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

A Five-Week Periodized Carbohydrate Diet Does Not Improve Maximal Lactate Steady-State Exercise Capacity and Substrate Oxidation in Well-Trained Cyclists compared to a High-Carbohydrate Diet

There is a growing interest in studies involving carbohydrate (CHO) manipulation and subsequent adaptations to endurance training. This study aimed to analyze whether a periodized carbohydrate feeding strategy based on a daily training session has any advantages compared to a high-carbohydrate diet in well-trained cyclists. Seventeen trained cyclists (VO2peak = 70.8 ± 6.5 mL·kg-1·min-1) were divided into two groups, a periodized (PCHO) group and a high-carbohydrate (HCHO) group. Both groups performed the same training sessions for five weeks. In the PCHO group, 13 training sessions were performed with low carbohydrate availability. In the HCHO group, all sessions were completed following previous carbohydrate intake to ensure high pre-exercise glycogen levels. In both groups, there was an increase in the maximal lactate steady state (MLSS) (PCHO: 244.1 ± 29.9 W to 253.2 ± 28.4 W; p = 0.008; HCHO: 235.8 ± 21.4 W to 246.9 ± 16.7 W; p = 0.012) but not in the time to exhaustion at MLSS intensity. Both groups increased the percentage of muscle mass (PCHO: p = 0.021; HCHO: p = 0.042) and decreased the percent body fat (PCHO: p = 0.021; HCHO: p = 0.012). We found no differences in carbohydrate or lipid oxidation, heart rate, and post-exercise lactate concentration. Periodizing the CHO intake in well-trained cyclists during a 5-week intervention did not elicit superior results to an energy intake-matched high-carbohydrate diet in any of the measured outcomes.

Issues related to the assessment of energy balance during short-term over-, under- and refeeding in normal weight men

BACKGROUND

In humans, it is unclear how different estimates of energy balance (EB) compare with each other and whether the resulting changes in body weight (bw) and body composition (BC) are predictable and reproducible.

METHODS

This is a secondary data analysis of effects of sequential 7d over- (OF), 21d under- (UF) and 14d refeeding (RF) on EB. Energy intake (EI) was controlled at +/- 50% of energy needs in a 32 normal weight men (see Am J Clin Nutr. 2015; 102:807-819). EB was calculated (i) directly from the difference between EI and energy expenditure (EE) and (ii) indirectly from changes in BC. Changes in fat mass (FM) were compared with predicted changes according to Hall et al. (Lancet 2011; 378:826-37). Finally, within-subject reproducibility of changes in bw and BC was tested in a subgroup.

RESULTS

There were interindividual and day-by-day variabilities in changes in bw and BC. During OF and RF, the two estimates of EB were similar while with UF the indirect approach underestimated the direct estimate by 10593 ± 7506 kcal/21d (p < 0.001). Considerable differences became evident between measured and predicted changes in FM. Adjusting measured for predicted values did not reduce their interindividual variance. During UF, changes in bw and BC were reproducible, while corresponding changes during OF were not.

CONCLUSION

During hypercaloric nutrition the direct estimate of EB corresponded to the indirect estimate whereas this was not true during UF. Changes in bw and BC in response to OF were not reproducible while they were during UF.

Six HIT Sessions Improve Cardiorespiratory Fitness and Metabolic Flexibility in Insulin Resistant and Insulin Sensitive Adolescents with Obesity

To evaluate the effect of high-intensity interval training (HIT) on the cardiorespiratory performance and substrate oxidation pattern in insulin-resistant and insulin-sensitive obese adolescents.

METHODS

We recruited 25 obese adolescents in three schools, and trained them in six HIT sessions, comprising of six series at 100% and recovery at 50% peak velocity (Vpeak). For the evaluation, the participants were divided into two groups: insulin-resistant (IR, n = 12; HOMA index ≥3.16) and insulin-sensitive (IS, n = 13). All participants underwent cardiopulmonary and indirect calorimetry testing. We compared the effects of HIT before and after the intervention among the two groups. The data were analyzed using Student's t and Mann-Whitney (intergroup comparisons) and Student's t and Wilcoxon (pre- and post-training comparisons) tests; and Cohen's d (influence of HIT).

