Adaptive thermogenesis: why does the body resist weight loss?

It is not easy to get rid of extra pounds, and it is even more difficult to maintain the result. After all, many different processes in the human body influence weight change. One of them is adaptive thermogenesis. Researchers have proven that reducing body weight affects energy exchange. Let’s understand why this happens and how the body reacts to weight loss.

Efficient energy expenditure

Thermogenesis is the ability to convert calories into heat. The phenomenon of adaptive thermogenesis is that due to a caloric deficit during weight loss, the body tries to maintain balance and reduces energy expenditure. Although energy expenditure decreases naturally because weight loss, the body still activates defense mechanisms. Calorie consumption falls out of proportion to the lost pounds.

Specialists have studied this phenomenon and have come to unexpected conclusions. Even a year after successful weight loss, the body remains in the mode of reduced energy consumption, which affects the effectiveness of training.

In 1995, a group of scientists from the U.S. led by Rudolf Leibel conducted an experiment. It involved people who lost 10% or more of their starting weight.

Test subjects were divided into groups – each group consisted of three people with the same body weight and gender. One of them maintained weight loss for 5-8 weeks, the second – for more than a year, and the third participant had never lost weight before. Volunteers lived on the territory of the research center and adhered to a liquid diet, allowing to maintain a stable weight.

During the experiment, scientists observed how much energy the subjects spent on different activities during the day, including how many calories they needed to digest food, maintain physical activity and vital functions.

It turned out that the participants’ daily energy expenditures varied. The highest were in subjects who had never struggled with being overweight. Lower – in those who have lost weight. In total, the difference is 428-514 kcal per day.

The fact is that people who exercise are more efficient at expending energy, and they need fewer calories to maintain strength.

Reduced activity outside of the gym

Adaptive thermogenesis is also associated with a reduction in muscle metabolic rate, changes in hormonal background and internal organ mass.

Energy expenditure is also reduced because there is less physical activity in everyday life. Scientists are sure: when losing weight, a person unconsciously reduces extra-training activity.

Basically, the body uses energy for three main processes:

digestion of food – about 8%;

basic metabolism, i.e. breathing, heartbeat, etc. – 50-75%;

physical activity – 17-32%.

The latter, in turn, is divided into exercise and informal activity – unconscious movements, shopping, moving around the house and other daily activities. Roland Weinzer’s research has shown that it is the reduction in informal activity that often leads to weight gain.

You can stay in shape by increasing your exercise at the gym or simply changing your habits. Stop using the elevator – take the stairs instead, take morning walks, get a team together with friends and play volleyball.

Defense against extreme weight loss

In addition to Rudolf Leibel, other scientists have studied adaptive thermogenesis. Some of them have found no change in energy metabolism with weight loss in their experiments.

James Amatruda, a professor at the Keck School of Medicine at the University of Southern California conducted a similar study to calculate energy expenditure. Eighteen women participated in the experiment. However, they were not under constant observation, but led normal lifestyles, which violates the purity of the experiment. In this case, it is not possible to accurately measure the calorie intake and expenditure of the study participants.

Nevertheless, recent studies have proven that metabolic adaptation does exist. Today, it is possible to perform a number of analyses and estimate how energy expenditure will change with weight loss. On average, for those whose weight has decreased by 10% or more, the net difference is 100-150 kcal per day. This is how much the metabolic rate is reduced. Therefore, it is unlikely that adaptive thermogenesis can cause weight gain again if physical activity levels are maintained. On the contrary, this defense mechanism does not allow rapid weight loss, bringing the body to extremes.

So if weight loss is slow, don’t be upset – it’s your body’s way of taking care of your health.