Scientists have a new explanation for this "super confusing" phenomenon in the weight loss world →

For people who want to lose weight, the most frustrating thing is to sweat for 2 hours in the gym and then weigh 2 kilograms when you get home!

This is not an isolated case. A large number of studies have shown that the weight loss effect of exercise is often lower than generally expected. Why is this the case? In fact, it is related to our daily consumption metabolism. Our daily consumption metabolism is divided into four parts: basal metabolism, non-exercise consumption, exercise consumption and food thermal effect. To achieve weight loss, what we have to do is to ensure that the total daily calorie consumption is greater than the total daily calorie intake .

Among them, basal metabolism refers to the energy consumption required to maintain the most basic life activities of the human body, such as body temperature, breathing, heartbeat, blood circulation, etc. The thermal effect of food is the energy consumption required for the digestion and absorption of nutrients after eating. The part of these two energy consumption methods that we can control is quite limited, so if we want to lose weight, we mainly start with exercise consumption and non-exercise consumption. Exercise consumption is to consume calories through fitness, running, swimming, etc. As for non-exercise consumption, many people ignore its importance.

Non-Exercise Activity Thermogenesis (NEAT) refers to the energy consumed in our activities other than sleeping, eating and exercising. These activities include but are not limited to walking, doing housework, going to work, typing, sitting, and they are called non-exercise physical activity (NEPA). The energy consumption from non-exercise physical activity is the most variable component of total energy consumption. Studies have shown that non-exercise physical activity and the non-exercise consumption it produces are closely related to fat accumulation and obesity risk.

Previous studies have shown that the effect of exercise on weight loss is often lower than expected, probably because the increased energy expenditure caused by exercise will lead to increased energy intake or reduced energy expenditure in non-exercise physical activities. Simply put, after exercise, we may eat more and do less non-exercise physical activities such as walking, doing housework, going to work, typing, sitting, etc., resulting in increased energy intake, which will partially offset the contribution of exercise consumption to total calorie consumption, resulting in unsatisfactory weight loss results, or even a rebound effect.

But how does exercise affect subsequent non-exercise physical activity and weight? There has been no clear conclusion. In June 2024, Daisuke Funabashi and other researchers from the University of Tsukuba in Japan published a research paper titled Acute Vigorous Exercise Decreases Subsequent Non-Exercise Physical Activity and Body Temperature Linked to Weight Gain in the journal Medicine & Science In Sports & Exercise. The study showed that intense exercise can disrupt the circadian rhythm of corticosterone, leading to reduced non-exercise physical activity, decreased body temperature and weight gain after exercise.

In this study, the researchers divided the mice into a rest group, a moderate-intensity exercise group, and a high-intensity exercise (vigorous exercise) group. That is, the mice's non-exercise physical activity, core body temperature, and corticosterone levels were measured at different exercise intensities.

Figure 1 Schematic overview of the experiment. Figure A is a schematic diagram of the experimental process. The exercise group performed 30 minutes of treadmill training. The NEPA and body temperature were monitored two days before and after exercise and three days after exercise by implanting an activity monitor in the abdominal cavity. Plasma corticosterone levels were measured 6 hours and 24 hours after exercise. Figure B shows that the mice were placed in home cages.

First, the researchers explored the changes in non-exercise physical activity and body temperature after exercise. The results showed that compared with the rest group and the moderate-intensity exercise group, the mice in the vigorous exercise group had significantly less non-exercise physical activity after exercise, and their body temperature also decreased. These results indicate that vigorous exercise can cause a decrease in non-exercise physical activity and a decrease in body temperature after exercise; the decrease in body temperature is related to the decrease in non-exercise physical activity, suggesting that the heat production process is disturbed.

Figure 2: Vigorous exercise reduces subsequent non-exercise physical activity

Figure 3 Intense exercise increases body weight and lowers body temperature

The researchers also investigated whether non-exercise physical activity levels and body temperature were associated with changes in weight after exercise. The results showed that the decrease in body temperature during exercise was associated with weight gain in the mice in the strenuous exercise group, that is, the lower the body temperature, the more weight they gained, but the food intake after exercise was similar in each group. These results suggest that when food intake remains unchanged, strenuous exercise may cause a drop in body temperature by reducing heat production, leading to weight gain after exercise.

Finally, to explore the mechanism of reduced non-exercise physical activity after exercise, the researchers analyzed the relationship between non-exercise physical activity, body temperature, body weight, and corticosterone levels. The results showed that plasma corticosterone levels before awakening were associated with less changes in non-exercise physical activity after exercise, that is, when corticosterone levels before awakening decreased, non-exercise physical activity after exercise also decreased.

Figure 4 Plasma corticosterone levels were associated with changes in non-exercise physical activity after exercise in all exercise groups

Therefore, the researchers speculated that the reduction in non-exercise physical activity is related to the circadian rhythm disturbance of plasma corticosterone levels caused by strenuous exercise. Corticosterone is a hormone secreted by the adrenal cortex. Its concentration is higher during the day and lower at night, showing obvious circadian rhythm changes. The circadian rhythm of corticosterone can regulate the body's metabolism, immunity and stress response, and help adapt to different environments and living conditions. However, strenuous exercise may break this rhythm, ultimately leading to a reduction in non-exercise physical activity after exercise. The researchers pointed out that in the future, it is still necessary to further explore the potential mechanisms related to corticosterone in order to better understand the phenomenon of reduced non-exercise physical activity after strenuous exercise.

This study showed that non-exercise physical activity decreased only after vigorous exercise, not moderate-intensity exercise. This suggests that the reduction in non-exercise physical activity after exercise was caused by vigorous exercise. These results suggest that if we want to promote health by participating in sports, we should choose sports of different intensities according to individual circumstances.

For example, a person who wants to lose weight can choose moderate intensity rather than vigorous exercise, and can spend 2 hours a day exercising. Excluding 8 hours of sleep, the remaining 12 hours can be used for more non-exercise physical activities. For example, people who sit for a long time can get up and move around every once in a while, and do more housework, such as sweeping and mopping the floor. A person who wants to gain weight may choose vigorous exercise instead of low-to-moderate intensity exercise, and reduce non-exercise physical activities after exercise and increase nutrient intake.

References:

[1] Funabashi, Daisuke et al. “Acute Vigorous Exercise Decreases Subsequent Non-Exercise Physical Activity and Body Temperature Linked to Weight Gain.” Medicine and science in sports and exercise, 10.1249/MSS.0000000000003487. 6 Jun. 2024, doi:10.1249/MSS.0000000000003487