RESULTS

There was a significant post-training increase in Vpeak, oxygen consumption (VO2), velocity (V), and heart rate (HR) at the exertion intensity at the first ventilatory anaerobic threshold (VAT1) in both groups (p < 0.05; d < 0.02). The exercise promoted changes in substrate oxidation rates of the groups, with an increase in carbohydrate oxidation (CHOox) for both IR (p = 0.064) and IS (p = 0.034).

CONCLUSION

Six HIT sessions improved cardiorespiratory performance in both groups and increased CHOox in insulin-sensitive obese adolescents, suggesting its utility for increasing physical fitness and controlling glycemia in these population groups.

Association Between Adipose Tissue Characteristics and Metabolic Flexibility in Humans: A Systematic Review

Adipose tissue total amount, distribution, and phenotype influence metabolic health. This may be partially mediated by the metabolic effects that these adipose tissue characteristics exert on the nearby and distant tissues. Thus, adipose tissue may influence the capacity of cells, tissues, and the organism to adapt fuel oxidation to fuel availability, i.e., their metabolic flexibility (MetF). Our aim was to systematically review the evidence for an association between adipose tissue characteristics and MetF in response to metabolic challenges in human adults. We searched in PubMed (last search on September 4, 2021) for reports that measured adipose tissue characteristics (total amount, distribution, and phenotype) and MetF in response to metabolic challenges (as a change in respiratory quotient) in humans aged 18 to <65 years. Any study design was considered, and the risk of bias was assessed with a checklist for randomized and non-randomized studies. From 880 records identified, 22 remained for the analysis, 10 of them measured MetF in response to glucose plus insulin stimulation, nine in response to dietary challenges, and four in response to other challenges. Our main findings were that: (a) MetF to glucose plus insulin stimulation seems inversely associated with adipose tissue total amount, waist circumference, and visceral adipose tissue; and (b) MetF to dietary challenges does not seem associated with adipose tissue total amount or distribution. In conclusion, evidence suggests that adipose tissue may directly or indirectly influence MetF to glucose plus insulin stimulation, an effect probably explained by skeletal muscle insulin sensitivity.

Systematic Review Registration: PROSPERO [CRD42020167810].

Relationships between diet and basal fat oxidation and maximal fat oxidation during exercise in sedentary adults

BACKGROUND AND AIMS

To study the relationships between different dietary factors (i.e., energy, macronutrient and fatty acid intake, food group consumption, and dietary pattern) and basal fat oxidation (BFox) and maximal fat oxidation during exercise (MFO) in sedentary adults.

METHOD AND RESULTS

A total of 212 (n = 130 women; 32.4 ± 15.1 years) sedentary healthy adults took part in the present study. Information on the different dietary factors examined was gathered through a food frequency questionnaire and three nonconsecutive 24 h recalls. Energy and macronutrient intakes and food consumption were then estimated and dietary patterns calculated. BFox and MFO were measured by indirect calorimetry following standard procedures. Our study shows that dietary fiber intake was positively associated with BFox after taking into consideration the age, sex, and energy intake. A significant positive association between nut consumption and BFox was observed, which became nonsignificant after taking into consideration the age and energy intake. Fat intake and the dietary quality index (DQI), and the DQI for the Mediterranean diet were positively associated with MFO, which was attenuated after taking sex, age, and energy intake into consideration.

CONCLUSION

A higher dietary fiber intake and fat intake are associated with higher BFox and MFO, respectively, in sedentary adults.

CLINICAL TRIALS

ClinicalTrials.gov, ID: NCT02365129 (https://clinicaltrials.gov/ct2/show/study/NCT02365129) & ID: NCT03334357 (https://clinicaltrials.gov/ct2/show/NCT03334357).

