Correction: A novel scaling methodology to reduce the biases associated with missing data from commercial activity monitors.

[This corrects the article DOI: 10.1371/journal.pone.0235144.].

A novel scaling methodology to reduce the biases associated with missing data from commercial activity monitors.

BACKGROUND: Commercial physical activity monitors have wide utility in the assessment of physical activity in research and clinical settings, however, the removal of devices results in missing data and has the potential to bias study conclusions. This study aimed to evaluate methods to address missingness in data collected from commercial activity monitors. METHODS: This study utilised 1526 days of near complete data from 109 adults participating in a European weight loss maintenance study (NoHoW). We conducted simulation experiments to test a novel scaling methodology (NoHoW method) and alternative imputation strategies (overall/individual mean imputation, overall/individual multiple imputation, Kalman imputation and random forest imputation). Methods were compared for hourly, daily and 14-day physical activity estimates for steps, total daily energy expenditure (TDEE) and time in physical activity categories. In a second simulation study, individual multiple imputation, Kalman imputation and the NoHoW method were tested at different positions and quantities of missingness. Equivalence testing and root mean squared error (RMSE) were used to evaluate the ability of each of the strategies relative to the true data. RESULTS: The NoHoW method, Kalman imputation and multiple imputation methods remained statistically equivalent (p<0.05) for all physical activity metrics at the 14-day level. In the second simulation study, RMSE tended to increase with increased missingness. Multiple imputation showed the smallest RMSE for Steps and TDEE at lower levels of missingness (<19%) and the Kalman and NoHoW methods were generally superior for imputing time in physical activity categories. CONCLUSION: Individual centred imputation approaches (NoHoW method, Kalman imputation and individual Multiple imputation) offer an effective means to reduce the biases associated with missing data from activity monitors and maximise data retention.

Prevalence and predictors of weight loss maintenance: a retrospective population-based survey of European adults with overweight and obesity.

BACKGROUND: The prevalence of weight loss attempts has increased worldwide, although the extent to which sustained weight loss is achieved is unknown. There is insufficient research into weight loss maintenance (WLM) in individuals with overweight or obesity who have recently lost clinically significant amounts of weight (≥5%), particularly in the European general population. The present study aimed to determine the prevalence and retrospective predictors of WLM in population-based samples of European adults with overweight or obesity who had made a recently completed weight loss attempt. METHODS: Participants (N = 2000) in UK, Denmark and Portugal completed an online survey about loss and regain in their most recent completed weight loss attempt, features of their attempt (duration, self-weighing, lapses, strategies), as well as loss of control and binge eating. Multiple regression analysis was used to determine factors retrospectively associated with WLM in those who achieved clinically significant weight loss (n = 1272). RESULTS: Mean (SD) self-reported weight loss was 9% (8%) and mean (SD) regain was 96.3% (9%) of participants' start weight. Twenty-three percent of the total sample had maintained weight loss of ≥5% for at least 1 month. Controlling for weight loss and time since attempt, predictors of better WLM were avoidance of a temporary lapse, infrequent/absent loss of control and binge eating, and use of a greater number of dietary strategies for WLM (r2  = 0.338, P < 0.001). PRINCIPAL CONCLUSIONS: Factors associated with recent successful WLM indicate the importance of the continued use of dietary and other strategies for WLM, particularly in the face of a lapse, as well as the need to manage dysfunctional eating behaviours.

Modelling the associations between fat-free mass, resting metabolic rate and energy intake in the context of total energy balance.

