Glycaemic index effects on fuel partitioning in humans

Low Glycemic Index Prototype Isomaltulose-Update of Clinical Trials

Low glycemic index diets are supposed to achieve a more beneficial effect on blood glucose control in people with diabetes mellitus and may also provide metabolic benefits for the general population. A prototype of a low-glycemic index carbohydrate is the natural occurring disaccharide isomaltulose that can be commercially produced from sucrose (beet sugar) to industrial scale. It is currently used in various food and drink applications as well as special and clinical nutrition feeds and formula diet as a food ingredient and alternative sugar. Here we provide an overview on clinical trials with isomaltulose including an analysis of its effects on glycemia and fat oxidation as compared to high glycemic index sugars and carbohydrates. In addition, we discuss recent reports on beneficial effects in weight-loss maintenance and pregnancy.

Impact of dietary glycemic challenge on fuel partitioning

The 'carbohydrate-insulin theory of obesity' is used to justify popular health claims stating that carbohydrates make you fat or a high glycemic load and consumption of sugar-sweetened beverages (SSBs) and breakfast skipping increase fat gain. According to this theory, the elevated postprandial insulin secretion to a high glycemic challenge is blamed as a causal mechanism by directing nutrients away from oxidation in muscle towards storage in adipose tissue. Scientific evidence is however largely disagreeing with an adverse effect of postprandial hyperinsulinemia on fuel partitioning. Possible reasons for this disagreement are differences in insulin sensitivity and energy balance. Diet-induced hyperinsulinemia may lead to a higher fat storage only at a positive energy balance. A shift in fuel partitioning towards fat storage requires improved or maintained insulin sensitivity in adipose tissue when compared with skeletal muscle. This may be the case during refeeding (after weight loss), physical inactivity or in metabolically healthy obese subjects (relative to insulin-resistant subjects). The adverse effect of a high-glycemic diet, SSBs consumption or breakfast skipping on body weight is likely due to increased energy consumption rather than to increased fat storage.

Effect of low-glycemic-sugar-sweetened beverages on glucose metabolism and macronutrient oxidation in healthy men

BACKGROUND/OBJECTIVES

Sugar-sweetened-beverages (SSB) provide high amounts of rapidly absorbable sugar and have been shown to impair insulin sensitivity and promote weight gain. We hypothesized that when compared with high-glycemic index (GI) SSB low-GI SSB lead to lower insulin secretion and thus an improved preservation of insulin sensitivity and fat oxidation during an inactive phase.

SUBJECTS/METHODS

In a controlled cross-over dietary intervention 13 healthy men (age: 23.7±2.2 years, body mass index: 23.6±1.9 kg m(-)(2)) consumed low-GI (isomaltulose) or high-GI (75% maltodextrin+25% sucrose, adapted for sweetness) SSBs providing 20% of energy requirement for 7 days. During this phase, participant's habitual high physical activity (11 375±3124 steps per day) was reduced (2363±900 steps per day). The provided ad libitum diet comprised 55% CHO, 30% fat and 15% protein. Glycemic and insulinemic responses were assessed: Day-long (7-day continuous interstitial glucose monitoring, 24-h-urinary c-peptide excretion), during meal test (37 g isomaltulose vs 28 g maltodextrin+9g sucrose) and measures of insulin sensitivity (basal: homeostasis model assessment of insulin resistance (HOMA-IR), postprandial: Matsuda-ISI). Macronutrient oxidation was assessed by non-protein respiratory quotient (npRQ) in the fasted state (npRQfasting) and postprandial as the area under the npRQ-curve during meal test (npRQtAUC-meal).

RESULTS

Day-long glycemia was lower with low-GI compared with high-GI SSB (-5%, P<0.05). Low-GI SSB led to lower insulin secretion during meal test (-28%, P<0.01) and throughout the day (-31%, P<0.01), whereas postprandial glucose levels did not differ between low-GI and high-GI SSBs. Insulin sensitivity deteriorated on inactivity with both SSBs, but was better preserved with low-GI isomaltulose compared with high-GI maltodextrin-sucrose (ΔHOMA-IR: +0.37±0.52 vs +0.85±0.86; ΔMatsuda-ISI: -5.1±5.5 vs -9.6±5.1, both P<0.05). Both, fasting and postprandial fat oxidation declined on inactivity, with no difference between high-GI and low-GI SSBs.

CONCLUSIONS

Compared with high-GI SSB, 7-day consumption of beverages sweetened with low-GI isomaltulose had beneficial effects on inactivity-induced impairment of glucose metabolism without effecting fuel selection.

