Exercise enthusiasts often wonder whether it’s better to eat or fast before a workout. A study, published in the ‘American Journal of Physiology – Endocrinology and Metabolism’, has investigated the effects of eating versus fasting on gene expression in the fat tissue in response to exercise. This has highlighted the different roles that fat plays in powering and responding to exercise.
Researchers from the University of Bath in the UK studied a group of overweight men. The volunteers walked for 60 minutes at 60% maximum oxygen consumption on an empty stomach and, on another occasion, two hours after having a high-calorie carbohydrate-rich breakfast. The research team took multiple blood samples after eating or fasting and after exercising. They also collected fat tissue samples immediately before and one hour after walking.
They found that gene expression in the fat tissue differed significantly in the two trials. The expression of two genes, PDK4 and HSL, increased when the men fasted and exercised and decreased when they ate before exercising. This rise in PDK4 likely indicates that stored fat was used to fuel metabolism during exercise instead of carbohydrates from the recent meal. HSL typically increases when fat tissue uses stored energy to support increased activity, such as during exercise. Explains Dylan Thompson, corresponding author of the study, “After eating, the fat tissue is busy responding to the meal and a bout of exercise at this time will not stimulate the same (beneficial) changes in the tissue.” He noted that this meant, exercise in a fasted state brought about better, more favourable changes in the fat tissue, and this could be beneficial for health in the long term.
An earlier study in 2013 by researchers in Northumbria University had found that people burn up to 20% more body fat by exercising in the morning on an empty stomach. A similar 2016 study in the ‘British Journal of Nutrition’ had concluded that aerobic exercise performed empty stomach burnt fat better than exercise after eating.
However, experts would like to believe that the advice on eating and exercise is not one-size-fits-all. Some nutritionists would advocate that it’s better to have a healthy meal one or two hours before exercise, and another after an hour or two post exercise can help you sustain energy, boost performance, stay hydrated, preserve muscle mass and speed up recovery. Talk to your healthcare expert for advice depending on what suits your individual needs. Your needs will vary depending on your size, goals, genetics, and the duration and intensity of your activity.
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