BACKGROUND: The relationship between body composition, energy expenditure and ad libitum energy intake (EI) has rarely been examined under conditions that allow any interplay between these variables to be disclosed. OBJECTIVE: The present study examined the relationships between body composition, energy expenditure and EI under controlled laboratory conditions in which the energy density and macronutrient content of the diet varied freely as a function of food choice. METHODS: Fifty-nine subjects (30 men: mean body mass index=26.7±4.0 kg m(-2); 29 women: mean body mass index=25.4±3.5 kg m(-)(2)) completed a 14-day stay in a residential feeding behaviour suite. During days 1 and 2, subjects consumed a fixed diet designed to maintain energy balance. On days 3-14, food intake was covertly measured in subjects who had ad libitum access to a wide variety of foods typical of their normal diets. Resting metabolic rate (RMR; respiratory exchange), total daily energy expenditure (doubly labelled water) and body composition (total body water estimated from deuterium dilution) were measured on days 3-14. RESULTS: Hierarchical multiple regression indicated that after controlling for age and sex, both fat-free mass (FFM; P<0.001) and RMR (P<0.001) predicted daily EI. However, a mediation model using path analysis indicated that the effect of FFM (and fat mass) on EI was fully mediated by RMR (P<0.001). CONCLUSIONS: These data indicate that RMR is a strong determinant of EI under controlled laboratory conditions where food choice is allowed to freely vary and subjects are close to energy balance. Therefore, the conventional adipocentric model of appetite control should be revised to reflect the influence of RMR.

Plausible self-reported dietary intakes in a residential facility are not necessarily reliable.

BACKGROUND/OBJECTIVES: Comparing reported energy intakes with estimated energy requirements as multiples of basal metabolic rate (Ein:BMR) is an established method of identifying implausible food intake records. The present study aimed to examine the validity of self-reported food intakes believed to be plausible. SUBJECTS/METHODS: One hundred and eighty men and women were provided with all food and beverages for two consecutive days in a residential laboratory setting. Subjects self-reported their food and beverage intakes using the weighed food diary method (WDR). Investigators covertly measured subjects' actual consumption over the same period. Subjects also reported intakes over four consecutive days at home. BMR was measured by indirect calorimetry. RESULTS: Average reported energy intakes were significantly lower than actual intakes (11.2 and 11.8 MJ/d, respectively, P<0.001). Two-thirds (121) of the WDR were under-reported to varying degrees. Only five of these were considered as implausible using an Ein:BMR cut-off value of 1.03*BMR. Under-reporting of food and beverage intakes, as measured by the difference between reported and actual intake, was evident at all levels of Ein;BMR. Reported energy intakes were lower still (10.2 MJ/d) while subjects were at home. CONCLUSIONS: Under-recording of self-reported food intake records was extensive but very few under-reported food intake records were identified as implausible using energy intake to BMR ratios. Under-recording was evident at all levels of energy intake.

Attendance and weight outcomes in 4754 adults referred over 6 months to a primary care/commercial weight management partnership scheme.

WHAT IS ALREADY KNOWN ON THIS SUBJECT: • There is growing evidence of the effectiveness of commercial weight management programmes in the community. A recent randomized controlled trial has shown commercial providers to be more effective than NHS providers for weight management solutions in primary care. Some commercial weight management providers have established national slimming on referral schemes for weight management, which result on average in weight losses of 4-5% over a 12-week referral period. A recent randomized controlled trial of a similar scheme over 12 months yielded similar weight loses. Another RCT comparing commercial providers over 6 months showed average weight losses of ∼6.6% across providers. WHAT THIS STUDY ADDS: • The present study shows that when local primary care practitioners target resources to where they, as health professionals, felt they would have the most beneficial effect in their local communities, greater weight losses can be achieved. • Different NHS Trusts extended 12-week referrals by an additional 12 weeks in a total of 4754 patients. • Mean weight losses of 8.6% were achieved suggesting that local targeting of primary care resources can maximize returns for NHS investments in commissioning the services of commercial weight management organizations. SUMMARY: This project audited attendance and weight loss in a primary care/commercial weight management partnership scheme in patients who participated over 6 months. 4754 adult patients (575 men, 4179 women) were referred to Slimming World for 24 weekly sessions. Data were analysed using individual weekly weight records. Mean (standard deviation, SD) body mass index (BMI) change was -3.3 kg m(-2) (2.2), weight change -8.9 kg (6.0), percent weight change -8.6% (5.3) and number of sessions attended 21.3 (3.2) of 24. For patients attending at least 20 of 24 sessions (n = 3626 or 76.3%), mean (SD) BMI change was -3.6 kg m(-2) (2.2), weight change -9.6 kg (6.1), percent weight change -9.3% (5.3). Weight loss was greater in men than women (P < 0.001). 74.5% of all patients enrolled, and 79.3% of patients attending 20 or more sessions achieved at least 5% weight loss. 37.3% of the whole population lost ≥10% of their weight. Weight gain was prevented in 96.3% of all patients referred. Referral to a commercial organization for community-based lifestyle intervention is a practical option for longer-term National Health Service weight management strategies.

