A report published in October in the British Journal of Nutrition highlighting research from Glasgow University and the Universiti Kebangsaan in Malaysia suggests that by doing exercise before breakfast it's possible to burn more calories and lose weight more easily than if you exercise later in the day.
In a small trial among overweight men, researchers compared the effects of a single exercise session performed either before or after breakfast and how this affected the metabolism of fats and carbohydrates afterwards.
The same group of men was also measured for carb and fat breakdown after doing no exercise at all.
The results showed that the calorie burn was greatest when men exercised before breakfast. The relatively small sample survey has, for some, confirmed a long-held belief that working out before the first meal can significantly contribute to a shift in weight. Other health advisers, however, are treating the results more cautiously. In the UK, the National Health Service insisted that "further research is required to determine whether these findings are similar under 'normal' living conditions, outside of the laboratory setting".
Experts within the fitness industry echo this view. "There's no reliable evidence to say that calories are burned more efficiently at particular times of day," says Fiona Donald, a trainer with urbanenergyfitness.com. "The time of day you exercise may influence how you feel. The most important thing is to choose a time of day that you can stick with."
However, Darryn Whitsitt, a personal trainer at Platform3 Dubai, says you may find your ability or motivation to work out could be influenced by the time of day. "Morning yoga practice wakes you up, stretches stiff muscles you haven't used all night, increases blood circulation," Whitsitt says. "Or choosing to do yoga in the evening may help to relax the body and mind."
Donald agrees that morning sessions have their benefits. "Research does suggest that people who exercise in the morning tend to do better with regard to forming a regular exercise habit," she says.
While fitness experts are sceptical about the effect early morning exercise can have on weight loss, they are wary of how working out too late in the day can disrupt sleep, which in turn can have negative consequences on your diet.
"Exercising right before bed or within about three hours of your bedtime can make it harder to fall asleep because exercise stimulates your heart, brain and muscles and raises your body temperature," Donald says. "Instead, exercising in the late afternoon or early evening seems to be beneficial for getting a good night's sleep." That's because body temperature, which rises as you exercise, is starting to come down as you prepare for bed, and this decrease seems to be a trigger that eases you into sleep.
And following a late-night workout with a hearty meal could do some serious damage to your weight-loss regime.
Within days of the exercise study being published, research from the University of Pennsylvania revealed that if you want to avoid serious weight gain then it's not just a case of watching what you eat but also when you eat it.
In studies carried out on laboratory mice researchers found that fat cells behave differently when the natural eating times of the body clock are thrown off rhythm. Consuming food at an "inappropriate" time - daytime in mice, late at night in humans - affected the metabolism in ways that increased fat retention.
The studies shed some light on the reasons why night-shift workers have a greater prevalence of obesity and metabolic syndrome - and why sleep disorder sufferers also have a higher risk for developing obesity.