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Changes in meal timings may reduce body fat

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September 7, 2018

Practicing time-restricted feeding that pushes breakfast later and dinner earlier, a type of intermittent fasting, may help people lose body fat, according to a study published in the Journal of Nutritional Science.

“Although this study is small, it has provided us with invaluable insight into how slight alterations to our meal times can have benefits to our bodies,” Jonathan D. Johnston, PhD, reader in chronobiology and integrative physiology at the University of Surrey, United Kingdom, said in a press release. “Reduction in body fat lessens our chances of developing obesity and related diseases, so is vital in improving our overall health.”

Johnston and colleagues recruited 13 adults aged 29 to 57 years with BMI between 20 kg/m2 and 30 kg/m2 to investigate the outcomes of time-restricted feeding. After a 2-week baseline period in which all participants maintained their usual sleep-wake and feed-fast cycles followed by a laboratory visit to measure body weight and composition and to obtain a blood test, researchers divided participants into the control group (n = 6; mean age, 45 years; six women; mean BMI, 28.6 kg/m2; 34.6% body fat) or the time-restricted feeding group (n = 7; mean age, 47 years; six women; mean BMI, 29 kg/m2; 36% body fat).

For 10 weeks, participants in the time-restricted feeding group were required to eat breakfast 90 minutes later than usual while eating dinner 90 minutes earlier. Those in the control group continued to eat how they typically would. The times to eat were determined by dietary patterns recorded in baseline diaries. Both groups maintained habitual sleeping and waking cycles. Participants then recorded the timing and composition of energy intake in diet diaries over 4 consecutive days at week 5 and week 10.

After 10 weeks, participants again went to the laboratory and ate the same dinner-time meal that they had eaten before the first visit.

Researchers also gave participants a questionnaire that evaluated the experience of following the dietary pattern.

Based on the 4-day dietary records from baseline and week 10 of the intervention, researchers found that, for the time-restricted feeding group, the total time possible to eat per day was reduced by approximately 4.5 hours (from 743 minutes per day to 517 minutes per day) and that participants achieved a target-eating window of at least a 3-hour reduction about 2.5 days out of 4 days in week 10. The feeding-window for the control group went from 652 minutes per day to 677 minutes per day (P < .001).


Researchers also found that participants in the time-restricted feeding group lessened their total daily energy intake from baseline (P = .019) and experienced an average reduction of 1.9% in adiposity (P = .047).

No significant change in body weight was observed in either group. A non-significant trend toward LDL cholesterol reduction from baseline was observed in the time-restricted feeding group. A unexplained change from baseline in fasting plasma glucose was observed in the control group, but not in the time-restricted feeding group, according to researchers.

In response to questionnaires, the time-restricted feeding group ranked the average difficulty of following the dietary pattern as a 7 on a scale of 1 to 10, with 1 being “easy” and 10 being “extremely difficult.” In addition, 57% did not think they could have maintained the eating schedule beyond 10 weeks.

Fasting diets are sometimes difficult to follow and may not always be compatible with family and social life, according to Johnston.

“We therefore need to make sure they are flexible and conducive to real life, as the potential benefits of such diets are clear to see,” Johnston said. “We are now going to use these preliminary findings to design larger, more comprehensive studies of time-restricted feeding.” – by Melissa J. Webb

Disclosures: The authors report no relevant financial disclosures.

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Marie St-Onge

This is a very interesting pilot study. I commend the investigators for attempting to restrict food consumption in a way that minimizes extreme time-of-day differences, which would occur if feeding was restricted to the early part of the day or the later part of the day. It’s important to note, however, that despite the strength of considering time-of-day effects, this may have contributed to difficulties in adopting this eating pattern for the long-term. In fact, the authors note that participants were discontent with the eating window, as it interfered with social eating occasions or work schedules. They rated adherence difficulty as 7/10 (10 being most difficult), and 57% of participants reported they would not have been able to sustain this longer than 10 weeks. This raises issues with potential adoption in the general population as study participants are typically compensated for their adherence to a study protocol whereas free-living adults do not have this incentive.

Given the small sample size and lack of difference in body weight change between groups, I would take the change in percent body fat with a grain of salt. The authors should have reported on fat-free mass, and I don’t understand why they mention that these data are not available since bioelectrical impedance analysis, which they used to assess body composition, is a 2-compartment model and provides information on fat mass and fat-free mass. The model they used to assess body composition is a higher-level model that provides information on body fat, muscle mass, total body water as well as intra- and extra-cellular water. It is likely that the change in percent body fat observed is a result of differences in fasting duration and hydration status from the intervention.

Thus, in my opinion, this is an interesting concept for weight-management, but this study does not provide strong convincing evidence that time-restricted feeding, as done in this study, is a sustainable lifestyle approach to eating and provides health benefits beyond those that could be expected from reduced energy intakes. Moreover, participants reported less healthful dietary patterns because they did not have time to prepare healthy meals.

Marie-Pierre St-Onge, PhD, FAHA, CCSH

Associate Professor of Nutritional Medicine, Department of Medicine
Center Director, CUIMC Go Red for Women SFRN
Director, CUIMC Sleep center of excellence
Columbia University Irving Medical Center

Disclosure: St-Onge reports no relevant financial disclosures.