Blood glucose patterns and appetite in time-blinded humans: carbohydrate versus fat

Low-calorie diet-induced weight loss is associated with altered brain connectivity and food desire in obesity

OBJECTIVE

The main objective of this study is to better understand the effects of diet-induced weight loss on brain connectivity in response to changes in glucose levels in individuals with obesity.

METHODS

A total of 25 individuals with obesity, among whom 9 had a diagnosis of type 2 diabetes, underwent functional magnetic resonance imaging (fMRI) scans before and after an 8-week low-calorie diet. We used a two-step hypereuglycemia clamp approach to mimic the changes in glucose levels observed in the postprandial period in combination with task-mediated fMRI intrinsic connectivity distribution (ICD) analysis.

RESULTS

After the diet, participants lost an average of 3.3% body weight. Diet-induced weight loss led to a decrease in leptin levels, an increase in hunger and food intake, and greater brain connectivity in the parahippocampus, right hippocampus, and temporal cortex (limbic-temporal network). Group differences (with vs. without type 2 diabetes) were noted in several brain networks. Connectivity in the limbic-temporal and frontal-parietal brain clusters inversely correlated with hunger.

CONCLUSIONS

A short-term low-calorie diet led to a multifaceted body response in patients with obesity, with an increase in connectivity in the limbic-temporal network (emotion and memory) and hormone and eating behavior changes that may be important for recovering the weight lost.

The development of interoceptive hunger signals

Hunger is often reported when people experience certain internal sensations (e.g., fatigue) or when they anticipate that a food will be good to eat. The latter results from associative learning, while the former was thought to signal an energy deficit. However, energy-deficit models of hunger are not well supported, so if interoceptive hungers are not "fuel gauges," what are they? We examined an alternate perspective, where internal states signaling hunger, which are quite diverse, are learned during childhood. A basic prediction from this idea is offspring-caregiver similarity, which should be evident if caregivers teach their child the meaning of internal hunger cues. We tested 111 university student offspring-primary caregiver pairs, by having them complete a survey about their internal hunger states, alongside other information that may moderate this relationship (i.e., gender, body mass index, eating attitudes, and beliefs about hunger). We observed substantial similarity between offspring-caregiver pairs (Cohen's ds from 0.33 to 1.55), with the main moderator being beliefs about an energy-needs model of hunger, which tended to increase similarity. We discuss whether these findings may also reflect heritable influences, the form that any learning might take, and the implications for child feeding practices.

Effect of processing and microstructural properties of chickpea-flours on in vitro digestion and appetite sensations

Nowadays, pulse flours are ingredients that are more and more used as substitutes in traditional staples (i.e., pasta, bread). In this study, cellular chickpea-flour was used as an ingredient to replace conventional raw-milled chickpea-flour in suspensions and semi-solid purees. The contribution of cellular integrity on in vitro macronutrient digestion and the subsequent effect on in vivo appetite sensations were investigated. Alternating the flour preparation sequence by interchanging hydrothermal treatment and mechanical disintegration (thermo-mechanical treatment) resulted in three chickpea-flours with distinct levels of cellular integrity, and thus nutrient accessibility. The study showed that cellular integrity in chickpea-flours was preserved upon secondary hydrothermal treatment and led to significant attenuation of in vitro macronutrient digestion as compared to conventional chickpea-flour. In a randomized crossover design, significant increase of mean in vivo subjective appetite sensations satiety and fullness along with decreases in hunger, desire to eat, and prospective food consumption were achieved when cellular integrity was kept without an effect on palatability and appearance of the purees (n = 22). In vitro digestion along with microstructural assessment confirmed the importance of cellular integrity for attenuating macronutrient digestion and thereby contributing to enhanced subjective satiety and fullness in pulses. Overall, this study highlights the promising potential of altarenating the flour preparation sequence resulting in macronutrient and energy-matched flours with different nutrient encapsulation which lead to different in vitro digestion kinetics and in vivo appetite sensations.

Effects of Acute Heat and Cold Exposures at Rest or during Exercise on Subsequent Energy Intake: A Systematic Review and Meta-Analysis

The objective of this meta-analysis was to assess the effect of acute heat/cold exposure on subsequent energy intake (EI) in adults. We searched the following sources for publications on this topic: PubMed, Ovid Medline, Science Direct and SPORTDiscus. The eligibility criteria for study selection were: randomized controlled trials performed in adults (169 men and 30 women; 20–52 years old) comparing EI at one or more meals taken ad libitum, during and/or after exposure to heat/cold and thermoneutral conditions. One of several exercise sessions could be realized before or during thermal exposures. Two of the thirteen studies included examined the effect of heat (one during exercise and one during exercise and at rest), eight investigated the effect of cold (six during exercise and two at rest), and three the effect of both heat and cold (two during exercise and one at rest). The meta-analysis revealed a small increase in EI in cold conditions (g = 0.44; p = 0.019) and a small decrease in hot conditions (g = −0.39, p = 0.022) for exposure during both rest and exercise. Exposures to heat and cold altered EI in opposite ways, with heat decreasing EI and cold increasing it. The effect of exercise remains unclear.

Exiguous premeal saccharide intake reduces subsequent food intake in men

Purpose

Satiety is a crucial factor in the attempt to reduce food intake for long-term body weight loss. Since there is evidence for a negative correlation between cerebral energy levels and food intake, the provision of the primary energy substrate glucose to the brain through oral ingestion of carbohydrates could trigger feelings of satiety. Therefore, we hypothesized that a low-calorie saccharide preload would increase satiety, reduce subsequent food intake, and thereby decrease overall calorie consumption.

