Does exercising have to last more than 30 minutes to lose weight? 29 minutes won’t do?

" Exercise for less than 30 minutes is equivalent to wasted exercise "

Rumor Analysis

That is not the case.

This statement is not rigorous. The so-called 30 minutes of exercise is required to lose fat. A more scientific statement is: after 30 minutes of exercise, fat consumption will be significantly accelerated.

I believe you have seen similar headlines on many social platforms: Exercising for less than 30 minutes is equivalent to exercising in vain! Only exercising for more than 30 minutes can really reduce fat! These statements may not make you stick to exercising for a longer time, but may make you hesitate before starting: since exercising for 1 minute and 29 minutes is the same, it is better to exercise properly when you have plenty of time. And the weight loss plan for aesthetic or health considerations is delayed again and again.

In fact, on the road to weight loss, what is even more scarce than perseverance is the truth about how to lose weight correctly.

Can 30 minutes of exercise help you lose fat?

This statement is like saying: there is a switch in your body, from the first second to the 29th minute and 59th second of exercise, the fat remains motionless, but if the second hand jumps one second, the fat will rush out like a wild horse. As you can imagine, this is really exaggerated.

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When the human body starts to exercise, whether it is a light walk or an intense run, the body will use both glycogen and fat as energy sources. This is because the body needs energy to support muscle activity. In the early stages of exercise, glycogen will be used first due to its rapid energy release characteristics. However, as exercise continues, especially when performing low-to-moderate intensity aerobic exercise, the proportion of fat as an energy source will gradually increase.

The statement that "30 minutes of exercise is required to lose fat" is actually a simplified statement. The scientific basis behind this statement is that at the beginning of exercise, the proportion of energy supplied by fat is relatively low, about 40%. But as the exercise time increases, especially after about 10 minutes, the proportion of energy supplied by fat will rise to a level equivalent to glycogen, about 50%. This means that although fat is also consumed in the first 10 minutes of exercise, the proportion is not particularly high.

When the exercise time exceeds 30 minutes, the glycogen reserves in the body begin to decrease, and the body will rely more on fat as an energy source. After 30 minutes of exercise, the proportion of fat consumption will increase significantly, but this does not mean that fat was not consumed before 30 minutes. In fact, fat consumption is a gradual increase, not a sudden change.

In addition, the type and intensity of exercise will also affect the ratio of fat and glycogen consumption. For example, in high-intensity interval training (HIIT), although glycogen consumption may be faster, due to the high-intensity nature of the exercise, the body will still maintain a high metabolic rate after exercise, which helps to continue to consume fat after exercise.

Therefore, a more accurate statement is that if you exercise for more than 30 minutes, fat consumption will accelerate, but this does not mean that only exercise for more than 30 minutes can reduce fat. Any form of exercise that can increase energy consumption is likely to help reduce fat. The key is to continue to exercise in moderation and combine it with a healthy diet plan to achieve the best fat loss effect. At the same time, in order to avoid physical fatigue and sports injuries, it is recommended to control the exercise time to less than one hour.

Does more sweating mean faster fat burning?

Some people believe that "sweating" is a sign of "burning fat". The more you sweat, the more fat you burn. Based on these views, there are more and more products that aim to make people sweat, such as sweat-inducing suits.

In fact, this view is not correct. There is no direct causal relationship between sweating and fat burning.

The main way fat is metabolized is to be oxidized into carbon dioxide and water to produce energy. Some scholars have measured through isotope labeling that 84% of fat is excreted from the body in the form of carbon dioxide, and the remaining 16% is not only sweat, but also urine.

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Sweating is the body's way of regulating temperature. When the core temperature of the body rises, it is necessary to sweat to cool down the body. The amount of sweating varies from person to person. People with many sweat glands and high body fat tend to sweat more, while people with low basal metabolism tend to sweat less.

Relying on sweat suits to lose weight is not only putting the cart before the horse, but also potentially dangerous. Its principle is to increase the core temperature while preventing the body from dissipating heat. This will not only fail to cause fat changes, but may also cause many harms to the body. As early as the last century, there were cases in the United States where people suffered cardiac arrest due to exercising in sweat suits and failed to be rescued.

