The importance of fat-free mass and constituent tissue-organs in the control of human appetite.

PURPOSE OF REVIEW: Traditional models of human appetite focus on the contribution of adipose tissue and the gastrointestinal tract, both of which exert mainly inhibitory influences. The purpose of this review is to consider the biological factors that influence the drive to eat. RECENT FINDINGS: Fat-free mass is positively associated with objectively measured meal size and daily energy intake. These findings have been replicated in multiple populations across the life-course in laboratory and free-living studies. Studies have shown that the effect of fat-free mass is statistically mediated by resting metabolic rate, suggesting that energy expenditure per se may influence energy intake. A recent MRI study has reported that fasting hunger was associated with high metabolic rate organ (heart, liver, brain, kidneys) and skeletal muscle mass. Integrating measures of body composition at the tissue-organ level and markers of their metabolic function with appetitive measures could provide novel insight into the mechanisms that influence appetite. SUMMARY: These recent findings suggest that fat-free mass and resting metabolic rate are determinants of energy intake. Consideration of fat-free mass and energy expenditure as physiological sources of appetitive signals helps reconcile the mechanisms underpinning the inhibition of eating with those that drive eating.

The complex pattern of the effects of prolonged frequent exercise on appetite control, and implications for obesity.

From a public health perspective, much of the interest in the relationship between exercise and appetite rests on the implications for energy balance and obesity. Energy balance reflects a dynamic 2-way interaction between energy expenditure (EE) and energy intake (EI). Physical activity and exercise, and appetite are the behavioural components of EE and EI, respectively. Beyond EE, exercise is a powerful and complex physiological stimulus acting on several bodily systems. There are multiple effects of frequent and prolonged exercise on appetite which include inter alia an increase in fasting hunger, an enhancement of post-prandial satiety, a modulation of the hedonic responses to food and improvements in eating behaviour traits. These lead to variable adjustments in EI and in a reduction in the susceptibility to overconsumption. Frequent and prolonged physical activity and exercise behaviour can strengthen and sensitise the appetite control system, whilst physical inactivity and sedentariness (low level of EE) fails to downregulate EI and can permit overconsumption. Not all of the effects of exercise operate uniformly to drive appetite in the same direction. The complexity of the interaction between EE and EI means that the effects of prolonged exercise are characterised by substantial individual heterogeneity. This leads to variable effects on energy balance and body mass.

Fat-Free Mass and Total Daily Energy Expenditure Estimated Using Doubly Labeled Water Predict Energy Intake in a Large Sample of Community-Dwelling Older Adults.

BACKGROUND: Up to 30% of community-based older adults report reduced appetite and energy intake (EI), but previous research examining the underlying physiological mechanisms has focused on the mechanisms that suppress eating rather than the hunger drive and EI. OBJECTIVES: We examined the associations between fat-free mass (FFM), physical activity (PA), total daily energy expenditure (TDEE), and self-reported EI in older adults. METHODS: The present study was a secondary analysis of the Interactive Diet and Activity Tracking in AARP study. Body composition (deuterium dilution), PA (accelerometry), and TDEE (doubly labeled water) were measured in 590 older adults (age, 63.1 ± 5.9 years; BMI, 28.1 ± 4.9 kg/m2). The total daily EI was estimated from a single 24-hour dietary recall (EIsingle; ±1 month of PA and TDEE measurement) and the mean of up to 6 recalls over a 12-month period (EImean), with misreporters classified using the 95% CIs between the EImean and TDEE. RESULTS: After controlling for age and sex, linear regression demonstrated that FFM and TDEE predicted EI when estimated from a single 24-hour dietary recall (P < 0.05), from the mean of up to 6 dietary recalls (P < 0.05), and after the removal of those classified as underreporters (P < 0.001). Age moderated the associations between FFM and EIsingle (P < 0.001), FFM and EImean (P < 0.001), and TDEE with EIsingle (P = 0.016), with associations becoming weaker across age quintiles. CONCLUSIONS: These data suggest that the total daily EI is proportional to the FFM and TDEE, but not fat mass, in older adults. These associations may reflect an underling drive to eat that influences the daily food intake. While the associations between FFM or TDEE and EI existed across all age quintiles, these associations weakened with increasing age.

