Different glycemic indexes of breakfast cereals are not due to glucose entry into blood but to glucose removal by tissue

The Effects of Low– and High–Glycemic Index Meals on Time Trial Performance

Purpose:

The aim of this work was to determine whether the consumption of pre-exercise high– or low–glycemic index (GI) meals has a beneficial effect on time trial performance.

Methods:

Eight male cyclists were provided with either a high-GI or low-GI meal, providing 1 g·kg−1 body mass of carbohydrate, 45 min before performing a 40-km time trial on a Velotron cyclePro.

Results:

Time trial performance was significantly improved in the low-GI trial (92.5 ± 5.2 min) compared with the high-GI trial (95.6 ± 6.0 min) (P = .009). Blood glucose concentrations at the point of exhaustion were significantly higher in the low-GI trial (5.2± 0.6 mmol·L−1) compared with the high-GI trial (4.7 ± 0.7 mmol·L−1) (P = .001). There was no significant difference in estimated carbohydrate oxidation data between the low-GI (2.51 ± 1.74 g·min−1) and high-GI (2.18 ± 1.53 g·min−1) meals (P = .195). No significant difference in estimated fat oxidation was observed between the low-GI (0.15 ± 0.15 g·min−1) and high-GI (0.29 ± 0.18 g·min−1) diets (P = .83).

Conclusions:

The improvement in time trial performance for the low-GI trial may be associated with an increased availability of glucose to the working muscles, contributing additional carbohydrate for oxidation and possibly sparing limited muscle and liver glycogen stores.

Papel do índice glicêmico e da carga glicêmica na prevenção e no controle metabólico de pacientes com diabetes melito tipo 2

O controle glicêmico intensificado pode prevenir e/ou retardar o aparecimento das complicações crônicas do diabetes melito (DM). O carboidrato da dieta é o principal determinante da glicemia pós-prandial, sendo o índice glicêmico (IG) e a carga glicêmica úteis para prever a resposta glicêmica aos alimentos. O objetivo deste manuscrito foi revisar criticamente o papel das dietas de baixo IG na prevenção e controle metabólico do diabetes melito tipo 2 (DMT2). O risco para desenvolvimento de DMT2 com dietas de alto IG variou de 1,21 a 1,59. A redução de 12 a 32 unidades no IG da dieta diminuiu em 0,39 a 0,50 pontos percentuais a HbA1c. Os efeitos dessas dietas no perfil lipídico e peso corporal no DMT2 permanecem controversos. Em conclusão, as evidências atuais indicam que a incorporação do IG no planejamento dietético de pacientes com DMT2 contribui para a melhora do controle glicêmico.

Reduced energy intake at breakfast is not compensated for at lunch if a high-insoluble-fiber cereal replaces a low-fiber cereal

BACKGROUND

In cohort studies, insoluble fiber has been associated with a reduced risk of obesity and diabetes; however, compared with soluble fiber, its role in the regulation of short-term food intake (FI) and satiety has received little attention.

OBJECTIVE

Our aim was to compare the effects of a high-insoluble-fiber (HF) cereal with a low-fiber (LF) cereal on FI, subjective appetite (SA), and plasma glucose (PG) in healthy individuals.

DESIGN

Males and females (n = 32) were randomly assigned to consume 60 g of either HF (26 g insoluble fiber, 120 kcal) or LF (1 g fiber, 217 kcal) breakfast cereal. Pre- and postlunch SA and PG were measured regularly for 4 h, and ad libitum FI was measured at 3 h.

RESULTS

The prelunch SA area under the curve did not differ between the 2 cereals, but when expressed as change in appetite per kilocalorie of cereal, HF suppressed SA more than did LF (-17.6 +/- 1.8 compared with -10.0 +/- 1.1 mm . min . kcal(-)(1), respectively; P < 0.01). Lunchtime FI did not differ between cereals, but cumulative energy intake (cereal + lunch) was lower after the HF than after the LF cereal (1330 +/- 57 compared with 1422 +/- 66 kcal, respectively; P = 0.01). The prelunch PG area under the curve (P < 0.0001) and the immediate postlunch PG (P = 0.01) were lower after HF cereal consumption.

