Can intermittent fasting and exercise be combined without risk to health?

Today the World Food Day with the aim of raising awareness about the food problem and malnutrition in many societies. But, surprisingly, in some areas of the planet and in some social groups the intermittent fasting has become one of the most popular diets, in the way of eating to make peace with the scale and improve, by the way, general health. The idea of ​​combining this restriction with exercise seems tempting, but is it healthy?

Stopping eating for an extended period of time has multiple benefits associated with it. Some like weight loss, cardiovascular health, or a drop in blood sugar levels. However, this practice can increase tiredness, fatigue and, of course, feeling hungry, and is not exempt from controversy.

Performing vigorous exercise on an empty stomach can increase fatigue (Tero Vesalainen / Getty Images / iStockphoto)

Still, it seems that combining it with a sports routine could even increase its effectiveness. “Studies have shown that exercise and fasting they can help in the prevention and treatment of obesity together with the metabolic syndrome and its associated diseases ”, indicates the sports physical educator Ignacio Hernando Valle. But be careful, because in some cases, training without anything in your stomach can work against. These are the basic guidelines to integrate fasting and sport without putting health in question.

Attentive to the sensations

Can intermittent fasting be combined with sport? In short yes. “Above all, it is interesting to combine it in people who want to lose weight, since physical exercise (even low and moderate intensities) added to intermittent fasting produces a increased fat oxidation”Hernando explains.

But, one of the basic premises is to listen to the organism. If after fasting the feeling is weakness, it is advisable to eat something before breaking a sweat, as these symptoms may indicate low blood sugar or dehydration.

Feeling weak may indicate low blood sugar or dehydration

“Whenever a diet is made it is important to combine it with exercise. Of course, be careful with practicing it on an empty stomach, especially during the first days, since the body needs to adapt ”, shares Lina Robles, nutritionist at the Sanitas La Zarzuela University Hospital. It is important to remember that water is a permitted and necessary element during fasting.

Fortunately, there are several ways to apply it. One of them is stop eating during 16 hours a day. Another, eat a single meal (approximately 500-600 kcal.) biweekly and the rest of the time follow a normal diet. The type of exercise and the time of day it is performed can determine which intermittence formula works best.

The benefits

The most obvious is weight loss, something that can be accelerated when fasting and physical activity are combined. According to a study published in the Journal of Nutrition and MetabolismTraining on an empty stomach increases fat oxidation, which means that the body burns stored carbohydrates to supply itself during exercise.

Separately, both fasting and training have health benefits. “Both methods can help us increase HDL cholesterol, to reduce the amount of triglycerides, to tolerate better glucose and to generate less oxidative stress, related to muscle damage. In addition, it has the great advantage that there is no associated loss of muscle mass. It can even be increased along with improvements in strength levels ”, indicates Hernando.

But the expert warns that fasting has no positive effect about him physical performance: “It seems not to report benefits at the level of sports performance, especially in those activities of long duration or carried out at high intensities, in which having an optimal availability of muscle glycogen will be essential”.


People with previous pathologies should consult with their doctor before combining fasting and exercise. “It is not recommended to do this type of diet without supervision for patients with low blood pressure, diabetes, high uric acid, chronic diseases … Neither during pregnancy or breastfeeding”, shared Robles.

People with obesity should also seek medical advice. “It would be advisable to do a stress test prior to avoid setbacks, as well as to adapt the physical program to their needs and circumstances, always under the authorization of a doctor ”, adds the physical educator.


Although this type of diet is more focused on when you eat than what you eat, not everything goes if you want to improve health and perform well in training. The general diet recommendations are also applicable to periods when you do not fast. “Must be complete and nutritious meals. That is, combine vegetables with proteins and carbohydrates. Ideally, divide the plate in two: one half for vegetables or salads and the other for proteins and carbohydrates (one quarter for each). The dessert of meals should always be fruit or yogurt ”, advises the nutritionist.

For health it is important not only how often you eat, but what you eat

For health it is important not only how often you eat, but what you eat (Domepitipat / Getty Images / iStockphoto)

The exercise

If you practice the 16/8 formula –16 hours of fasting daily–, medium intensity cardio training on an empty stomach can be more comfortable. However, in cases where fasting consists of go 24 hours without eating, they are advised very gentle exercises such as restorative yoga, gentle Pilates, or walking. The right time to perform aerobic work is located near the breaking of the fast, to recover the body after the effort.

But for the training to be compensated, the ideal is to balance cardiovascular exercises with other strengthening. The second case is related to the creation of muscle mass, which requires a supply of proteins and complex carbohydrates. In this way, enough fuel is ensured so that the fibers do not break. Therefore, it is advisable to do this type of work in the period in which you do not fast.

“To begin to test this technique together with exercise, it is best to start with known activities, at a moderate-low intensity of performance, since an adaptation time of one or two weeks is usually needed, depending on each person”, Hernando exposes.

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