Fat-Free Mass and Total Daily Energy Expenditure Estimated Using Doubly Labeled Water Predict Energy Intake in a Large Sample of Community-Dwelling Older Adults.

BACKGROUND: Up to 30% of community-based older adults report reduced appetite and energy intake (EI), but previous research examining the underlying physiological mechanisms has focused on the mechanisms that suppress eating rather than the hunger drive and EI. OBJECTIVES: We examined the associations between fat-free mass (FFM), physical activity (PA), total daily energy expenditure (TDEE), and self-reported EI in older adults. METHODS: The present study was a secondary analysis of the Interactive Diet and Activity Tracking in AARP study. Body composition (deuterium dilution), PA (accelerometry), and TDEE (doubly labeled water) were measured in 590 older adults (age, 63.1 ± 5.9 years; BMI, 28.1 ± 4.9 kg/m2). The total daily EI was estimated from a single 24-hour dietary recall (EIsingle; ±1 month of PA and TDEE measurement) and the mean of up to 6 recalls over a 12-month period (EImean), with misreporters classified using the 95% CIs between the EImean and TDEE. RESULTS: After controlling for age and sex, linear regression demonstrated that FFM and TDEE predicted EI when estimated from a single 24-hour dietary recall (P < 0.05), from the mean of up to 6 dietary recalls (P < 0.05), and after the removal of those classified as underreporters (P < 0.001). Age moderated the associations between FFM and EIsingle (P < 0.001), FFM and EImean (P < 0.001), and TDEE with EIsingle (P = 0.016), with associations becoming weaker across age quintiles. CONCLUSIONS: These data suggest that the total daily EI is proportional to the FFM and TDEE, but not fat mass, in older adults. These associations may reflect an underling drive to eat that influences the daily food intake. While the associations between FFM or TDEE and EI existed across all age quintiles, these associations weakened with increasing age.

Validation of the Activity Preference Assessment: a tool for quantifying children's implicit preferences for sedentary and physical activities.

BACKGROUND: High levels of sedentary behavior and low physical activity are associated with poor health, and the cognitive determinants of these behaviors in children and adolescents are not well understood. To address this gap, we developed a novel, non-verbal, computer-based assessment to quantify the degree to which youth prefer to be sedentary relative to physically active in their leisure time. METHODS: The Activity Preference Assessment (APA) uses a forced-choice paradigm to understand implicit decision-making processes when presented with common sedentary and physical activities. The APA bias score ranges from - 100 to + 100, with positive scores indicating a relative preference for sedentary activities, and negative scores representing a preference for physical activities. In 60 children ages 8-17 years, we assessed the validity of this behavioral task against a free-choice play observation, accelerometry-measured activity, anthropometrics and body composition, and cardiorespiratory fitness. We explored neighborhood, family, and individual-level factors that may influence implicit activity preferences. Test-retest reliability was assessed over one week. RESULTS: The majority of children (67%) preferred sedentary relative to physical activities. APA bias scores were positively associated with sedentary time during free-choice play. In girls, bias scores were negatively associated with average daily MVPA. APA bias scores were positively associated with body fat and negatively associated with cardiorespiratory fitness. These findings were independent of age, sex, and race/ethnicity. Neighborhood access to physical activity spaces, the number of people in the home, perceived physical self-competence (e.g., coordination, strength), and self-reported depressive symptoms were associated with activity preferences. The intra-class correlation for test-retest reliability was r = 0.59. CONCLUSIONS: The APA shows promise as a novel tool for quantifying children's relative preference for sedentary versus physical activities. Implicit bias scores from the APA are clinically meaningful, as shown by significant associations with adiposity and cardiorespiratory fitness. Future longitudinal studies should examine the directionality of the association between preferences and health markers, and the degree to which implicit activity preferences are modifiable. Importantly, the task only takes an average of 10 min to complete, highlighting a potential role as an efficient screening tool for the propensity to be sedentary versus physically active. TRIAL REGISTRATION: ClinicalTrials.gov NCT03624582 .