Methods

In a randomized single-blind crossover study, 17 healthy young normal-weight men received saccharide (26 kcal in total) or placebo capsules 30 min before a standardized breakfast buffet. We analysed food intake from the test buffet as well as plasma glucose and serum insulin levels.

Results

The saccharide preload reduced food intake from the buffet by 168 (± 34) kcal (p < 0.001) compared to control. This corresponds to a net reduction in total calorie consumption by 142 (± 34) kcal (p < 0.001) or 9.3% due to saccharide capsules.

Conclusion

A very low-calorie saccharide preload considerably reduces subsequent food intake leading to decreased overall calorie consumption. A saccharide preload before meals could, therefore, be a promising support for reducing caloric intake.

German Clinical Trials Register

DRKS00010281 (date of registration: 11.04.2016)

Association between Inflammatory Biomarkers and Nutritional Status in Fatty Liver

The prevalence and progression of non-alcoholic fatty liver disease (NAFLD) is mediated via several factors correlating with hepatic necroinflammation (adipokines/cytokines). This study was performed to analyze the level of inflammatory markers according to the presence of NAFLD and to identify related nutritional factors. A total of 80 adults were classified into 2 groups (healthy and NAFLD), and their body composition, blood tests, and eating habits were evaluated. In addition, inflammatory markers (adiponectin, high-sensitivity C-reactive protein [CRP], and tumor necrosis factor-alpha [TNF-α]), nutrient intake status, and dietary quality were compared. The quality of diet was assessed according to the nutrient adequacy ratio and the mean adequacy ratio (MAR). The NAFLD group had a higher body mass index (p < 0.001) than the healthy group and also carried significantly higher CRP levels (p < 0.001) but lower adiponectin (p = 0.001). TNF-α levels increased significantly with fatty liver grade (p = 0.023). The NAFLD group showed significantly higher intake of energy, carbohydrates, iron, sodium, vitamin A and saturated fatty acids, but significantly lower intake of zinc and vitamin E than the healthy group. The MAR values were slightly higher in the NAFLD group but without any significant difference. The levels of adiponectin and vitamin E showed a significant inverse correlation (p < 0.05). Nutritional management of NAFLD patients is important, and the intake of antioxidant and anti-inflammatory nutrients such as zinc and vitamin E should be emphasized.

Biomarkers of appetite: is there a potential role for metabolomics?

Knowing the biological signals associated with appetite control is crucial for understanding the regulation of food intake. Biomarkers of appetite have been defined as physiological measures that relate to subjective appetite ratings, measured food intake, or both. Several metabolites including amino acids, lipids and glucose were proposed as key molecules associated with appetite control over 60 years ago, and along with bile acids are all among possible appetite biomarker candidates. Additional metabolites that have been associated with appetite include endocannabinoids, lactate, cortisol and β-hydroxybutyrate. However, although appetite is a complex integrative process, studies often investigated a limited number of markers in isolation. Metabolomics involves the study of small molecules or metabolites present in biological samples such as urine or blood, and may present a powerful approach to further the understanding of appetite control. Using multiple analytical techniques allows the characterisation of molecules, such as carbohydrates, lipids, amino acids, bile acids and fatty acids. Metabolomics has proven successful in identifying markers of consumption of certain foods and biomarkers implicated in several diseases. However, it has been underexploited in appetite control or obesity. The aim of the present narrative review is to: (1) provide an overview of existing metabolites that have been identified in human biofluids and associated with appetite control; and (2) discuss the potential of metabolomics to deepen understanding of appetite control in humans.

Impact of intermittent vs. continuous energy restriction on weight and cardiometabolic factors: a 12-month follow-up

BACKGROUND AND OBJECTIVE

Intermittent energy restriction continues to gain popularity as a weight loss strategy; however, data assessing it's long-term viability is limited. The objective of this study was to follow up with participants 12 months after they had completed a 12-month dietary intervention trial involving continuous energy restriction and two forms of intermittent energy restriction; a week-on-week-off energy restriction and a 5:2 programme, assessing long-term changes on weight, body composition, blood lipids and glucose.

SUBJECTS AND METHODS

109 overweight and obese adults, aged 18-72 years, attended a 12-month follow-up after completing a 12-month dietary intervention involving three groups: continuous energy restriction (1000 kcal/day for women and 1200 kcal/day for men), week-on-week-off energy restriction (alternating between the same energy restriction as the continuous group for one week and one week of habitual diet), or 5:2 (500 kcal/day on modified fast days each week for women and 600 kcal/day for men). The primary outcome was weight change at 24 months from baseline, with secondary outcomes of change in body composition, blood lipids and glucose.

RESULTS

For the 109 individuals who completed the 12-month follow-up (82 female, 15 male, mean BMI 33 kg/m²), weight decreased over time with no differences between week-on and week-off and continuous energy restriction or 5:2 and continuous energy restriction with -4.5 ± 4.9 kg for continuous energy restriction, -2.8 ± 6.5 kg for week-on, week-off and -3.5 ± 5.1 kg for 5:2. Total cholesterol reduced over time and glucose, HDL, LDL and triglycerides were unchanged.

DISCUSSION AND CONCLUSION

Intermittent energy restriction was as successful in achieving modest weight loss over a 24-month period as continuous energy restriction.

In a Free-Living Setting, Obesity Is Associated with Greater Food Intake in Response to a Similar Pre-Meal Glucose Nadir

PURPOSE

Changes in blood glucose levels have been shown to influence eating in healthy individuals; however, less is known about glucose's effects on food intake in obese (OB) individuals. The goal of this study was to determine the predictive effect of circulating glucose levels on eating in free-living OB and normal weight (NW) individuals.

