Bath Breakfast Project (BBP)--examining the role of extended daily fasting in human energy balance and associated health outcomes: study protocol for a randomised controlled trial [ISRCTN31521726]

Breaking prolonged sitting increases 24-h physical activity and self-perceived energy levels but does not acutely affect cognition in healthy adults

INTRODUCTION

It is unknown whether predetermined (un)interrupted sitting within a laboratory setting will induce compensatory changes in human behaviours (energy intake and physical activity) once people return to a free-living environment. The effects of breaking up prolonged sitting on cognition are also unclear.

METHODS

Twenty-four (male = 13) healthy participants [age 31 ± 8 y, BMI 22.7 ± 2.3 kg/m2 (mean ± SD)] completed 320 min mixed-feeding trials under prolonged sitting (SIT) or with 2 min walking at 6.4 km/h every 20 min (ACTIVE), in a randomised crossover design. Human behaviours were recorded post-trial under free-living conditions until midnight. Cognitive performance was evaluated before and immediately after SIT and ACTIVE trials. Self-perceived sensations (appetite, energy and mood) and finger prick blood glucose levels were collected at regular intervals throughout the trials.

RESULTS

There were no differences between trials in eating behaviour and spontaneous physical activity (both, p > 0.05) in free-living conditions, resulting in greater overall total step counts [11,680 (10740,12620) versus 6049 (4845,7253) steps] and physical activity energy expenditure (PAEE) over 24-h period in ACTIVE compared to SIT (all, p < 0.05). Greater self-perceived levels of energy and lower blood glucose iAUC were found in ACTIVE trial compared to SIT trial (both, p < 0.05). No differences were found in cognitive performance between trials (all, p > 0.05).

CONCLUSION

Breaking up sitting does not elicit subsequent behavioural compensation, resulting in greater 24-h step counts and PAEE in healthy adults. Breaking up sitting reduces postprandial glucose concentrations and elicits greater self-perceived energy levels, but these positive effects do not acutely translate into improved cognitive function.

Effects of neuromuscular electrical stimulation on energy expenditure and postprandial metabolism in healthy men

It is unclear whether neuromuscular electrical stimulation (NMES) has meaningful metabolic effects when users have the opportunity to self-select the intensity to one that can be comfortably tolerated. Nine healthy men aged 28 ± 9 y (mean ± SD) with a body mass index 22.3 ± 2.3 kg/m2 completed 3 trials involving a 2-h oral glucose tolerance test whilst, in a randomised counterbalanced order, (1) sitting motionless (SIT), (2) standing motionless (STAND); and (3) sitting motionless with NMES of quadriceps and calves at a self-selected tolerable intensity. The mean (95% confidence interval [CI]) total energy expenditure was greater in the NMES trial (221 [180-262] kcal/2 h) and STAND trial (178 [164-191] kcal/2 h) than during SIT (159 [150-167] kcal/2 h) (both, p < 0.05). This was primarily driven by an increase in carbohydrate oxidation in the NMES and STAND trials compared with the SIT trial (p < 0.05). Postprandial insulin iAUC was lower in both NMES and STAND compared with SIT (16.4 [7.7-25.1], 17 [7-27] and 22.6 [10.8-34.4] nmol·120 min/L, respectively; both, p < 0.05). Compared with sitting, both NMES and STAND increased energy expenditure and whole-body carbohydrate oxidation and reduced postprandial insulin concentrations in healthy men, with more pronounced effects seen with NMES. Self-selected NMES is a potential strategy for improving metabolic health. This trial is registered at ClinicalTrials.gov (ID: NCT04389736). Novelty: NMES at a comfortable intensity enhances energy expenditure and carbohydrate oxidation, and reduces postprandial insulinemia. Thus, self-selected NMES represents a potential strategy to improve metabolic health.

Influence of upper-body continuous, resistance or high-intensity interval training (CRIT) on postprandial responses in persons with spinal cord injury: study protocol for a randomised controlled trial

Background

Chronic spinal cord injury (SCI) increases morbidity and mortality associated with cardiometabolic diseases, secondary to increases in central adiposity, hyperlipidaemia and impaired glucose tolerance. While upper-body Moderate Intensity Continuous Training (MICT) improves cardiorespiratory fitness, its effects on cardiometabolic component risks in adults with SCI appear relatively modest. The aim of this study is to assess the acute effects of Continuous Resistance Training (CRT), High Intensity Interval Training (HIIT), MICT and rest (CON) on fasting and postprandial systemic biomarkers and substrate utilisation.