Biological and psychological mediators of the relationships between fat mass, fat-free mass and energy intake.

BACKGROUND: While recent studies in humans indicate that fat-free mass (FFM) is closely associated with energy intake (EI) when in energy balance, associations between fat mass (FM) and EI are inconsistent. OBJECTIVES: The present study used a cross-sectional design to examine the indirect and direct effects of FFM, FM and resting metabolic rate (RMR) on EI in individuals at or close to energy balance. METHODS: Data for 242 individuals (114 males; 128 females; BMI = 25.7 ± 4.9 kg/m2) were collated from the non-intervention baseline conditions of five studies employing common measures of body composition (air-displacement plethysmography), RMR (indirect calorimetry) and psychometric measures of eating behaviours (Dutch Eating Behaviour Questionnaire). Daily EI (weighed dietary records) and energy expenditure (flex heart rate) were measured for 6-7 days. Sub-analyses were conducted in 71 individuals who had additional measures of body composition (dual-energy X-ray absorptiometry) and fasting glucose, insulin and leptin. RESULTS: After adjusting for age, sex and study, linear regression and mediation analyses indicated that the effect of FFM on EI was mediated by RMR (P < 0.05). FM also independently predicted EI, with path analysis indicating a positive indirect association (mediated by RMR; P < 0.05), and a stronger direct negative association (P < 0.05). Leptin, insulin and insulin resistance failed to predict EI, but cognitive restraint was a determinant of EI and partially mediated the association between FM and EI (P < 0.05). CONCLUSIONS: While the association between FFM and EI was mediated by RMR, FM influenced EI via two separate and opposing pathways; an indirect 'excitatory' effect (again, mediated by RMR), and a stronger direct 'inhibitory' effect. Psychological factors such as cognitive restraint remain robust predictors of EI when considered alongside physiological determinants of EI, and indeed, have the potential to play a mediating role in the overall expression of EI.

Activity energy expenditure is an independent predictor of energy intake in humans.

BACKGROUND: There is evidence that the energetic demand of metabolically active tissue is associated with day-to-day food intake (EI). However, the extent to which behavioural components of total daily energy expenditure (EE) such as activity energy expenditure (AEE) are also associated with EI is unknown. Therefore, the present study examined the cross-sectional associations between body composition, resting metabolic rate (RMR), AEE and EI. METHODS: Data for 242 individuals (114 males; 128 females; BMI = 25.7 ± 4.9 kg/m2) were collated from the baseline control conditions of five studies employing common measures of body composition (air displacement plethysmography) and RMR (indirect calorimetry). Daily EI (weighed-dietary records) and EE (FLEX heart rate) were measured over 6-7 days, and AEE was calculated as total daily EE minus RMR. RESULTS: Linear regression indicated that RMR (ß = 0.39; P < 0.001), fat mass (ß = -0.26; P < 0.001) and AEE (ß = 0.18; P = 0.002) were independent predictors of mean daily EI, with AEE adding ≈3% of variance to the model after controlling for age, sex and study (F(10, 231) = 18.532, P < 0.001; R2 = 0.445). Path analyses indicated that the effect of FFM on mean daily EI was mediated by RMR (P < 0.05), while direct (ß = 0.19; P < 0.001) and indirect (ß = 0.20; P = 0.001) associations between AEE and mean daily EI were observed. CONCLUSIONS: When physical activity was allowed to vary under free-living conditions, AEE was associated with mean daily EI independently of other biological determinants of EI arising from body composition and RMR. These data suggest that EE per se exerts influence over daily food intake, with both metabolic (RMR) and behavioral (AEE) components of total daily EE potentially influencing EI via their contribution to daily energy requirements.

Women with a low-satiety phenotype show impaired appetite control and greater resistance to weight loss.