METHODS

Interstitial glucose levels, measured with a continuous glucose monitor (CGM) system, were obtained from 15 OB and 16 NW volunteers (age: 40±14, 37±12 yr; weight: 91±13, 68±12 kg; HbA1c: 5.1±0.7, 5.2±0.4%, respectively). While wearing the CGM participants filled up a food log (meal time, hunger rating and amount of food). Glucose profiles were measured in relation to their meals (macro program (CGM Peak and Nadir Analysis (CPNA)) in Microsoft® Excel).

RESULTS

OB and NW individuals showed comparable CGM glucose levels: mean (OB=99±13, NW=100±8 mg/dL, p=NS) and standard deviation (OB=18±4, NW=18±5 mg/dL, p=NS). Obesity was associated with slower post-prandial rate of changing glucose levels (p=0.04). Pre-prandial nadir glucose levels predicted hunger and food intake in both groups (p<0.0001), although hunger was associated with greater food intake in OB, in comparison to NW individuals (p=0.008 for group interaction).

CONCLUSIONS

Pre-meal glucose nadir predicted hunger and food intake in a group of free-living healthy non-diabetic NW and OB individuals, however for a similar low glucose level stimulus, greater hunger-induced food intake was recorded by OB in comparison to NW individuals.

Low glucose availability stimulates progesterone production by mouse ovaries in vitro

Steroid production by the ovary is primarily stimulated by gonadotropins but can also be affected by biological cues that provide information about energy status and environmental stress. To further understand which metabolic cues the ovary can respond to, we exposed gonadotropin-stimulated mouse ovaries in vitro to glucose metabolism inhibitors and measured steroid accumulation in media. Gonadotropin-stimulated ovaries exposed to 2-deoxy-d-glucose increased progesterone production and steroidogenic acute regulatory protein mRNA levels. However, oocytes and granulosa cells in antral follicles do not independently mediate this response because targeted treatment of these cell types with a different inhibitor of glucose metabolism (bromopyruvic acid) did not affect progesterone production. Elevated progesterone production is consistent with the homeostatic role of progesterone in glucose regulation in mammals. It also may regulate follicle growth and/or atresia within the ovary. These results suggest that ovaries can regulate glucose homeostasis in addition to their primary role in reproductive activity.

Does Hunger Contribute to Socioeconomic Gradients in Behavior?

Recent research has uncovered many examples of socioeconomic gradients in behavior and psychological states. As yet there is no theoretical consensus on the nature of the causal processes that produce these gradients. Here, I present the hunger hypothesis, namely the claim that part of the reason that people of lower socioeconomic position behave and feel as they do is that they are relatively often hungry. The hunger hypothesis applies in particular to impulsivity-hyperactivity, irritability-aggression, anxiety, and persistent narcotic use, all of which have been found to show socioeconomic gradients. I review multiple lines of evidence showing that hunger produces strong increases in these outcomes. I also review the literatures on food insufficiency and food insecurity to show that, within affluent societies, the poor experience a substantial burden of hunger, despite obtaining sufficient or excess calories on average. This leads to the distinctive prediction that hunger is an important mediator of the relationships between socioeconomic variables and the behavioral/psychological outcomes. This approach has a number of far-reaching implications, not least that some behavioral and psychological differences between social groups, though persistent under current economic arrangements, are potentially highly reversible with changes to the distribution of financial resources and food.

Methodological Challenges in Studies Examining the Effects of Breakfast on Cognitive Performance and Appetite in Children and Adolescents

Breakfast is purported to confer a number of benefits on diet quality, health, appetite regulation, and cognitive performance. However, new evidence has challenged the long-held belief that breakfast is the most important meal of the day. This review aims to provide a comprehensive discussion of the key methodological challenges and considerations in studies assessing the effect of breakfast on cognitive performance and appetite control, along with recommendations for future research. This review focuses on the myriad challenges involved in studying children and adolescents specifically. Key methodological challenges and considerations include study design and location, sampling and sample section, choice of objective cognitive tests, choice of objective and subjective appetite measures, merits of providing a fixed breakfast compared with ad libitum, assessment and definition of habitual breakfast consumption, transparency of treatment condition, difficulty of isolating the direct effects of breakfast consumption, untangling acute and chronic effects, and influence of confounding variables. These methodological challenges have hampered a clear substantiation of the potential positive effects of breakfast on cognition and appetite control and contributed to the debate questioning the notion that breakfast is the most important meal of the day.

Blood sugar level follows perceived time rather than actual time in people with type 2 diabetes

The current study investigates whether perceived time has an effect on blood glucose level in people with type 2 diabetes. The hypothesis is that perceived time will have a greater influence over blood glucose level than actual time. Changes in blood glucose levels were measured in 46 participants with diabetes while they completed simple tasks during a 90-min period. Participants' perception of time was manipulated by having them refer to clocks that were either accurate or altered to run fast or slow. Blood glucose levels changed in accordance with how much time they believed had passed instead of how much time had actually passed. These results are an example of the influence psychological processes can directly exert on the body.

Factors that determine energy compensation: a systematic review of preload studies

Insufficient energy compensation after a preload (meal, snack, or beverage) has been associated with excess energy intake, but experimental studies have used heterogeneous methodologies, making energy compensation difficult to predict. The aim of this systematic review was to analyze the relative contributions of two key variables, preload physical form and intermeal interval (IMI), to differences in energy compensation. Forty-eight publications were included, from which percent energy compensation (%EC) data were extracted for 253 interventions (121 liquid, 69 semisolid, 20 solid, and 43 composite preloads). Energy compensation ranged from −370% (overconsumption, mostly of liquids) to 450% (overcompensation). A meta-regression analysis of studies reporting positive energy compensation showed that IMI (as the predominant factor) together with preload physical form and energy contributed significantly to %EC differences, accounting for 50% of the variance, independently from gender and BMI. Energy compensation was maximized when the preload was in semisolid/solid form and the IMI was 30–120 min. These results may assist in the interpretation of studies assessing the relative efficacy of interventions to enhance satiety, including functional foods and weight management products.