Methods

Eleven healthy, chronic SCI (> 1 year, ASIA A-C) men will be recruited. Following preliminary testing, each will complete four experimental conditions, where they will report to the laboratory following an ~ 10-h overnight fast. A venous blood sample will be drawn and expired gases collected to estimate resting metabolic rate (RMR). In order to ensure an isocaloric exercise challenge, each will complete CRT first, with the remaining three conditions presented in randomised order: (1) CRT, ~ 45 min of resistance manoeuvres (weight lifting) interspersed with low-resistance, high-speed arm-crank exercise; (2) CON, seated rest; (3) MICT, ~ 45 min constant arm-crank exercise at a resistance equivalent to 30–40% peak power output (PPO) and; (4) HIIT, ~ 35 min arm-crank exercise with the resistance alternating every 2 min between 10% PPO and 70% PPO. After each ~ 45-min condition, participants will ingest a 2510-kJ liquid test meal (35% fat, 50% carbohydrate, 15% protein). Venous blood and expired gas samples will be collected at the end of exercise and at regular intervals for 120 min post meal.

Discussion

This study should establish the acute effects of different forms of exercise on fasting and postprandial responses in chronic SCI male patients. Measures of glucose clearance, insulin sensitivity, lipid and inflammatory biomarker concentrations will be assessed and changes in whole-body substrate oxidation estimated from expired gases.

Trial registration

ClinicalTrials.gov, ID: NCT03545867. Retrospectively registered on 1 June 2018. 

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3583-1) contains supplementary material, which is available to authorized users.

Nutritional Quality of Breakfast Consumed by the Low-Income Population in Brazil: A Nationwide Cross-Sectional Survey

Objective: This study aimed to characterize the nutritional quality of breakfast consumed by the low-income Brazilian population. Methods: A cross-sectional study was conducted with a sample of 1547 low-income individuals attending 36 Community Restaurants (CRs) in Brazil. Food consumption was analyzed by the frequency of food groups presented in the 24 h recall for three days. The nutritional consumption consisted of the analysis of the total energetic value (TEV) and the macronutrients, fibers, monounsaturated fatty acids, saturated fatty acids, trans fatty acids, calcium, and sodium. The nutrients were evaluated considering the percentage of contribution concerning the daily recommendation of consumption. Results: Among the 4641 breakfasts expected to be consumed and reported, 17.2% (n = 797) of the consumers did not consume breakfast. Therefore, we analyzed the 3844 breakfasts. The analysis of food groups showed a high consumption of dairy and cereals, and low consumption of fruits, roots/tubers, and meat/eggs. The percentages of energy contribution of the macronutrients in the TEV were adequate for a balanced diet. The mean intake of monounsaturated fatty acids was low, and the contribution percentages of saturated fatty acids and trans fatty acids were within the recommendations. The mean fiber intake of the breakfast was low, agreeing with the result of low fruit consumption. Calcium intake covered 73.49% of that expected for this meal, and sodium intake was adequate in breakfast. Conclusion: The individuals studied consumed a nutritionally balanced breakfast. Although dairy was one of the most consumed groups, calcium consumption was low, indicating the need to consume higher portions of food sources of this nutrient.

Six Weeks of Morning Fasting Causes Little Adaptation of Metabolic or Appetite Responses to Feeding in Adults with Obesity

OBJECTIVE

The aim of this study was to determine the effects of sustained morning fasting or breakfast consumption on metabolism, energy intake, and appetite in healthy adults with obesity.

METHODS

An independent-measures randomized controlled trial with baseline and follow-up laboratory assessment days separated by a 6-week intervention of either morning fasting (0 kcal until 12:00 pm) or daily breakfast (> 700 kcal by 11:00 am) was performed. Measures included metabolic outcomes (glucose, insulin, nonesterified fatty acids), hormones regulating appetite (total/acylated ghrelin, peptide YY, leptin), and energy expenditure (diet-induced thermogenesis) parameters throughout a laboratory test day and ad libitum intake following a fixed breakfast.

RESULTS

Allocation to fasting versus breakfast resulted in minimal adaptation as reflected by the metabolic outcomes or the majority of appetite regulatory outcomes for either area under curve or time-course-based measures (P > 0.05). Ad libitum lunch intake was not different (P = 0.13), nor was diet-induced thermogenesis or a composite appetite score (both P > 0.10). However, there was a reduced total area under the curve for peptide YY (P = 0.05) and increased postprandial hunger ratings (P = 0.05) in the breakfast group.

