A cross-over experiment to investigate possible mechanisms for lower BMIs in people who habitually eat breakfast

Effects of Intermittent Fasting on Cardiometabolic Health: An Energy Metabolism Perspective

This review summarizes the effects of different types of intermittent fasting (IF) on human cardiometabolic health, with a focus on energy metabolism. First, we discuss the coordinated metabolic adaptations (energy expenditure, hormonal changes and macronutrient oxidation) occurring during a 72 h fast. We then discuss studies investigating the effects of IF on cardiometabolic health, energy expenditure and substrate oxidation. Finally, we discuss how IF may be optimized by combining it with exercise. In general, IF regimens improve body composition, ectopic fat, and classic cardiometabolic risk factors, as compared to unrestricted eating, especially in metabolically unhealthy participants. However, it is still unclear whether IF provides additional cardiometabolic benefits as compared to continuous daily caloric restriction (CR). Most studies found no additional benefits, yet some preliminary data suggest that IF regimens may provide cardiometabolic benefits in the absence of weight loss. Finally, although IF and continuous daily CR appear to induce similar changes in energy expenditure, IF regimens may differentially affect substrate oxidation, increasing protein and fat oxidation. Future tightly controlled studies are needed to unravel the underlying mechanisms of IF and its role in cardiometabolic health and energy metabolism.

Breakfast Consumption Suppresses Appetite but Does Not Increase Daily Energy Intake or Physical Activity Energy Expenditure When Compared with Breakfast Omission in Adolescent Girls Who Habitually Skip Breakfast: A 7-Day Randomised Crossover Trial

With concerns that adolescent girls often skip breakfast, this study compared the effects of breakfast consumption versus breakfast omission on free-living physical activity (PA) energy expenditure (PAEE) and dietary intakes among adolescent girls classified as habitual breakfast skippers. The participants went through two 7-day conditions in a trial with a crossover design: daily standardised breakfast consumption (energy content: 25% of resting metabolic rate) before 09:00 (BC) and daily breakfast omission (no energy-providing nutrients consumed) until 10:30 (BO). Free-living PAEE, dietary intakes, and perceived appetite, tiredness, and energy levels were assessed. Analyses were linear mixed models. Breakfast manipulation did not affect PAEE or PA duration. Daily fibre intake was higher (p = 0.005; d = 1.31), daily protein intake tended to be higher (p = 0.092; d = 0.54), post-10:30 carbohydrate intake tended to be lower (p = 0.096; d = 0.41), and pre-10:30 hunger and fullness were lower and higher, respectively (p ≤ 0.065; d = 0.33-1.01), in BC versus BO. No other between-condition differences were found. Breakfast-skipping adolescent girls do not compensate for an imbalance in energy intake caused by breakfast consumption versus omission through subsequent changes in PAEE but may increase their carbohydrate intakes later in the day to partially compensate for breakfast omission. Furthermore, breakfast can make substantial contributions to daily fibre intake among adolescent girls.

Eating versus skipping breakfast has no discernible effect on obesity-related anthropometric outcomes: a systematic review and meta-analysis

Background: Eating or skipping breakfast for weight interests scientific and lay communities. Our objective was to systematically review and meta-analyze causal effects of eating versus skipping breakfast on obesity-related anthropometric outcomes in humans. Methods: Six databases were searched for obesity- and breakfast-related terms (final search: 02 JAN 2020). Studies needed to isolate eating versus skipping breakfast in randomized controlled trials. Mean differences were synthesized using inverse variance random effects meta-analysis for each outcome. Positive estimates indicate higher outcomes in breakfast conditions (e.g., weight gain). Leave-one-out sensitivity analysis, secondary baseline habit-by-breakfast assignment analysis, and study duration cumulative analysis were performed. Risk of bias was assessed using Cochrane risk of bias tool. Results: Ten articles (12 comparisons; 6d-12wk) were included. Conditions included recommendations to eat versus skip breakfast, or provision of some or all meals. 95% confidence intervals of all main analyses included the null value of no difference for each outcome: body weight (0.17 kg [-0.40,0.73], k=12, n=487, I 2=74.5), BMI (0.07 kg/m 2 [-0.10,0.23, k=8, n=396, I 2=54.1), body fat percentage (-0.27% [-1.01,0.47], k=6, n=179, I 2=52.4), fat mass (0.24 kg [-0.21,0.69], k=6, n=205, I 2=0.0), lean mass (0.18 kg [-0.08,0.44], k=6, n=205, I 2=6.7), waist circumference (0.18 cm [-1.77,2.13], k=4, n=102, I 2=78.7), waist:hip ratio (0.00 [-0.01,0.01], k=4, n=102, I 2=8.0), sagittal abdominal diameter (0.19 cm [-2.35,2.73], k=2, n=56, I 2=0.0), and fat mass index (0.00 kg/m 2 [-0.22,0.23], k=2, n=56, I 2=0.0). Subgroup analysis showed only one statistically significant result. The interaction effect for BMI (–0.36[-0.65,-0.07]) indicates assignment to conditions consistent with baseline habits had lower BMI. Leave-one-out analysis did not indicate substantial influence of any one study. Conclusions: There was no discernible effect of eating or skipping breakfast on obesity-related anthropometric measures when pooling studies with substantial design heterogeneity and sometimes statistical heterogeneity. Registration: PROSPERO CRD42016033290.

