses was sampled in tubes containing fluoride and EDTA. Glucose concentrations were determined with a Cobas Mira blood sample analyzer (Roche Diagnostic System, Basel, Switzerland) by using an endpoint analysis with MPR3 Gluco-quant R glucose/HK kinetic 1442457 (Boehringer Mannheim GmbH Diagnostica, Mannheim, Germany) and the hexokinase-glucose-6-phosphate 1-dehydrogenase method (23). Lactate concentrations were determined by using a Cobas Mira analyzer with an MPR3 lactate 256773 kit (Boehringer Mannheim GmbH Diagnostica) according to a method modified by Noll (24). Blood for insulin analysis was sampled in dry tubes. Serum insulin was determined with an enzyme-linked immunosorbent assay; we used a noncompetitive sandwich assay with a DAKO RIA insulin kit (code no. K6219; DAKO A/S, Glostrup, Denmark). An index of insulin resistance was obtained by using the homeostasis model assessment (HOMA; 25):
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where glucose is in mmol/L and insulin is in mU/L.
Plasma glycerol was determined enzymatically after protein precipitation in blood collected in heparin-prepared tubes (26). Blood for analysis of serum triacylglycerol was collected in dry tubes. Triacylglycerol was determined by enzymatic hydrolysis and subsequent determination of liberated glycerol by colorimetry (27). An MPR2 triacylglycerol GPO-PAP 701912 kit (Boeringer Mannheim GmbH Diagnostica) and a Cobas Mira analyzer (Roche Diagnostic System) were used. Blood for determination of serum nonesterified fatty acid (NEFA) concentrations was sampled in dry tubes and was immediately centrifuged, extracted, and stored at -20°C. NEFA concentrations were determined by an enzymatic colorimetric method (ACS-ACOD method, NEFA C code no. 99475409E; Wako Chemicals Inc, Richmond, VA) by using a Cobas Mira Plus analyzer (Roche Diagnostic System).
GIP, glucagon, and GLP-1 concentrations in plasma were all measured after extraction of plasma with 70% ethanol (vol:vol, final concentration). For the GIP radioimmunoassay (28), we used the C-terminally directed antiserum R65, which cross-reacts fully with human GIP but not with the so-called GIP 8000, whose chemical nature and relation to GIP secretion is uncertain. Human GIP and 125I human GIP (70 Mbq/nmol) were used for standards and tracer. The glucagon radioimmunoassay was directed against the C-terminus of the glucagon molecule (antibody code no. 4305) and therefore mainly measured glucagon of pancreatic origin (29). The plasma concentrations of GLP-1 were measured against standards of synthetic GLP-1 736 amide by using antiserum code no. 89390, which is specific for the amidated C-terminus of GLP-1 and therefore mainly reacts with GLP-1 of intestinal origin (30). For these 3 assays, sensitivity was <1 pmol/L, the intraassay CV was <6% at 20 pmol/L, and the recovery of standard (added to plasma before extraction) was
100% when corrected for losses inherent in the plasma extraction procedure.
Statistical analyses
All results are given as means ± SEMs. Initial group characteristics were compared by using unpaired t tests (Table 1
). The areas under the curves (AUCs) were calculated separately for each subject as the difference between the integrated area of the response curve and the rectangular area determined by the basal values. For
AUC, ie, the change from fasting concentrations, negative areas were included. The normal distributions of all data were verified by residual plots before further data analysis. Differences in fasting concentrations and AUCs among the 3 diets and 2 subject groups were tested by parametric analysis of variance (ANOVA) with the general linear model (GLM) procedure in SAS (SAS Institute Inc, Cary, NC). The factors were group x diet, group, and diet using subject(group) as an error term for group effects. For significant values, a t test on least-squares means (for unbalanced designs) was used to test for differences between groups or diets. Differences in postprandial responses were tested with ANOVA by using GLM in SAS and with diet x time x group, diet x group, time x group, diet x time, time, diet, and group as factors and subject(group) as the error term for all group effects.
To explain observed differences between diets and groups, we performed simple linear regression analyses by using the means of groups and diets (n = 6). A plot was used to determine whether a significant correlation was valid. To investigate whether observed differences in AUCs were the result of differences in ad libitum energy intake on day 15, the latter was included as a covariate in the ANOVA. Changes in fasting blood concentrations were also reanalyzed with the following as covariates: 14-d changes in body weight and 14-d average energy, carbohydrate, fat, and sucrose intakes.