This trial compared weight loss outcomes over 14 weeks in women showing low- or high-satiety responsiveness (low- or high-satiety phenotype (LSP, HSP)) measured by a standardised protocol. Food preferences and energy intake (EI) after low and high energy-density (LED, HED) meals were also assessed. Ninety-six women (n 52 analysed; 41·24 (SD 12·54) years; 34·02 (sd 3·58) kg/m2) engaged in one of two weight loss programmes underwent LED and HED laboratory test days during weeks 3 and 12. Preferences for LED and HED food (Leeds Food Preference Questionnaire) and ad libitum evening meal and snack EI were assessed in response to equienergetic LED and HED breakfasts and lunches. Weekly questionnaires assessed control over eating and ease of adherence to the programme. Satiety quotients based on subjective fullness ratings post LED and HED breakfasts determined LSP (n 26) and HSP (n 26) by tertile splits. Results showed that the LSP lost less weight and had smaller reductions in waist circumference compared with HSP. The LSP showed greater preferences for HED foods, and under HED conditions, consumed more snacks (kJ) compared with HSP. Snack EI did not differ under LED conditions. LSP reported less control over eating and reported more difficulty with programme adherence. In conclusion, low-satiety responsiveness is detrimental for weight loss. LED meals can improve self-regulation of EI in the LSP, which may be beneficial for longer-term weight control.

A Low Energy-Dense Diet in the Context of a Weight-Management Program Affects Appetite Control in Overweight and Obese Women.

Background: Low energy-dense (LED) foods reduce energy intake (EI); whether this effect is sustained over time and during weight loss is unknown. Objective: This trial examined the effects of LED compared with high energy-dense (HED) meals on appetite, EI, and control over eating in the laboratory and during a weight-management program that encourages unrestricted intake of LED foods [Slimming World, UK (SW)] compared with a self-led Standard Care program [NHS weight-loss plan (SC)]. Methods: Overweight and obese women [n = 96; mean ± SD age: 41.03 ± 12.61 y; mean ± SD body mass index (in kg/m2): 34.00 ± 3.61] were recruited from the SW or SC programs. Primary outcomes included appetite, food preferences (liking and wanting for LED and HED foods), cravings, and evening meal EI (LED, HED) in response to calorie-matched LED (≤0.8 kcal/g) and HED (≥2.5 kcal/g) breakfast and lunch meals. Probe-day tests were conducted at weeks 3 and 4 and repeated at weeks 12 and 13 in a within-day crossover design. Secondary outcomes, including body weight and program experience, were measured from weeks 1 to 14 in a parallel-group design. Dietary compliance was monitored with the use of weighed food diaries at weeks 3 and 12. Results: Intention-to-treat (ITT) and completers analyses showed that the SW group lost more weight than the SC group [ITT: -5.9% (95% CI: -4.7%, -7.2%) compared with -3.5% (-2.3%, -4.8%), P < 0.05; completers: -6.2% (-4.8%, -7.6%) compared with 3.9% (-2.5%, -5.2%), P < 0.05]. The SW group reported greater control over eating and more motivation to continue the program compared with the SC group. LED meals increased sensations of fullness and reduced hunger on probe days (P < 0.001). Total-day EI was 1057 ± 73 kcal less (95% CI: 912, 1203 kcal; 36%) under LED compared with HED conditions (P < .001). Liking for LED and HED foods and wanting for HED foods were lower before lunch under LED compared with HED conditions, and liking decreased to a greater extent after the LED lunch. The SW group reported fewer cravings under LED compared with HED conditions (P < 0.05). On probe days, appetite and EI outcomes did not differ between weeks 3 and 12 or between the SW and SC groups. Conclusion: LED meals improve appetite control in women attempting weight loss and the effect is sustainable. Consumption of LED meals likely contributed to weight loss in the SW program. This study was registered at clinicaltrials.gov as NCT02012426.

Energy depletion by 24-h fast leads to compensatory appetite responses compared with matched energy depletion by exercise in healthy young males.