CONCLUSIONS

There was little evidence of metabolic adaptation to acute feeding or negative consequences from sustained morning fasting. This indicates that previously observed differences between breakfast consumers and skippers may be acute effects of feeding or may have resulted from other lifestyle factors.

High-intensity interval training or continuous training, combined or not with fasting, in obese or overweight women with cardiometabolic risk factors: study protocol for a randomised clinical trial

INTRODUCTION

Physical inactivity and increased caloric intake play important roles in the pathophysiology of obesity. Increasing physical activity and modifying eating behaviours are first-line interventions, frequently hampered by lack of time to exercise and difficulties in coping with different diets. High-intensity interval training (HIIT) may be a time-efficient method compared with moderate-intensity continuous training (CT). Conversely, diets with a fasting component may be more effective than other complex and restrictive diets, as it essentially limits caloric intake to a specified period without major diet composition changes. Therefore, the combination of HIIT and fasting may provide incremental benefits in terms of effectiveness and time efficiency in obese and sedentary populations. The aim of this study is to determine the effect of HIIT versus CT, combined or not with fasting, on microcirculatory function, cardiometabolic parameters, anthropometric indices, cardiorespiratory fitness and quality of life in a population of sedentary overweight or obese women with cardiometabolic risk factors.

METHODS AND ANALYSIS

Sedentary women aged 30-50 years, with a body mass index ≥25 kg/m2 and cardiometabolic risk factors, will be randomised to HIIT performed in the fasting state, HIIT performed in the fed state, CT in the fasting state or CT in the fed state. Cardiometabolic parameters, anthropometric indices, cardiorespiratory fitness, quality of life and microvascular function (cutaneous capillary density and microvascular reactivity evaluated by laser speckle contrast imaging) will be evaluated before initiation of the interventions and 16 weeks thereafter.

ETHICS AND DISSEMINATION

The trial complies with the Declaration of Helsinki and has been approved by the local ethics committee (Instituto Nacional de Cardiologia, Rio de Janeiro, Brazil). All patients provide written informed consent before enrolment and randomisation. The study's results will be disseminated to the healthcare community by publications and presentations at scientific meetings.

TRIAL REGISTRATION NUMBER

NCT03236285.

The effects of different forms of daily exercise on metabolic function following short-term overfeeding and reduced physical activity in healthy young men: study protocol for a randomised controlled trial

BACKGROUND

Short-term overfeeding combined with reduced physical activity impairs metabolic function and alters the expression of key genes within adipose tissue. We have shown that daily vigorous-intensity running can prevent these changes independent of any net effect on energy imbalance. However, which type, intensity and/or duration of exercise best achieves these benefits remains to be ascertained.

METHODS/DESIGN

Forty-eight healthy young men will be recruited and randomly allocated to one of four experimental conditions for 1 week: (1) to ingest 50% more energy than normal by over-consuming their habitual diet whilst simultaneously restricting their physical activity below 4000 steps day^-1 (i.e. energy surplus; SUR group); (2) the same regimen but with a daily 45-min bout of vigorous-intensity arm crank ergometry at 70% of maximum oxygen uptake (SUR + ARM group); (3) the same regimen but with a daily 45-min bout of moderate-intensity treadmill walking at 50% of maximum oxygen uptake (SUR + MOD group); (4) the same regimen but with the addition of intermittent short bouts of walking during waking hours (SUR + BREAKS group). Critically, all exercise groups will receive additional dietary energy intake to account for the energy expended by exercise, thus maintaining a matched energy surplus. At baseline and follow-up, fasted blood samples, abdominal subcutaneous adipose tissue and skeletal muscle biopsies will be obtained and oral glucose tolerance tests conducted.

DISCUSSION

This study will establish the impact of different forms of daily exercise on metabolic function at the whole-body level as well as within adipose tissue and skeletal muscle in the context of a standardised energy surplus.

TRIAL REGISTRATION

ISRCTN, ISRCTN18311163 . Registered on 24 June 2015.

