Study challenges myth that eating at different times of day leads to differential energy metabolism

Eating the bulk of your daily calories at different times of the day makes no difference to your metabolism, new research has revealed.

Scientists led by Professor Alexandra Johnstone from the University of Aberdeen’s Rowett Institute in collaboration with Professor Jonathan Johnston from the University of Surrey, found that energy is similarly utilised, regardless of when the calories are consumed.

Funded by the Medical Research Council, the findings challenge previous studies which have suggested that ‘evening eaters’ have a greater likelihood of gaining weight and are less able to lose it.

Analysis of current eating habits in the UK show that many people consume most of their calories during the evening, although this can vary.

Published in the high-profile scientific journal, Cell Metabolism, the study was the first of its kind in the UK to compare the impact of breakfast calories versus evening calories in adult men and women who are overweight and obese.

It found that when calories are consumed can affect appetite and hunger but does not change energy metabolism in adults who are obese and overweight, but otherwise healthy.

Professor Johnstone explains: “Participants were provided with all their meals for eight weeks and their energy expenditure and body composition monitored for changes, using gold standard techniques at the Rowett Institute.

“The same number of calories were consumed by volunteers at different times of the day with energy expenditure measures using analysis of urine.

“This study is important because it challenges the previously held belief that eating at different times of the day leads to differential energy expenditure. The research shows that under weight loss conditions there is no optimum time to eat in order to manage weight, and that change in body weight is determined by energy balance.

“We know that appetite control is important to achieve weight loss, and our study suggests that those consuming the most calories in the morning felt less hungry, in contrast to when they consumed more calories in the evening period.

“The grant for this research was awarded in 2017 with the volunteer study completed in 2020 and analysis recently undertaken. It has been a huge team effort over a lengthy period. I welcome the findings and the contribution the paper makes to the field of circadian rhythm, and chrono-nutrition.

“It is testament to my Rowett colleagues for their efforts to support this study. It is the most important paper of my career, and I am excited to share this research with the academic community, and I am looking forward to where it will take us with our future research.”

Jonathan Johnston, Professor of Chronobiology and Integrative Physiology at the University of Surrey, added: “This is a major finding for the field of meal timing (‘chrono-nutrition’) research. Many aspects of human biology change across the day and we are starting to understand how this interacts with food intake. Our new research shows that, in weight loss conditions, the size of breakfast and dinner regulates our appetite but not the total amount of energy that our bodies use.

"We plan to build upon this research to improve the health of the general population and specific groups, e.g. shift workers.”