Use of the cellular model of body composition to describe changes in body water compartments after total fasting, very low calorie diet and low calorie diet in obese men.

INTRODUCTION: The cellular model of body composition divides the body in body cell mass (BCM), extracellular solids and extracellular fluids. This model has been infrequently applied for the evaluation of weight loss (WL) programmes. OBJECTIVES: (1) To assess changes in body compartments in obese men undergoing fasting, very low calorie diet (VLCD) and low calorie diet (LCD); (2) to evaluate two cellular models for the determination of changes in BCM, fat mass (FM) and body fluids. MATERIALS AND METHODS: Three groups of six, obese men participated in a total fast (F) for 6 days, a VLCD (2.5 MJ per day) for 3 weeks or an LCD (5.2 MJ per day) for 6 weeks. Body composition was measured at baseline and after small ( approximately 5%) and moderate ( approximately 10%) WL. FM was measured using a four-compartment model. Total body water (TBW) and extracellular water (ECW) were, respectively, measured by deuterium and sodium bromide dilution and intracellular water (ICW) calculated by difference. Two cellular models were used to measure BCM, FM and body fluids distribution. RESULTS: After about 5%WL changes in TBW were F=-3.2+/-1.2 kg (P<0.01), VLCD=-1.2+/-0.6 kg (P<0.01), LCD=-0.3+/-0.9 kg(n.s.). The contribution of TBW to total body mass loss was indirectly associated with FM loss. ECW increased during fasting (+1.5+/-3.1 kg, n.s.), decreased during the VLCD (-2.0+/-1.5 kg, P<0.05) and remained unchanged at the end of the LCD (-0.3+/-1.6 kg, n.s.). ICW significantly decreased during fasting (-4.7+/-3.9 kg, P<0.05) but did not change in the LCD and VLCD groups. The loss of BCM was more significant in the fasting group and it was directly associated with changes in ICW. CONCLUSIONS: After a 6-day period of fasting we observed more ICW losses and less fat mobilization compared with VLCD and LCD. The cellular model of body composition is suitable for the characterization of changes in body fluids distribution during WL.

Beneficial effects of exercise: shifting the focus from body weight to other markers of health.

BACKGROUND: Exercise is widely promoted as a method of weight management, while the other health benefits are often ignored. The purpose of this study was to examine whether exercise-induced improvements in health are influenced by changes in body weight. METHODS: Fifty-eight sedentary overweight/obese men and women (BMI 31.8 (SD 4.5) kg/m(2)) participated in a 12-week supervised aerobic exercise intervention (70% heart rate max, five times a week, 500 kcal per session). Body composition, anthropometric parameters, aerobic capacity, blood pressure and acute psychological response to exercise were measured at weeks 0 and 12. RESULTS: The mean reduction in body weight was -3.3 (3.63) kg (p<0.01). However, 26 of the 58 participants failed to attain the predicted weight loss estimated from individuals' exercise-induced energy expenditure. Their mean weight loss was only -0.9 (1.8) kg (p<0.01). Despite attaining a lower-than-predicted weight reduction, these individuals experienced significant increases in aerobic capacity (6.3 (6.0) ml/kg/min; p<0.01), and a decreased systolic (-6.00 (11.5) mm Hg; p<0.05) and diastolic blood pressure (-3.9 (5.8) mm Hg; p<0.01), waist circumference (-3.7 (2.7) cm; p<0.01) and resting heart rate (-4.8 (8.9) bpm, p<0.001). In addition, these individuals experienced an acute exercise-induced increase in positive mood. CONCLUSIONS: These data demonstrate that significant and meaningful health benefits can be achieved even in the presence of lower-than-expected exercise-induced weight loss. A less successful reduction in body weight does not undermine the beneficial effects of aerobic exercise. From a public health perspective, exercise should be encouraged and the emphasis on weight loss reduced.

Low-energy reporting and duration of recording period.

Three-day, rather than 7-day, food records are frequently used because mis-reporting of food intake is believed to increase with recording period. Data from the National Diet and Nutrition Survey of adults were used to explore trends in reported energy intake (REI) with day of recording and to compare average REIs from Thursday to Saturday and from Sunday to Tuesday to the complete 7-day record. Although REIs decreased from days 2 to 7, this was by a quantitatively insignificant 49 kJ per day (P=0.026) and well within the measurement error of recorded food intakes. Furthermore, REIs were lowest on the first recording day. The 3- and 7-day averages were similar (mean difference 0.039 (s.d.+/-1.0) MJ (NS), range -3.3 to +4.2 MJ). However, the difference was greater for those reporting higher than average energy intakes because of higher REIs on weekend days. Food intake reporting periods of longer than 3 days and ideally 7 days are preferable.

Comparing different measures of energy expenditure in human subjects resident in a metabolic facility.

OBJECTIVE: To compare energy expenditure (EE) measured by doubly labeled water (DLW) with other measures, both physical and based on subjective questionnaires. DESIGN: A comparison of methods in a stratified sample of adult volunteers. SETTING: The feeding behaviour suite (FBS) at the Rowett Research Institute, Aberdeen. SUBJECTS: A total of 59 subjects, stratified for age, sex and body mass index (BMI). INTERVENTIONS: EE was assessed by DLW (validated using measurements of energy balance), heart rate monitor (HRM), activity monitor (Caltrac), 24-h physical activity diary (PAD) and 7-day physical activity recall. Energy intake was assessed using covert (investigator-weighed) food intake (EI). Data were collected over a 12-day period of residence in the Rowett's FBS. RESULTS: No methods correlated highly with physical activity assessed by DLW. Physical methods correlated more closely than did subjective recording. All methods (except EI) significantly underestimated EE, estimated by DLW. There were no significant differences in association between methods and sex, age, BMI or fat-free mass. CONCLUSION: EE is difficult to measure precisely or accurately with current approaches but physical methods are slightly better than subjective accounts.

Individual variability following 12 weeks of supervised exercise: identification and characterization of compensation for exercise-induced weight loss.

OBJECTIVE: To identify and characterize the individual variability in compensation for exercise-induced changes in energy expenditure (EE). DESIGN: Twelve-week exercise intervention. SUBJECTS: Thirty-five overweight and obese sedentary men and women (body mass index, 31.8+/-4.1 kg m(-2); age, 39.6+/-11.0 years) were prescribed exercise five times per week for 12 weeks under supervised conditions. MEASUREMENTS: Body weight, body composition, resting metabolic rate (RMR), total daily energy intake (EI) and subjective appetite sensations were measured at weeks 0 and 12. RESULTS: When all subjects' data were pooled, the mean reduction in body weight (3.7+/-3.6 kg) was significant (P<0.0001) and as predicted, which suggested no compensation for the increase in EE. However, further examination revealed a large individual variability in weight change (-14.7 to +1.7 kg). Subjects were identified as compensators (C) or noncompensators (NC) based on their actual weight loss (mean NC=6.3+/-3.2 kg and C=1.5+/- 2.5 kg) relative to their predicted weight loss. C and NC were characterized by their different metabolic and behavioural compensatory responses. Moderate changes in RMR occurred in C (-69.2+/-268.7 kcal day(-1)) and NC (14.2+/-242.7 kcal day(-1)). EI and average daily subjective hunger increased by 268.2+/-455.4 kcal day(-1) and 6.9+/-11.4 mm day(-1) in C, whereas EI decreased by 130+/-485 kcal day(-1) and there was no change in subjective appetite (0.4+/-9.6 mm day(-1)) in NC. CONCLUSION: These results demonstrate that expressing the exercise-induced change in body weight as a group mean conceals the large inter-individual variability in body weight and compensatory responses. Individuals who experience a lower than predicted weight loss are compensating for the increase in EE.

