It’s long been assumed that calories are calories and, when it comes to losing weight, it doesn’t matter when they are consumed during the day.
Recent studies, however, have challenged this notion, suggesting that timing of calorie intake – and how you distribute your calories across the day – may influence weight loss effectiveness.
These findings imply that meal timing that’s mismatched to your body’s circadian rhythm – the 24-hour cycle that governs calorie-burning, digestion, nutrient metabolism and other bodily processes – may contribute to weight gain in ways beyond the number of calories you consume each day.
Now, two rigorously controlled trials, both published this month in the journal Cell Metabolism, lend support to the theory that the right timing and allocation of daily calories may offer benefits to weight loss.
Here’s what to know about the latest research – and how the findings might apply to you.
Larger breakfast curbs hunger
One study, conducted by researchers from the University of Aberdeen in the U.K., investigated whether eating bigger breakfast and smaller dinner – or the opposite – produced greater weight loss.
Thirty participants with overweight or obesity were assigned to one of two diets: half consumed the bulk of their daily calories (45 per cent) at breakfast, fewer at lunch (35 per cent) and the least at dinner (20 per cent). The other group ate 20 per cent of daily calories at breakfast, 35 per cent at lunch and 45 per cent at dinner.
After four weeks, the groups switched and followed the opposite diet.
Calories (1,700 per day), diet composition (e.g., protein, carbohydrate, fat) and meal frequency were matched for both diets; the only difference was calorie-loading at breakfast or dinner.
The researchers provided all foods and beverages. Participants’ daily energy expenditure, resting metabolism, appetite and weight loss was measured throughout the study.
Both diets resulted in near-identical weight loss after four weeks (seven pounds). There was also no difference in daily calorie-burning or resting metabolism between the two groups.
Calorie distribution did affect appetite control. Eating a bigger breakfast resulted in significantly lower hunger and greater satiety during the day compared to eating bigger dinner.
These findings contradict earlier studies that suggested eating a big breakfast and light dinner helps people burn more calories.
Instead, they imply that eating the largest meal of the day in the morning may contribute to weight loss over time by decreasing appetite and, therefore, calorie intake.
Late eating increases hunger, reduces calorie-burning
Previous research has shown that eating late in the day is tied to increased obesity risk and impaired weight loss success, outcomes that couldn’t be explained by differences in calorie intake or physical activity.
For the second study, investigators from Brigham and Women’s Hospital in Boston set out to determine how the late eating might influence obesity risk.
The in-laboratory experiment had 16 healthy adults with overweight or obesity complete two six-day diet protocols: an early eating protocol with meals at 8 a.m., noon and 4 p.m. and a late eating protocol with the exact same meals scheduled at noon, 4 p.m. and 8 p.m.
Physical activity, posture, sleep and light exposure were tightly controlled.
The researchers measured perceived hunger and appetite, levels of appetite-regulating hormones and calorie-burning. They also looked at gene activity in adipose tissue.
Late eaters were twice as likely to report hunger during the day than were early eaters. Levels of leptin, a hormone that signals satiety, were decreased during the late eating protocol compared to the early eating protocol.
When participants ate later, they also burned, on average, 60 fewer calories per day than when they ate earlier. Among late eaters, gene activity in adipose tissue showed changes indicating increased fat storage and decreased fat burning.
The researchers noted the increased drive to eat observed with late eating may be even more pronounced in a real-world setting where people can eat as much and as often as they like.
Limitations, implications
Both studies were small and of short duration. It’s not known, for instance, if the observed effects of late eating would persist over time.
And it remains to be demonstrated if a reduced appetite associated with eating a larger breakfast translates into a lower calorie intake, or if this effect depends on timing of the evening meal.
Still, these findings are intriguing and might give you pause for skipping breakfast and/or eating dinner late.
If you are doing time-restricted eating, they might prompt you to shift your eating window from the evening to the morning or afternoon.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD