Altering when you consume your calories doesn’t change weight loss

Whether your biggest meal of the day is breakfast or dinner seems to make no difference when it comes to losing weight if you are eating the same number of calories

By Grace Wade

Whether people on a diet eat most of their calories at breakfast or at dinner has no effect on weight loss, but it does affect how hungry they are.

Previous research on the importance of calorie distribution across meals for weight loss has been mixed. Some studies have suggested that filling up at breakfast improves weight loss, while others have concluded that it doesn’t make a difference, even if you skip breakfast altogether.

Settling questions like this is difficult because most nutrition research is observational and often relies on people’s own reports of what they consumed and when, which can be unreliable.

To get a clearer picture, Alexandra Johnstone at the University of Aberdeen in the UK and her colleagues recruited 30 adults who were overweight or obese and had no other underlying health conditions. The researchers then provided participants with food and beverages for 10 weeks.

For the first week of the study, the participants followed a weight maintenance diet, consuming 1.5 times the number of calories needed at their resting metabolic rate. This is the amount of energy required to maintain routine bodily functions and was determined by researchers for each participant at the start of the study. Calories were evenly distributed across three meals each day.

For the following four weeks, participants were divided into two groups: 14 people ate 45 per cent of their calories at breakfast, 35 per cent at lunch and 20 per cent at dinner. The other 16 ate 20 per cent of their calories at breakfast, 35 per cent at lunch and 45 per cent at dinner. Both groups were restricted to the calories required at their resting metabolic rate, and had 35 per cent of calories from fat, 30 per cent from protein and 35 per cent from carbohydrates.

After the four weeks, both groups followed the weight maintenance diet again for one week before switching to the opposite diet for the next four weeks. So, people on the big breakfast diet ate the big dinner diet and vice versa.

By the end of the study, the researchers found that there was little difference in how much weight participants lost when they ate more in the morning or the evening: people lost an average of 3.33 kilograms during the large breakfast diet compared with an average of 3.38 kilograms during the large dinner diet. That suggests calories are metabolised the same regardless of when they are consumed, says Johnstone.

People did, however, report feeling fuller throughout the day when they ate a larger breakfast. Towards the end of each diet, participants scored their hunger over three consecutive days on a scale of 0 to 100, with zero meaning satiated. On average, people rated their hunger a few points lower, around 30, when eating a larger breakfast compared with about 33 when eating a large dinner. When on the big breakfast diet, participants also reported feeling less desire to eat and had lower levels of the appetite-stimulating hormone ghrelin and higher levels of hormones associated with satiety.

“One of the main reasons people fail to lose weight or comply to a weight loss diet is because they’re hungry,” says Johnstone. “So, this could be a really beneficial strategy to help people stick to that calorie deficit.”

One limitation of this study is its length, says Mindy Patterson at Texas Woman’s University. Previous research has found that front-loading calories earlier in the day leads to significant differences in weight loss after five weeks, not four, she says. “Perhaps they should have gone a little bit longer in duration and then we would have seen that difference.”

Journal reference: Cell Metabolism, DOI: 10.1016/j.cmet.2022.08.001

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