Control of energy balance in relation to energy intake and energy expenditure in animals and man: an ecological perspective.

In this paper, we consider the control of energy balance in animals and man. We argue that patterns of mammalian feeding have evolved to control energy balance in uncertain environments. It is, therefore, expected that, under sedentary conditions in which the diet is rich in nutrients and abundantly available, animals and man will overeat. This suggests that no physiological defects are needed to induce overweight and ultimately obesity in man. Several considerations arise from these observations. The time period over which energy balance is controlled is far longer than allowed by most experiments. Physiological models of energy balance control often treat excess energy intake as a defect of regulation; ecological models view the same behaviour as part of normal energy balance control in environments where resources are uncertain. We apply these considerations to common patterns of human and animal feeding. We believe that the ecological perspective gives a more accurate explanation for the functionality of excess fat and the need to defend nutrient balance and avoid gross imbalances, as well as explaining hyperphagia in the face of plenty. By emphasising the common features of energy balance control in different mammalian species, the importance of changes in behaviour to accommodate changes in the environment becomes apparent. This also opens up possibilities for the control of body weight and the treatment of obesity in man.

Energy density and weight of food effect short-term caloric compensation in men.

OBJECTIVE: The purpose of the study was to examine the effect of energy density and food weight (volume) on subsequent intake. DESIGN: Sixteen lean men were each studied four times during a 2-d protocol at the Rowett's Human Nutrition Unit. On day 1, subjects were fed a mandatory diet at 1.6 x resting metabolic rate (RMR). On day 2, during the mandatory morning period (08.30-12.30) subjects consumed a fixed breakfast (08.30) plus a snack (10.30) in one of four treatments [with values in weight (kg), ED (kJ/100g), Energy (MJ)]: (i) zero intake, 0:0:0 (ii) low energy density (LED), 0.615: 400: 2.46; (iii) high energy density (HED), 0.615: 800: 4.92; (iv) 2 x LED, 1.225: 400: 4.91. From 12.30, throughout the remainder of the day, subjects had ad libitum access to 15 high-protein, 15 high-fat and 15 high-carbohydrate foods. Motivation to eat was tracked hourly using 100 mm line scales. RESULTS: ANOVA showed subjects were hungrier after the zero and LED treatments in the mandatory period (p<0.001). Lunch time EI was 5.0, 3.1, 4.2 and 3.2 MJ on the zero, HED, LED and 2 x LED treatments, respectively (p<0.001). Total ad libitum EI was 11.7, 9.6, 10.3 and 9.5 MJ/d, respectively (p=0.033). Total ad libitum plus mandatory intakes amounted to 11.7, 14.5, 12.6 and 14.4 MJ/d, respectively (p=0.001). Corresponding food intakes were 2.18, 2.39, 2.51 and 3.06 kg/d, respectively (p<0.001). CONCLUSIONS: The present study showed that subjects respond to both the amount of food eaten in the morning and to the energy density of those foods. However, compensation was only partial and short-term. Subjects only compensated EI by approximately 40% and that compensation only occurred at the next meal.

The evaluation of an electronic visual analogue scale system for appetite and mood.

Our objective was to evaluate a new electronic visual analogue scale (VAS) system for logging subjective motivation to eat ratings. In total, 10 men and 10 women completed both electronic and traditional pen and paper versions of the questionnaire every hour of the waking day. Subjects consumed a standard medium-fat diet, which was fixed at 1.6.BMR. Correlation coefficients for scores obtained by both methods were significant for all questions, with R(2) values ranging from 67 to 87%. However, Bland and Altman plots and paired t-tests identified significant bias between the two methods for five of the nine individual questions. These were questions that tended to be scored more towards the ends of the VAS. The new electronic VAS produces comparable, but not interchangeable, results to the traditional pen and paper method in the study of appetite and mood, while offering advantages of improved reliability in data collection.

Resistance and susceptibility to weight gain: individual variability in response to a high-fat diet.

An obesigenic environment is a potent force for promoting weight gain. However, not all people exposed to such an environment become obese; some remain lean. This means that some people are susceptible to weight gain (in a weight-promoting environment) and others are resistant. Identifying the characteristics of appetite control and food motivation in these two groups could throw light on the causes of weight gain and how this can be either treated or prevented. We have investigated the issue experimentally by identifying people who habitually consume a high-fat diet (greater than 43% fat energy). These individuals have been termed high-fat phenotypes. We have compared individuals, of the same age (mean=37 years old) and gender (male), who have gained weight (BMI=34) or who have remained lean (BMI=22). The susceptible individuals are characterised by a cluster of characteristics including a weak satiety response to fatty meals, a maintained preference for high-fat over low-energy foods in the post-ingestive satiety period, a strong hedonic attraction to palatable foods and to eating, and high scores on the TFEQ factors of Disinhibition and Hunger. The analysis of large databases suggests that this profile of factors contributes to an average daily positive energy balance from food of approximately 0.5 MJ. This profile of characteristics helps to define the symptomatology of a thrifty phenotype.

Energy density, diet composition and palatability: influences on overall food energy intake in humans.

This paper considers the role of energy density (ED), diet composition and palatability in the control of energy intake (EI) in humans through several related considerations: (i) the relationship between ED and diet composition, (ii) the relationship between ED, diet composition and EI, (iii) the relationship between palatability and EI, (iv) the relationship between ED, palatability and EI, (v) the importance of postingestive factors in influencing palatability in the longer term, (vi) the contribution of sensory and nutritional factors to dietary hyperphagia and (vii) the implications these considerations have for people living their normal lives in their natural environment. The main factors influencing ED are the fat and water content of foods. Energy density does elevate EI, especially in short-term studies where it can account for >40% of the variance in EI. In real life, ED accounts for only approximately 7% of the variance in EI. This is because the determinants of EI are multifactorial and also because the short-term effects of ED on EI do not translate into the longer term. We argue that part of the longer term amelioration of short-term effects of ED on EI is due to learned compensation, based on the postingestive consequences of consuming familiar food that differ in ED. More energy-dense foods tend to be more palatable but we learn to consume them in smaller portion sizes. In the longer term, the perceived palatability of a food is strongly influenced by the postingestive consequences of eating it. This effect can override sensory factors alone. This implies that nutrient mimetics, if used continuously, would not be as efficacious as initially supposed and that their ad hoc use may undermine the stability of learned appetites and satieties for foods with different EDs and contribute to the poor weight control capability exhibited by consumers at large.

Rate and extent of compensatory changes in energy intake and expenditure in response to altered exercise and diet composition in humans.

We assessed the effect of no exercise (Nex; control) and high exercise level (Hex; approximately 4 MJ/day) and two dietary manipulations [a high-fat diet (HF; 50% of energy, 700 kJ/100 g) and low-fat diet (LF; 20% of energy, 300 kJ/100 g)] on compensatory changes in energy intake (EI) and energy expenditure (EE) over 7-day periods. Eight lean men were each studied four times in a 2 x 2 randomized design. EI was directly quantified by weight of food consumed. EE was assessed by heart rate (HR) monitoring. Body weight was measured daily. Mean daily EE was 17.6 and 11.5 MJ/day (P < 0.001) on the pooled Hex and Nex treatments, respectively. EI was higher on HF diets (13.4 MJ/day pooled) compared with the LF diets (9.0 MJ/day). Regression analysis showed that these energy imbalances induced significant compensatory changes in EB over time of approximately 0.3-0.4 MJ/day (P < 0.05). These were due to changes in both EI and EE in the opposite direction to the perturbation in energy balance. These changes were significant, small but persistent, amounting to approximately 0.2 and approximately 0.35 MJ/day for EI and EE, respectively.