Effects of increased meal frequency on fat oxidation and perceived hunger

OBJECTIVE

Consuming smaller, more frequent meals is often advocated as a means of controlling body weight, but studies demonstrating a mechanistic effect of this practice on factors associated with body weight regulation are lacking. The purpose of this study was to compare the effect of consuming three (3M) vs. six meals (6M) per day on 24-h fat oxidation and subjective ratings of hunger.

DESIGN AND METHODS

Lean (body mass index <25 kg/m(2) ) subjects (7M, 8F) were studied in a whole-room calorimeter on two occasions in a randomized cross-over design. Subjects were provided isoenergetic, energy balanced diets with a 1- to 2-week washout between conditions. Hunger, fullness, and "desire to eat" ratings were assessed throughout the day using visual analog scales and quantified as area under the curve (AUC).

RESULTS

There were no differences (P < 0.05) in 24-h energy expenditure (8.7 ± 0.3 vs. 8.6 ± 0.3 mj d(-1) ), 24-h respiratory quotient (0.85 ± 0.01 vs. 0.85 ± 0.01), or 24-h fat oxidation (82 ± 6 vs. 80 ± 7 g day(-1) ) between 3M and 6M, respectively. There was no difference in fullness 24-h AUC, but hunger AUC (41850 ± 2255 vs. 36612 ± 2556 mm.24 h, P = 0.03) and "desire to eat" AUC (47061 ± 1791 vs. 41170 ± 2574 mm.24 h, P = 0.03) were greater during 6M than 3M.

CONCLUSION

We conclude that increasing meal frequency from three to six per day has no significant effect on 24-h fat oxidation, but may increase hunger and the desire to eat.

Protein v. carbohydrate intake differentially affects liking- and wanting-related brain signalling

Extreme macronutrient intakes possibly lead to different brain signalling. The aim of the present study was to determine the effects of ingesting high-protein v. high-carbohydrate food on liking and wanting task-related brain signalling (TRS) and subsequent macronutrient intake. A total of thirty female subjects (21·6 (sd 2·2) years, BMI 25·0 (sd 3·7) kg/m2) completed four functional MRI scans: two fasted and two satiated on two different days. During the scans, subjects rated all food items for liking and wanting, thereby choosing the subsequent meal. The results show that high-protein (PROT) v. high-carbohydrate (CARB) conditions were generated using protein or carbohydrate drinks at the first meal. Energy intake and hunger were recorded. PROT (protein: 53·7 (sd 2·1) percentage of energy (En%); carbohydrate: 6·4 (sd 1·3) En%) and CARB conditions (protein: 11·8 (sd 0·6) En%; carbohydrate: 70·0 (sd 2·4) En%) were achieved during the first meal, while the second meals were not different between the conditions. Hunger, energy intake, and behavioural liking and wanting ratings were decreased after the first meal (P< 0·001). Comparing the first with the second meal, the macronutrient content changed: carbohydrate − 26·9 En% in the CARB condition, protein − 37·8 En% in the PROT condition. After the first meal in the CARB condition, wanting TRS was increased in the hypothalamus. After the first meal in the PROT condition, liking TRS was decreased in the putamen (P< 0·05). The change in energy intake from the first to the second meal was inversely related to the change in liking TRS in the striatum and hypothalamus in the CARB condition and positively related in the PROT condition (P< 0·05). In conclusion, wanting and liking TRS were affected differentially with a change in carbohydrate or protein intake, underscoring subsequent energy intake and shift in macronutrient composition.

Circulating glucose levels modulate neural control of desire for high-calorie foods in humans

Obesity is a worldwide epidemic resulting in part from the ubiquity of high-calorie foods and food images. Whether obese and nonobese individuals regulate their desire to consume high-calorie foods differently is not clear. We set out to investigate the hypothesis that circulating levels of glucose, the primary fuel source for the brain, influence brain regions that regulate the motivation to consume high-calorie foods. Using functional MRI (fMRI) combined with a stepped hyperinsulinemic euglycemic-hypoglycemic clamp and behavioral measures of interest in food, we have shown here that mild hypoglycemia preferentially activates limbic-striatal brain regions in response to food cues to produce a greater desire for high-calorie foods. In contrast, euglycemia preferentially activated the medial prefrontal cortex and resulted in less interest in food stimuli. Indeed, higher circulating glucose levels predicted greater medial prefrontal cortex activation, and this response was absent in obese subjects. These findings demonstrate that circulating glucose modulates neural stimulatory and inhibitory control over food motivation and suggest that this glucose-linked restraining influence is lost in obesity. Strategies that temper postprandial reductions in glucose levels might reduce the risk of overeating, particularly in environments inundated with visual cues of high-calorie foods.

