Some of the most popular diet advice in recent years has centered around the idea that timing your meals right can make a big difference in the amount of weight you lose. It was long said that if you wanted to lose weight, it was best to eat a large meal at the beginning of the day and keep any later meals smaller.
The logic behind this theory is understandable, especially considering that almost every cell in the body follows the same 24-hour cycle that we do. Circadian clocks are found throughout the body and regulate the daily rhythms of most of our biological functions, including metabolism.
Because of these metabolic rhythms, scientists have proposed that the way we process meals varies at different times of the day. This field of research is called “chrono-nutrition”, and it has great potential to help improve people’s health.
Two 2013 studies suggested that consuming more calories early in the day and fewer calories in the evening helps people lose weight. Yet a large new study has found that while the relative size of breakfast and dinner affects self-reported appetite, it has no effect on metabolism and weight loss.
To investigate the relationship between the size of breakfast and dinner and their effect on hunger, a team of researchers at the Universities of Aberdeen and Surrey conducted a controlled study in healthy but obese people. The participants were fed two diets, each for four weeks: a large breakfast and a small dinner, and a small breakfast with a large dinner. We kept the lunches the same.
We provided all the meals so we knew exactly how many calories the study participants consumed. We measured the participants’ metabolism, including monitoring how many calories they burned.
All study participants undertook both dietary conditions so that the effect of meal patterns could be compared in the same people.
We predicted that a large breakfast and a small dinner would increase calories burned and weight loss. Instead, the results of the experiment found no differences in body weight or any biological measures of energy expenditure between the two meal patterns.
Measurements of energy expenditure included basal metabolic rate (how many calories your body uses at rest), physical activity and use of a chemical form of water that allows total daily energy expenditure to be assessed.
There were also no differences in daily levels of blood glucose, insulin or lipids. This is important because changes in these factors in the blood are associated with metabolic health.
Our results are consistent with short-term (one to six days) mealtime studies in which participants live in a laboratory air chamber (a small, airtight room equipped with basic amenities) for the duration of the experiment. Taken together, the research suggests that the way our bodies process calories in the morning versus the evening does not affect weight loss in the way that has been reported in other studies.
In our study, the only difference was a change in the self-reported feeling of hunger and related factors, such as the amount of food they wanted to eat. During the day, the meal pattern of a large breakfast and small dinner caused participants to report less hunger during the day. This effect can be useful for people who want to lose weight, as it can help them better control their hunger and eat less.
As with all research, there were some limitations to our study. We only studied participants for four weeks for each meal pattern. Previous research has shown the biggest differences in the effects of early versus late energy intake at four weeks. But the fact that neither calories eaten nor calories burned changed over four weeks shows that body weight is unlikely to have changed if the study was longer.
Study participants were also allowed to choose the exact time for each meal. Despite this, there was an insignificant difference in the timing of each meal pattern.
Chrono-nutrition remains an exciting area of research, and there is growing evidence that meal timing can play an important role in improving the health of many people. However, our latest research indicates that the time of day you eat your biggest meal is not as important to weight loss as previously thought.