Cross talk between physical activity and appetite control: does physical activity stimulate appetite?

Physical activity has the potential to modulate appetite control by improving the sensitivity of the physiological satiety signalling system, by adjusting macronutrient preferences or food choices and by altering the hedonic response to food. There is evidence for all these actions. Concerning the impact of physical activity on energy balance, there exists a belief that physical activity drives up hunger and increases food intake, thereby rendering it futile as a method of weight control. There is, however, no evidence for such an immediate or automatic effect. Short (1-2 d)-term and medium (7-16 d)-term studies demonstrate that men and women can tolerate substantial negative energy balances of < or = 4 MJ energy cost/d when performing physical activity programmes. Consequently, the immediate effect of taking up exercise is weight loss (although this outcome is sometimes difficult to assess due to changes in body composition or fluid compartmentalization). However, subsequently food intake begins to increase in order to provide compensation for about 30% of the energy expended in activity. This compensation (up to 16 d) is partial and incomplete. Moreover, subjects separate into compensators and non-compensators. The exact nature of these differences in compensation and whether it is actually reflective of non-compliance with protocols is yet to be determined. Some subjects (men and women) performing activity with a cost of < or = 4 MJ/d for 14 d, show no change in daily energy intake. Conversely, it can be demonstrated that when active individuals are forced into a sedentary routine food intake does not decrease to a lower level to match the reduced energy expenditure. Consequently, this situation creates a substantial positive energy balance accompanied by weight gain. The next stage is to further characterize the compensators and non-compensators, and to identify the mechanisms (physiological or behavioural) that are responsible for the rate of compensation and its limits.

Effect of an acute fast on energy compensation and feeding behaviour in lean men and women.

AIM: Humans appear to defend against energy deficit to a greater extent than energy surplus. Severe dietary energy restriction resulting in 5-30% weight loss often leads to hyperphagia and weight regain in lean subjects. However, the period of time over which fasting is often endured in Western society are far shorter, approximately 1-2 days. This study examined how a 36 h fast effected the subsequent day's energy and nutrient intake in a group of 24 healthy, lean men and women. METHOD: Subjects underwent two 2 day treatments, termed 'fast' and 'maintenance'. During the 'fast' treatment, subjects were fed a maintenance diet on the day prior to the fast (day -1) to prevent overeating. They then consumed non-energy drinks only, from 20:00 h on day -1 to 08:00 h on day 2 (ad libitum feeding day), thus fasting for 36 h. On the 'maintenance' protocol, subjects received a maintenance diet throughout day 1. Throughout day 2 they had ad libitum access to a range of familiar foods, which were the same for both treatments. Body weight, blood glucose and respiratory quotient were used as compliance checks. Hunger was monitored on day's -1, 1 and 2 for the fast treatment only. RESULTS: On day 2, average energy intake was 10.2 vs 12.2 MJ/day (s.e.d. 1.0) on the post-maintenance and post-fast periods, respectively (P=0.049). Subjects altered feeding behaviour, in response to the fast, only at breakfast time, selecting a higher-fat meal (P<0.005). Compared to day -1, motivation to eat was elevated during the fast (P<0.05). This continued until breakfast was consumed during the re-feeding period (day 2), when values then returned to baseline. CONCLUSION: These data suggest that a 36 h fast, which generated a negative energy balance of approximately 12 MJ, did not induce a powerful, unconditioned stimulus to compensate on the subsequent day.