Invited commentary: Gene X lifestyle interactions and complex disease traits--inferring cause and effect from observational data, sine qua non

Observational epidemiology has made outstanding contributions to the discovery and elucidation of relations between lifestyle factors and common complex diseases such as type 2 diabetes. Recent major advances in the understanding of the human genetics of this disease have inspired studies that seek to determine whether the risk conveyed by bona fide risk loci might be modified by lifestyle factors such as diet composition and physical activity levels. A major challenge is to determine which of the reported findings are likely to represent causal interactions and which might be explained by other factors. The authors of this commentary use the Bradford-Hill criteria, a set of tried-and-tested guidelines for causal inference, to evaluate the findings of a recent study on interaction between variation at the cyclin-dependent kinase 5 regulatory subunit-associated protein 1-like 1 (CDKAL1) locus and total energy intake with respect to prevalent metabolic syndrome and hemoglobin A₁(c) levels in a cohort of 313 Japanese men. The current authors conclude that the study, while useful for hypothesis generation, does not provide overwhelming evidence of causal interactions. They overview ways in which future studies of gene × lifestyle interactions might overcome the limitations that motivated this conclusion.

Appetite control: methodological aspects of the evaluation of foods

This report describes a set of scientific procedures used to assess the impact of foods and food ingredients on the expression of appetite (psychological and behavioural). An overarching priority has been to enable potential evaluators of health claims about foods to identify justified claims and to exclude claims that are not supported by scientific evidence for the effect cited. This priority follows precisely from the principles set down in the PASSCLAIM report. The report allows the evaluation of the strength of health claims, about the effects of foods on appetite, which can be sustained on the basis of the commonly used scientific designs and experimental procedures. The report includes different designs for assessing effects on satiation as opposed to satiety, detailed coverage of the extent to which a change in hunger can stand alone as a measure of appetite control and an extensive discussion of the statistical procedures appropriate for handling data in this field of research. Because research in this area is continually evolving, new improved methodologies may emerge over time and will need to be incorporated into the framework. One main objective of the report has been to produce guidance on good practice in carrying out appetite research, and not to set down a series of commandments that must be followed.

Genetic variant in the glucose transporter type 2 is associated with higher intakes of sugars in two distinct populations

Glucose sensing in the brain has been proposed to be involved in regulating food intake, but the mechanism is not known. Glucose transporter type 2 (GLUT2)-null mice fail to control their food intake in response to glucose, suggesting a potential role for this transporter as a glucose sensor in the brain. Here we show that individuals with a genetic variation in GLUT2 (Thr110Ile) have a higher daily intake of sugars in two distinct populations. In the first population, compared with individuals with the Thr/Thr genotype, carriers of the Ile allele had a significantly higher intake of sugars as assessed from 3-day food records administered on two separate visits (visit 1: 112 +/- 9 vs. 86 +/- 4 g/day, P = 0.01; visit 2: 111 +/- 8 vs. 82 +/- 4 g/day, P = 0.003), demonstrating within-population reproducibility. In a second population, carriers of the Ile allele also reported consuming a significantly greater intake of sugars (131 +/- 5 vs. 115 +/- 3 g/day, P = 0.007) over a 1-mo period as measured from a food frequency questionnaire. GLUT2 genotypes were not associated with fat, protein, or alcohol intake in either population. These observations were consistent across older and younger adults as well as among subjects with early Type 2 diabetes and healthy individuals. Taken together, our findings show that a genetic variation in GLUT2 is associated with habitual consumption of sugars, suggesting an underlying glucose-sensing mechanism that regulates food intake.

Association of sleep duration with type 2 diabetes and impaired glucose tolerance

AIMS/HYPOTHESIS

The aim of this study was to assess the relationship between sleep duration and type 2 diabetes or impaired glucose tolerance (IGT).

METHODS

Anthropometric measurements and self-reported sleep duration were determined in a cross-sectional sample of 323 men and 417 women aged 21-64 years from the Quebec Family Study. Glucose homeostasis indicators were compared between short (5-6 h), 'normal' (7-8 h) and long (9-10 h) sleeper groups.

RESULTS

Using adults with 7-8 h of sleep as a reference, the adjusted odds ratio for type 2 diabetes/IGT was 1.58 (1.13-2.31) for those with 9-10 h of sleep and 2.09 (1.34-2.98) for those with 5-6 h of sleep, after adjustment for potential confounding variables. The short and long sleepers presented significantly higher total insulin AUC (p < 0.05), whereas total glucose AUC was not different between the three sleeper groups in both sexes. The mean glucose area below fasting glucose concentrations was significantly higher in short (p < 0.01) and long sleepers (p < 0.05) compared with 'normal' sleepers, and significantly higher in short (p < 0.05) compared with long sleepers in both sexes.

CONCLUSIONS/INTERPRETATION

The present study provides evidence that short- and long-duration sleep times are associated with type 2 diabetes/IGT in adults, even after adjustment for several confounders. These results also showed that the lower glucose concentrations at the end of the OGTT were observed in short sleepers. According to the glucostatic theory of appetite control, this represents a stimulus that can trigger episodes of hunger and spontaneous food intake, which may explain at least in part the greater risk of overweight displayed by short sleepers, as shown in previous studies.

Glucose response to an oral glucose tolerance test predicts weight change in non-diabetic subjects

OBJECTIVE

Glucose exerts a dual action in the regulation of energy balance, consisting of inhibition of energy intake and stimulation of energy expenditure. Whether blood glucose affects long-term regulation of body weight in humans remains to be established. We sought to test the hypothesis that the post-challenge glucose response is a predictor of weight change.

RESEARCH METHODS AND PROCEDURES

We performed a prospective analysis of the impact of glucose response to an oral glucose tolerance test (OGTT) and a mixed-meal test (MT) on subsequent changes in body weight (BW) on 253 Pima Indians (166 men and 87 women) with normal glucose regulation at baseline and follow-up (follow-up: 7 +/- 4 years). Main outcome measures included BW change (total, percent, and annual), plasma glucose and insulin concentrations during OGTT and MT [total and incremental areas under the curve (AUCs)], resting metabolic rate (RMR; indirect calorimetry), and insulin action (euglycemic-hyperinsulinemic clamp).