Although there is a growing interest for the effects of intermittent fasting on energy balance, this study aimed to compare appetite, energy intake and food reward responses with an energy depletion induced either by 24-h food restriction or an equivalent deficit with exercise in healthy males. In all, twelve healthy lean males (21·5 (sd 0·5) years old; BMI: 22·5 (sd 1·7) kg/m2) participated in this study. Body composition, aerobic capacity, food preferences and energy intake were assessed. They randomly completed three conditions: (i) no depletion (CON); (ii) full 24-h energy restrictions (Def-EI); and (iii) exercise condition (Def-EX). Ad libitum energy intake and food reward were assessed at the end of each session. Appetite feelings were assessed regularly. Ad libitum energy intake was higher on Def-EI (7330 (sd 2975) kJ (1752 (sd 711) kcal) compared with that on CON (5301 (sd 1205) kJ (1267 (sd 288) kcal)) (P<0·05), with no difference between CON and Def-EX (6238 (sd 1741) kJ (1491 (sd 416) kcal) (P=0·38) and between Def-EX and Def-EI (P=0·22). There was no difference in the percent energy ingested from macronutrients. Hunger was lower on CON and Def-EX compared with Def-EI (P<0·001). Satiety was higher on CON and Def-EI compared with that on Def-EX (P<0·001). There was a significant interaction condition × time for food choice fat bias (P=0·04), showing a greater preference for high-fat v. low-fat food during Def-EI and Def-EX. Although 24-h fasting leads to increased energy intake at the following test meal (without total daily energy intake difference), increased hunger profile and decreased post-meal food choice fat bias, such nutritional responses are not observed after a similar deficit induced by exercise.

Development and validation of the Child Three-Factor Eating Questionnaire (CTFEQr17).

OBJECTIVE: To develop and validate a child and adolescent version of the Three-Factor Eating Questionnaire (CTFEQr17) and to assess its psychometric properties and factor structure. We also examined associations between the CTFEQr17 and BMI and food preferences. DESIGN: A two-phase approach was utilized, employing both qualitative and quantitative methodologies. SETTING: Primary and secondary schools, UK. SUBJECTS: In phase 1, seventy-six children (thirty-nine boys; mean age 12·3 (sd 1·4) years) were interviewed to ascertain their understanding of the original TFEQr21 and to develop accessible and understandable items to create the CTFEQr17. In phase 2, 433 children (230 boys; mean age 12·0 (sd 1·7) years) completed the CTFEQr17 and a food preference questionnaire, a sub-sample (n 253; 131 boys) had their height and weight measured, and forty-five children (twenty-three boys) were interviewed to determine their understanding of the CTFEQr17. RESULTS: The CTFEQr17 showed good internal consistency (Cronbach's α=0·85) and the three-factor structure was retained: cognitive restraint (CR), uncontrolled eating (UE) and emotional eating (EE). Qualitative data demonstrated a high level of understanding of the questionnaire (95 %). High CR was found to be significantly associated with a higher body weight, BMI and BMI percentile. High UE and EE scores were related to a preference for high-fat savoury and high-fat sweet foods. The relationships between CTFEQr17, anthropometry and food preferences were stronger for girls than boys. CONCLUSIONS: The CTFEQr17 is a psychometrically sound questionnaire for use in children and adolescents, and associated with anthropometric and food preference measures.

Impact of a non-restrictive satiating diet on anthropometrics, satiety responsiveness and eating behaviour traits in obese men displaying a high or a low satiety phenotype.

The aim of this study was to evaluate the impact of a non-restrictive satiating diet in men displaying various degrees of satiety efficiency. In all, sixty-nine obese men aged 41·5 (sd 5·7) years were randomly assigned to a control (10-15, 55-60 and 30 % energy as protein, carbohydrate and lipid, respectively; n 34) or satiating (20-25, 45-50 and 30-35 % energy as protein, carbohydrate and lipid, respectively; n 35) diet for 16 weeks, and were classified as having a low (LSP) or high (HSP) satiety phenotype. Both diets were consumed ad libitum. Changes in body weight, BMI, percent fat mass, waist circumference, satiety responsiveness and eating behaviour traits were assessed following the intervention. Dropout rates were higher in the control diet (44·1 %) compared with the satiating diet (8·6 %). Decreases in body weight, BMI and waist circumference were significant in both groups, yet HSP individuals lost more body weight than LSP individuals (P=0·048). Decreases in % fat mass were greater in the satiating diet (LSP: -2·1 (sd 2·1) %; P<0·01 and HSP: -3·0 (sd 2·5) %; P<0·001) compared with the control diet (LSP: -1·1 (sd 2·5) % and HSP: -1·3 (sd 2·6) %) (P=0·034). Satiety responsiveness was markedly improved in the satiating diet, whereas no significant changes were observed in the control group. Changes in dietary restraint (+3·3 (sd 2·9) to +7·2 (sd 5·5)), flexible control (+0·9 (sd 1·4) to +2·3 (sd 2·7)), rigid control (+2·2 (sd 1·5) to +2·5 (sd 2·8)), disinhibition (-2·8 (sd 3·7) to -3·2 (sd 2·6)) and susceptibility to hunger (-2·7 (sd 4·1) to -4·6 (sd 3·9)) were similar between the diets. Compared with the control diet, the satiating diet favoured adherence, decreased % fat mass and improved satiety responsiveness in both HSP and LSP individuals.