Molecular adaptations of adipose tissue to 6 weeks of morning fasting vs. daily breakfast consumption in lean and obese adults

KEY POINTS

In lean individuals, 6 weeks of extended morning fasting increases the expression of genes involved in lipid turnover (ACADM) and insulin signalling (IRS2) in subcutaneous abdominal adipose tissue. In obese individuals, 6 weeks of extended morning fasting increases IRS2 expression in subcutaneous abdominal adipose tissue. The content and activation status of key proteins involved in insulin signalling and glucose transport (GLUT4, Akt1 and Akt2) were unaffected by extended morning fasting. Therefore, any observations of altered adipose tissue insulin sensitivity with extended morning fasting do not necessarily require changes in insulin signalling proximal to Akt. Insulin-stimulated adipose tissue glucose uptake rates are lower in obese versus lean individuals, but this difference is abolished when values are normalised to whole-body fat mass. This suggests a novel hypothesis which proposes that the reduced adipose glucose uptake in obesity is a physiological down-regulation to prevent excessive de novo lipogenesis.

ABSTRACT

This study assessed molecular responses of human subcutaneous abdominal adipose tissue (SCAT) to 6 weeks of morning fasting. Forty-nine healthy lean (n = 29) and obese (n = 20) adults provided SCAT biopsies before and after 6 weeks of morning fasting (FAST; 0 kcal until 12.00 h) or daily breakfast consumption (BFAST; ≥700 kcal before 11.00 h). Biopsies were analysed for mRNA levels of selected genes, and GLUT4 and Akt protein content. Basal and insulin-stimulated Akt activation and tissue glucose uptake rates were also determined. In lean individuals, lipid turnover and insulin signalling genes (ACADM and IRS2) were up-regulated with FAST versus BFAST (ACADM: 1.14 (95% CI: 0.97-1.30) versus 0.80 (95% CI: 0.64-0.96), P = 0.007; IRS2: 1.75 (95% CI: 1.33-2.16) versus 1.09 (95% CI: 0.67-1.51), P = 0.03, respectively). In obese individuals, no differential (FAST versus BFAST) expression was observed in genes involved in lipid turnover (all P > 0.1). GLUT4, Akt protein content and insulin-stimulated Akt phosphorylation were unaffected by FAST versus BFAST in both lean and obese cohorts (all P > 0.1). Lower insulin-stimulated glucose uptake rates in obese versus lean individuals were eradicated when normalised to whole-body fat mass (P = 0.416). We conclude that morning fasting up-regulates lipid turnover genes in SCAT of lean individuals. Secondly, altered SCAT insulin sensitivity with morning fasting is unlikely to be explained by signalling proximal to Akt. Finally, lower insulin-stimulated SCAT glucose uptake rates in obese individuals are proportional to whole-body fat mass, suggesting a compensatory down-regulation, presumably to prevent excessive de novo lipogenesis in adipose tissue. This trial was registered as ISRCTN31521726.

Postprandial Metabolism and Appetite Do Not Differ between Lean Adults that Eat Breakfast or Morning Fast for 6 Weeks

Background

It remains unknown whether sustained daily feeding-fasting patterns modify the acute response to specific feedings on a given day.

Objective

We conducted a randomized controlled trial to establish if daily breakfast consumption or fasting until noon modifies the acute metabolic and appetitive responses to a fixed breakfast and ad libitum lunch.

Methods

With the use of a parallel group design, we randomly assigned 31 healthy, lean men and women (22-56 y) to 6 wk of either consuming ≥700 kcal of self-selected items before 1100 or fasting (0 kcal) until 1200 daily. Following 48 h of diet and physical activity standardization, we examined metabolic and appetite responses to a standardized breakfast and ad libitum lunch before and after the intervention. Data were analyzed using 3- and 2-way ANCOVA.

Results

Systemic concentrations of energy balance regulatory hormones total and acylated ghrelin, leptin, and peptide tyrosine-tyrosine) responded similarly to breakfast and lunch before and after 6 wk of either morning fasting or regular breakfast, with the exception of a tendency for increased glucagon-like peptide-1 concentrations from baseline to follow-up in the Breakfast Group compared with a decrease over that period in the Fasting Group [P = 0.06, partial eta squared value (ƞ2) = 0.16]. Subjective appetite sensations also did not differ over the course of the day, and ad libitum energy intake at lunch was not systematically affected by either intervention, decreasing by 27 kcal (95% CI: -203, 149 kcal) with fasting and by 77 kcal (95% CI: -210, 56 kcal) with breakfast. Similarly, glycemic, insulinemic, lipemic, and thermogenic responses to breakfast and lunch were very stable at baseline and follow-up and, thus, did not differ between treatment groups.