The biology of human overfeeding: A systematic review

This systematic review has examined more than 300 original papers dealing with the biology of overfeeding. Studies have varied from 1 day to 6 months. Overfeeding produced weight gain in adolescents, adult men and women and in older men. In longer term studies, there was a clear and highly significant relationship between energy ingested and weight gain and fat storage with limited individual differences. There is some evidence for a contribution of a genetic component to this response variability. The response to overfeeding was affected by the baseline state of the groups being compared: those with insulin resistance versus insulin sensitivity; those prone to obesity versus those resistant to obesity; and those with metabolically abnormal obesity versus those with metabolically normal obesity. Dietary components, such as total fat, polyunsaturated fat and carbohydrate influenced the patterns of adipose tissue distribution as did the history of low or normal birth weight. Overfeeding affected the endocrine system with increased circulating concentrations of insulin and triiodothyronine frequently present. Growth hormone, in contrast, was rapidly suppressed. Changes in plasma lipids were influenced by diet, exercise and the magnitude of weight gain. Adipose tissue and skeletal muscle morphology and metabolism are substantially altered by chronic overfeeding.

Association between sleep quality and time with energy metabolism in sedentary adults

The aim of the present study was to investigate the relationship of sleep quality and time with basal metabolic rate (BMR) and fuel oxidation in basal conditions and during exercise in sedentary middle-aged adults. We also studied the mediation role of dietary intake and adherence to the traditional Mediterranean Diet in the relationship between sleep parameters and energy metabolism parameters.A secondary analysis of the FIT-AGEING study was undertaken. 70 middle-aged sedentary adults (40-65 years old) participated in the present study. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) and wrist accelerometers (ActiSleep, Actigraph, Pensacola, Florida, USA) for 7 consecutive days. BMR was measured with indirect calorimetry and fuel oxidation was estimated through stoichiometric equations. Maximal fat oxidation was determined by a walking graded exercise test and dietary intake with 24 h recalls. Adherence to the traditional Mediterranean diet was assessed through the PREDIMED questionnaire. PSQI global score (poor sleep quality) was associated with lower basal fat oxidation (BFox), both expressed in g/min and as a percentage of BMR, independently of confounders. We did not find any association between other sleep and energy metabolism parameters. No mediating role of the dietary intake or PREDIMED global score was observed in the association of PSQI and BFox. In conclusion, our study showed that a subjective poor sleep quality was associated with lower BFox, which is not mediated by dietary intake in sedentary adults.

Effects of a whole diet approach on metabolic flexibility, insulin sensitivity and postprandial glucose responses in overweight and obese adults - A randomized controlled trial

BACKGROUND & AIMS

Metabolic flexibility is the ability to adapt fuel oxidation to fuel availability. Metabolic inflexibility has been associated with obesity, the metabolic syndrome and insulin resistance, and can be improved by exercise or weight loss. Dietary changes can modulate metabolic flexibility; however, the effect of a whole diet approach on metabolic flexibility has never been studied. Therefore, our objective was to assess the effect of a healthy diet (HD), as compared to a typical Western diet (WD), on several fasting and postprandial markers of metabolic flexibility and insulin sensitivity.

METHODS

In this parallel randomized trial, overweight or obese men and women (50-70 years; BMI 25-35 kg/m²) consumed a healthy diet (HD; high in fruits and vegetables, pulses, fibers, nuts, fatty fish, and low in high-glycemic carbohydrates; n = 19) or a typical Western diet (WD; n = 21) for six weeks, following a two-week run-in period. The change in respiratory quotient upon insulin stimulation (ΔRQ), and insulin sensitivity, expressed as the M-value, were both determined with a hyperinsulinemic euglycemic clamp. Additionally, other fasting and postprandial markers of metabolic flexibility were assessed during a 5-h high-fat high-glycemic mixed meal challenge.

RESULTS

ΔRQ (p = 0.730) and insulin sensitivity (p = 0.802) were not significantly affected by diet. Postprandial RQ did also not show significant differences (p = 0.610), whereas postprandial glucose excursions were significantly higher in the HD group at T30 (p = 0.014) and T45 (p = 0.026) after mixed meal ingestion (p = 0.037). Fasting glucose (p = 0.530) and HbA1c (p = 0.124) remained unchanged, whereas decreases in fasting insulin (p = 0.038) and the HOMA-IR (p = 0.050) were significantly more pronounced with the HD.