The effects of partial sleep restriction and altered sleep timing on appetite and food reward.

We examined the effects of partial sleep restriction (PSR) with an advanced wake-time or delayed bedtime on measures of appetite, food reward and subsequent energy intake (EI). Twelve men and 6 women (age: 23 ± 4 years, body fat: 18.8 ± 10.1%) participated in 3 randomized crossover sessions: control (habitual bed- and wake-time), 50% PSR with an advanced wake-time and 50% PSR with a delayed bedtime. Outcome variables included sleep architecture (polysomnography), ad libitum EI (validated food menu), appetite sensations (visual analogue scales), satiety quotient (SQ; mm/100 kcal) and food reward (Leeds Food Preference Questionnaire and the relative-reinforcing value (RRV) of preferred food task). Increased fasting and post-standard breakfast appetite ratings were noted following PSR with an advanced wake-time compared to the control and PSR with a delayed bedtime sessions (Fasting hunger ratings: 77 ± 16 vs. 65 ± 18 and 64 ± 16; P = 0.01; Post-meal hunger AUC: 5982 ± 1781 vs. 4508 ± 2136 and 5198 ± 2201; P = 0.03). Increased explicit wanting and liking for high- relative to low-fat foods were also noted during the advanced wake-time vs. control session (Explicit wanting: -3.5 ± 12.5 vs. -9.3 ± 8.9, P = 0.01; Explicit liking: -1.6 ± 8.5 vs. -7.8 ± 9.6, P = 0.002). No differences in the RRV of preferred food, SQ and ad libitum lunch intake were noted between sessions. These findings suggest that appetite sensations and food reward are increased following PSR with an advanced wake-time, rather than delayed bedtime, vs. CONTROL: However, this did not translate into increased EI during a test meal. Given the increasing prevalence of shift workers and incidences of sleep disorders, additional studies are needed to evaluate the prolonged effects of voluntary sleep restriction with altered sleep timing on appetite and EI measurements.

Cross-sectional and longitudinal associations between different exercise types and food cravings in free-living healthy young adults.

INTRODUCTION: An increase in energy intake due to alterations in hedonic appetite sensations may, at least in part, contribute to lower-than-expected weight loss in exercise interventions. The aim of this study was to examine cross-sectional and longitudinal associations between habitual exercise participation and food cravings in free-living young adults. METHODS: A total of 417 adults (49% male, 28 ± 4 years) reported frequency and duration of walking, aerobic exercise, resistance exercise and other exercise at baseline and every 3 months over a 12-month period. Food cravings were assessed via the Control of Eating Questionnaire at baseline and 12-month follow-up. RESULTS: Cross-sectional analyses revealed more frequent cravings for chocolate and a greater difficulty to resist food cravings in women compared to men (p < 0.01). Only with resistance exercise significant sex by exercise interaction effects were observed with favorable responses in men but not in women. Significant main effects were shown for walking and aerobic exercise with exercisers reporting more frequent food cravings for chocolate and fruits and greater difficulty to resist eating compared to non-exercisers (p < 0.05). Longitudinal analyses revealed significant interaction effects for other exercise (p < 0.05) with favorable results in men but not women. Furthermore, significant main effects were observed for aerobic exercise, resistance exercise and total exercise with an increase in exercise being associated with a reduced difficulty to resist food cravings (p < 0.05). DISCUSSION: The association between exercise participation and hedonic appetite sensations varies by exercise type and sex. Even though exercise was associated with more frequent and greater difficulty to food cravings in the cross-sectional analyses, which may be attributed to greater energy demands, longitudinal results indicate beneficial effects of increased exercise on appetite control, particularly in men.