Conclusions

Our results indicate that a sustained period of either extended morning fasting or eating a daily breakfast has minimal effect upon acute metabolic and appetite responses in lean adults. This trial was registered at www.isrctn.org as ISRCTN31521726.

Feeding influences adipose tissue responses to exercise in overweight men

Feeding profoundly affects metabolic responses to exercise in various tissues, but the effect of feeding status on human adipose tissue responses to exercise has never been studied. Ten healthy overweight men aged 26 ± 5 yr (mean ± SD) with a waist circumference of 105 ± 10 cm walked at 60% of maximum oxygen uptake under either fasted or fed conditions in a randomized, counterbalanced design. Feeding comprised 648 ± 115 kcal 2 h before exercise. Blood samples were collected at regular intervals to examine changes in metabolic parameters and adipokine concentrations. Adipose tissue samples were obtained at baseline and 1 h after exercise to examine changes in adipose tissue mRNA expression and secretion of selected adipokines ex vivo. Adipose tissue mRNA expression of pyruvate dehydrogenase kinase isozyme 4 (PDK4), adipose triglyceride lipase, hormone-sensitive lipase (HSL), fatty acid translocase/CD36, glucose transporter type 4 (GLUT4), and insulin receptor substrate 2 (IRS2) in response to exercise were lower in fed compared with fasted conditions (all P ≤ 0.05). Postexercise adipose IRS2 protein was affected by feeding (P ≤ 0.05), but Akt2, AMPK, IRS1, GLUT4, PDK4, and HSL protein levels were not different. Feeding status did not impact serum and ex vivo adipose secretion of IL-6, leptin, or adiponectin in response to exercise. This is the first study to show that feeding before acute exercise affects postexercise adipose tissue gene expression, and we propose that feeding is likely to blunt long-term adipose tissue adaptation to regular exercise.

Ramadan model of intermittent fasting for 28 d had no major effect on body composition, glucose metabolism, or cognitive functions in healthy lean men

OBJECTIVES

There has been a parallel increase in the incidence of obesity and diabetes as well as the number of daily meals. However, evidence is lacking regarding the role of intermittent fasting. The aim of this study was to determine the effects of a Ramadan model of intermittent fasting (RIF; 14 h of daytime abstinence from food and drinking) for 28 d on body composition, glucose metabolism, and cognitive function.

METHODS

Ten healthy, lean men were included in a nonrandomized, crossover, intervention study. Testing was performed before a control period of 28 d, as well as before and after 28 d of RIF. Whole-body dual-energy x-ray absorptiometry, magnetic resonance imaging of the abdomen, fitness test, oral glucose tolerance test, and cognitive function tests were performed. As secondary outcome, the participants' physical activity and 72-h glycemic responses were monitored 6 d within each of the periods. Dietary intake, appetite, and mood questionnaires also were assessed.

RESULTS

Comparing Δ differences from testing days; body mass index changes from the control period (Δ mean: 0.2 kg/m², 95% confidence interval [CI], -2 to 0.5) and the RIF period (Δ mean: -0.3 kg/m², 95% CI, -0.6 to -0.1) were significantly different (P < 0.05). Secondary outcomes within the RIF period showed an increased area under curve (AUC) for hunger accompanied by a reduced AUC for satiety (both, P < 0.05), less mean steps per day (P < 0.05), and less positive feelings in the afternoon (P < 0.01) compared with the control period. No changes were observed in any of the other evaluated parameters.

CONCLUSIONS

Free-living participants were able to comply with 14 h of daily daytime abstinence from food and drinking for 28 d with only a minor effect on body mass index and without any effects on body composition, glucose metabolism, and cognitive function.

Is breakfast the most important meal of the day?

The Bath Breakfast Project is a series of randomised controlled trials exploring the effects of extended morning fasting on energy balance and health. These trials were categorically not designed to answer whether or not breakfast is the most important meal of the day. However, this review will philosophise about the meaning of that question and about what questions we should be asking to better understand the effects of breakfast, before summarising how individual components of energy balance and health respond to breakfast v. fasting in lean and obese adults. Current evidence does not support a clear effect of regularly consuming or skipping breakfast on body mass/composition, metabolic rate or diet-induced thermogenesis. Findings regarding energy intake are variable, although the balance of evidence indicates some degree of compensatory feeding later in the day such that overall energy intake is either unaffected or slightly lower when breakfast is omitted from the diet. However, even if net energy intake is reduced, extended morning fasting may not result in expected weight loss due to compensatory adjustments in physical activity thermogenesis. Specifically, we report that both lean and obese adults expended less energy during the morning when remaining in the fasted state than when consuming a prescribed breakfast. Further research is required to examine whether particular health markers may be responsive to breakfast-induced responses of individual components of energy balance irrespective of their net effect on energy balance and therefore body mass.