CONCLUSIONS

An HF breakfast cereal contributes to a cumulative reduction in breakfast and lunch energy intake, possibly due to its high satiety value per kilocalorie. A short-term benefit of the HF cereal, compared with LF cereal, was lower PG concentration before and immediately after lunch.

Butyrate ingestion improves hepatic glycogen storage in the re-fed rat

Background

Butyrate naturally produced by intestinal fiber fermentation is the main nutrient for colonocytes, but the metabolic effect of the fraction reaching the liver is not totally known. After glycogen hepatic depletion in the 48-hour fasting rat, we monitored the effect of (butyrate 1.90 mg + glucose 14.0 mg)/g body weight versus isocaloric (glucose 18.2 mg/g) or isoglucidic (glucose 14.0 mg/g) control force-feeding on in vivo changes in hepatic glycogen and ATP contents evaluated ex vivo by NMR in the isolated and perfused liver.

Results

The change in glycogen was biphasic with (i) an initial linear period where presence of butyrate in the diet increased (P = 0.05) the net synthesis rate (0.20 ± 0.01 μmol/min.g^-1 liver wet weight, n = 15) versus glucose 14.0 mg/g only (0.16 ± 0.01 μmol/min.g^-1 liver ww, n = 14), and (ii) a plateau of glycogen store followed by a depletion. Butyrate delayed the establishment of the equilibrium between glycogenosynthetic and glycogenolytic fluxes from the 6^th to 8^th hour post-feeding. The maximal glycogen content was then 97.27 ± 10.59 μmol/g liver ww (n = 7) at the 8^th hour, which was significantly higher than with the isocaloric control diet (64.34 ± 8.49 μmol/g, n = 12, P = 0.03) and the isoglucidic control one (49.11 ± 6.35 μmol/g liver ww, n = 6, P = 0.003). After butyrate ingestion, ATP content increased from 0.95 ± 0.29 to a plateau of 2.14 ± 0.23 μmol/g liver ww at the 8^th hour post-feeding (n = 8) [P = 0.04 versus isoglucidic control diet (1.45 ± 0.19 μmol/g, n = 8) but was not different from the isocaloric control diet (1.70 ± 0.18 μmol/g, n = 12)].

Conclusion

The main hepatic effect of butyrate is a sparing effect on glycogen storage explained (i) by competition between butyrate and glucose oxidation, glucose being preferentially directed to glycogenosynthesis during the post-prandial state; and (ii) by a likely reduced glycogenolysis from the newly synthesized glycogen. This first demonstration of the improvement of liver glycogen storage by acute butyrate supply may be an important contribution to explaining the beneficial effects on glucose homeostasis of nutritional supply increasing butyrate amount such as fiber diets.

Acute effects of dietary fibre and glycaemic carbohydrate on appetite and food intake in healthy males

The aim of this research was to describe the effect of equal weights of insoluble fibre (wheat bran) and glycaemic carbohydrate (glucose) on appetite and food intake over 1 and 2h in healthy men. In a crossover design, high-fibre (F; 41 g insoluble fibre) cereal, low-fibre (W; 1g fibre) cereal, F plus glucose (FG; 41 g glucose), and W plus glucose (WG; 41 g glucose) were administered to young men after an overnight fast. Treatments had similar fat, protein, volume and weight. In the first experiment, subjective appetite was measured at 15 min intervals before an ad libitum meal at 60 min. In the second experiment, subjective appetite was measured at 15 min intervals for the first 60 and 30 min intervals for the second 60 min before an ad libitum meal at 120 min. In experiment 1, ad libitum food intake was lower after the F, WG and FG cereals compared to W (3.1, 2.98, 2.96 and 3.59 MJ, respectively). Total energy intake (cereal+ad libitum) was lower after F compared to W and WG (4.1, 4.6, and 4.7 MJ, respectively). In experiment 2, the WG cereal significantly reduced ad libitum food intake compared to W (3.90 and 4.57 MJ, respectively). These results suggest that a serving of 41 g insoluble fibre reduces food intake independent of its weight and volume and similar to an equal weight of glucose within 60 min, but this effect is not maintained after 120 min.