Postprandial thermogenesis and respiratory quotient in response to galactose: comparison with glucose and fructose in healthy young adults

Circumstantial evidence suggests that substitution of glucose or sucrose by the low-glycaemic index sugar galactose in the diet may lead to greater thermogenesis and/or fat oxidation. Using ventilated hood indirect calorimetry, we investigated, in twelve overnight-fasted adults, the resting energy expenditure (REE) and respiratory quotient (RQ) for 30 min before and 150 min after ingestion of 500 ml of water containing 60 g of glucose, fructose or galactose in a randomised cross-over design. REE increased similarly with all three sugars, reaching peak values after 50–60 min, but its subsequent fall towards baseline values was faster with galactose and glucose than with fructose (P < 0·001). RQ increased with all three sugars, but to a much greater extent with galactose and fructose than with glucose, particularly after 1 h post-ingestion. When ingested as a sugary drink, postprandial thermogenesis and utilisation of fat after galactose are not higher than after glucose or fructose.

Impact of carbohydrates on weight regain

PURPOSE OF REVIEW

Research on obesity treatment has shifted its focus from weight loss to weight-loss maintenance strategies. The conventional approach of a low-fat diet is challenged by insights from glycemic effects of carbohydrates on body weight regulation.

RECENT FINDINGS

Metabolic and endocrine adaptations to weight loss that contribute to weight regain involve reduced energy expenditure, increased insulin sensitivity, and enhanced orexigenic signals. This review summarizes the impact of carbohydrates on energetic efficiency, partitioning of weight regain as fat and lean mass, and appetite control. Both the amount and frequency of postprandial glycemia add to body weight regulation after weight loss and strengthen the concept of glycemic index and glycemic load. In addition, dietary fiber and slowly or poorly absorbable functional sugars modify gastrointestinal peptides involved in appetite and metabolic regulation and exert prebiotic effects.

SUMMARY

Current evidence suggests that a low-glycemic load diet with a preference for low-glycemic index foods and integration of slowly digestible, poorly absorbable carbohydrates may improve weight-loss maintenance. Future studies should investigate the health benefits of low glycemic functional sweeteners (e.g., isomaltulose and tagatose).

Carbohydrate intake and glycemic index affect substrate oxidation during a controlled weight cycle in healthy men

BACKGROUND/OBJECTIVES

Because both, glycemic index (GI) and carbohydrate content of the diet increase insulin levels and could thus impair fat oxidation, we hypothesized that refeeding a low GI, moderate-carbohydrate diet facilitates weight maintenance.

SUBJECTS/METHODS

Healthy men (n=32, age 26.0±3.9 years; BMI 23.4±2.0 kg/m(2)) followed 1 week of controlled overfeeding, 3 weeks of caloric restriction and 2 weeks of hypercaloric refeeding (+50, -50 and +50% energy requirement) with low vs high GI (41 vs 74) and moderate vs high CHO intake (50% vs 65% energy). We measured adaptation of fasting macronutrient oxidation and the capacity to supress fat oxidation during an oral glucose tolerance test. Changes in fat mass were measured by quantitative magnetic resonance.

RESULTS

During overfeeding, participants gained 1.9±1.2 kg body weight, followed by a weight loss of -6.3±0.6 kg and weight regain of 2.8±1.0 kg. Subjects with 65% CHO gained more body weight compared with 50% CHO diet (P<0.05) particularly with HGI meals (P<0.01). Refeeding a high-GI diet led to an impaired basal fat oxidation when compared with a low-GI diet (P<0.02), especially at 65% CHO intake. Postprandial metabolic flexibility was unaffected by refeeding at 50% CHO but clearly impaired by 65% CHO diet (P<0.05). Impairment in fasting fat oxidation was associated with regain in fat mass (r=0.43, P<0.05) and body weight (r=0.35; P=0.051).

CONCLUSIONS

Both higher GI and higher carbohydrate content affect substrate oxidation and thus the regain in body weight in healthy men. These results argue in favor of a lower glycemic load diet for weight maintenance after weight loss.

Effect of the glycemic index of the diet on weight loss, modulation of satiety, inflammation, and other metabolic risk factors: a randomized controlled trial

BACKGROUND

Low-glycemic index (GI) diets have been proven to have beneficial effects in such chronic conditions as type 2 diabetes, ischemic heart disease, and some types of cancer, but the effect of low-GI diets on weight loss, satiety, and inflammation is still controversial.

OBJECTIVE

We assessed the efficacy of 2 moderate-carbohydrate diets and a low-fat diet with different GIs on weight loss and the modulation of satiety, inflammation, and other metabolic risk markers.

