The effect of modest time changes to breakfast and dinner times on body fat

alarm clock on plate

The Nutrition Society Paper of the Month for September is from the Journal of Nutritional Science and is entitled ‘A pilot feasibility study exploring the effects of a moderate time-restricted feeding intervention on energy intake, adiposity and metabolic physiology in free-living human subjects’ by Authors: Rona Antoni, Tracey M. Robertson, M. Denise Robertson and Jonathan D. Johnston.

There is increasing evidence to support the idea that our metabolic health is not just regulated by what we eat, but also when we eat. This interaction between circadian rhythms and nutrition is often referred to as “chrononutrition”.

Time-restricted feeding (TRF, a form of intermittent fasting) is a new dietary concept that involves reducing the time between the first and last calorie consumed each day. There is strong evidence to support the health benefits of TRF in animals, and as evidenced by our recent study, there is the suggestion of possible benefits for humans, too.

During our pilot study, we investigated the feasibility and impact that a moderate change in meal times has on dietary intake, body composition and blood risk markers for diabetes and heart disease. 

Participants were split into two groups – those who were required to delay their breakfast by 90 minutes and have their dinner 90 minutes earlier, and those who ate meals as they would normally (the controls). Participants were required to provide blood samples and complete diet diaries before and during the 10-week intervention and complete a feedback questionnaire immediately after the study.

We found that those who changed their mealtimes lost an average of 2% of their body fat (no significant change was observed in the control group). There was also a suggestion of positive effects of TRF on metabolic risk markers (e.g. fasting blood glucose levels); interpretation of the blood glucose data is complicated however as fasting glucose levels unexpectedly increased in the control group.

Unlike many previous studies in this area, participants were not asked to stick to a strict diet and could eat freely, provided it was within a certain eating window. Interestingly, we found that those who changed their mealtimes ate less food overall than the control group. This result was supported by questionnaire responses which found that 57 % of participants noted a reduction in food intake either due to reduced appetite, decreased eating opportunities or a cutback in snacking (particularly in the evenings).

It should be noted that 57% of participants also felt they could not have maintained the new meal times beyond the prescribed 10 weeks because of their incompatibility with family and social life. However, 43 per cent of participants would consider continuing if eating times were more flexible.

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. Reduction in body fat lessens our chances of developing obesity and related diseases, so is vital in improving our overall health.

However, as we have seen with these participants, fasting diets are difficult to follow and may not always be compatible with family and social life. 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.

We are now going to use these preliminary findings to design larger, more comprehensive studies of TRF in humans.