Metabolic effects of dietary fiber consumption and prevention of diabetes

A high dietary fiber (DF) intake is emphasized in the recommendations of most diabetes and nutritional associations. It is accepted that viscous and gel-forming properties of soluble DF inhibit macronutrient absorption, reduce postprandial glucose response, and beneficially influence certain blood lipids. Colonic fermentation of naturally available high fiber foods can also be mainly attributed to soluble DF, whereas no difference between soluble and insoluble DF consumption on the regulation of body weight has been observed. However, in prospective cohort studies, it is primarily insoluble cereal DF and whole grains, and not soluble DF, that is consistently associated with reduced diabetes risk, suggesting that further, unknown mechanisms are likely to be involved. Recent research indicates that DF consumption contributes to a number of unexpected metabolic effects independent from changes in body weight, which include improvement of insulin sensitivity, modulation of the secretion of certain gut hormones, and effects on various metabolic and inflammatory markers that are associated with the metabolic syndrome. In this review, we briefly summarize novel findings from recent interventions and prospective cohort studies. We discuss concepts and potential mechanisms that might contribute to the further understanding of the involved processes.

Diets influence the diabetic phenotype of transgenic mice expressing a dominant negative glucose-dependent insulinotropic polypeptide receptor (GIPRdn)

Transgenic mice overexpressing a dominant negative glucose-dependent insulinotropic polypeptide receptor (GIPR(dn)) have recently been shown to develop diabetes mellitus due to disturbed postnatal development of the endocrine pancreas. In this study, the effects of feeding a high fibre/low calorie diet on the diabetic phenotype of GIPR(dn) transgenic mice were examined. Transgenic and control animals received either a conventional breeding diet (BD) or a high fibre diet (HF). Both fasting and postprandial blood glucose levels and HbA1C levels were largely elevated in transgenic mice vs. controls (p<0.05), irrespective of the diet fed. Food and water intake and the daily urine volume of GIPR(dn) transgenic mice were higher than that of control mice (p<0.05). Transgenic animals receiving the HF diet showed significantly lower blood glucose and HbA1C levels as well as less food and water intake than transgenic mice fed BD. The 365-day survival of transgenic mice was significantly lower than that of control mice. Transgenic animals fed the HF diet lived significantly longer than their counterparts receiving BD. GIPR(dn) transgenic mice develop a severe diabetic phenotype which can be ameliorated by a HF diet, thereby resembling some aspects of the pathophysiology of human type 2 diabetes mellitus.

Effect of commercial breakfast fibre cereals compared with corn flakes on postprandial blood glucose, gastric emptying and satiety in healthy subjects: a randomized blinded crossover trial

Background

Dietary fibre food intake is related to a reduced risk of developing diabetes mellitus. However, the mechanism of this effect is still not clear. The aim of this study was to evaluate the effect of commercial fibre cereals on the rate of gastric emptying, postprandial glucose response and satiety in healthy subjects.

Methods

Gastric emptying rate (GER) was measured by standardized real time ultrasonography. Twelve healthy subjects were assessed using a randomized crossover blinded trial. The subjects were examined after an 8 hour fast and after assessment of normal fasting blood glucose level. Satiety scores were estimated and blood glucose measurements were taken before and at 0, 20, 30, 40, 60, 80, 100 and 120 min after the end of the meal. GER was calculated as the percentage change in the antral cross-sectional area 15 and 90 min after ingestion of sour milk with corn flakes (GER1), cereal bran flakes (GER2) or wholemeal oat flakes (GER3).

Results

The median value was, respectively, 42% for GER1, 33 % for GER2 and 51% for GER3. The difference between the GER after ingestion of bran flakes compared to wholemeal oat flakes was statistically significant (p = 0.023). The postprandial delta blood glucose level was statistically significantly lower at 40 min (p = 0.045) and 120 min (p = 0.023) after the cereal bran flakes meal. There was no statistical significance between the areas under the curve (AUCs) of the cereals as far as blood glucose and satiety were concerned.

Conclusion

The result of this study demonstrates that the intake of either bran flakes or wholemeal oat flakes has no effect on the total postprandial blood glucose response or satiety when compared to corn flakes. However, the study does show that the intake of cereal bran flakes slows the GER when compared to oat flakes and corn flakes, probably due to a higher fibre content. Since these products do not differ in terms of glucose response and satiety on healthy subjects, they should be considered equivalent in this respect.

