The “fat burning” does it exist ?

La «zone de combustion des graisses» existe-t-elle ?

La «zone de combustion des graisses» existe-t-elle ?


June 5, 2020 12h29


The “fat burning” does it exist ?

Justin Roberts

Master conference, University of Anglia Ruskin

Ash Willmott

Sports Science and exercise, University of Anglia Ruskin

Dan Gordon

Sports Science and exercise, University of Anglia Ruskin

THE SCIENCE IN HIS WORDS / The people who want to lose weight are looking to know what is the most effective way to lose their extra pounds — and the plans or the workouts in the mode that claim to have the “secret” to melt the fat abound.

According to one theory, in which approximately 60 % of its maximum heart rate, the body is found in the “zone of fat burning”, which would be optimal for weight loss. But this zone does it exist really ?

It is necessary to first understand the functioning of the metabolism. Even if you are sitting all day at a desk, to meet its energy needs, the body uses “fuel” from carbohydrates, proteins, lipids (or fats) and phosphates. However, the rate at which energy is used and the amount available vary from one person to another. This depends on a number of factors, such as food intake, age, sex, and the amount or frequency of physical exercise.

In general, the exercises at a low intensity — such as walking at a steady pace or light jogging — do not require as much effort from our muscles and the sprint, for example. This means that the body has less energy requirements and, in this case, it is supplied primarily in the fat.

However, when the intensity increases, the body is unable to metabolize fat quickly enough to meet its energy needs. It then uses the carbohydrates, it may metabolize it more quickly. It can be concluded that there is in fact an exercise intensity where fat is the main source of energy.

When the body is at rest, the number of calories it needs to function is particularly low, so that it gets its energy from the fats. This means that the possible “area of fat burning” would be between the rest state and the level of exercise intensity where carbohydrates become the main energy source (in terms of percentage contribution to energy demand).

So we are talking of a zone which extends from a resting heart rate of about 70 beats per minute to a pace of about 160 beats per minute during exercise stress moderate (such as cycling at a constant speed where holding a conversation becomes a challenge), where we pass from the use of fat to those carbs.

The problem with such a large area is that the person who makes the exercise does not optimize its capacity to metabolize fat, because as the intensity of exercise increases, there is a gradual change in the proportion of fats and carbohydrates that serves the body.

Area of fat burning

How can we know when our body switches from using fat to other fuels to produce energy ? One of the approaches adopted by researchers is to evaluate the amount of fat that serves as a source of energy during exercises of different intensities.

By measuring the amount of air a person expels during a stress test that becomes increasingly more difficult, the physiologists have been able to calculate the proportion of lipids and carbohydrates used to meet energy needs at different intensities. The largest amount of fat burned is called the “maximum rate of fat oxidation” (or NTM for English maximum fat oxidation rate), and the intensity at which it occurs is called “FATmax”.

La «zone de combustion des graisses» existe-t-elle ?

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Since researchers have used this method of calculation for the first time, studies have shown that when the intensity increases from about 40 % to 70 % of VO2 max (maximum amount of oxygen that the body can consume during training), there is an increase in the rate of carbohydrate and fat used. The rate of fat starts to decrease beyond this level, because the body needs to get energy more quickly.

It is known as the “fat burning” is between 50% and 72% of the VO2 max of a person. However, the fat burning capacity also depends on genetic factors, and studies have shown that, in people who are overweight or obese, this area is generally lower — about 24 to 46 % of their VO2 max — and it is higher among endurance athletes.

Another question to ask is : how much fat burn-we exercise (in grams per minute) ? The answer is : surprisingly little. Even in studies conducted with athletes who were training at FATmax, the participants burned, on average, than 0.5 grams of fat per minute, which gives 30 grams per hour.

In the average individual, this figure is 0.1 to 0.4 gram of fat per minute. To put things in perspective, a pound of fat weighs approximately 454 grams. Therefore, although training in the area of fat burning helps to lose fat, this could explain why in general, it takes a lot of time to lose weight training.

However, it has been proven that by following certain regimes(such as intermittent fasting or a ketogenic diet rich in fat) and doing longer workouts, you can increase the amount of fat that is burned.

It may be time to stop looking for the best zone for burning fat and consider that there is a “sweet spot” is unique to each, which can be used to optimize its weight loss by physical exercise.

Regular physical activity aimed at this “perfect point” (which generally occurs when a sensation of effort low to moderate, approximately 30% to 60% of maximum effort, or a level of effort of a four-in-ten) is likely to improve the efficiency of the body to use the energy of the lipids and result in a body fat percentage lower.

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This text first appeared on the website of the franco-canadian of The Conversation. Reproduced with permission.

“The science in her words” is a forum where scientists of all disciplines can take the floor, either in open letters, or excerpts from books.

La «zone de combustion des graisses» existe-t-elle ?

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