The significance level was set at P < 0.05. STATGRAPHICS software (version 4.2; Graphic Software Systems Inc, Rockville, MD) and the STATISTICAL ANALYSIS PACKAGE (version 6.12 for WINDOWS; SAS Institute) were used to perform the statistical calculations.
| RESULTS |
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AUCs than did never-obese subjects. The above findings were not altered by adjustment analyses.
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AUC in postobese than in never-obese subjects. Adjusting for differences in energy intake on day 15 did not alter these findings. HOMA-R did not differ significantly between diets, but was significantly lower in postobese than in never-obese subjects for all diets, whether we used fasting values (day 15) or AUC values (Table 5
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AUCs did not differ significantly between groups (Figure 4
AUCs became lower in postobese subjects for all 3 diets.
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AUCs were lower after the high-sucrose and high-starch diets than after the high-fat diet (Figure 5
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AUCs did not differ significantly between diets or subject groups, and adjustment for energy intake did not alter these findings.
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AUCs were also higher after the high-fat diet than after the high-sucrose or high-starch diets (Figure 8
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AUCs were larger after the high-fat diet than after the high-starch diet (Figure 9
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Correlation analyses
For fasting concentrations on day 15 (n = 6 for the 2 subject groups during the 3 diets), there were positive correlations between lactate and triacylglycerol (r = 0.81, P < 0.05), insulin and triacylglycerol (r = 0.93, P < 0.01), and glucose and GLP-1 (r = 0.84, P < 0.05). No significant correlations were found between the changes (days 15-1) in fasting blood concentrations. The AUCs for insulin and triacylglycerol were positively correlated (r = 0.94, P < 0.01). Positive correlations were also seen between the
AUCs for GLP-1 and NEFA (r = 0.85, P < 0.05) and GLP-1 and glycerol (r = 0.87, P < 0.05).
| DISCUSSION |
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After both breakfast and lunch, lactate concentrations increased more during the high-sucrose diet than during the high-starch diet. It is likely that the fructose part of the high-sucrose diet caused this effect (7). With the high-starch diet, the increase in lactate must have been caused primarily by anaerobic glucose breakdown in extramuscular tissues (33).
Lipidemia
Fasting triacylglycerol concentrations increased with both the high-starch and high-sucrose diets, thereby supporting some previous studies that found increased triacylglycerol after subjects followed carbohydrate-rich diets for a few days or weeks (8, 11). Interestingly, however, these differences between diets disappeared after adjustment for differences in 14-d energy intake, differences in macronutrient intake, or changes in body weight. This highlights the results of a recent meta-analysis that showed positive relations between changes in dietary fat, changes in body weight, and changes in triacylglycerol (10). Triacylglycerol concentrations showed quite different postprandial responses to the 3 diets, especially after lunch. The continued increase in triacylglycerol with the high-sucrose diet could be a result of increased VLDL triacylglycerol synthesis in the liver from the metabolism of fructose during the high-sucrose diet (7, 34, 35). The greater triacylglycerol AUC with the high-sucrose diet than with the high-starch diet also supports the findings of Daly et al (31). The larger incremental AUCs after the high-fat diet than after the high-starch and high-sucrose diets probably reflect the higher fat content of the meals during the high-fat diet (
80 g) compared with the high-sucrose diet (
50 g) and high-starch diet (
40 g). Taken together with the other measurements of risk factors for coronary heart disease that we presented elsewhere (20), substituting a high-sucrose diet for a high-starch diet does not seem advisable. However, different subjects may display different degrees of sensitivity to hypertriglyceridemia induced by sucrose and fructose, and dose-dependent effects probably also occur (7, 36, 37).
In the present study, decrements in total NEFA concentrations were most pronounced after the high-sucrose diet. The same result was found in the study by Daly et al (31) and in another study after 30 d of a high-glycemic, high-sucrose diet compared with a low-glycemic, low-sucrose diet (32). The reason for this was most likely the higher insulin peaks during the high-sucrose diet than during the other diets. On the basis of the NEFA responses, insulin sensitivity was therefore not impaired during a sucrose-rich diet in the studies cited above (31, 32, 38, 39) or in the present study.