Trial registration

ISRCTN90535566

Low-glycaemic diets and health: implications for obesity

The present review considers the background to terminology that relates foods, glycaemia and health, including ‘available carbohydrate’, ‘glycaemic index’ (GI), 'glycaemic glucose equivalent', 'glycaemic response index' and 'net carbohydrate', and concludes that central to each of these terms is 'glycaemic load' (GL). GL represents the acute increase in exposure of tissue to glucose determined by foods; it is expressed in ingested glucose equivalents (per 100 g fresh weight or per serving), and is regarded as independent of the state of glucose metabolism from normal to type 2 diabetes mellitus (T2DM). Ad libitum studies in overweight or obese adults and children show that low-GL diets are associated with marked weight benefits, loss of adiposity and reduced food intake. Weight benefits appear on low-glycaemic v. high-glycaemic available carbohydrates, unavailable v. available carbohydrates and protein v. available carbohydrate. Energy intake immediately after lowering of meal GL via carbohydrate exchanges is apparent only after a threshold cumulative intake of >2000 MJ. Various epidemiological and interventional studies are discussed. A relationship between GL and the development of T2DM and CHD is evident. Studies that at first seem conflicting are actually consistent when data are overlaid, such that diets with a GL of >120 glucose equivalents/d would appear to be inadvisable. Whereas certain studies might place GI as being slightly stronger than GL in relationto T2DM risk, this situation appears to be associated with observations in a lower range of GL or when the range of GI is too narrow for accuracy; nevertheless, authors emphasise the importance of GL. Among the studies reviewed, GL offers a better or stronger explanation than GI in various observations including body weight, T2DM in nurses, CHD, plasma triacylglycerols, HDL-cholesterol, high-sensitivity C-reactive protein and protein glycation. Where information is available, the associations between risk factors and GL are either similar or stronger in the overweight or obese, as judged by BMI, and apply to both body weight and blood risk factors. The implications tend to favour a long-term benefit of reducing GL, for which further study is necessary to eliminate any possibility of publication bias and to establish results in clinical trials with overweight and obese patients.

The influence of the subjects' training state on the glycemic index

OBJECTIVE

To determine the glycemic index (GI) dependence on the training state of healthy adult males.

SUBJECTS AND DESIGN

Young, adult males of normal body mass index and normal glucose tolerance were tested twice with a 50 g reference glucose solution and twice with a breakfast cereal containing 50 g of available carbohydrates in a randomized order. Ten subjects were sedentary (SE), 12 were moderately trained (MT) and 12 were endurance trained (ET). Blood glucose, insulin and glucagon were measured.

RESULTS

The GI differed significantly between SE and ET subjects (P=0.02, mean difference: 23 GI units, 95% CI=3-42 GI units). The GI of the MT subjects was intermediary, but did not differ significantly from the SE or ET subjects. The insulin index did not differ significantly between the groups (P=0.65).

CONCLUSION

The GI of the commercially available breakfast cereal depended on the training state of the healthy males. The training state is the first reported factor influencing the GI that is subject specific rather than food specific.

Effect of Acute Prior Exercise on Glycemic and Insulinemic Indices

BACKGROUND

Acute exercise is associated with increased insulin sensitivity characterized by increased insulin-induced glucose transport for periods of up to 48 h after the bout of exercise. This suggests that the glycemic response to a meal may be altered by prior exercise.

OBJECTIVE

We tested the hypothesis that the glycemic and insulinemic responses to a test food consumed following exercise would be lower than when consumed without prior exercise.

DESIGN

Four lean males (age: 27 +/- 4 y) and 4 females (age: 23 +/- 3 y) completed 3 experimental conditions in random order: ExCHO-Subjects exercised on a cycle ergometer at 70% VO2peak with a net energy cost of 400 kcal, which was followed by consumption of a high carbohydrate (CHO) energy bar; NoExCHO-Same as ExCHO except subjects sat quietly rather than exercised; and NoExGlc-Same as NoExCHO except subjects consumed a 50 g glucose (glc) drink as the reference CHO for GI and insulinemic index (II) determination. For each condition, following exercise or rest, baseline venous blood samples were obtained. Postprandial blood samples were obtained at 15 min intervals for 2 h.