CONCLUSION

A healthy diet for six weeks, without further life-style changes, did not improve metabolic flexibility and whole-body insulin sensitivity, when compared to a Western-style diet. It remains to be determined whether the short time increase in postprandial glucose is physiologically relevant or detrimental to metabolic health. This trial was registered at clinicaltrials.gov as NCT02519127.

Examining changes in respiratory exchange ratio within an 8-week weight loss intervention

BACKGROUND

Maintaining weight loss is difficult, partly as a result of accompanying reductions in fat oxidation. The present study examined fat oxidation [reflected by respiratory exchange ratio (RER)] within an 8-week, self-led weight loss intervention. Changes in RER, body fat (BF%) and estimated energy expenditure (EE) were examined.

METHODS

Twenty-two adults [13 females, nine males; mean (SD) age 34.6 (16.5) years; body mass index 32.0 (4.3) kg m^-2 ] received a self-directed workbook; twelve were also randomised to receive a self-monitoring wrist-worn device. At weeks 0 and 8, RER (indirect calorimetry), BF% (BodPod) and estimated EE [7-day physical activity recall (PAR-EE) were collected. Participants were pooled and paired t-tests were used to examine changes over time. Correlations explored associations among variables. Participants were then dichotomised into weight loss group (WL) or weight stable/gainers group (WSG) and eating behaviours [Intuitive Eating Scale (IES-2)] were examined by 2 × 2 repeated measures multivariate analysis of covariance.

RESULTS

There were no significant changes in RER, body fat percentage and PAR-EE. A significant negative association was found between week 8 PAR-EE and week 8 RER, as well as between BF% change and RER change. There was a significant time by WL versus WSG group effect of IES-2 scores, with the WL group self-reporting significantly increased scores in Eating for Physical Reasons rather than Emotional Reasons (EPR) subscale.

CONCLUSIONS

Increased physical activity after an 8-week weight loss intervention was associated with a higher fasting fat oxidation. Participants who increased EPR scores were more successful in weight loss than those without a change in this subscale.

Basal Levels of Salivary Alpha-Amylase Are Associated with Preference for Foods High in Sugar and Anthropometric Markers of Cardiovascular Risk

Salivary alpha-amylase (sAA) influences the perception of taste and texture, features both relevant in acquiring food liking and, with time, food preference. However, no studies have yet investigated the relationship between basal activity levels of sAA and food preference. We collected saliva from 57 volunteers (63% women) who we assessed in terms of their preference for different food items. These items were grouped into four categories according to their nutritional properties: high in starch, high in sugar, high glycaemic index, and high glycaemic load. Anthropometric markers of cardiovascular risk were also calculated. Our findings suggest that sAA influences food preference and body composition in women. Regression analysis showed that basal sAA activity is inversely associated with subjective but not self-reported behavioural preference for foods high in sugar. Additionally, sAA and subjective preference are associated with anthropometric markers of cardiovascular risk. We believe that this pilot study points to this enzyme as an interesting candidate to consider among the physiological factors that modulate eating behaviour.

Pathways and mechanisms linking dietary components to cardiometabolic disease: thinking beyond calories

Calories from any food have the potential to increase risk for obesity and cardiometabolic disease because all calories can directly contribute to positive energy balance and fat gain. However, various dietary components or patterns may promote obesity and cardiometabolic disease by additional mechanisms that are not mediated solely by caloric content. Researchers explored this topic at the 2017 CrossFit Foundation Academic Conference 'Diet and Cardiometabolic Health - Beyond Calories', and this paper summarizes the presentations and follow-up discussions. Regarding the health effects of dietary fat, sugar and non-nutritive sweeteners, it is concluded that food-specific saturated fatty acids and sugar-sweetened beverages promote cardiometabolic diseases by mechanisms that are additional to their contribution of calories to positive energy balance and that aspartame does not promote weight gain. The challenges involved in conducting and interpreting clinical nutritional research, which preclude more extensive conclusions, are detailed. Emerging research is presented exploring the possibility that responses to certain dietary components/patterns are influenced by the metabolic status, developmental period or genotype of the individual; by the responsiveness of brain regions associated with reward to food cues; or by the microbiome. More research regarding these potential 'beyond calories' mechanisms may lead to new strategies for attenuating the obesity crisis.

Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition

Weight changes are accompanied by imbalances between calorie intake and expenditure. This fact is often misinterpreted to suggest that obesity is caused by gluttony and sloth and can be treated by simply advising people to eat less and move more. Rather various components of energy balance are dynamically interrelated and weight loss is resisted by counterbalancing physiological processes. While low-carbohydrate diets have been suggested to partially subvert these processes by increasing energy expenditure and promoting fat loss, our meta-analysis of 32 controlled feeding studies with isocaloric substitution of carbohydrate for fat found that both energy expenditure (26 kcal/d; P <.0001) and fat loss (16 g/d; P <.0001) were greater with lower fat diets. We review the components of energy balance and the mechanisms acting to resist weight loss in the context of static, settling point, and set-point models of body weight regulation, with the set-point model being most commensurate with current data.

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.

Exercise training-induced improvement in skeletal muscle PGC-1α-mediated fat metabolism is independent of dietary glycemic index

OBJECTIVE

This study hypothesized that a low-glycemic diet combined with exercise would increase expression of nuclear regulators of fat transport and oxidation in insulin-resistant skeletal muscle.

METHOD

Nineteen subjects (64 ± 1 y; 34 ± 1 kg/m² ) were randomized to receive isocaloric high-glycemic-index (HiGIX; 80 ± 0.6 units, n = 10) or low-glycemic-index (LoGIX; 40 ± 0.3 units, n = 9) diets combined with supervised exercise (1 h/d, 5 d/wk at ∼85% HR_max ) for 12 weeks. Insulin sensitivity was determined by hyperinsulinemic-euglycemic clamp. Skeletal muscle biopsies were obtained before and after the intervention to assess fasting gene and protein expression.

RESULTS

Weight loss was similar for both groups (9.5 ± 1.3 kg). Likewise, improvements in insulin sensitivity (P < 0.002) and PPARγ (P < 0.002), PGC-1α (P = 0.003), CD36 (P = 0.003), FABP3 (mRNA, P = 0.01 and protein, P = 0.02), and CPT1B (mRNA, P = 0.03 and protein, P = 0.008) expression were similar for both interventions. Increased insulin sensitivity correlated with increased PGC-1α expression (P = 0.04), and increased fasting fat oxidation correlated with increased FABP3 (P = 0.04) and CPT1B (P = 0.05) expression.

CONCLUSIONS

An exercise/diet program resulting in 8% to 10% weight loss improved insulin sensitivity and key molecular mechanisms in skeletal muscle that are controlled by PGC-1α. These effects were independent of the glycemic index of the diets.

A review of the carbohydrate-insulin model of obesity

The carbohydrate-insulin model of obesity theorizes that diets high in carbohydrate are particularly fattening due to their propensity to elevate insulin secretion. Insulin directs the partitioning of energy toward storage as fat in adipose tissue and away from oxidation by metabolically active tissues and purportedly results in a perceived state of cellular internal starvation. In response, hunger and appetite increases and metabolism is suppressed, thereby promoting the positive energy balance associated with the development of obesity. Several logical consequences of this carbohydrate-insulin model of obesity were recently investigated in a pair of carefully controlled inpatient feeding studies whose results failed to support key model predictions. Therefore, important aspects of carbohydrate-insulin model have been experimentally falsified suggesting that the model is too simplistic. This review describes the current state of the carbohydrate-insulin model and the implications of its recent experimental tests.

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.

Metabolic characterization of overweight and obese adults

OBJECTIVES

Traditional evaluations of metabolic health may overlook underlying dysfunction in individuals who show no signs of insulin resistance or dyslipidemia. The purpose of this study was to characterize metabolic health in overweight and obese adults using traditional and non-traditional cardiometabolic variables. A secondary purpose was to evaluate differences between overweight/obese and male/female cohorts, respectively.

