Burn My Calories: Why can’t I lose weight even though I exercise every day?

Many people rely on exercise to lose weight, but find that they can't lose weight even if they exercise a lot. Sometimes this is because they exercise too hard and eat more delicious food, but sometimes it is likely that you overestimate your body's consumption. In fact, the body has its own unique "algorithm" - research shows that more exercise does not consume more calories, and the basal metabolism does not decrease a lot in middle age. Therefore, if you want to lose weight, "control your mouth" may be more important; while "moving your legs" will make us healthier.

Written by Gu Shuchen

"Control your mouth and move your legs" has always been regarded as the golden rule for weight loss. Faced with the temptation of delicious food (calories), you are either persuaded by your companions or comfort yourself: "It's okay, I will exercise more later to consume the extra food!" Because exercise can burn calories. But have you found that the effect of "moving legs" is very mysterious - exercise every day, but the weight remains unchanged? As the saying goes: you have your weight loss plan, and the body has its own unique algorithm.

If we want to lose weight effectively, we need to first understand how the body's energy expenditure works. Total energy expenditure (TEE) is the amount of calories consumed by the body's 37 trillion cells within 24 hours. It is the sum of energy expenditure, including basal energy expenditure (BEE) and physical activity. Basal energy expenditure is the energy needed to maintain life, such as breathing and digestion. Physical activity is the main part of energy expenditure, and the amount of energy expenditure depends on the intensity and duration of physical activity.

Searching for an accurate measure of energy metabolism

Public health experts have long told us that due to changes in modern lifestyles, people do too little exercise in their daily lives, and the energy that is not consumed is converted into fat, which has led to the prevalence of obesity in modern society. Therefore, we should exercise more and eat less to control our weight. However, in fact, the total energy consumption accumulation model has no accurate experimental data support, because we have no way to accurately measure the energy consumption value of the human body.

There are many ways to measure energy metabolism, such as direct calorimetry, indirect calorimetry, heart rate detection, motion sensor method, self-report method, etc. Indirect calorimetry was once widely used. Its principle is to calculate energy consumption by measuring oxygen consumption and carbon dioxide production through some devices. The classic one is the Douglas bag, but this device is cumbersome to use. Other equipment includes the human energy metabolism test cabin, which uses a nearly closed cabin to continuously collect oxygen and carbon dioxide, so as to analyze the changes in the content of the two gases in the cabin and calculate energy consumption. However, the indirect calorimetry method has many limitations in specific use, and the measurement is relatively accurate only when it is quiet or during steady-state exercise.

It was not until the 1980s and 1990s that the doubly labeled water (DLW) method became available, making it possible to accurately measure energy expenditure. The principle of doubly labeled water is to let the test subject drink water containing stable isotopes of deuterium (2H) and heavy oxygen (18O), and then analyze the changes in the peak value of the markers in the urine to understand the body's energy metabolism [1]. This method is simpler and more accurate, and is currently the gold standard for measuring energy metabolism. However, it is precisely because of the emergence of this precise measurement that we have discovered some "heartbreaking" facts.

How much does exercise consume?

Let's look at these mind-blowing calorie-burning facts from two perspectives of total energy expenditure. First, in terms of physical activity, does more exercise really burn more energy?

In 2012, American evolutionary anthropologist Herman Pontzer and his team investigated the energy consumption of the Hadza people on the plains of Tanzania. This is a tribe that lives on hunting and gathering, and has maintained a lifestyle that was ten thousand years ago. Men walk an average of 10 kilometers a day to hunt, while women go around digging for wild vegetables and picking berries. According to our understanding, their daily energy consumption must be much higher than that of office workers. However, the results of the study are very surprising: the Hadza people consume only a little more calories per day than those who sit in the office all day [2].

Another Loyola University Chicago professor, Lara Dugas, and her team conducted an 8-day activity monitoring program for nearly 2,000 residents from the United States, Ghana, Jamaica, South Africa, and the Seychelles, assessing their basic physical activity patterns and tracking their weight over the following years. The results showed that there was no clear correlation between a person’s exercise level and weight; according to the monitoring data, people who did 150 minutes of moderate-intensity exercise per week even gained more weight than those who exercised less [3].