RESULTS

Neither the 2-h glucose area under the curve (AUC) or the GI were different between ExCHO and NoExCHO. The insulin AUC for ExCHO was 28% lower than the insulin AUC for NoExCHO (p = 0.03). The calculated II for the ExCHO condition was 30% lower than that of NoExCHO (p = 0.05).

CONCLUSIONS

An acute bout of prior exercise had no effect on the GI of an energy bar compared to that of the same food determined under the standard no-exercise conditions. However, prior exercise resulted in a lower 2-h insulin response to the CHO-rich energy bar.

Carob pulp preparation rich in insoluble dietary fiber and polyphenols enhances lipid oxidation and lowers postprandial acylated ghrelin in humans

Ghrelin is an orexigenic hormone that may affect substrate utilization in humans. Ghrelin is influenced by macronutrients, but the effects of insoluble dietary fiber and polyphenols are unknown. We investigated the effects of a polyphenol-rich insoluble dietary fiber preparation from carob pulp (carob fiber) on postprandial ghrelin responses and substrate utilization. Dose-dependent effects of the consumption of carob fiber were investigated in a randomized, single-blind, crossover study in 20 healthy subjects, aged 22-62 y. Plasma total and acylated ghrelin, triglycerides, and serum insulin and nonesterified fatty acids (NEFA) levels were repeatedly assessed before and after ingestion of an isocaloric standardized liquid meal with 0, 5, 10, or 20 g of carob fiber over a 300-min period. The respiratory quotient (RQ) was determined after consumption of 0 or 20 g of carob fiber. Carob fiber intake lowered acylated ghrelin to 49.1%, triglycerides to 97.2%, and NEFA to 67.2% compared with the control meal (P < 0.001). Total ghrelin and insulin concentrations were not affected by consumption of a carob fiber-enriched liquid meal. Postprandial energy expenditure was increased by 42.3% and RQ was reduced by 99.9% after a liquid meal with carob fiber compared with a control meal (P < 0.001). We showed that the consumption of a carob pulp preparation, an insoluble dietary fiber rich in polyphenols, decreases postprandial responses of acylated ghrelin, triglycerides, and NEFA and alters RQ, suggesting a change toward increased fatty acid oxidation. These results indicate that carob fiber might exert beneficial effects in energy intake and body weight.

Maximizing acute fat utilization: effects of exercise, food, and individual characteristics

In discussion of the physiological mechanisms that regulate fat metabolism, and with consideration of the metabolic stimuli that modulate substrate metabolism, the issue of how an acute state of negative lipid balance can be maximized is addressed. The regulation of lipolysis by catecholamines and insulin is reviewed, and the mechanisms of fatty acid mobilization and uptake by muscle are also briefly discussed. The implications of substrate availability and the hormonal response during physiological states such as fasting, exercise, and after food intake are also addressed, with particular regard to the influences on fatty acid mobilization and/or oxidation from eliciting these stimuli conjointly. Finally, a brief discussion is given of both the nature of exercise and the exercising individual, and how these factors influence fat metabolism during exercise. It is also a primary thrust of this paper to underline gaps in the existing literature with regard to exercise timing concerning food ingestion for maximizing acute lipid utilization.

Impact of cereal fibre on glucose-regulating factors

AIMS/HYPOTHESIS

Insoluble dietary fibre intake is associated, by unknown mechanisms, with a reduced risk of type 2 diabetes. We investigated whether a short-term dietary intervention with purified insoluble fibres influences acute and delayed responses of glucose, insulin, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1.

METHODS

Fourteen healthy women with NGT were studied for 300 min on six to eight occasions. Subjects consumed three matched portions of control (C) or fibre-enriched bread (10.4-10.6 g/portion; wheat fibre [WF], oat fibre [OF], and, in a substudy [n=9], resistant starch [RS]) followed by control (C-C, C-WF, C-OF, C-RS) on subsequent days.