METHODS

Forty-nine overweight and obese adults (Mean ± SD; Age = 35.0 ± 8.9 yrs; Body mass index = 33.6 ± 5.2 kg·m-2; Percent body fat [%fat] = 36.7 ± 7.9%) were characterized. Body composition (fat mass [FM], lean mass [LM], %fat) was calculated using a 4-compartment model; visceral adipose tissue (VAT) was quantified using B-mode ultrasound. Resting metabolic rate (RMR) and respiratory exchange ratio (RER) were evaluated using indirect calorimetry. Fasted blood and saliva samples were analyzed for total cholesterol (TC), high-density lipoproteins (HDL), low-density lipoproteins (LDL), triglycerides (TRG), glucose (GLUC), insulin, leptin, estradiol, and cortisol.

RESULTS

The prevalence of individuals with two or more cardiometabolic risk factors increased from 13%, using traditional risk factors (GLUC, TRG, HDL), to 80% when non-traditional metabolic factors (VAT, LM, RMR, RER, TC, LDL, HOMA-IR) were considered. Between overweight/obese, there were no significant differences in %fat (p = 0.152), VAT (p = 0.959), RER (p = 0.493), lipids/GLUC (p > 0.05), insulin (p = 0.143), leptin (p = 0.053), or cortisol (p = 0.063); obese had higher FM, LM, RMR, and estradiol (p < 0.01). Males had greater LM, RMR, and TRG (p < 0.01); females had greater %fat, and leptin (p < 0.001). There were no significant sex differences in RER, estradiol, insulin, or cortisol (p > 0.05).

CONCLUSIONS

Evaluating metabolic health beyond BMI and traditional cardiometabolic risk factors can give significant insights into metabolic status. Due to high variability in metabolic health in overweight and obese adults and inherent sex differences, implementation of body composition and visceral fat measures in the clinical setting can improve early identification and approaches to disease prevention.

Measuring the short-term substrate utilization response to high-carbohydrate and high-fat meals in the whole-body indirect calorimeter

The paper demonstrates that minute‐to‐minute metabolic response to meals with different macronutrient content can be measured and discerned in the whole‐body indirect calorimeter. The ability to discriminate between high‐carbohydrate and high‐fat meals is achieved by applying a modified regularization technique with additional constraints imposed on oxygen consumption rate. These additional constraints reduce the differences in accuracy between the oxygen and carbon dioxide analyzers. The modified technique was applied to 63 calorimeter sessions that were each 24 h long. The data were collected from 16 healthy volunteers (eight males, eight females, aged 22–35 years). Each volunteer performed four 24‐h long calorimeter sessions. At each session, they received one of four treatment combinations involving exercise (high or low intensity) and diet (a high‐fat or high‐carbohydrate shake for lunch). One volunteer did not complete all four assignments, which brought the total number of sessions to 63 instead of 64. During the 24‐h stay in the calorimeter, subjects wore a continuous glucose monitoring system, which was used as a benchmark for subject's postprandial glycemic response. The minute‐by‐minute respiratory exchange ratio (RER) data showed excellent agreement with concurrent subcutaneous glucose concentrations in postprandial state. The averaged minute‐to‐minute RER response to the high‐carbohydrate shake was significantly different from the response to high‐fat shake. Also, postprandial RER slopes were significantly different for two dietary treatments. The results show that whole‐body respiration calorimeters can be utilized as tools to study short‐term kinetics of substrate oxidation in humans.

Weight restoration on a high carbohydrate refeeding diet promotes rapid weight regain and hepatic lipid accumulation in female anorexic rats

Background

There is currently no standard clinical refeeding diet for the treatment of anorexia nervosa (AN). To provide the most efficacious AN clinical care, it is necessary to define the metabolic effects of current refeeding diets.

Methods

An activity-based model of anorexia nervosa (AN) was used in female rats. AN was induced over 7d by timed access to low fat (LF) diet with free access to a running wheel. Plasma hormones/metabolites and body composition were assessed at baseline, AN diagnosis (day 0), and following 28d of refeeding on LF diet. Energy balance and expenditure were measured via continuous indirect calorimetry on days −3 to +3.