DESIGN

The GLYNDIET study is a 6-mo randomized, parallel, controlled clinical trial conducted in 122 overweight and obese adults. Participants were randomly assigned to one of the following 3 isocaloric energy-restricted diets for 6 mo: 1) a moderate-carbohydrate and high-GI diet (HGI), 2) a moderate-carbohydrate and low-GI diet (LGI), and 3) a low-fat and high-GI diet (LF).

RESULTS

At weeks 16 and 20 and the end of the intervention, changes in body mass index (BMI; in kg/m(2)) differed significantly between intervention groups. Reductions in BMI were greater in the LGI group than in the LF group, whereas in the HGI group, reductions in BMI did not differ significantly from those in the other 2 groups (LGI: -2.45 ± 0.27; HGI: -2.30 ± 0.27; LF: -1.43 ± 0.27; F = 4.616, P = 0.012; pairwise comparisons: LGI compared with HGI, P = 1.000; LGI compared with LF, P = 0.016; HGI compared with LF, P = 0.061). The decrease in fasting insulin, homeostatic model assessment of insulin resistance, and homeostatic model assessment of β cell function was also significantly greater in the LGI group than in the LF group (P < 0.05). Despite this tendency for a greater improvement with a low-GI diet, the 3 intervention groups were not observed to have different effects on hunger, satiety, lipid profiles, or other inflammatory and metabolic risk markers.

CONCLUSION

A low-GI and energy-restricted diet containing moderate amounts of carbohydrates may be more effective than a high-GI and low-fat diet at reducing body weight and controlling glucose and insulin metabolism. This trial was registered at Current Controlled Trials (www.controlled-trials.com) as ISRCTN54971867.

Body weight regulation and obesity: dietary strategies to improve the metabolic profile

This review discusses dietary strategies that may improve the metabolic profile and body weight regulation in obesity. Recent evidence demonstrated that long-term health effects seem to be more beneficial for low-glycemic index (GI) diets compared to high-protein diets. Still, these results need to be confirmed by other prospective cohort studies and long-term clinical trials, and the discrepancy between these study designs needs to be explored in more detail. Furthermore, the current literature is mixed with regard to the efficacy of increased meal frequency (or snacking) regimens in causing metabolic alterations, particularly in relation to body weight control. In conclusion, a growing body of evidence suggests that dietary strategies with the aim to reduce postprandial insulin response and increase fat oxidation, and that tend to restore metabolic flexibility, have a place in the prevention and treatment of obesity and associated metabolic disorders.

Cereal processing influences postprandial glucose metabolism as well as the GI effect

Objective: Technological processes may influence the release of glucose in starch. The aim of this study was to compare the metabolic response and the kinetics of appearance of exogenous glucose from 2 cereal products consumed at breakfast.

Methods: Twenty-five healthy men were submitted to a randomized, open, crossover study that was divided into 2 parts: 12 of the 25 subjects were included in the “isotope part,” and the 13 other subjects were included in the “glycemic part.” On test days, subjects received biscuits (low glycemic index [GI], high slowly available glucose [SAG]) or extruded cereals (medium GI, low SAG) as part of a breakfast similar in terms of caloric and macronutrient content. The postprandial phase lasted 270 minutes.

Results: The rate of appearance (RaE) of exogenous glucose was significantly lower after consumption of biscuits in the first part of the morning (90–150 minutes) than after consumption of extruded cereals (p ≤ 0.05). Conversely, at 210 minutes, it was significantly higher with biscuits (p ≤ 0.01). For the first 2 hours, plasma glucose and insulin were significantly lower after biscuits during the glycemic part. C-peptide plasma concentrations were significantly lower at 90, 120, and 150 minutes after ingestion of the biscuits (p ≤ 0.05).

Conclusion: The consumption of biscuits with a high content of slowly digestible starch reduces the appearance rate of glucose in the first part of the morning and prolongs this release in the late phase of the morning (210 minutes). Our results also emphasize that modulation of glucose availability at breakfast is an important factor for metabolic control throughout the morning in healthy subjects due to the lowering of blood glucose and insulin excursions.

A low-glycemic diet lifestyle intervention improves fat utilization during exercise in older obese humans

OBJECTIVE

To determine the influence of dietary glycemic index on exercise training-induced adaptations in substrate oxidation in obesity.

DESIGN AND METHODS

Twenty older, obese individuals undertook 3 months of fully supervised aerobic exercise and were randomized to low- (LoGIX) or high-glycemic (HiGIX) diets. Changes in indirect calorimetry (VO2 ; VCO2 ) were assessed at rest, during a hyperinsulinemic-euglycemic clamp, and during submaximal exercise (walking: 65% VO2 max, 200 kcal energy expenditure). Intramyocellular lipid (IMCL) was measured by (1) H-magnetic resonance spectroscopy.