RESULTS

Fibre enrichment accelerated the early insulin response (fibrextime interaction p=0.026 for WF, p<0.001 for OF, p=0.126 for RS; time of maximal concentration [T(max)], C 57.9+/-5.9, WF 49.3+/-2.5 [p=0.086], OF 46.1+/-2.9 [p=0.026], RS 46.7+/-5.8 min [p=0.029]). It was also associated with an earlier postprandial GIP response after OF (T(max), C 83.6+/-7.2, WF 70.7+/-6.0 [p=0.054], OF 64.3+/-6.9 [p=0.022], RS 60.0+/-5.0 [p>0.15]). Increased fibre intake for 24 h was further associated with a reduced postprandial glucose response on the following day subsequent to ingestion of a control meal (AUC(C-C) 4,140+/-401, AUC(C-WF) 2,850+/-331 [p=0.007], AUC(C-OF) 2,830+/-277 [p=0.011]), with no difference in maximal concentration and T(max) of glucose responses. No differences in insulin responses were observed 24 h after the fibre-enriched diets compared with control (p>0.15). Colonic fermentation was increased only on study days C-OF (p=0.017) and C-RS (p=0.016).

CONCLUSIONS/INTERPRETATION

The consumption of highly purified insoluble dietary fibres accelerated the acute GIP and insulin response and was further associated with enhanced postprandial carbohydrate handling the following day upon ingestion of a control meal.

Glycemic responses of oat bran products in type 2 diabetic patients

BACKGROUND AND AIM

Cereal products with low postprandial glycemic response are encouraged in the management of hyperglycemia. In this study, we determined the postprandial glycemic response of two different oat bran products in patients with type 2 diabetes. In addition, we investigated the effects of oat bran flour on postprandial glucose response following an oral glucose load.

METHODS AND RESULTS

A randomized, controlled, repeated measures design with two test series was used. Twelve type 2 diabetic patients participated in five 2-h meal glucose tolerance tests on separate occasions. Volunteers were given in random order oat bran flour, oat bran crisp and glucose load providing 12.5 g glycemic carbohydrate (series 1), 25 g glucose load alone and 25 g glucose load with 30 g oat bran flour (series 2). Finger-prick capillary blood analysis was carried out fasting and then 15, 30, 45, 60, 90 and 120 min after the start of the meal. The oat bran flour had a lower 0-120 min area under the glucose response curve (AUC) (47+/-45 mmol min/L) than the glucose load (118+/-40 mmol min/L) (p<0.002), but there was no difference between the oat bran crisp (93+/-41 mmol min/L) and the glucose load in this respect. The oat bran flour decreased the glucose excursion from baseline by 1.6 mmol/l (2.4, 0.8) (mean (95% CI)) and 1.5 mmol/l (2.0, 1.1) at 30 and 45 min after the glucose load, respectively.

CONCLUSIONS

Oat bran flour high in beta-glucan had a low glycemic response and acted as an active ingredient decreasing postprandial glycemic response of an oral glucose load in subjects with type 2 diabetes.

Glycemic index and load-dynamic dietary guidelines in the context of diseases

The concepts of glycemic index (GI) and glycemic load (GL) are among a new generation of so-called dynamic dietary guidelines. In contrast to classical static guidelines, these new guidelines do not primarily consider the absolute amount of energy or nutrient to be ingested within 24 h, but rather are focused on the postprandial response. It is claimed that low-GI and -GL diets favorably affect many noncommunicable diseases that are prevalent in developed countries, including type II diabetes, insulin resistance, obesity, cardiovascular disease (CVD), and cancer. During the past 20 years, considerable evidence has accumulated suggesting that low-GI or -GL diets indeed positively influence some but not all diseases. Because virtually no deleterious effects of low-GI and -GL diets have been documented thus far or are to be expected, the promotion of these diets should be considered in the management of noncommunicable diseases.