Energy balance, body composition, sedentariness and appetite regulation: pathways to obesity.

Energy balance is not a simple algebraic sum of energy expenditure and energy intake as often depicted in communications. Energy balance is a dynamic process and there exist reciprocal effects between food intake and energy expenditure. An important distinction is that of metabolic and behavioural components of energy expenditure. These components not only contribute to the energy budget directly, but also by influencing the energy intake side of the equation. It has recently been demonstrated that resting metabolic rate (RMR) is a potential driver of energy intake, and evidence is accumulating on the influence of physical activity (behavioural energy expenditure) on mechanisms of satiety and appetite control. These effects are associated with changes in leptin and insulin sensitivity, and in the plasma levels of gastrointestinal (GI) peptides such as glucagon-like peptide-1 (GLP-1), ghrelin and cholecystokinin (CCK). The influence of fat-free mass on energy expenditure and as a driver of energy intake directs attention to molecules emanating from skeletal tissue as potential appetite signals. Sedentariness (physical inactivity) is positively associated with adiposity and is proposed to be a source of overconsumption and appetite dysregulation. The molecular signals underlying these effects are not known but represent a target for research.

Differing effects of high-fat or high-carbohydrate meals on food hedonics in overweight and obese individuals.

Although the effects of dietary fat and carbohydrate on satiety are well documented, little is known about the impact of these macronutrients on food hedonics. We examined the effects of ad libitum and isoenergetic meals varying in fat and carbohydrate on satiety, energy intake and food hedonics. In all, sixty-five overweight and obese individuals (BMI=30·9 (sd 3·8) kg/m2) completed two separate test meal days in a randomised order in which they consumed high-fat/low-carbohydrate (HFLC) or low-fat/high-carbohydrate (LFHC) foods. Satiety was measured using subjective appetite ratings to calculate the satiety quotient. Satiation was assessed by intake at ad libitum meals. Hedonic measures of explicit liking (subjective ratings) and implicit wanting (speed of forced choice) for an array of HFLC and LFHC foods were also tested before and after isoenergetic HFLC and LFHC meals. The satiety quotient was greater after ad libitum and isoenergetic meals during the LFHC condition compared with the HFLC condition (P=0·006 and P=0·001, respectively), whereas ad libitum energy intake was lower in the LFHC condition (P<0·001). Importantly, the LFHC meal also reduced explicit liking (P<0·001) and implicit wanting (P=0·011) for HFLC foods compared with the isoenergetic HFLC meal, which failed to suppress the hedonic appeal of subsequent HFLC foods. Therefore, when coupled with increased satiety and lower energy intake, the greater suppression of hedonic appeal for high-fat food seen with LFHC foods provides a further mechanism for why these foods promote better short-term appetite control than HFLC foods.

Effects of targeted delivery of propionate to the human colon on appetite regulation, body weight maintenance and adiposity in overweight adults.

OBJECTIVE: The colonic microbiota ferment dietary fibres, producing short chain fatty acids. Recent evidence suggests that the short chain fatty acid propionate may play an important role in appetite regulation. We hypothesised that colonic delivery of propionate would increase peptide YY (PYY) and glucagon like peptide-1 (GLP-1) secretion in humans, and reduce energy intake and weight gain in overweight adults. DESIGN: To investigate whether propionate promotes PYY and GLP-1 secretion, a primary cultured human colonic cell model was developed. To deliver propionate specifically to the colon, we developed a novel inulin-propionate ester. An acute randomised, controlled cross-over study was used to assess the effects of this inulin-propionate ester on energy intake and plasma PYY and GLP-1 concentrations. The long-term effects of inulin-propionate ester on weight gain were subsequently assessed in a randomised, controlled 24-week study involving 60 overweight adults. RESULTS: Propionate significantly stimulated the release of PYY and GLP-1 from human colonic cells. Acute ingestion of 10 g inulin-propionate ester significantly increased postprandial plasma PYY and GLP-1 and reduced energy intake. Over 24 weeks, 10 g/day inulin-propionate ester supplementation significantly reduced weight gain, intra-abdominal adipose tissue distribution, intrahepatocellular lipid content and prevented the deterioration in insulin sensitivity observed in the inulin-control group. CONCLUSIONS: These data demonstrate for the first time that increasing colonic propionate prevents weight gain in overweight adult humans. TRIAL REGISTRATION NUMBER: NCT00750438.