The causal role of breakfast in energy balance and health: a randomized controlled trial in obese adults

BACKGROUND

The causal nature of associations between breakfast and health remain unclear in obese individuals.

OBJECTIVE

We sought to conduct a randomized controlled trial to examine causal links between breakfast habits and components of energy balance in free-living obese humans.

DESIGN

The Bath Breakfast Project is a randomized controlled trial with repeated measures at baseline and follow-up among a cohort in South West England aged 21-60 y with dual-energy X-ray absorptiometry-derived fat mass indexes of ≥13 kg/m(2) for women (n = 15) and ≥9 kg/m(2) for men (n = 8). Components of energy balance (resting metabolic rate, physical activity thermogenesis, diet-induced thermogenesis, and energy intake) were measured under free-living conditions with random allocation to daily breakfast (≥700 kcal before 1100) or extended fasting (0 kcal until 1200) for 6 wk, with baseline and follow-up measures of health markers (e.g., hematology/adipose biopsies).

RESULTS

Breakfast resulted in greater physical activity thermogenesis during the morning than when fasting during that period (difference: 188 kcal/d; 95% CI: 40, 335) but without any consistent effect on 24-h physical activity thermogenesis (difference: 272 kcal/d; 95% CI: -254, 798). Energy intake was not significantly greater with breakfast than fasting (difference: 338 kcal/d; 95% CI: -313, 988). Body mass increased across both groups over time but with no treatment effects on body composition or any change in resting metabolic rate (stable within 8 kcal/d). Metabolic/cardiovascular health also did not respond to treatments, except for a reduced insulinemic response to an oral-glucose-tolerance test over time with daily breakfast relative to an increase with daily fasting (P = 0.05).

CONCLUSIONS

In obese adults, daily breakfast leads to greater physical activity during the morning, whereas morning fasting results in partial dietary compensation (i.e., greater energy intake) later in the day. There were no differences between groups in weight change and most health outcomes, but insulin sensitivity increased with breakfast relative to fasting. This trial was registered at www.isrctn.org as ISRCTN31521726.

The effect of breakfast on appetite regulation, energy balance and exercise performance

The belief that breakfast is the most important meal of day has been derived from cross-sectional studies that have associated breakfast consumption with a lower BMI. This suggests that breakfast omission either leads to an increase in energy intake or a reduction in energy expenditure over the remainder of the day, resulting in a state of positive energy balance. However, observational studies do not imply causality. A number of intervention studies have been conducted, enabling more precise determination of breakfast manipulation on indices of energy balance. This review will examine the results from these studies in adults, attempting to identify causal links between breakfast and energy balance, as well as determining whether consumption of breakfast influences exercise performance. Despite the associations in the literature, intervention studies have generally found a reduction in total daily energy intake when breakfast is omitted from the daily meal pattern. Moreover, whilst consumption of breakfast supresses appetite during the morning, this effect appears to be transient as the first meal consumed after breakfast seems to offset appetite to a similar extent, independent of breakfast. Whether breakfast affects energy expenditure is less clear. Whilst breakfast does not seem to affect basal metabolism, breakfast omission may reduce free-living physical activity and endurance exercise performance throughout the day. In conclusion, the available research suggests breakfast omission may influence energy expenditure more strongly than energy intake. Longer term intervention studies are required to confirm this relationship, and determine the impact of these variables on weight management.

Adipose tissue metabolic and inflammatory responses to a mixed meal in lean, overweight and obese men

PURPOSE

Most of what we know about adipose tissue is restricted to observations derived after an overnight fast. However, humans spend the majority of waking hours in a postprandial (fed) state, and it is unclear whether increasing adiposity impacts adipose tissue responses to feeding. The aim of this research was to investigate postprandial responses in adipose tissue across varying degrees of adiposity.