Results

AN induction caused stress as indicated by higher levels of corticosterone versus controls (p < 0.0001). The rate of weight gain during refeeding was higher in AN rats than controls (p = 0.0188), despite lower overall energy intake (p < 0.0001). This was possible due to lower total energy expenditure (TEE) at the time of AN diagnosis which remained significantly lower during the entire refeeding period, driven by markedly lower resting energy expenditure (REE). AN rats exhibited lower lipid accumulation in visceral adipose tissues (VAT) but much higher liver accumulation (62 % higher in AN than control; p < 0.05) while maintaining the same total body weight as controls. It is possible that liver lipid accumulation was caused by overfeeding of carbohydrate suggesting that a lower carbohydrate, higher fat diet may be beneficial during AN treatment. To test whether such a diet would be accepted clinically, we conducted a study in adolescent female AN patients which showed equivalent palatability and acceptability for LF and moderate fat diets. In addition, this diet was feasible to provide clinically during inpatient treatment in this population.

Conclusion

Refeeding a LF diet to restore body weight in female AN rats caused depressed TEE and REE which facilitated rapid regain. However, this weight gain was metabolically unhealthy as it resulted in elevated lipid accumulation in the liver. It is necessary to investigate the use of other diets, such as lower carbohydrate, moderate fat diets, in pre-clinical models to develop the optimal clinical refeeding diets for AN.

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.

High carbohydrate intake from starchy foods is positively associated with metabolic disorders: a Cohort Study from a Chinese population

Starchy foods are the main sources of carbohydrates; however, there is limited information on their metabolic impact. Therefore, we assessed the association between carbohydrates from starchy foods (Carb-S) intakes and the metabolic disorders of metabolic syndrome (MetS) and hyperlipidemia. In this study, 4,154 participants from Northern China were followed up for 4.2 years. Carb-S included rice, refined wheat, tubers, and their products. Multivariable regression models were used to calculate risk ratios (RRs) for MetS and hyperlipidemia from Carb-S, total carbohydrates, and carbohydrates from other food sources (Carb-O). Receiver operating characteristic analysis was used to determine a Carb-S cut-off value. High total carbohydrate intake was associated with increased risks of MetS (RR: 2.24, 95% CI: 1.00–5.03) and hyperlipidemia (RR: 3.05, 95% CI: 1.25–7.45), compared with the first quartile. High Carb-S intake (fourth quartile) was significantly associated with MetS (RR: 1.48, 95% CI: 1.01–2.69) and hyperlipidemia (RR: 1.73, 95% CI: 1.05–3.35). No associations with Carb-O were observed. Visceral adiposity, triglyceride levels, and high-density lipoprotein cholesterol significantly contributed to the metabolic disorders. The Carb-S cut-off value was 220 g. Both high total carbohydrate and Carb-S intakes were associated with hyperlipidemia and MetS; Carb-S appears to contribute more to these disorders.

Assessment of fat and lean mass by quantitative magnetic resonance: a future technology of body composition research?

PURPOSE OF REVIEW

For the assessment of energy balance or monitoring of therapeutic interventions, there is a need for noninvasive and highly precise methods of body composition analysis that are able to accurately measure small changes in fat and fat-free mass (FFM).

RECENT FINDINGS

The use of quantitative magnetic resonance (QMR) for measurement of body composition has long been established in animal studies. There are, however, only a few human studies that examine the validity of this method. These studies have consistently shown a high precision of QMR and only a small underestimation of fat mass by QMR when compared with a 4-compartment model as a reference. An underestimation of fat mass by QMR is also supported by the comparison between measured energy balance (as a difference between energy intake and energy expenditure) and energy balance predicted from changes in fat mass and FFM. Fewer calories were lost and gained as fat mass compared with the value expected from measured energy balance.

SUMMARY

Current evidence in healthy humans has shown that QMR is a valid and precise method for noninvasive measurement of body composition. Contrary to standard reference methods, such as densitometry and dual X-ray absorptiometry, QMR results are independent of FFM hydration. However, despite a high accuracy and a low minimal detectable change, underestimation of fat mass by QMR is possible and limits the use of this method for quantification of energy balance.

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).

Endocrine determinants of changes in insulin sensitivity and insulin secretion during a weight cycle in healthy men

Objective

Changes in insulin sensitivity (IS) and insulin secretion occur with perturbations in energy balance and glycemic load (GL) of the diet that may precede the development of insulin resistance and hyperinsulinemia. Determinants of changes in IS and insulin secretion with weight cycling in non-obese healthy subjects remain unclear.

Methods

In a 6wk controlled 2-stage randomized dietary intervention 32 healthy men (26±4y, BMI: 24±2kg/m²) followed 1wk of overfeeding (OF), 3wks of caloric restriction (CR) containing either 50% or 65% carbohydrate (CHO) and 2wks of refeeding (RF) with the same amount of CHO but either low or high glycaemic index at ±50% energy requirement. Measures of IS (basal: HOMA-index, postprandial: Matsuda-ISI), insulin secretion (early: Stumvoll-index, total: tAUC-insulin/tAUC-glucose) and potential endocrine determinants (ghrelin, leptin, adiponectin, thyroid hormone levels, 24h-urinary catecholamine excretion) were assessed.

Results

IS improved and insulin secretion decreased due to CR and normalized upon RF. Weight loss-induced improvements in basal and postprandial IS were associated with decreases in leptin and increases in ghrelin levels, respectively (r = 0.36 and r = 0.62, p<0.05). Weight regain-induced decrease in postprandial IS correlated with increases in adiponectin, fT3, TSH, GL of the diet and a decrease in ghrelin levels (r-values between -0.40 and 0.83, p<0.05) whereas increases in early and total insulin secretion were associated with a decrease in leptin/adiponectin-ratio (r = -0.52 and r = -0.46, p<0.05) and a decrease in fT4 (r = -0.38, p<0.05 for total insulin secretion only). After controlling for GL associations between RF-induced decrease in postprandial IS and increases in fT3 and TSH levels were no longer significant.

Conclusion

Weight cycling induced changes in IS and insulin secretion were associated with changes in all measured hormones, except for catecholamine excretion. While leptin, adiponectin and ghrelin seem to be the major endocrine determinants of IS, leptin/adiponectin-ratio and fT4 levels may impact changes in insulin secretion with weight cycling.

Trial Registration

ClinicalTrials.gov NCT01737034

Deep body composition phenotyping during weight cycling: relevance to metabolic efficiency and metabolic risk

Weight cycling may lead to adverse effects on metabolic efficiency (i.e. adaptive thermogenesis or 'metabolic slowing') and metabolic risks (e.g. increased risk for insulin resistance and the metabolic syndrome). In order to investigate these topics, the partitioning of fat and lean mass (i.e. the change in the proportion of both compartments) needs to be extended to the organ and tissue level because metabolic risk differs between adipose tissue depots and lean mass is metabolically heterogeneous being composed of organs and tissues differing in metabolic rate. Contrary to data obtained with severe weight loss and regain in lean people, weight cycling most likely has no adverse effects on fat distribution and metabolic risk in obese patients. There is even evidence for an increased ability of fat storage in subcutaneous fat depots (at the trunk in men and at the limbs in women) with weight cycling that may provide a certain protection from ectopic lipid deposition and thus explain the preservation of a favourable metabolic profile despite weight regain. On the other hand, the mass-specific metabolic rate of lean mass may increase with weight gain and decrease with weight loss mainly because of an increase and respective decrease in the proportion (and/or activity) of metabolically active organ mass. Obese people could therefore have a higher slope of the regression line between resting energy expenditure (REE) and fat-free mass that leads to an overestimation of metabolic efficiency when applied to normalize REE data after weight loss. Furthermore, in addressing the impact of macronutrient composition of the diet on partitioning of lean and fat mass, and the old controversy about whether a calorie is a calorie, we discuss recent evidence in support of a low glycaemic weight maintenance diet in countering weight regain and challenge this concept for weight loss by proposing the opposite.