In a study of 10 men, skipping breakfast led to a dip in athletic performance hours later, even after a larger lunch.

Despite the bigger lunch, skipping breakfast led to a slightly lower overall calorie count for the day. But if weight loss is not the priority, researchers say, forgoing breakfast might backfire by reducing the effectiveness of the day’s workout.

“Many athletes as well as recreational exercisers do so in the evening and breakfast skipping is a relatively common dietary practice,” said senior author Dr. Lewis J. Jamesof the School of Sport, Exercise and Health Sciences at Loughborough University in the U.K.

“Whilst we know that consuming breakfast is likely to be the best dietary strategy in most situations to maximize exercise performance in the morning, we did not know how or if breakfast skipping/ consumption influenced evening exercise performance in a situation where the exerciser ate lunch,” James told Reuters Health by email.

The researchers had 10 men who were regular breakfast eaters complete an evening athletic trial twice, once after eating breakfast in the morning and once after skipping it.

The men arrived at the lab having fasted overnight and either ate a breakfast of about 700 calories or did not. They then ate lunch about four hours later and dinner about 11 hours later, and the researchers kept track of how much the men consumed at each meal.

Between lunch and dinner the men performed an exercise trial of 30 minutes of steady-state cycling at 60 percent of their max effort followed by another 30 minutes of a performance test, when they were told to push themselves as much as possible during the remaining time.

After they completed the exercise test and had eaten as much of the provided pasta dinner as they liked, they were transported home and told not to eat again until the next morning, when they returned to the lab to be weighed and complete appetite questionnaires.

On days when they skipped breakfast, the men consumed an average of almost 200 more calories at lunch compared to days when they ate breakfast, but total calorie intake tended to be lower on days without breakfast.

Average heart rate and total fat oxidation during the cycling test was greater after skipping breakfast compared to after eating breakfast.

The men worked harder, expending marginally more calories, on days when they had eaten breakfast, as reported in Medicine and Science in Sports and Exercise.

“Skipping breakfast reduces the amount of available energy (glucose) for muscular activity and therefore it would be important to know if this had a functional consequence – i.e. reduced performance,” David Levitsky, a professor of nutrition at Cornell University in Ithaca, New York, told Reuters Health by email.

But the difference in performance was quite small, and may depend on the kind of exercise, he said. Some kinds may be impaired by skipping breakfast, others may not, said Levitsky, who was not part of the new research.

Although it impaired performance, skipping breakfast or exercising with suboptimal carbohydrate status might enhance training adaptation in some cases, so sometimes it can be the right choice, James said.

The findings indicate that skipping breakfast could be used as a strategy to reduce overall energy intake, in habitual breakfast consumers at least, where weight management is the key goal, he said.

“I would add a word of caution and say that weight loss will depend on the balance of energy intake and energy expenditure and if skipping breakfast resulted in more feelings of tiredness and reduced physical activity over the day this might attenuate the energy deficit created by skipping breakfast,” James said.

This was only a small study of 10 men who were all fairly similar, he noted.

“Certainly more work is needed to see whether the effects persist in other populations,” he said.