METHODS

Thirty males aged 35-55 years with waist circumference 81-118 cm were divided equally into groups categorized as either lean, overweight or obese. Participants consumed a meal and insulinaemic, glycaemic and lipidaemic responses were monitored over 6 h. Subcutaneous adipose tissue samples were obtained at baseline and after 6 h to examine changes in gene expression and adipose tissue secretion of various adipokines.

RESULTS

Following consumption of the meal, insulin and glucose responses were higher with increased adiposity (total AUC effects of group; p = 0.058 and p = 0.027, respectively). At 6 h, significant time effects reflected increases in IL-6 (F = 14.7, p = 0.001) and MCP-1 (F = 10.7, p = 0.003) and reduction in IRS2 adipose tissue gene expression (F = 24.6, p < 0.001), all independent of adiposity. Ex vivo adipokine secretion from adipose tissue explants remained largely unchanged after feeding.

CONCLUSIONS

Increased systemic measures of postprandial metabolism with greater adiposity do not translate into increased inflammatory responses within adipose tissue. Instead, postprandial adipose tissue changes may represent a normal response to feeding or a (relatively) normalized response with increased adiposity due to either similar net exposure (i.e. per g of adipose) or reduced adipose tissue responsiveness.

Effect of extended morning fasting upon ad libitum lunch intake and associated metabolic and hormonal responses in obese adults

Background/Objectives:

Breakfast omission is positively associated with obesity and increased risk of disease. However, little is known about the acute effects of extended morning fasting upon subsequent energy intake and associated metabolic/regulatory factors in obese adults.

Subjects/Methods:

In a randomised cross-over design, 24 obese men (n=8) and women (n=16) extended their overnight fast by omitting breakfast consumption or ingesting a typical carbohydrate-rich breakfast of 2183±393 kJ (521±94 kcal), before an ad libitum pasta lunch 3 h later. Blood samples were obtained throughout the day until 3 h post lunch and analysed for hormones implicated in appetite regulation, along with metabolic outcomes and subjective appetite measures.

Results:

Lunch intake was unaffected by extended morning fasting (difference=218 kJ, 95% confidence interval −54 kJ, 490 kJ; P=0.1) resulting in lower total intake in the fasting trial (difference=−1964 kJ, 95% confidence interval −1645 kJ, −2281 kJ; P<0.01). Systemic concentrations of peptide tyrosine–tyrosine and leptin were lower during the afternoon following morning fasting (P⩽0.06). Plasma-acylated ghrelin concentrations were also lower following the ad libitum lunch in the fasting trial (P<0.05) but this effect was not apparent for total ghrelin (P⩾0.1). Serum insulin concentrations were greater throughout the afternoon in the fasting trial (P=0.05), with plasma glucose also greater 1 h after lunch (P<0.01). Extended morning fasting did not result in greater appetite ratings after lunch, with some tendency for lower appetite 3 h post lunch (P=0.09).

Conclusions:

We demonstrate for the first time that, in obese adults, extended morning fasting does not cause compensatory intake during an ad libitum lunch nor does it increase appetite during the afternoon. Morning fasting reduced satiety hormone responses to a subsequent lunch meal but counterintuitively also reduced concentrations of the appetite-stimulating hormone-acylated ghrelin during the afternoon relative to lunch consumed after breakfast.

Carbohydrate-rich breakfast attenuates glycaemic, insulinaemic and ghrelin response to ad libitum lunch relative to morning fasting in lean adults

Breakfast omission is associated with obesity and CVD/diabetes, but the acute effects of extended morning fasting upon subsequent energy intake and metabolic/hormonal responses have received less attention. In a randomised cross-over design, thirty-five lean men (n 14) and women (n 21) extended their overnight fast or ingested a typical carbohydrate-rich breakfast in quantities relative to RMR (i.e. 1963 (sd 238) kJ), before an ad libitum lunch 3 h later. Blood samples were obtained hourly throughout the day until 3 h post-lunch, with subjective appetite measures assessed. Lunch intake was greater following extended fasting (640 (sd 1042) kJ, P< 0.01) but incompletely compensated for the omitted breakfast, with total intake lower than the breakfast trial (3887 (sd 1326) v. 5213 (sd 1590) kJ, P< 0.001). Systemic concentrations of peptide tyrosine-tyrosine and leptin were greater during the afternoon following breakfast (both P< 0.05) but neither acylated/total ghrelin concentrations were suppressed by the ad libitum lunch in the breakfast trial, remaining greater than the morning fasting trial throughout the afternoon (all P< 0.05). Insulin concentrations were greater during the afternoon in the morning fasting trial (all P< 0.01). There were no differences between trials in subjective appetite during the afternoon. In conclusion, morning fasting caused incomplete energy compensation at an ad libitum lunch. Breakfast increased some anorectic hormones during the afternoon but paradoxically abolished ghrelin suppression by the second meal. Extending morning fasting until lunch altered subsequent metabolic and hormonal responses but without greater appetite during the afternoon. The present study clarifies the impact of acute breakfast omission and adds novel insights into second-meal metabolism.

