People who eat breakfast burn more kilojoules and have tighter blood sugar control than those who are fasting, a new study has shown.
Researchers made the findings in the first randomised controlled trial to examine the effect of daily breakfast on energy balance compared with morning fasting.
In the University of Bath study, people aged between 21 and 60 were randomly allocated into a 'fasting' group and a 'breakfast' group for six weeks.
The fasting group consumed no calories until 12pm each day, with the breakfast group eating 700 calories before 11am - 350 within two hours of waking.
Those who ate breakfast experienced little impact on snacking or portion sizes or a change in their resting metabolism, contrary to popular belief.
However, they were likely to expend more energy - around 442 calories - by being active, mainly in the morning after eating.
And as the day went on, those who ate breakfast experienced better blood sugar control compared with those who had fasted.
Dr James Betts, of the University of Bath's department of health, was principal investigator in the study, published in leading nutrition journal American Journal of Clinical Nutrition today.
"The main finding from our study is that people who eat breakfast burn more calories," he said.
"Most people would think this is because of reduced snacking and increased metabolic rate but actually this is due to moving around.
"They were more active during the period that they had eaten breakfast. People moved around if they had been fed and there are many benefits to being active."
Researchers asked 35 lean people to either abstain from food before 12pm or eat 700 calories before 11am for a six-week period.
The rest of their daily diets did not change and those who consumed breakfast were not told what to eat, Dr Betts said.
They were fitted with an Actiheart monitor to accurately measure their daily activities as well as an iPro, a portable device that recorded glucose levels every five minutes.
Dr Dylan Thomas, co-author on the study, added: "We previously found that these monitors are highly sensitive to changes in spontaneous low-to-moderate intensity activities and this new study shows that these are precisely the type of activities that differ depending on whether a person has or has not eaten in the morning."
The monitors showed people who had eaten breakfast were more active than those who had not, despite waking and going to sleep at the same times on average.
However, the study found no evidence of any change in resting metabolism between the breakfast and fasting groups.
"The rate was stable within just 11 calories per day, there was absolutely no change," Dr Betts added. "People who fast do not slow down their metabolism and people who eat breakfast do not speed it up."
Through the study, the fasting group consumed around 20 per cent less calories than the breakfast group overall each day, suggesting they did not compensate for missing breakfast by eating more later on.
The study also found no negative cardiovascular effects of fasting until midday for the six-week period but there was an impact on metabolic control.
Researchers assessed whole-body metabolic control in response to ingested sugar, which primarily reflects muscle metabolism, as well as glucose metabolism specific to fat tissue using biopsies.
These molecular assessments were complemented by data from the iPro, which measured glucose levels with a catheter placed 2cm into stomach fat tissue.
The fasting group experienced impaired glucose control in the afternoon and evening - with effects taking hold after they had eaten post 12pm - compared with the breakfast group.
This decline in glucose control was found in the final week of the trial.
The findings are part of the Bath Breakfast Project, a three-year randomised controlled trial funded by the Biotechnology & Biological Sciences Research Council.
Researchers are currently examining data from the second phase of the trial, which featured a more overweight study population.
The causal role of breakfast in energy balance and health: a randomised controlled trial in lean adults is published on American Journal of Clinical Nutrition today.