At first, scientists speculated that people have a "compensation psychology" or "reward psychology" after exercise, and they comfort themselves by eating more, and as a result, they eat back the energy consumed during exercise, so their weight does not decrease, and may even increase. However, this does not explain the results of the Hadza people's research, that is, the amount of exercise and calorie consumption are not proportional.

In order to study this exercise paradox, the two scientists began to work together in 2016 to observe more than 300 people in Professor Dugas' previous study in more detail. The results showed that at the beginning, those who exercised consumed 200 calories more per day than those who sat still, but soon, the energy consumption of the exercising population stabilized, which means that those who exercised every day did not consume more calories than those who only exercised a few times a week. In other words, when you reach a certain amount of exercise, your body will actively reduce calorie consumption and stabilize over time, and the relationship between exercise and energy consumption does not seem to be proportional.

To further verify the results, they studied the "world's longest long-distance race" - Race Across the USA, which is a super-devil event from California on the Pacific coast to Washington on the Atlantic coast. Participants basically need to run a marathon every day for 140 days. The study found that in the first week of the race, the overall energy consumption of the participants was high, averaging about 6200Kcal per day, and then gradually stabilized, dropping to about 4900Kcal per day at the end of the race. In other words, the participants' daily exercise volume is the same, but their bodies consume less and less energy. The human body seems to have turned on some kind of "energy saving" method, which keeps the total energy consumption at a relatively stable level by reducing the energy consumed in other parts of the body. This is the total energy consumption constrained model [4].

But why does this happen? The human body's energy consumption mechanism has its own "algorithm", which is much more complicated than we think, but its core logic is to ensure our "survival" rather than lose weight. If exercise consumes too much energy, we will face energy depletion, affecting our health and even endangering our lives, while the human body's "algorithm" essentially prioritizes basic survival.

Figure 1: Additive model and constrained model of total energy consumption [4]

Interestingly, humans are not the only species to maintain similar energy expenditure. Scientists have found that despite the wide range of activity levels among wild primates (monkeys, apes, lemurs, etc.) kept in zoos or laboratories, their energy expenditure is essentially the same[5]. Chinese scientists have also found a similar phenomenon in captive and wild giant pandas[6].

However, scientists are still unclear about the mechanism by which the human body maintains a constant level of energy consumption when the amount of exercise increases. One possible explanation is that when the amount of exercise increases, the body will reduce energy consumption in other areas, such as cell repair. Therefore, obesity is not caused by less exercise but by eating more!

“Middle-aged weight gain”: basal metabolism is not to blame

Of course, some people may say that they don’t eat much, but as they age, their weight still increases uncontrollably, which is the so-called “middle-aged obesity”. This should be another aspect of total energy consumption - there is a problem with basic energy consumption, because with age, the basal metabolism decreases, energy consumption is reduced, and it is naturally easier to gain weight.

But is this really the case? I don't take the blame for "middle-aged weight gain" because of my metabolism. On August 24, 2021, researchers from more than 100 international teams, including the Shenzhen Institutes of Advanced Technology of the Chinese Academy of Sciences, Duke University in the United States, and Kyoto University of Advanced Science in Japan, published a study titled "Daily energy expenditure through the human life course" online in the top academic journal Science. The research team analyzed the average calories consumed in daily life by more than 6,600 people from 29 countries and regions around the world, ranging in age from one-week-old babies to 95 years old.

