Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans

Abstract

Objective: Eating earlier in the daytime to align with circadian rhythms in metabolism enhances weight loss. However, it is unknown whether these benefits are mediated through increased energy expenditure or decreased food intake. Therefore, this study performed the first randomized trial to determine how meal timing affects 24-hour energy metabolism when food intake and meal frequency are matched.

Methods: Eleven adults with overweight practiced both early time-restricted feeding (eTRF) (eating from 8 am to 2 pm) and a control schedule (eating from 8 am to 8 pm) for 4 days each. On the fourth day, 24-hour energy expenditure and substrate oxidation were measured by whole-room indirect calorimetry, in conjunction with appetite and metabolic hormones.

Results: eTRF did not affect 24-hour energy expenditure (Δ = 10 ± 16 kcal/d; P = 0.55). Despite the longer daily fast (intermittent fasting), eTRF decreased mean ghrelin levels by 32 ± 10 pg/mL (P = 0.006), made hunger more even-keeled (P = 0.006), and tended to increase fullness (P = 0.06-0.10) and decrease the desire to eat (P = 0.08). eTRF also increased metabolic flexibility (P = 0.0006) and decreased the 24-hour nonprotein respiratory quotient (Δ = -0.021 ± 0.010; P = 0.05).

Conclusions: Meal-timing interventions facilitate weight loss primarily by decreasing appetite rather than by increasing energy expenditure. eTRF may also increase fat loss by increasing fat oxidation.

Trial registration: ClinicalTrials.gov NCT02247076.

Conflict of interest statement

Disclosure: RAB, EP, DSH, and CMP declared no conflicts of interest. ER reports past consulting activities with Energesis Pharmaceuticals and Amway and personal fees from serving on the Nutrilite Scientific Advisory Board, outside the submitted work. This research was funded by The Obesity Society, which operates the journal Obesity. Since ER is the Editor-in-Chief of Obesity, he recused himself from being involved in any way in the review process for this manuscript.

© 2019 The Obesity Society.

Figures

Figure 1.

Study Protocol. (A) Each intervention arm consisted of 4 days of early time-restricted feeding (eTRF) or the control eating schedule. On Day 4 of each cycle, participants ate 3 identical meals according to their assigned schedule while spending 24 hours in a respiratory chamber. (B) Chamber measurements were performed as illustrated below and included resting energy expenditure (REE), the thermic effect of food (TEF), sleeping energy expenditure (SEE), and Visual Analog Scales (VAS) to measure appetite, energy levels, and awakeness.

Figure 2.

Participant Flow Diagram.

Figure 3.

(A) Hourly values of energy expenditure (EE) differed between the early time-restricted feeding (eTRF) and control arms, primarily in the postprandial periods for lunch and dinner. (B) eTRF increased the thermic effect of food (TEF) at lunch, at dinner, and when averaged across the three meals but not at breakfast. (C) 24-hour EE was similar in the eTRF and control arms. Although eTRF increased EE during the daytime, this was offset by a decrease in EE at nighttime and during sleep. Resting energy expenditure (“Rest”) was not different between arms. *P ≤ 0.05.

Figure 4.

Early time-restricted feeding (eTRF) increased 24-hour protein oxidation. *P ≤ 0.05

Figure 5.

(A) Hourly values of the non-protein respiratory quotient (npRQ) differed between the early time-restricted feeding (eTRF) and control arms, particularly at nighttime. (B) eTRF decreased the 24-hr npRQ, and this was driven by decreases in npRQ during the nighttime, while sleeping, and while fasting in the morning (“Rest”). (C) eTRF increased metabolic flexibility, which was defined as the difference between the maximum and minimum hourly values of npRQ *P ≤ 0.05

Figure 6.

Early time-restricted feeding (eTRF) decreased fasting levels of (A) active ghrelin, (C) leptin, and (D) GLP-1 in the morning, while it (A) tended to decrease active ghrelin and (B) increased PYY in the evening. When averaged together, eTRF lowered mean active ghrelin levels and tended to increase mean leptin values (data not shown). * P ≤ 0.05

Figure 7.

Early time-restricted feeding (eTRF) modified temporal patterns of (A-E) appetite, (F) perceived body temperature, (G) energy levels, and (H) awakeness across the waking day. *P ≤ 0.05

Figure 8.

Early time-restricted feeding (eTRF) (A) increased minimum hunger levels, (B) tended to decrease mean desire to eat, (C) tended to increase mean fullness, (D) decreased minimum stomach fullness but tended to increase mean stomach fullness, (F) increased the maximum perceived body temperature, and (G) decreased minimum energy levels. The daily means and ranges for all other facets of appetite and energy levels were similar. * P ≤ 0.05