The use of glycaemic index tables to predict glycaemic index of composite breakfast meals

The applicability of the glycaemic index (GI) in the context of mixed meals and diets is still debatable. The objective of the present study was to investigate the predictability of measured GI in composite breakfast meals when calculated from table values, and to develop prediction equations using meal components. Furthermore, we aimed to study the relationship between GI and insulinaemic index (II). The study was a randomised cross-over meal test including twenty-eight healthy young men. Thirteen breakfast meals and a reference meal were tested. All meals contained 50 g available carbohydrate, but differed considerably in energy and macronutrient composition. Venous blood was sampled for 2 h and analysed for glucose and insulin. Prediction equations were made by regression analysis. No association was found between predicted and measured GI. The meal content of energy and fat was inversely associated with GI (R(2) 0.93 and 0.88, respectively; P<0.001). Carbohydrate content (expressed as percentage of energy) was positively related to GI (R(2) 0.80; P<0.001). Using multivariate analysis the GI of meals was best predicted by fat and protein contents (R(2) 0.93; P<0.001). There was no association between GI and II. In conclusion, the present results show that the GI of mixed meals calculated by table values does not predict the measured GI and furthermore that carbohydrates do not play the most important role for GI in mixed breakfast meals. Our prediction models show that the GI of mixed meals is more strongly correlated either with fat and protein content, or with energy content, than with carbohydrate content alone. Furthermore, GI was not correlated with II.

Carbohydrate and weight control: where do we stand?

PURPOSE OF THE REVIEW

The Atkins diet has been criticized and vilified by much of the scientific community since it was proposed 30 years ago, because it challenged nutritional recommendations and dietary guidelines for a healthy diet. However, in spite of such recommendations the prevalence of obesity continues to rise. The present review evaluates recent scientific evidence and attempts to reach consensus on the confusion of weight-reducing diets.

RECENT FINDINGS

Many dietary macronutrient paradigms have been proposed for the treatment of obesity. Since obesity in its dynamic phase is the result of energy intake exceeding energy expenditure, intuitively to lose weight energy intake should be less than energy expenditure, and one might expect that the macronutrient composition of the diet would have very little, if any, effect. However, short- and long-term therapies with low-carbohydrate or high-protein diets appear to offer advantages over conventional weight-loss regimens for weight loss, body composition and cardiovascular risk factors.

SUMMARY

Low-carbohydrate, Atkins-type diets have been demonstrated to have positive effects on weight loss and biomarkers of cardiovascular risk, which has prompted some researchers to question the validity of present-day dietary guidelines. Although evidence is accumulating in their favour, the safety and efficacy of low-carbohydrate, high-protein diets needs further long-term verification.

High-fiber cereal reduces postprandial insulin responses in hyperinsulinemic but not normoinsulinemic subjects

OBJECTIVE

The objective of this study was to compare the plasma glucose and insulin responses elicited by two ready-to-eat breakfast cereals (one being high and the other being low in cereal fiber) and to see if the differences in response depended on subjects' fasting plasma insulin.

RESEARCH DESIGN AND METHODS

Nondiabetic men (n = 77) were studied on two occasions after 10- to 14-h overnight fasts. They consumed 25 g of available carbohydrate from high- or low-fiber breakfast cereals in random order with blood taken at intervals for 2 h. Data from the 42 men with high fasting plasma insulin (FPI) on screening (>40 pmol/l) were compared with those from the 35 men with normal FPI (< or =40 pmol/l).

RESULTS

Hyperinsulinemic men had significantly higher waist circumference and BMI, lower HDL cholesterol, and a trend toward higher triglycerides (P = 0.07) than control subjects. In all 77 subjects, the incremental area under the glucose response curve (AUC) after high-fiber cereal was 11.8 +/- 5.5% (P = 0.036) less than after low-fiber cereal with the reductions being equivalent in the hyperinsulinemic (12.6 +/- 8.3%) and control (10.9 +/- 9.1%) groups. However, insulin peak rise was reduced by the high-fiber cereal only in hyperinsulinemic men (351 +/- 29 vs. 485 +/- 55 pmol/l) but not in control subjects (211 +/- 20 vs. 220 +/- 20 pmol/l; cereal x group interaction P = 0.044). Insulin AUC after the high-fiber cereal, expressed as a percentage of that after low-fiber cereal, was negatively related to FPI (P = 0.009) but not to age, BMI, or waist circumference.

CONCLUSIONS

The high-fiber cereal reduced glucose responses to the same extent in normal and hyperinsulinemic men, but reduced insulin responses only in hyperinsulinemic subjects.