Studies have found that the total energy consumption of the human body increases in a power law with the increase of "fat-free body mass". Fat-free body mass is the weight of other body components other than fat, of which muscle is the main part. After using mathematical methods to adjust, the researchers eliminated differences such as body shape and used age as a single variable to summarize and analyze the daily energy consumption of the participants. Based on the changes in metabolic levels, a person's life was divided into four stages: 0-1 years old, 1-20 years old, 20-60 years old, and over 60 years old. The results showed that the energy consumption level of newborns is similar to that of adults. From birth to 1 year old, the metabolic level rises rapidly to 150% of that in adulthood. After 1 year old, the metabolism will slowly begin to decline, tend to calm down at the age of 20, and remain stable between 20 and 60 years old. It will only begin to slowly decline again after the age of 60, and the metabolic capacity will drop to 75% of that of adults after the age of 90 [7]. Therefore, metabolism has not started to decline in middle age, and middle-aged fatness may still be due to excessive food intake.

Figure 2: Schematic diagram of energy expenditure changes (A: adjusted daily energy expenditure B: adjusted basal metabolism)

For health, get moving

So how should we lose weight?

In fact, "control your mouth and move your legs" is still the best way. The research results mentioned above all show that compared with exercise, less and more reasonable intake can make you lose weight more easily. But does that mean we don't need to exercise? Of course not.

The Hadza people's physical activity is about three times that of Westerners. Although the total consumption is not much different, their hearts are very good, and they are not found to have diseases such as diabetes. They age very healthily (of course, due to living conditions and medical and health conditions, their average life expectancy is not longer than that of modern people, and may even be shorter). Exercise reduces the body's inflammatory response and reproductive hormone levels. Animal experiments have also shown that increasing daily exercise does not increase energy consumption, but can improve cardiopulmonary function, improve immune system capacity, improve brain function, and so on. Therefore, active exercise can improve our overall health, mobility, and brain function. Many studies have shown that exercise reduces the risk of many chronic diseases such as Alzheimer's disease, and its health-promoting effect far exceeds its ability to regulate weight.

According to the exercise recommendations in the "China Obesity and Prevention and Control Blue Book", you should do at least 150 minutes of moderate-intensity aerobic exercise per week to exercise your cardiopulmonary function, such as jogging, swimming, etc. At the same time, do at least 2 resistance exercises to strengthen your skeletal muscles, such as doing push-ups or lifting dumbbells. Studies have shown that during a 12-week exercise intervention, the combined intervention of resistance exercise and aerobic exercise (5 times a week, 15 minutes of low-intensity resistance exercise + 15 minutes of moderate-intensity aerobic exercise) has the best effect. Professor Pang Ze also proposed a weight loss plan to increase our resting metabolic rate (RMR). The resting metabolic rate is the total calorie ratio consumed by the human body to maintain all body functions when at rest, and this plan also requires strength training to increase the body's muscle content, thereby increasing the resting metabolic rate.

Regarding the issue of middle-aged weight gain that many people are concerned about, there are many possible reasons, such as stress, activity level, illness, changes in lifestyle habits, etc., so don't use a slower metabolism as an excuse. Every time you gain an extra pound of weight, ask yourself: Have you controlled your diet?

References

[1] Wikipedia "Double labeled water" https://en.wikipedia.org/wiki/Doubly_labeled_water

[2] Pontz, H., et al., Hunter-Gatherer Energetics and Human Obesity, PLOS ONE, Vol. 7, No. 7, Article No. e40503.

[3] Luke, A., et al., Energy expenditure in adults living in developing compared with industrialized countries: a meta-analysis of doubly labeled water studies, Am J Clin Nutr. 2011 Feb; 93(2): 427–441.

[4] Pontzer H., et al., Constrained Total Energy Expenditure and Metabolic Adaptation to Physical Activity in Adult Humans, Curr Biol. 2016 Feb 8;26(3):410-7.

[5] Pontzer, H., Energy Expenditure in Humans and Other Primates: A New Synthesis, Annual Review of Anthropology, Vol. 44:169-187

[6] Nie Y, et al., ANIMAL PHYSIOLOGY. Exceptionally low daily energy expenditure in the bamboo-eating giant panda. Science. 2015 Jul 10;349(6244):171-4.

[7] Pontzer, H., et al., Daily energy expenditure through the human life course. Science. 2021 Aug 13;373(6556):808-812.

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