Does exercising on an empty stomach help burn more fat?

The discussion about exercising on an empty stomach has been going on for a long time. Supporters believe that it is easier to burn fat and lose weight faster. Opponents believe that exercising without food will lead to low blood sugar and is too dangerous. In fact, exercising on an empty stomach is indeed more effective in burning fat, but its triggering conditions are also more stringent.

After eating, not only will the storage of glycogen increase greatly, but the secretion of insulin will also inhibit the decomposition of fat. The effect of exercise in burning fat will naturally be greatly reduced.

This theory has a direct example to prove it. A study divided volunteers into two groups. One group fasted for 7 hours and the other group ate for two hours before letting them exercise for 30 minutes. The results showed that the amount of fat oxidation formed by the former - fasting exercise was about twice as high as that formed by the latter - after eating.

However, don’t be too quick to be tempted, as exercising on an empty stomach is not suitable for everyone.

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Exercising on an empty stomach does not mean that fat is completely consumed. In this process, glycogen consumption is still ongoing. If the blood sugar regulation ability is poor, the old is exhausted and the new can't keep up, it is easy to have hypoglycemia, leading to dizziness. If you really want to try it, it is best to eat something before exercising, but not too much.

If you want to lose weight, you can only eat less

Is it difficult to lose weight through exercise?

An important reason why many people give up on losing weight through exercise is that compared to losing weight by “not eating”, the speed of losing weight through exercise is too slow.

Compared with the posts on various social platforms that say people can lose a pound a day by skipping meals, it seems that exercise is indeed very inexpensive to lose weight. But in fact, these data are just superficial.

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The scale can only show the current weight, but it is difficult to measure the proportion of each component in the human body. Muscle loss, water loss, and fat burning can all lead to weight loss, but only the latter is truly healthy and long-lasting.

Only through exercise can fat be truly consumed. In particular, visceral fat is closely related to people's health. The report of the Japanese Obesity Society pointed out that if the area of ​​visceral fat exceeds 100 square centimeters, the number of complications will increase significantly. The so-called complications actually refer to type 2 diabetes, high blood pressure, etc. caused by obesity, and these symptoms often lead to a series of other diseases.

Therefore, if you want to lose weight, especially in a healthy way, there is only one way: maintain a proper diet and exercise. An expert once asked overweight people to exchange diets with normal-weight people. After a week, the overweight people lost a lot of weight, while the normal-weight people, without exception, all gained weight. In other words, weight loss is just a gift from a healthy body.

Relying on exercise to lose weight actually means letting your body gradually return to a healthy state.

Looking in the mirror of rumors

The core of weight loss is not just to reduce your weight, but to keep your body healthy. When we encounter assertive statements about weight loss on the Internet, we should cultivate critical thinking, not blindly accept them, but analyze them rationally to avoid being swayed by them.

References

[1]Thomas AB Sanders (2016): "The Role of Fats in Human Diet". Pages 1-20 of Functional Dietary Lipids. Woodhead/Elsevier, 332 pages.

[2]Sadava, David E.; Purves, William K.; Hillis, David M.; Orians, Gordon H.; Heller, H. Craig (2011). Life (9th ed.). WH Freeman.

[3]Khalafi M, Symonds ME, Ghasemi F, Rosenkranz SK, Rohani H, Sakhaei MH. The effects of exercise training on postprandial glycemia and insulinemia in adults with overweight or obesity and with cardiometabolic disorders: A systematic review and meta-analysis. Diabetes Res Clin Pract. 2023;201:110741.

[4]Verheggen RJ, Maessen MF, Green DJ, Hermus AR, Hopman MT, Thijssen DH. A systematic review and meta-analysis on the effects of exercise training versus hypocaloric diet: distinct effects on body weight and visceral adipose tissue. Obes Rev. 2016 Aug;17(8):664-90. doi: 10.1111/obr.12406. Epub 2016 May 23. PMID: 27213481.

Planning and production

Author: Li Mi, popular science creator

Review丨Zhang Yu, researcher/PhD, Chinese Center for Disease Control and Prevention, national health science expert

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