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

Abstract

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.

Keywords: appetite regulation; breakfast; energy balance; energy intake; fasting; metabolism; obesity; physical activity.

Figures

FIGURE 1

Components of energy balance under free-living conditions with either the ingestion of ≥700 kcal before 1100 daily (breakfast group) or abstinence from all energy-providing nutrients until at least 1200 daily (fasting group). Data are means with SE bars compared with use of independent t tests. Estimated energy intake values for comparison of relative differences between groups are the mean of the first (breakfast, n = 11: 2820 ± 595 kcal/d; fasting, n = 11: 2459 ± 780 kcal/d; P = 0.2) and last (breakfast, n = 11: 2618 ± 833 kcal/d; fasting, n = 11: 2303 ± 792 kcal/d; P = 0.4) weeks of intervention, for which a loss of data was caused by a loss of diet record. Resting metabolic rate values (breakfast group, n = 11; fasting group, n = 11) were data-recorded at follow-up, with 1 individual unable to complete the follow-up resting metabolic rate collection. Diet-induced thermogenesis values (breakfast group, n = 11; fasting group, n = 11) were estimated from reported energy intake, for which a loss of data was caused by a loss of diet record. Physical activity values are the mean of the first (breakfast, n = 9: 1204 ± 322 kcal/d; fasting, n = 10: 997 ± 887 kcal/d; P = 0.5) and last (breakfast, n = 9: 1238 ± 220 kcal/d; fasting, n = 10: 902 ± 543 kcal/d; P = 0.1) week of intervention.

FIGURE 2

Physical activity thermogenesis under free-living conditions with either the ingestion of ≥700 kcal before 1100 daily (breakfast group, n = 9) or abstinence from all energy-providing nutrients until at least 1200 daily (fasting group, n = 10). Data are means with SE bars. P values represent the comparison between the 2 groups’ data for the mean of the 2 wk (1 and 6) of physical activity measurement with use of an independent t test. Missing data are the result of monitor failure or data of insufficient quality for analysis. Values are partitioned by the time of day and intensity of energy expenditure. MET, metabolic equivalent.

FIGURE 3

Insulinemic responses to the oral-glucose-tolerance test measured at baseline and after 6 wk (follow-up) of ingestion of ≥700 kcal before 1100 daily (breakfast group, n = 9) or abstinence from all energy-providing nutrients until at least 1200 daily (fasting group, n = 9), for which missing data resulted from cannula failure. Bars are mean incremental AUCs with SE bars, and lines are paired individual responses from baseline to follow-up. There was no main effect of treatment or time detected by 2-factor ANOVA. *Treatment × time interaction (F = 4.7; P = 0.05) for the insulinemic response to the oral-glucose-tolerance test.

FIGURE 4

Rates of [U-14C]d-glucose uptake in adipocytes under basal, physiologic (50 pmol/L insulin) and supraphysiologic (20 nmol/L insulin) conditions, measured at baseline and after 6 wk of ingestion of ≥700 kcal before 1100 daily (breakfast group, n = 9) or abstinence from all energy-providing nutrients until at least 1200 daily (fasting group, n = 10), for which missing data resulted from insufficient adipose tissue obtained from the biopsy. Data are means with SE bars. Three-factor ANOVA (treatment × time × insulin) reveals a significant main effect of insulin (F = 23; P < 0.001) but with no significant main effects of treatment, time, or any interaction of these factors (all P > 0.05). Lean data displayed in gray have previously been published (15) and are included to provide a frame of reference for these obese data. Ins, insulin.