Gastrointestinal hormones
Both GIP and GLP-1 are potent stimulators of glucose-induced insulin secretion. Furthermore, GLP-1 was shown to reduce gastric emptying rate (40) and is considered a potential therapeutic agent for the treatment of hyperglycemia in type 2 diabetes and hyperphagia in obesity (41, 42). In the present study, GIP increased by
30% more after the high-fat diet than after the high-sucrose and high-starch diets, and this was also found after adjustment for differences in energy intake on day 15. This supports the theory that dietary fat is a more potent stimulator of GIP secretion than is carbohydrate (43, 44) and also shows that sucrose and starch apparently had the same effect on GIP. The latter finding is in contrast with an earlier study by Reiser et al (45), but can probably be explained to a large extent by the use of different methods or possibly different degrees of adaptation to the diets (44, 45). In the present study, total AUCs for GLP-1 were highest during the high-fat diet and lowest during the high-starch diet. After adjustment for energy intake, however, GLP-1 responses were
20% higher during the high-fat diet than during both the high-starch and high-sucrose diets. Therefore, fat seems to be a more potent stimulator of GLP-1 than is carbohydrate, with no difference between the types of carbohydrate used here.
Postobese compared with never-obese subjects
After the 3 ad libitum diets, we saw no differences between postobese and never-obese subjects in the changes in concentrations of fasting substrates and hormones. However, some interesting postprandial responses were observed. First, postobese women had lower glucose and insulin responses than did never-obese women during all 3 diets. This cannot be explained by differences in energy intake because postobese subjects consumed the same amount of energy or more energy than did never-obese subjects and because energy adjustment had no effect. Instead, this indicates higher insulin sensitivity overall in postobese women, a theory supported by the lower HOMA-R in postobese than in never-obese women. Increased insulin sensitivity in adipose tissue was found previously in similar subjects (14) and data from Pima Indians also support this finding, in that increased insulin sensitivity was found to be a risk factor for weight gain (46). Second, we also found lower postprandial triacylglycerol concentrations in postobese women than in never-obese women during all 3 diets. This probably reflects a lipid storage capacity that is higher overall in postobese than in never-obese subjects, which is supported by previous studies (1517). Third, no group differences were found in GIP or GLP-1 responses. This suggests that these hormones are not involved in the development of obesity, in contrast with the findings of previous studies (15, 47, 48).
Methods
The design of the present study had some advantages over previous studies. First, not only fasting concentrations, but also postprandial responses, were measured. The measurement of postprandial responses has long been recognized as necessary for evaluation of the risk factors for diabetes, but now is also being recognized as important in evaluations of risk factors for cardiovascular diseases (7). Second, we used 2 test meals instead of only 1 (15, 49, 50), because a meal given in the morning after a 1012-h fast may produce a different response than does a meal given for lunch (51, 52). This was supported by our observations of different response patterns after breakfast and lunch for glucose (especially in never-obese subjects), lactate, triacylglycerol, glycerol, GIP, and GLP-1. Third, the diets were given for 14 d instead of just 1 or 2 d, allowing some habituation to the diets. Fourth, we used an ad libitum design to mimic a more realistic situation than would the use of energy-fixed diets. A disadvantage of the present study design, however, was that we did not measure postprandial blood concentrations before the experimental diets began. We did not collect these data for both practical and theoretical reasons. We were more interested in observing the diet-induced changes after some habituation to the diets than in studying the acute changes, which were studied to some extent before (15, 31). Whether 14 d of a diet is long enough to habituate subjects is questionable; therefore, longer intervention periods are preferable in future studies.
Conclusions
In healthy, normal-weight women, carbohydrate-rich, low-fat diets with large amounts of either starch or sucrose (25% of energy as sucrose) had no adverse effects on postprandial glycemia, insulinemia, or lipidemia compared with a fat-rich diet. Comparison of the high-starch diet with the high-sucrose diet showed lower postprandial glucose concentrations and higher triaclyglycerol concentrations during the high-sucrose diet and similar insulin concentrations during the 2 diets. Comparisons of the subject groups indicated that the postobese women were more insulin-sensitive and more efficient at storing triacylglycerol than were the never-obese women, regardless of the diets they were consuming. Conversely, no group differences in concentrations of gastrointestinal hormones (GIP and GLP-1) were seen.
| ACKNOWLEDGMENTS |
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