Why People Gain Weight

Gaining or losing weight is a purely mathematical matter, except for the case of the presence of certain diseases. In this article, discover why people gain weight.
Why People Gain Weight

Last update: 18 January, 2021

People gain weight simply when they eat more calories than they’re capable of burning. Despite this simple equation, both variables can be modified by different factors.

Hormonal mechanisms may reduce energy expenditure or bad habits can increase caloric intake. In this formula, any small imbalance could lead to weight gain or weight loss.

Below, we’ll explain this in more detail.

Why do people gain weight?

Energy expenditure

This is a factor that can be modified. The simple fact of being alive makes us expend energy. This is known as basal energy expenditure. Any physical activity you do increases your daily energy expenditure.

Physical activity has two functions. On one hand, it involves energy expenditure as such. On the other hand, it increases muscle tone and volume, which translates into increased resting energy expenditure. To maximize this effect, strength training should be prioritized over aerobic training, which could even make you lose muscle mass.

Therefore, according to an article published in the journal Metabolism, regular exercise is an excellent way to manage your weight. It can help both prevent and fight obesity.

Sedentary people gain weight more easily, since they usually need to consume less food than their appetite, which leads to overeating.

Therefore, a possible answer to the question of why people gain weight is because they don’t exercise.

An obese woman with her doctor.

Why do people gain weight?

Caloric intake

This is the other modifiable variable in the weight gain equation. You need to try to adapt the foods you eat to your activity levels. Thus, people who do physical activity need more energy than sedentary people to maintain their weight.

Normally, appetite tends to adapt to energy needs, especially in individuals with ecto and mesomorphic morphotypes. However, some people are unable to regulate their appetite, either due to hormonal imbalances (thyroid hormones and ghrelin) or due to calorie underestimation.

Many people believe they consume fewer calories than they actually do, which translates into weight gain. This would be another possible answer to the question of why people gain weight.

Excessive consumption of oil, bread, or processed products can be harmful. Likewise, sauces are products that also increase a meal’s calorie density. A study published in the journal Obesity also mentioned alcohol.

Medical conditions associated with weight gain

However, some people can gain weight even if they eat healthily. For example, this is the case of those who suffer from hypothyroidism. These people suffer from a deficit in the production of a hormone that regulates energy expenditure. Therefore, their needs are diminished, and the amount of food they need is much less than an individual who doesn’t suffer from this condition.

On the other hand, some people suffer from ghrelin production alterations. This hormone controls appetite and is mediated by a series of receptors. When one of these receptors fails to work, it can produce an excessive production of this hormone, even when the energy demands are met. Therefore, the consequence will be weight gain.

All of these situations often require pharmacological treatment. In fact, drugs regulate hormonal systems and simplify nutritional management.

A woman who wants to lose weight.

Medical conditions associated with weight loss

Apart from the diseases that throw the equation out of balance and lead to weight gain, others cause the opposite effect. A clear example is hyperthyroidism or cancer, conditions that increase resting energy expenditure, and nutrient requirements.

Thus, people who suffer from these conditions must consume more calories. If they don’t, they may suffer from weight loss that can make it difficult to control the disease.

The role of gut microbiota

However, in recent years, experts introduced a third variable into this equation, which is living organisms in the gut. This is because gut microbiota could have a key impact on nutrient absorption and weight gain.

Thus, probiotic supplementation could represent a turning point in weight loss strategies. However, experts are still studying this and have yet to draw clear conclusions.

People gain weight due to an energy imbalance

Gaining or losing weight is a purely mathematical matter, except due to certain diseases. If you eat more calories than you need or can expend, you’ll gain weight. Otherwise, you’ll lose weight.

For this reason, nutrition education is important, as it allows you to know how many calories you’re consuming. This will prevent both calorie underestimation and overestimation of the foods you eat and will facilitate weight control and the prevention of complex diseases.

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  • Petridou A., Siopi A., Mougios V., Exercise in the maganement of obesity. Metabolism, 2019. 92: 163-169.
  • Chao AM., Wadden TA., Tronieri JS., Berkowitz RI., Alcohol intake and weight loss during intensive lifestyle intervention for adults with overweight or obesity and diabetes. Obesity, 2019. 27 (1): 30-40.