RESULTS

Total and incremental glucose AUCs during the OGTT (but not the MT) were negatively associated with BW change (total, percent, and annual), both before and after adjusting for sex, age, initial BW, follow-up time, insulin action, RMR, fasting plasma glucose and insulin concentrations, and insulin response. Total and incremental glucose AUCs during the OGTT were independent determinants of final BW with age, initial BW, follow-up time, fasting plasma insulin concentrations, and RMR.

DISCUSSION

Higher post-challenge glucose response protects against BW gain in subjects with normal glucose regulation. We propose that this action may be because of the effect of glucose on food intake and/or thermogenesis.

Modulation of food intake by glucose in patients with type 2 diabetes

OBJECTIVE

A gain in body weight is a common adverse effect of glucose-lowering therapies in patients with type 2 diabetes, the mechanisms of which are not completely understood. Blood glucose is considered to play a crucial role in the regulation of food intake. On this background, we hypothesized that a short-term reduction of blood glucose concentration to normal values acutely increases food intake in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

To test this hypothesis, 12 patients with type 2 diabetes were examined twice, once during a euglycemic (5.0 mmol/l) clamp experiment and another time during a hyperglycemic (10.5 mmol/l) clamp. The experiments were performed in a single-blind fashion with the order of conditions balanced across patients. On both clamp conditions, insulin was infused at a constant rate of 2.5 mU/kg per min for 125 min. Simultaneously, a glucose solution was infused at a variable rate to achieve target glycemic levels. During the final 30 min of the clamps, the patients were allowed to eat as much as they liked from a standard breakfast buffet.

RESULTS

Compared with the hyperglycemic condition, the patients ingested on average 25 +/- 10% more energy during euglycemia (645 +/- 75 vs. 483 +/- 37 kcal; P = 0.029). The increased energy intake during euglycemia was equally distributed across macronutrient components, i.e., during euglycemia the patients ate more carbohydrates (+27.1 +/- 11.4%; P = 0.037), fat (+22.5 +/- 10.0%; P = 0.046), and proteins (+25.2 +/- 11.2%; P = 0.046) than during hyperglycemia. Circulating levels of insulin, amylin, leptin, ghrelin, and glucagon-like peptide-1 did not differ between the euglycemic and hyperglycemia clamp, excluding a major contribution of these hormones to the difference in food intake. Summing up the glucose administered intravenously and the food ingested yielded a remarkably similar total energy influx in both conditions (794 +/- 64 vs. 790 +/- 53 kcal; P = 0.961).

CONCLUSIONS

Together our data suggest that total energy supply to the organism is tightly regulated on a short-term basis independent of the route of influx. Alternatively, it can be hypothesized that euglycemia stimulated or that hyperglycemia suppressed food intake at the subsequent buffet meal in our type 2 diabetic patients. Regardless of these different interpretations, our data indicate an important regulatory role of glucose for food intake in type 2 diabetic patients that is of considerable clinical relevance.

Appetite: measurement and manipulation misgivings

Humans appear to have a genotype that permits, or even encourages, an energy intake that is greater than energy expenditure when food is available. This was functional throughout most of human evolution but is less so in the current environment of inexpensive, palatable, and readily available foods. To achieve dietary goals of weight loss or maintenance, attempts have been made to influence appetitive sensations through the manipulation of the physical properties of foods, their composition, or their pattern of consumption. This has led to limited success, in part, because measurement of appetitive sensations is difficult but, more fundamentally, because the association between appetite and food choice or intake is not robust. This article critically reviews the most common methods for assessment of appetite and the effects of selected food constituents on appetitive sensations. Translation of current knowledge to dietetic practice must be made cautiously.

Effects of exercise training on glucose homeostasis: the HERITAGE Family Study

OBJECTIVE

To determine the effect of a 20-week endurance training program in healthy, previously sedentary participants on measures derived from an intravenous glucose tolerance test (i.v.GTT).

RESEARCH DESIGN AND METHODS

An i.v.GTT was performed before and after a standardized training program in 316 women and 280 men (173 blacks and 423 whites). Participants exercised on cycle ergometers 3 days per week for 60 sessions. The exercise intensity was progressively increased from 55% VO2max for 30 min per session to 75% VO2max for 50 min per session.

RESULTS

Mean insulin sensitivity increased by 10% (P < 0.001) following the intervention, but the variability in the changes was high. Men had larger improvements than women (P = 0.02). Improvements in fasting insulin were transitory, disappearing 72 h after the last bout of exercise. There were also significant mean increases in the glucose disappearance index (3%, P = 0.02) and in glucose effectiveness (11%, P < 0.001), measures of glucose tolerance and of the capacity of glucose to mediate its own disposal, respectively. The acute insulin response to glucose, a measure of insulin secretion, increased by 7% in the quartile with the lowest baseline glucose tolerance and decreased by 14% in the quartile with the highest baseline glucose tolerance (P < 0.001). The glucose area below fasting levels during the i.v.GTT was reduced by 7% (P = 0.02).

CONCLUSIONS

Although the effects of structured regular exercise were highly variable, there were improvements in virtually all i.v.GTT-derived variables. In the absence of substantial weight loss, regular exercise is required for sustained improvements in glucose homeostasis.

Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women

OBJECTIVE: To compare the effects of isocaloric, energy-restricted very low-carbohydrate ketogenic (VLCK) and low-fat (LF) diets on weight loss, body composition, trunk fat mass, and resting energy expenditure (REE) in overweight/obese men and women. DESIGN: Randomized, balanced, two diet period clinical intervention study. Subjects were prescribed two energy-restricted (-500 kcal/day) diets: a VLCK diet with a goal to decrease carbohydrate levels below 10% of energy and induce ketosis and a LF diet with a goal similar to national recommendations (%carbohydrate:fat:protein = ~60:25:15%). SUBJECTS: 15 healthy, overweight/obese men (mean +/- s.e.m.: age 33.2 +/- 2.9 y, body mass 109.1 +/- 4.6 kg, body mass index 34.1 +/- 1.1 kg/m2) and 13 premenopausal women (age 34.0 +/- 2.4 y, body mass 76.3 +/- 3.6 kg, body mass index 29.6 +/- 1.1 kg/m2). MEASUREMENTS: Weight loss, body composition, trunk fat (by dual-energy X-ray absorptiometry), and resting energy expenditure (REE) were determined at baseline and after each diet intervention. Data were analyzed for between group differences considering the first diet phase only and within group differences considering the response to both diets within each person. RESULTS: Actual nutrient intakes from food records during the VLCK (%carbohydrate:fat:protein = ~9:63:28%) and the LF (~58:22:20%) were significantly different. Dietary energy was restricted, but was slightly higher during the VLCK (1855 kcal/day) compared to the LF (1562 kcal/day) diet for men. Both between and within group comparisons revealed a distinct advantage of a VLCK over a LF diet for weight loss, total fat loss, and trunk fat loss for men (despite significantly greater energy intake). The majority of women also responded more favorably to the VLCK diet, especially in terms of trunk fat loss. The greater reduction in trunk fat was not merely due to the greater total fat loss, because the ratio of trunk fat/total fat was also significantly reduced during the VLCK diet in men and women. Absolute REE (kcal/day) was decreased with both diets as expected, but REE expressed relative to body mass (kcal/kg), was better maintained on the VLCK diet for men only. Individual responses clearly show the majority of men and women experience greater weight and fat loss on a VLCK than a LF diet. CONCLUSION: This study shows a clear benefit of a VLCK over LF diet for short-term body weight and fat loss, especially in men. A preferential loss of fat in the trunk region with a VLCK diet is novel and potentially clinically significant but requires further validation. These data provide additional support for the concept of metabolic advantage with diets representing extremes in macronutrient distribution.

Neuronal glucosensing: what do we know after 50 years?

Glucosensing neurons are specialized cells that use glucose as a signaling molecule to alter their action potential frequency in response to variations in ambient glucose levels. Glucokinase (GK) appears to be the primary regulator of most neuronal glucosensing, but other regulators almost certainly exist. Glucose-excited neurons increase their activity when glucose levels rise, and most use GK and an ATP-sensitive K(+) channel as the ultimate effector of glucose-induced signaling. Glucose-inhibited (GI) neurons increase their activity at low glucose levels. Although many use GK, it is unclear what the final pathway of GI neuronal glucosensing is. Glucosensing neurons are located in brain sites and respond to and integrate a variety of hormonal, metabolic, transmitter, and peptide signals involved in the regulation of energy homeostasis and other biological functions. Although it is still uncertain whether daily fluctuations in blood glucose play a specific regulatory role in these physiological functions, it is clear that large decreases in glucose availability stimulate food intake and counterregulatory responses that restore glucose levels to sustain cerebral function. Finally, glucosensing is altered in obesity and after recurrent bouts of hypoglycemia, and this altered sensing may contribute to the adverse outcomes of these conditions. Thus, although much is known, much remains to be learned about the physiological function of brain glucosensing neurons.

Plasma ghrelin levels and hunger scores in humans initiating meals voluntarily without time- and food-related cues

Ghrelin is an orexigenic hormone that is implicated in meal initiation, in part because circulating levels rise before meals. Because previous human studies have examined subjects fed on known schedules, the observed preprandial ghrelin increases could have been a secondary consequence of meal anticipation. A causal role for ghrelin in meal initiation would be better supported if preprandial increases occurred before spontaneously initiated meals not prompted by external cues. We measured plasma ghrelin levels among human subjects initiating meals voluntarily without cues related to time or food. Samples were drawn every 5 min between a scheduled lunch and a freely requested dinner, and hunger scores were obtained using visual analog scales. Insulin, glucose, fatty acids, leptin, and triglycerides were also measured. Ghrelin levels decreased shortly after the first meal in all subjects. A subsequent preprandial increase occurred over a wide range of intermeal intervals (IMI; 320-425 min) in all but one subject. Hunger scores and ghrelin levels showed similar temporal profiles and similar relative differences in magnitude between lunch and dinner. One subject displayed no preprandial ghrelin increase and was also the only individual whose insulin levels did not return to baseline between meals. This finding, along with a correlation between area-under-the-curve values of ghrelin and insulin, suggests a role for insulin in ghrelin regulation. The preprandial increase of ghrelin levels that we observed among humans initiating meals voluntarily, without time- or food-related cues, and the overlap between these levels and hunger scores are consistent with a role for ghrelin in meal initiation.