RESULTS

Weight loss (-8.6 ± 1.1%) and improvements (P < 0.05) in VO2 max, glycemic control, fasting lipemia, and metabolic flexibility were similar for both LoGIX and HiGIX groups. During submaximal exercise, energy expenditure was higher following the intervention (P < 0.01) in both groups. Respiratory exchange ratio during exercise was unchanged in the LoGIX group but increased in the HiGIX group (P < 0.05). However, fat oxidation during exercise expressed in relation to changes in body weight was increased in the LoGIX group (+10.6 ± 3.6%; P < 0.05). Fasting IMCL was unchanged, however, extramyocellular lipid was reduced (P < 0.05) after LoGIX.

CONCLUSIONS

A LoGIX/exercise weight-loss intervention increased fat utilization during exercise independent of changes in energy expenditure. This highlights the potential therapeutic value of low-glycemic foods for reversing metabolic defects in obesity.

Effect of glycemic index and fructose content in lunch on substrate utilization during subsequent brisk walking

The purpose of the present study was to investigate the effect of glycemic index (GI) and fructose content in lunch on substrate utilization during subsequent brisk walking. Ten healthy young males completed 3 main trials in a counterbalanced crossover design. They completed 60 min of brisk walking at approximately 50% maximal oxygen consumption after consuming a standard breakfast and 1 of 3 lunch meals, i.e., a low GI meal without fructose (LGI), a low GI meal that included fructose beverage (LGIF), or a high GI meal (HGI). The 3 lunch meals were isocaloric and provided 1.0 g·kg⁻¹ carbohydrate. Substrate utilization was measured using indirect respiratory calorimetry method. Blood samples were collected at certain time points. During the 2-h postprandial period after lunch, the incremental area under the blood response curve values of glucose and insulin were higher (p < 0.05) in the HGI trial than those in the LGI and LGIF trials (HGI vs. LGI and LGIF: glucose, 223.5 ± 24.4 vs. 92.5 ± 10.4 and 128.0 ± 17.7 mmol·min·L⁻¹; insulin, 3603 ± 593 vs. 1425 ± 289 and 1888 ± 114 mU·min·L⁻¹). During brisk walking, decreased carbohydrate oxidation was observed (p < 0.05) in the LGI trial than in the LGIF and HGI trials (LGI vs. LGIF and HGI: 60.8 ± 4.0 vs. 68.1 ± 6.0 and 74.4 ± 4.7 g). No difference was found in fat oxidation among the 3 trials (LGI vs. LGIF vs. HGI: 21.6 ± 2.3 vs. 19.2 ± 2.3 vs. 16.4 ± 2.2 g). It appeared that fructose content was an important influencing factor when considering the effect of different GI lunch meals on substrate utilization during subsequent moderate intensity exercise.

New perspectives on nutritional interventions to augment lipid utilisation during exercise

The enhancement of fat oxidation during exercise is an aim for both recreational exercising individuals and endurance athletes. Nutritional status may explain a large part of the variation in maximal rates of fat oxidation during exercise. This review reveals novel insights into nutritional manipulation of substrate selection during exercise, explaining putative mechanisms of action and evaluating the current evidence. Lowering the glycaemic index of the pre-exercise meal can enhance lipid utilisation by up to 100 % through reduced insulin concentrations, although its application may be restricted to specific training sessions rather than competition. Chronic effects of dietary glycaemic index are less clear and warrant future study before firm recommendations can be made. A flurry of recent advances has overthrown the conventional view of l-carnitine supplementation, with skeletal muscle uptake possible under certain dietary conditions and providing a strategy to influence energy metabolism in an exercise intensity-dependent manner. Use of non-carbohydrate nutrients to stimulate muscle l-carnitine uptake may prove more beneficial for optimising lipid utilisation, but this requires more research. Studies investigating fish oil supplementation on fat oxidation during exercise are conflicting. In spite of some strong putative mechanisms, the only crossover trial showed no significant effect on lipid use during exercise. Ca may increase NEFA availability although it is not clear whether these effects occur. Ca and caffeine can increase NEFA availability under certain circumstances which could theoretically enhance fat oxidation, yet strong experimental evidence for this effect during exercise is lacking. Co-administration of nutrients to maximise their effectiveness needs further investigation.