A Review of the Evidence Surrounding the Effects of Breakfast Consumption on Mechanisms of Weight Management

The recommendation to eat breakfast has received scrutiny due to insufficient causal evidence for improvements in weight management. Despite the limited number of randomized controlled trials examining the effects of breakfast consumption compared with skipping breakfast on weight loss, an increasing number of studies target the hormonal and behavioral mechanisms underlying weight management. This review provides a comprehensive examination of the intervention-based clinical trials that test whether breakfast consumption improves appetite control and satiety as well as energy expenditure compared with skipping breakfast. Several factors were considered when interpreting the body of evidence. These include, but were not limited to, the following: the composition of breakfast, with a specific focus on dietary protein; meal size and form; and habitual breakfast behaviors. The evidence within this review shows positive to neutral support for the inclusion of breakfast for improvements in appetite control, satiety, and postprandial energy expenditure. The protein content, energy content, and form of the meal (i.e., beverages compared with foods) are key modulating factors for ingestive behavior and energy expenditure mechanisms. Specifically, breakfast meals containing a larger amount of protein (≥30 g protein/meal) and energy (≥350 kcal/meal) and provided as solid foods increased the magnitude of the appetite and satiety response compared with breakfast skipping. Longer-term randomized controlled trials including the measurement of ingestive behavior and weight management are needed to identify the role of breakfast for health promotion.

Effects of Body Mass Index on Bone Loading Due to Physical Activity

The aim of the current study was to compare bone loading due to physical activity between lean, and overweight and obese individuals. Fifteen participants (lower BMI group: BMI < 25 kg/m², n = 7; higher BMI group: 25 kg/m² < BMI < 36.35 kg/m², n = 8) wore a tri-axial accelerometer on 1 day to collect data for the calculation of bone loading. The International Physical Activity Questionnaire (short form) was used to measure time spent at different physical activity levels. Daily step counts were measured using a pedometer. Differences between groups were compared using independent t-tests. Accelerometer data revealed greater loading dose at the hip in lower BMI participants at a frequency band of 0.1-2 Hz (P = .039, Cohen's d = 1.27) and 2-4 Hz (P = .044, d = 1.24). Lower BMI participants also had a significantly greater step count (P = .023, d = 1.55). This corroborated with loading intensity (d ≥ 0.93) and questionnaire (d = 0.79) effect sizes to indicate higher BMI participants tended to spend more time in very light activity, and less time in light and moderate activity. Overall, participants with a lower BMI exhibited greater bone loading due to physical activity; participants with a higher BMI may benefit from more light and moderate level activity to maintain bone health.

Physical Activity Duration but Not Energy Expenditure Differs between Daily and Intermittent Breakfast Consumption in Adolescent Girls: A Randomized Crossover Trial

Background

It is not known whether breakfast frequency affects physical activity (PA) in children or adolescents.

Objective

This study examined the effect of daily compared with intermittent breakfast consumption on estimated PA energy expenditure (PAEE) in adolescent girls.

Methods

Under a randomized crossover design, 27 girls [mean ± SD age: 12.4 ± 0.5 y, body mass index (in kg/m2): 19.3 ± 3.0] completed two 7-d conditions. A standardized breakfast (∼1674 kJ) was consumed every day before 0900 in the daily breakfast consumption (DBC) condition. The standardized breakfast was consumed on only 3 d before 0900 in the intermittent breakfast consumption (IBC) condition, alternating with breakfast omission on the remaining 4 d (i.e., only water consumed before 1030). Combined heart rate accelerometry was used to estimate PAEE throughout each condition. Statistical analyses were completed by using condition × time of day repeated-measures ANOVA. The primary outcome was PAEE and the secondary outcome was time spent in PA.

Results

Daily estimated PAEE from sedentary or light-, moderate-, or vigorous-intensity PA and total PAEE were not significantly different between the conditions. The condition × time of day interaction for sedentary time (P = 0.05) indicated that the girls spent an additional 11.5 min/d being sedentary in the IBC condition compared with the DBC condition from 1530 to bedtime (P = 0.04). Light PA was 19.8 min/d longer in the DBC condition than in the IBC condition (P = 0.05), which was accumulated from waking to 1030 (P = 0.04) and from 1530 to bedtime (P = 0.03). There were no significant differences in time spent in moderate PA or vigorous PA between the conditions.

Conclusions

Adolescent girls spent more time in light PA before 1030 and after school and spent less time sedentary after school when a standardized breakfast was consumed daily than when consumed intermittently across 7 d. However, breakfast manipulation did not affect estimated daily PAEE. This trial was registered at www.isrctn.com as ISRCTN74579070.

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.

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.

Leptin Level and Skipping Breakfast: The National Health and Nutrition Examination Survey III (NHANES III)

Skipping breakfast is a common dietary habit considered to be unhealthy. However, the mechanisms underlying skipping breakfast have not been fully explored. Leptin is a hormone that regulates food intake and energy storage and secretes in a diurnal rhythm with lowest levels in the morning. We examined the association between the serum leptin level and skipping breakfast in 5714 adults in the U.S. National Health and Nutrition Examination Survey III, 1988-1994. We defined breakfast as any food or beverage consumed between 5:00 a.m. and 10:00 a.m. using a single 24-h recall. Skipped breakfast was seen in 13.1%. In the logistic regression models with and without adjusting for adiposity and sex, leptin levels were not associated with skipping breakfast. After adjusting for age, race/ethnicity, and time of venipuncture, the association remained insignificant. After further adjusting for potential confounders: physical activity, alcohol intake, smoking and diabetes and after further adjusting for: dietary factors, insulin and glucose levels, there was a 9% and 11%-12%, respectively, statistically significantly higher likelihood of skipping breakfast if the leptin level was more than 50% greater. Further investigation into the biological reasons for skipping breakfast may be useful for promoting healthy lifestyles.

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.