A role for glucose and insulin preprandial profiles to differentiate meals and snacks

A physiological distinction between eating occasions may help account for contradictory findings on the role of eating frequency in energy homeostasis. We assessed this issue using a midafternoon eating occasion known in France as the goûter that often consists of snack foods. Among the 24 male subjects, 8 habitually consumed four meals per day, i.e., were usual goûter eaters (GE) and 16 habitually took 3 meals per day, i.e., usual non-goûter non-snack eaters (NGNSE). All subjects were time blinded from lunchtime and had to request subsequent meals. Blood was continuously withdrawn and collected with a change of tube every 10 min until dinner request. During the session, 8 of the non-goûter eaters (NGE) were offered a snack 210 min after lunch and were designated as non-goûter snack eaters (NGSE) if they ate. Results showed that the goûter was preceded by high hunger scores and a linear decline in plasma glucose (-9.0+/-3.0%, P<.05) and insulin concentrations (-22.9+/-6.0%, P<.05). These profiles were not observed before the snack. The dinner of GE was requested later and was smaller compared to NGNSE, whereas the snack altered neither time of request nor energy intake (EI) at dinner. Among blood variables, leptin at the onset of eating was the only factor that was predictive of both intermeal interval and EI. The glucose and insulin profiles indicate that snacks should not be considered as meals in studies on the role of eating frequency in energy homeostasis.

Blood glucose dynamics and control of meal initiation: a pattern detection and recognition theory

A new framework for understanding the control of feeding behavior, with special emphasis on the evolution of hunger, the initiation of feeding, and its dependence on patterns of blood glucose, is the subject of this review. A perspective on the current status and future directions of this search for a more complete understanding of the regulation of feeding behavior in laboratory rats and humans is presented including theoretical and experimental components. First, a historical perspective on the role of blood glucose in the control of feeding is presented. Next, the theoretical approaches that have been applied to the control of feeding and had a strong influence on experimental feeding research are summarized. This is followed by a statement and overview of a current theory that has emerged from studies of the role of transient declines in blood glucose in the control of meal initiation. The current working hypothesis that transient declines in blood glucose are endogenous metabolic patterns that are detected and recognized by the central nervous system and are mapped into meal initiation in rats and are correlated with meal requests in humans are then presented. Then, the experimental studies on meal initiation and its dependence on patterns of blood glucose, first in rats and then in humans, are reviewed in detail. Finally, the future directions of the work, limitations, and the implications for the understanding of the control of feeding behavior and the regulation of energy balance are discussed.

Behavioral, plasma, and calorimetric changes related to food texture modification in men

We hypothesized that food texture modifications might alter anticipatory reflexes, feeding behavior, and the postabsorptive consequences of ingestion. Two sets of complete meals with different textures but the same macronutrient composition were prepared. The first set was either a soup containing chunks of food (mixture) or the same soup blended until smooth (purée). The second set was either a rusk (R), a sandwich loaf (SL), or a liquid rusk meal (LR). We measured hunger and fullness feelings after ingestion of each food in a calibrated lunch, the ingestion rate, the duration between lunch and a spontaneous dinner request, the energy value, and the macronutrient composition of the ad libitum dinner. We also studied plasma modifications and respiratory gas exchanges from lunch to dinner. Feelings of hunger and fullness were not affected by texture modifications. The purée soup was consumed faster than the mixture (P < 0.05), and insulin, triacylglycerol, and energy expenditure were greater with the purée (P < 0.05). LR was less palatable than the other rusk lunch versions (P < 0.001), and R was ingested more slowly (P < 0.05). The lowest increase in plasma glucose occurred with SL, and the highest energy expenditure was seen with LR (P < 0.05). In humans, food texture modification affects not only eating patterns and palatability of ingestants but also metabolic management.

Habitual meal frequency and energy intake regulation in partially temporally isolated men

OBJECTIVE

Assessment of a possible relationship between habitual as well as manipulated meal frequency, blood glucose pattern, macronutrient- and energy intake (EI), and energy intake regulation in partially temporally isolated men.

DESIGN

A partially temporally isolated within-subject design assessing energy intake regulation in spite of intervention. Intervention consisted of manipulating meal frequency by offering iso-energetic (1 MJ) preloads high in fat or carbohydrate (CHO), with the same energy density. We have previously shown that after a high-CHO preload, inter-meal-interval was 1 h, while after a high-fat preload intermeal-interval was 2 h.

SUBJECTS

Twenty healthy young (18-31 y) normal weight (body mass index (BMI): 22.8+/-1.9 kg/m(2)) men.

MEASUREMENTS

On two separate days, each after a different preload: subsequent subjects' responses to the preload, eg manipulated meal frequency; continuous blood glucose levels and blood glucose patterns: macronutrient composition of food intake; EI; appetite ratings; and taste perception. From controlled 3-day food intake diaries: habitual meal frequency; EI; and macronutrient-intake.

RESULTS

Accuracy of energy intake regulation is expressed as minimizing the difference in energy intake, despite intervention. The difference in 24 h EI on the two test days after the preloads (r(2)=0.56; P<0.001) was a function of habitual meal frequency. Variation in energy intake was primarily explained by habitual meal frequency (r(2)=0.76; P<0.0001). Adding macronutrient composition and number of blood glucose declines to this increased the explained variation to 86 and 96%, respectively. Percentage energy from CHO or from fat explained the variation in habitual meal frequency (r(2)=0.84; P<0.0001). Adding the total number of blood-glucose declines to this increased the explained variation to 88%, and adding average baseline blood glucose levels, sweetness perception and hunger suppression during preload consumption increased the explained variation to 91%. Manipulated meal frequency was related to habitual meal frequency (r(2)=0.86; P<0.0001) and was a function of the number of transient and dynamic blood glucose declines (r(2)=0.74; P<0.0001).

CONCLUSION

Habitual meal frequency is of greater significance in energy intake regulation in healthy young men than manipulated meal frequency. Healthy young men with a high habitual meal frequency showed lower 24 h EI, and a smaller difference in EI after macronutrient specific preloads, compared to those with a low habitual meal frequency, thus showing a more accurate energy intake regulation. Habitual meal frequency is based upon a cluster of related factors including macronutrient composition of the food, sweetness perception, hunger suppression, blood glucose declines and average baseline blood glucose levels.