Coffee polyphenols modulate whole-body substrate oxidation and suppress postprandial hyperglycaemia, hyperinsulinaemia and hyperlipidaemia

Postprandial energy metabolism, including postprandial hyperglycaemia, hyperinsulinaemia and hyperlipidaemia, is related to the risk for developing obesity and CVD. In the present study, we examined the effects of polyphenols purified from coffee (coffee polyphenols (CPP)) on postprandial carbohydrate and lipid metabolism, and whole-body substrate oxidation in C57BL/6J mice. In mice that co-ingested CPP with a lipid-carbohydrate (sucrose or starch)-mixed emulsion, the respiratory quotient determined by indirect calorimetry was significantly lower than that in control mice, whereas there was no difference in VO2 (energy expenditure), indicating that CPP modulates postprandial energy partitioning. CPP also suppressed postprandial increases in plasma glucose, insulin, glucose-dependent insulinotropic polypeptide and TAG levels. Inhibition experiments on digestive enzymes revealed that CPP inhibits maltase and sucrase, and, to a lesser extent, pancreatic lipase in a concentration-dependent manner. Among the nine kinds of polyphenols (caffeoyl quinic acids (CQA), di-CQA, feruloyl quinic acids (FQA)) contained in CPP, di-CQA showed more potent inhibitory activity than CQA or FQA on these digestive enzymes, suggesting a predominant role of di-CQA in the regulation of postprandial energy metabolism. These results suggest that CPP modulates whole-body substrate oxidation by suppressing postprandial hyperglycaemia and hyperinsulinaemia, and these effects are mediated by inhibiting digestive enzymes.

A low glycemic index diet does not affect postprandial energy metabolism but decreases postprandial insulinemia and increases fullness ratings in healthy women

At present, it is difficult to determine whether glycemic index (GI) is an important tool in the prevention of lifestyle diseases, and long-term studies investigating GI with diets matched in macronutrient composition, fiber content, energy content, and energy density are still scarce. We investigated the effects of 2 high-carbohydrate (55%) diets with low GI (LGI; 79) or high GI (HGI; 103) on postprandial blood profile, subjective appetite sensations, energy expenditure (EE), substrate oxidation rates, and ad libitum energy intake (EI) from a corresponding test meal (LGI or HGI) after consuming the diets ad libitum for 10 wk. Two groups of a total of 29 healthy, overweight women (age: 30.5 ± 6.6 y; BMI: 27.6 ± 1.5 kg/m(2)) participated in the 10-wk intervention and a subsequent 4-h meal test. The breakfast test meals differed in GI but were equal in total energy, macronutrient composition, fiber content, and energy density. The LGI meal resulted in lower plasma glucose, serum insulin, and plasma glucagon-like peptide (GLP)-1 and higher plasma glucose-dependent insulinotropic polypeptide concentrations than the HGI meal (P ≤ 0.05). Ratings of fullness were slightly higher and the desire to eat something fatty was lower after the test meal in the LGI group (P < 0.05). Postprandial plasma GLP-2, plasma glucagon, serum leptin, plasma ghrelin, EE, substrate oxidation rates, and ad libitum EI at lunch did not differ between groups. In conclusion, postprandial glycemia, insulinemia, and subjective appetite ratings after a test meal were better after 10-wk ad libitum intake of a LGI compared to a HGI diet. EE and substrate oxidation rates were, however, not affected. These findings give some support to recommendations to consume a LGI diet.

Evidence-based review on the effect of normal dietary consumption of fructose on blood lipids and body weight of overweight and obese individuals

Although some investigators have hypothesized that ingestion of fructose from foods and beverages is responsible for the development of hyperlipidemia or obesity, a recent evidence-based review demonstrated that there was no relationship between the consumption of fructose in a normal dietary manner and the development of hyperlipidemia or increased weight in normal weight individuals. Because overweight and obese individuals may exhibit metabolic abnormalities such as insulin resistance, impaired glucose tolerance, hyperlipedemia, and/or alterations in gut hormones involved in appetite regulation, the findings of fructose studies performed in normal weight subjects may not be particularly relevant for overweight or obese subjects. A systematic assessment of the strength and quality of the studies and their relevance for overweight or obese humans ingesting fructose in a normal dietary manner has not been performed. The purpose of this review was to critically evaluate the existing database for a causal relationship between the ingestion of fructose in a normal, dietary manner and the development of hyperlipidemia or increased body weight in overweight or obese humans, using an evidence-based approach. The results of the analysis indicate that there is no evidence which shows that the consumption of fructose at normal levels of intake causes biologically relevant changes in triglycerides (TG) or body weight in overweight or obese individuals.

