Running on an empty stomach to lose weight faster

Some people are staunch advocates of fasted training and swear by this method for weight loss. Others, on the contrary, are absolutely against it, citing a risk of injury or excessive fatigue. How can you practice this type of training to make it truly effective?

Text: Bruno Cavelier – Photos: Ledlenser, Kalenji, Brooks / DR

Running is an excellent substitute activity for cyclists and triathletes who want to stay in shape during the winter. You fear the cold less, sessions are shorter and can be done at (almost) any time, and are especially effective for maintaining fitness. Based on this observation, many athletes take advantage of it to run fasted, hoping to optimize their weight loss or avoid gaining weight.

=> SEE ALSO: Your weight in questions

Lipid mobilization (lipolysis) is regulated by the balance between hormones that stimulate it (catecholamines, cortisol, and glucagon) and those that inhibit it (insulin). To lose weight effectively, blood insulin concentration must be low, while catecholamines, cortisol, and glucagon must be high. To determine which energy substrates are oxidized during exercise, the respiratory quotient is used. It represents the ratio between the volume of carbon dioxide exhaled and that of oxygen inhaled (VCO₂/VO₂). If the quotient is less than 0.7, lipids are the main energy source. A ratio close to 1, conversely, indicates carbohydrate oxidation. When fasted, the respiratory quotient is very low, significantly lower than that observed after a meal. Fasted running is an effective method for losing fat because fatty acid oxidation doubles.

Fasted running is an effective method for losing fat because fatty acid oxidation doubles.

When are you fasted?

Being fasted literally means “without having eaten“: digestion (and its metabolic, enzymatic, and hormonal implications) is completely finished. We are therefore theoretically fasted when our last food intake was 12 hours ago. But it’s not that strict: you are running fasted when your last energy intake, solid or liquid, was approximately 6 hours ago. Indeed, any food intake triggers the release of a pancreatic hormone: insulin. It is this hormone that maintains the stability of blood glucose, the sugar level in the blood. After its release, insulin returns to its basal value within twelve hours. But after six hours, its concentration has almost returned to its resting value, at least low enough to effectively stimulate lipolysis.

We need to redefine the different types of fasting, since obviously, originally, these were not conceived with a sporting logic in mind. We will then know which one best suits (or is least contradictory to) a fasted session.

Complete, dry, or absolute fasting: This consists of not drinking or eating anything, as in the practice of certain religious or pre-operative fasts, for example. This type of fasting is not very compatible with fasted running, as it increases the risks of dehydration and its consequences on the body.

Water fasting: This consists of not eating anything, but pure water is allowed ad libitum; it is therefore more accessible and, above all, more suitable, as it only replaces fluids and electrolytes (minerals), without providing calories. It allows lipolysis to occur under safe conditions.

Partial water fasting: This is a variation of water fasting. Other drinks besides water are allowed, such as vegetable broth, infusions, orange juice, coffee… Here, certain drink choices can be contradictory to the objectives pursued in the context of fasted training.

Can you drink coffee before going for a fasted run?

Drinking coffee is not the same as drinking pure water, because coffee has a diuretic effect. The fluid balance following its consumption is negative, meaning that this drink removes more water from your body than it provides (thus it dehydrates you). To rebalance the scale, it is therefore imperative to add a glass of water to your coffee. Furthermore, coffee consumption is often accompanied by sugar consumption. In this case, you are providing sugars and the fasted training is no longer truly fasted, especially if it is short-duration… Provided it is taken without sugar and accompanied by a glass of water, coffee can be consumed before a fasted workout.

What about orange juice?

A glass of orange juice provides too many calories (5 sugars per 25 cl) and can ruin the desired effects of fasted running; it should be remembered that a fasted workout consists only of a short run (45 minutes to 1 hour) and therefore sugar intake should be limited as much as possible to get the greatest benefit.

=> SEE ALSO: What is the benefit of a fasted sports session?

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