Why Do We Gain Body Fat: Explained

why do we gain weight

The never-ending quest for a truly effective weight loss program inadvertently leads us to the question as to why we gain body fat in the first place. There are a variety of factors that can lead us to gain more body fat at a much faster rate than normal. Science reveals, however, that our behavior has a great role to play in our gaining of body fat.

The Role of Behavior on Weight Gain

Commitment is a fundamental requirement for any weight loss program to really be effective. Any health and fitness guru will tell you that adhering to your weight loss goals is the key to effective weight management. Even manufacturers of diet and weight loss supplements will tell you to follow a very strict regimen regarding the intake of such supplements. They will ask you to take it with a low calorie diet or even in conjunction with exercise.

The fact is that these are rules or guidelines set by others that we have to comply with if we want to achieve weight loss. The success of our weight loss efforts is thus, dependent on how well we are able to comply with these rules or guidelines. If we are able to comply with them to the letter, then we’ll be successful. If not, then we fail.

Don’t believe us? Just look at dieters and weight loss fanatics who are very successful at minimizing their intake of calorie-rich foods as well as getting regular exercises. Now compare them with those who go on a diet now and then binge a few months later. You’ll see that the former will have body weights that are a lot closer to their ideal while the latter will have weight issues.

This is why, as much as we hate to admit it, gaining body fat and weight has a lot to do with our own mindset. And this is what dictates our behavior whether we want to achieve weight loss or not.

The Physiology of Gaining Body Fat

Now that we understand the role of behavior in gaining body fat, let us try to understand the physiology behind it.

  • Calories and Too Much of It 

The food that we eat contains energy which is needed by the body to perform a variety of physiologic processes. Carbohydrates supply the body with readily usable forms of energy. Anything that is not used is converted into glycogen and fat. The converted fat from carbohydrates joins the fat from the diet to be stored in fat depots. In instances where the body requires energy, these stored fat molecules are mobilized. Technically, the more calories we consume that are not used by the body, the greater are the number of fat conversions. This leads to the fat gain.

Technically, if you want to lose fat, you can either reduce the amount of calories you put in or you increase the amount of calories that you burn. The logic is quite simple, actually. Since calorie excess results in fat gain, then calorie deficit should induce fat loss. Unfortunately, this is not as easy as it sounds. You cannot really sustain eating less and moving more for a long period of time.

  • Leptin and the Fat Thermostat in the Brain 

Science has already uncovered one particular neuroendocrine mechanism that may affect how fat is stored in the body. In the brain is a system that helps regulate the amount of fat in the body. Studies reveal that a fat thermostat, possibly located in the hypothalamus, is constantly monitoring the levels of leptin in the body in an effort to stabilize body fat. Leptin is synthesized and secreted by fat tissues themselves and is a direct reflection of fat mass. If there’s a decrease in body fat, leptin levels also decrease. This stimulates the hunger center in the brain which leads to a decrease in energy expenditure in an effort to conserve energy. This continues until fat tissues are restored in their normal levels.

Unfortunately, individuals who have excess body fat have their fat thermostat set at a much higher level. When these individuals try to lose weight by reducing the amount of fat, the brain will tend to fight back by increasing the sensation of hunger while also decreasing energy expenditure. This occurs unconsciously so it is particularly difficult for obese people to really fight the urge to eat and move less.

  • Satiety and the Regulation of Meal Size 

Since the hungrier we get, the more calories we tend to eat, then it’s fitting that we also look at the signal that tells us when to stop eating. Satiety is that sensation of fullness and is sent to the brain by the neurotransmitter serotonin which is very abundant in the gastrointestinal tract. When we are hungry and we eat, food slowly distends the walls of the GI tract. This stimulates the serotonin-secreting cells in the GI tract which eventually send signals to the brain. As the meal progresses, the strength of these signals gets stronger and stronger until such time that the sensation of hunger is already replaced by satiety. So, we stop eating. Unfortunately, satiety only lasts as long as there are serotonin signals being sent to the brain. If this decreases, then hunger is perceived once again. And the cycle restarts.

It should be understood that the fat thermostat has a profound effect on satiety. Remember, if we lose fat, the more that we feel hungry; hence, more calories to consume with every meal. If we go on a calorie-restricted diet, there is a greater chance that we’ll grow even hungrier.


Connecting the dots, it’s easy to understand why we gain fat despite out best efforts to lose weight. Since calories are at the crux of the issue, reducing calorie intake or increasing its expenditure is not really a walk in the park. It is essential to look at the body’s fat thermostat as this dictates how fat is used and stored and has a profound effect on hunger. The hungrier we get, the more calories we consume, and the more fat we gain.

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