Impairment of fat oxidation under high- vs. low-glycemic index diet occurs before the development of an obese phenotype

Exposure to high vs. low glycemic index (GI) diets increases fat mass and insulin resistance in obesity-prone C57BL/6J mice. However, the longer-term effects and potentially involved mechanisms are largely unknown. We exposed four groups of male C57BL/6J mice (n = 10 per group) to long-term (20 wk) or short-term (6 wk) isoenergetic and macronutrient matched diets only differing in starch type and as such GI. Body composition, liver fat, molecular factors of lipid metabolism, and markers of insulin sensitivity and metabolic flexibility were investigated in all four groups of mice. Mice fed the high GI diet showed a rapid-onset (from week 5) marked increase in body fat mass and liver fat, a gene expression profile in liver consistent with elevated lipogenesis, and, after long-term exposure, significantly reduced glucose clearance following a glucose load. The long-term high-GI diet also led to a delayed switch to both carbohydrate and fat oxidation in the postprandial state, indicating reduced metabolic flexibility. In contrast, no difference in carbohydrate oxidation was observed after short-term high- vs. low-GI exposure. However, fatty acid oxidation was significantly blunted as early as 3 wk after beginning of the high-GI intervention, at a time where most measured phenotypic markers including body fat mass were comparable between groups. Thus long-term high-GI feeding resulted in an obese, insulin-resistant, and metabolically inflexible phenotype in obesity-prone C57BL/6J mice. Early onset and significantly impaired fatty acid oxidation preceded these changes, thereby indicating a potentially causal involvement.

Effect of postprandial modulation of glucose availability: short- and long-term analysis

Low glycaemic index (LGI) foods have been proposed as potential means to decrease postprandial glucose excursions and thus to improve diabetes management. We modulated glucose availability of cereal products and thus their glycaemic index to study the metabolic effect of LGI foods on daylong glucose control acutely and in the long term following a 5-week GI intervention diet in free-living subjects. In this randomised, parallel trial, two groups of nineteen overweight subjects followed an ad libitum 5-week intervention diet in which usual starch was replaced by either LGI or high GI (HGI) starch. During the exploration days (days 1 and 36), subjects ate their assigned 13C-labelled test breakfast (LGI or HGI), and total and exogenous glucose kinetics (using stable isotopes), postprandial concentrations of glucose, insulin, lipid profile and nutrient oxidation were assessed after the test breakfast and a standardised lunch. At day 1, LGI breakfast significantly decreased post-breakfast glycaemic response with a parallel decrease in exogenous and total glucose appearance (P < 0.05). Post-lunch and post-breakfast glycaemic responses were positively correlated (r 0.79, P < 0.0001). Following the 5-week diet, difference between the groups in terms of glucose kinetics and response was maintained (no significant interaction group x time) but tended to decrease over time for the post-breakfast glycaemic response. Post-lunch and post-breakfast glycaemic responses remained positively correlated (r 0.47, P = 0.004). Modulation of postprandial glucose availability at breakfast decreased plasma exogenous glucose appearance and improved glucose control at the subsequent lunch. After 5 weeks, these effects were maintained in healthy subjects but remained to be confirmed in the longer term.

Randomized trial on the effects of a 7-d low-glycemic diet and exercise intervention on insulin resistance in older obese humans

BACKGROUND

The optimal combination of diet and exercise that produces the greatest reversal of obesity-related insulin resistance is unknown.

OBJECTIVES

We examined the effects of a combined 7-d low-glycemic index (low-GI) diet and exercise training intervention on insulin sensitivity in older obese humans.

DESIGN

Participants [n = 32; mean (+/-SEM) age: 66 +/- 1 y; body mass index (in kg/m(2)): 33.8 +/- 0.7] were randomly assigned to a parallel, double-blind, controlled-feeding trial and underwent supervised aerobic exercise (EX; 60 min/d at 80-85% maximum heart rate) in combination with either a low-GI (LoGI + EX: 41.1 +/- 0.4) or a high-GI (HiGI + EX: 80.9 +/- 0.6) diet. All meals were provided and were isocaloric to individual energy requirements. Insulin sensitivity and hepatic glucose production were assessed with a 40-mU x m(-2) x min(-1) hyperinsulinemic euglycemic clamp combined with a [6,6-(2)H(2)]-glucose infusion.

RESULTS

After the intervention, small decreases were observed in body weight (-1.6 +/- 0.2 kg; P < 0.0001) and fat mass (-1.7 +/- 0.9%; P = 0.004) in both groups. Maximal aerobic capacity ( O(2)max) also improved slightly (0.06 +/- 0.02 L/min; P = 0.004). Resting systolic blood pressure, fasting glucose, insulin, triglycerides, and cholesterol all decreased after the study (all P < 0.05). Larger changes in systolic blood pressure and O(2max) were seen in the LoGI + EX group. Insulin-stimulated glucose disposal (P < 0.001), insulin suppression of hepatic glucose production (P = 0.004), and postabsorptive fat oxidation (P = 0.03) improved equally in both groups after the intervention.