Associations between sleep parameters and food reward.

This study examined the effects of acute, isocaloric aerobic and resistance exercise on different sleep parameters, and whether changes in these sleep parameters between sessions were related to next morning food reward. Fourteen men and women (age: 21.9 ± 2.7 years; body mass index: 22.7 ± 1.9 kg m(-) ²) participated in three randomized crossover sessions: aerobic exercise; resistance exercise; and sedentary control. Target exercise energy expenditure was matched at 4 kcal kg(-1) of body weight, and performed at 70% of VO2peak or 70% of 1 repetition-maximal. Sleep was measured (accelerometry) for 22 h following each session. The 'wanting' for visual food cues (validated computer task) was assessed the next morning. There were no differences in sleep parameters and food 'wanting' between conditions. Decreases in sleep duration and earlier wake-times were significantly associated with increased food 'wanting' between sessions (P = 0.001). However, these associations were no longer significant after controlling for elapsed time between wake-time and the food reward task. These findings suggest that shorter sleep durations and earlier wake-times are associated with increased food reward, but these associations are driven by elapsed time between awakening and completion of the food reward task.

The effects of a single bout of aerobic or resistance exercise on food reward.

It is unknown whether an acute bout of calorie-matched aerobic and resistance exercise alters food reward in a similar manner. Thus, we examined the effects of isocaloric resistance and aerobic exercise sessions on acute food reward. Sixteen men and women (age: 21.9 ± 2.6 years; BMI: 22.8 ± 1.8 kg/m(2)) participated in three randomized crossover sessions: aerobic exercise, resistance exercise, and sedentary control. The target exercise energy expenditure was matched at 4 kcal/kg of body weight, and performed at 70% of VO2peak or 12 repetition-maximum (equivalent to 70% of 1 repetition-maximum). A validated computer task assessed the wanting and liking for visual food cues following exercise, and following an ad libitum lunch. Decreases in the relative preference for high vs. low fat foods were noted following exercise compared to the control session, and this was independent of modality (aerobic: P = 0.04; resistance: P = 0.03). Furthermore, the explicit liking for high vs. low fat foods was lower following resistance exercise compared to the control session (P = 0.04). However, these changes in food reward were not correlated with changes in energy intake (EI) between sessions. Exercise, independent of modality, led to decreases in the relative preference for high fat relative to low fat foods. Additionally, decreases in the hedonic "liking" of high fat foods following resistance, but not aerobic, exercise may imply that modality does influence acute food hedonic responses. However, these decreases in food hedonics were not related to lower EI, thus suggesting that a dissociation may exist between food hedonics and actual EI.

Questionnaire and laboratory measures of eating behavior. Associations with energy intake and BMI in a community sample of working adults.

PURPOSE: The present research compared a self-report measure of usual eating behaviors with two laboratory-based behavioral measures of food reward and food preference. METHODS: Eating behaviors were measured among 233 working adults. A self-report measure was the Three Factor Eating Questionnaire (TFEQ) Restraint, Disinhibition and Hunger subscales. Laboratory measures were the (RVF) and Explicit Liking (EL) and Implicit Wanting (IW) for high fat food. Outcome measures were body mass index (BMI), and energy intake measured using three 24-h dietary recalls. RESULTS: Significant bivariate associations were observed between each of the eating behavior measures and energy intake, but only Disinhibition and Hunger were associated with BMI. Multiple regression results showed RVF and EL and IW predicted energy intake independent of the TFEQ scales but did not predict BMI. CONCLUSION: Laboratory and self-report measures capture unique aspects of individual differences in eating behaviors that are associated with energy intake.