Some of the most popular diet tips in recent years have focused on the idea that timing your meals can make a big difference in how much weight you lose.
It’s long been said that if you want to lose weight, it’s best to eat a big meal at the start of the day and cut back on later meals.
The logic behind this theory is understandable, especially since almost every cell in the body follows the same 24-hour cycle as 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 how we process meals varies at different times of the day. This search field is called “chrono-nutrition“, and it has great potential to help improve people’s health.
Two studies from 2013 suggested that consuming more calories early in the day and fewer calories in the evening helps people lose weight. Yet a major new study found that while the relative size of breakfast and dinner influences self-reported appetite, it has no effect on metabolism and weight loss.
To investigate the link between the size of breakfast and dinner and their effect on hunger, a team of researchers from the universities of Aberdeen and Surrey conducted a controlled study in healthy but overweight people.
Participants received two diets, each for four weeks: a large breakfast and a small dinner, and a breakfast with a large dinner. We kept the lunches the same.
We provided all meals so we knew exactly how many calories study participants were consuming. We measured participants’ metabolism, including tracking the number of calories burned.
All study participants undertook both diet conditions so that the effect of eating habits could be compared in the same people.
We predicted that a big breakfast and a small dinner would increase calories burned and weight loss. Instead, the results of the experiment revealed no differences in body weight or biological measures of energy consumption between the two meal patterns.
Measures of energy use included basal metabolic rate (how many calories your body uses at rest), physical activity, and use of a chemical form of water that helps gauge total daily energy use.
There were also no differences in daily blood glucose, insulin, or lipid levels. This is important because changes in these factors in the blood are associated with metabolic health.
Our conclusions are consistent short-term (one to six days) mealtime studieswhere participants live in a laboratory breathing chamber (a small airtight room equipped with basic comforts) for the duration of the experiment.
Together, the research suggests that how our bodies process calories in the morning versus evening does not influence weight loss as has been reported in other studies.
In our study, the only difference was a change in self-reported feelings of hunger and related factors, such as how much food they wanted to eat.
Throughout the day, the eating pattern consisting of a large breakfast and a small dinner caused participants to report less hunger throughout the day. This effect can be useful for people looking to lose weight, as it can help them control their hunger better 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 showed the greatest differences in the effects of early versus late energy intake after four weeks.
However, the fact that neither calories consumed nor calories burned changed over four weeks shows that body weight is unlikely to have changed if the study were longer.
Study participants were also allowed to choose the exact time of each meal. Despite this, there was negligible difference in the timing of each meal pattern.
Timing 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 when you eat your biggest meal isn’t as important for weight loss as previously thought.
jonathan johnsonProfessor of Chronobiology and Integrative Physiology, University of Surrey; Alex JohnsonPersonal Chair in Nutrition, The Rowett Institute, University of Aberdeenand Peter Morganfull professor, University of Aberdeen