CONCLUSIONS

These findings suggest that the metabolic improvements after short-term exercise training in older obese individuals are dependent on increased physical activity and are not influenced by a low-GI diet. However, a low-GI diet has added benefit in alleviating hypertension, thus reducing the risk of diabetic and vascular complications.

Metabolic effects of diets differing in glycaemic index depend on age and endogenous glucose-dependent insulinotrophic polypeptide in mice

AIMS/HYPOTHESIS

High- vs low-glycaemic index (GI) diets unfavourably affect body fat mass and metabolic markers in rodents. Different effects of these diets could be age-dependent, as well as mediated, in part, by carbohydrate-induced stimulation of glucose-dependent insulinotrophic polypeptide (GIP) signalling.

METHODS

Young-adult (16 weeks) and aged (44 weeks) male wild-type (C57BL/6J) and GIP-receptor knockout (Gipr ( -/- )) mice were exposed to otherwise identical high-carbohydrate diets differing only in GI (20-26 weeks of intervention, n = 8-10 per group). Diet-induced changes in body fat distribution, liver fat, locomotor activity, markers of insulin sensitivity and substrate oxidation were investigated, as well as changes in the gene expression of anorexigenic and orexigenic hypothalamic factors related to food intake.

RESULTS

Body weight significantly increased in young-adult high- vs low-GI fed mice (two-way ANOVA, p < 0.001), regardless of the Gipr genotype. The high-GI diet in young-adult mice also led to significantly increased fat mass and changes in metabolic markers that indicate reduced insulin sensitivity. Even though body fat mass also slightly increased in high- vs low-GI fed aged wild-type mice (p < 0.05), there were no significant changes in body weight and estimated insulin sensitivity in these animals. However, aged Gipr ( -/- ) vs wild-type mice on high-GI diet showed significantly lower cumulative net energy intake, increased locomotor activity and improved markers of insulin sensitivity.

CONCLUSIONS/INTERPRETATION

The metabolic benefits of a low-GI diet appear to be more pronounced in younger animals, regardless of the Gipr genotype. Inactivation of GIP signalling in aged animals on a high-GI diet, however, could be beneficial.

Early-phase adaptations to a split-body, linear periodization resistance training program in college-aged and middle-aged men

An 8-week, split-body, linear periodized resistance training program was completed by college-aged (CA: 18-22 years; n = 24) and middle-aged (MA: 35-50 years; n = 25) men to determine early-phase adaptations in body composition and upper- and lower-body strength. Participants completed 2 upper-body and 2 lower-body resistance training workouts each week. During weeks 1-4, subjects completed 3-6 sets at a 10-repetition maximum (RM) intensity and increased to 8RM for weeks 5-8. The 1RM strength levels were determined on the bench press and leg press, and 30-second Wingate tests were assessed at baseline and after 8 weeks of resistance training. Body composition was assessed using dual-energy X-ray absorptiometry (DXA). For selected data, delta values (post - pre values) were calculated and reported as mean +/- SEM. No changes (p > 0.05) were reported for peak and average Wingate power. Bench press (CA, 3.2 +/- 1.9 kg; MA, 6.2 +/- 3.3 kg; p < 0.001) and leg press (CA, 25.0 +/- 4.4 kg; MA, 18.2 +/- 13.3 kg; p < 0.001) 1RM significantly increased in both groups over time. Lean mass significantly increased over time in both groups (CA, 0.9 +/- 2.4 kg; MA, 1.1 +/- 1.9 kg; p < 0.001). Significant group x time effects were seen for fat mass changes (CA, 0.5 +/- 1.3 kg; MA, -0.5 +/- 1.1 kg; p = 0.01) and % body fat changes (CA, 0.4 +/- 1.4%; MA, -0.7 +/- 1.1%; p = 0.01). These results indicate that performing a split-body, linearly periodized resistance training program for 8 weeks significantly increases bench press 1RM, leg press 1RM, and DXA lean mass in CA and MA men. Furthermore, MA men lost significantly more fat mass and significantly decreased % body fat compared with CA men. A split-body, linearly periodized resistance training program may be used as an effective program to increase strength and lean mass in both young and MA populations.

