For years we’ve been told never skip the first meal of the day. But the question still remains among many fitness enthusiasts: Does exercise on an empty stomach burn more fat?

According to research, that depends. A recent study shows there may be a small benefit to doing fasted cardio, especially if you are trying to burn excess body fat. Although there have been several studies on the topic, this is the first to demonstrate the effects of eating vs. fasting on gene expression in adipose tissue during exercise.

The research, conducted by the University of Bath and published by the American Journal of Physiology, observed a group of overweight males. The participants were instructed to walk for 60 minutes at 60 per cent maximum oxygen consumption on an empty stomach. In the next trial, the same group of men were given a high-calorie, high-carbohydrate breakfast prior to exercising.

Researchers found that gene expression in the adipose tissue varied significantly between the two trials. After eating, fat cells are busy responding to the last meal. This means that exercising in a fasted state may actually promote fat burning, as the body does not have to break down food; thus relying on stored fat for fuel.

In a similar study conducted in 2014, participants were required to adhere to a strict diet and exercise regimen. As a result, the researchers found that overall body composition was similar between the fasted and non-fasted groups.

The findings from this particular study conclude that eating prior to working out when trying to burn body fat simply comes down to the individual and personal preference. The researchers also stated that given the small sample size of just 20 participants, it is possible that there could be a slight benefit when comparing one method to the other. Therefore, further trials with more participants would need to be conducted.

The difference between the two studies is that the first one measured gene expression in adipose tissue in response to a meal while the latter one relied on participant adherence to determine the effect of fasting vs. non-fasting on body composition. Therefore, human error could play a role in the outcome. 

According to Dr. Jim Stoppani (who holds a doctorate in exercise physiology and a mnor in biochemistry), fasted-cardio works well for men with body fat in the low single digits (5-6 percent) and females with body fat in the low teens (13-14 per cent); especially if they have problem areas such as the lower back or thighs.

“Although there’s no direct data to reference, it might be that when a person only has a small amount of fat lingering in hard-to-attack areas, exercising in a fasted state could spark those resistant fat cells to release stored fat so it can be burned for fuel,” according to Stoppani.

 

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