The causal role of breakfast in energy balance and health: a randomized controlled trial in lean adults

BACKGROUND

Popular beliefs that breakfast is the most important meal of the day are grounded in cross-sectional observations that link breakfast to health, the causal nature of which remains to be explored under real-life conditions.

OBJECTIVE

The aim was to conduct a randomized controlled trial examining causal links between breakfast habits and all components of energy balance in free-living humans.

DESIGN

The Bath Breakfast Project is a randomized controlled trial with repeated-measures at baseline and follow-up in a cohort in southwest England aged 21-60 y with dual-energy X-ray absorptiometry-derived fat mass indexes ≤11 kg/m² in women (n = 21) and ≤7.5 kg/m² in men (n = 12). Components of energy balance (resting metabolic rate, physical activity thermogenesis, energy intake) and 24-h glycemic responses were measured under free-living conditions with random allocation to daily breakfast (≥700 kcal before 1100) or extended fasting (0 kcal until 1200) for 6 wk, with baseline and follow-up measures of health markers (eg, hematology/biopsies).

RESULTS

Contrary to popular belief, there was no metabolic adaptation to breakfast (eg, resting metabolic rate stable within 11 kcal/d), with limited subsequent suppression of appetite (energy intake remained 539 kcal/d greater than after fasting; 95% CI: 157, 920 kcal/d). Rather, physical activity thermogenesis was markedly higher with breakfast than with fasting (442 kcal/d; 95% CI: 34, 851 kcal/d). Body mass and adiposity did not differ between treatments at baseline or follow-up and neither did adipose tissue glucose uptake or systemic indexes of cardiovascular health. Continuously measured glycemia was more variable during the afternoon and evening with fasting than with breakfast by the final week of the intervention (CV: 3.9%; 95% CI: 0.1%, 7.8%).

CONCLUSIONS

Daily breakfast is causally linked to higher physical activity thermogenesis in lean adults, with greater overall dietary energy intake but no change in resting metabolism. Cardiovascular health indexes were unaffected by either of the treatments, but breakfast maintained more stable afternoon and evening glycemia than did fasting.

Exercise counteracts the effects of short-term overfeeding and reduced physical activity independent of energy imbalance in healthy young men

Physical activity can affect many aspects of metabolism but it is unclear to what extent this relies on manipulation of energy balance. Twenty-six active men age 25 ± 7 years (mean ± SD) were randomly assigned either to consume 50% more energy than normal by over-consuming their habitual diet for 7 days whilst simultaneously restricting their physical activity below 4000 steps day(-1) to induce an energy surplus (SUR group; n = 14) or to the same regimen but with 45 min of daily treadmill running at 70% of maximum oxygen uptake (SUR+EX group; n = 12). Critically, the SUR+EX group received additional dietary energy intake to account for the energy expended by exercise, thus maintaining a matched energy surplus. At baseline and follow-up, fasted blood samples and abdominal subcutaneous adipose tissue biopsies were obtained and oral glucose tolerance tests conducted. Insulinaemic responses to a standard glucose load increased 2-fold from baseline to follow-up in the SUR group (17 ± 16 nmol (120 min) l(-1); P = 0.002) whereas there was no change in the SUR+EX group (1 ± 6 nmol (120 min) l(-1)). Seven of 17 genes within adipose tissue were differentially expressed in the SUR group; expression of SREBP-1c, FAS and GLUT4 was significantly up-regulated and expression of PDK4, IRS2, HSL and visfatin was significantly down-regulated (P ≤ 0.05). The pAMPK/AMPK protein ratio in adipose tissue was significantly down-regulated in the SUR group (P = 0.005). Vigorous-intensity exercise counteracted most of the effects of short-term overfeeding and under-activity at the whole-body level and in adipose tissue, even in the face of a standardised energy surplus.