Long-term effects of dietary glycemic index on adiposity, energy metabolism, and physical activity in mice

A high-glycemic index (GI) diet has been shown to increase adiposity in rodents; however, the long-term metabolic effects of a low- and high-GI diet have not been examined. In this study, a total of 48 male 129SvPas mice were fed diets high in either rapidly absorbed carbohydrate (RAC; high GI) or slowly absorbed carbohydrate (SAC; low GI) for up to 40 wk. Diets were controlled for macronutrient and micronutrient content, differing only in starch type. Body composition and insulin sensitivity were measured longitudinally by DEXA scan and oral glucose tolerance test, respectively. Food intake, respiratory quotient, physical activity, and energy expenditure were assessed using metabolic cages. Despite having similar mean body weights, mice fed the RAC diet had 40% greater body fat by the end of the study and a mean 2.2-fold greater insulin resistance compared with mice fed the SAC diet. Respiratory quotient was higher in the RAC group, indicating comparatively less fat oxidation. Although no differences in energy expenditure were observed throughout the study, total physical activity was 45% higher for the SAC-fed mice after 38 wk of feeding. We conclude that, in this animal model, 1) the effect of GI on body composition is mediated by changes in substrate oxidation, not energy intake; 2) a high-GI diet causes insulin resistance; and 3) dietary composition can affect physical activity level.

Treatment modalities of obesity: what fits whom?

The prevalence of obesity is increasing in both developed and developing countries, with rates reaching approximately 10-35% among adults in the Euro-American region. Obesity is associated with increased risks of cardiovascular diseases, type 2 diabetes, arthritis, and some type of cancers. Obesity significantly affects the quality of life and reduces the average life expectancy. The effective treatment of obesity should address both the medical and the social burden of this disease. Obesity needs to be treated within the health care system as any other complex disease, with empathy and without prejudice. Both health care providers and patients should know that the obesity treatment is a lifelong task. They should also set realistic goals before starting the treatment, whereas keeping in mind that even a modest weight loss of 5-15% significantly reduces obesity-related health risks. Essential treatment of obesity includes low-calorie low-fat diets, increased physical activity, and strategies contributing to the modification of lifestyle. Anti-obesity drugs facilitate weight loss and contribute to further amelioration of obesity-related health risks. A short-term weight loss, up to 6 months, is usually achieved easily. However, the long-term weight management is often associated with a lack of compliance, failures, and a high dropout rate. Regular physical activity, cognitive behavioral modification of lifestyle, and administration of anti-obesity drugs improve weight loss maintenance. Bariatric surgery is an effective strategy to treat severely obese patients. Bariatric surgery leads to a substantial improvement of comorbidities as well as to a reduction in overall mortality by 25-50% during the long-term follow-up. Obesity treatment should be individually tailored and the following factors should be taken into account: sex, the degree of obesity, individual health risks, psychobehavioral and metabolic characteristics, and the outcome of previous weight loss attempts. In the future, an evaluation of hormonal and genetic determinants of weight loss could also contribute to a better choice of individual therapy for a particular obese patient. A multilevel obesity management network of mutually collaborating facilities should be established to provide individually tailored treatment. Centers of excellence in obesity management represented by multidisciplinary teams should provide comprehensive programs for the treatment of obesity derived from evidence-based medicine.

No effect of a diet with a reduced glycaemic index on satiety, energy intake and body weight in overweight and obese women

OBJECTIVE

To investigate whether a diet with a reduced glycaemic index (GI) has effects on appetite, energy intake, body weight and composition in overweight and obese female subjects.

DESIGN

Randomized crossover intervention study including two consecutive 12-week periods. Lower or higher GI versions of key carbohydrate-rich foods (breads, breakfast cereals, rice and pasta/potatoes) were provided to subjects to be incorporated into habitual diets in ad libitum quantities. Foods intended as equivalents to each other were balanced in macronutrient composition, fibre content and energy density.

SUBJECTS

Nineteen overweight and obese women, weight-stable, with moderate hyperinsulinaemia (age: 34-65 years, body mass index: 25-47 kg m(-2), fasting insulin: 49-156 pmol l(-1)).

MEASUREMENTS

Dietary intake, body weight and composition after each 12-week intervention. Subjectively rated appetite and short-term ad libitum energy intake at a snack and lunch meal following fixed lower and higher GI test breakfasts (GI 52 vs 64) in a laboratory setting.

RESULTS

Free-living diets differed in GI by 8.4 units (55.5 vs 63.9), with key foods providing 48% of carbohydrate intake during both periods. There were no differences in energy intake, body weight or body composition between treatments. On laboratory investigation days, there were no differences in subjective ratings of hunger or fullness, or in energy intake at the snack or lunch meal.

CONCLUSION

This study provides no evidence to support an effect of a reduced GI diet on satiety, energy intake or body weight in overweight/obese women. Claims that the GI of the diet per se may have specific effects on body weight may therefore be misleading.