Gastroenterologist explains why some gain weight even when they eat less

People who try to eat healthy, either to lose or gain weight, or stay in shape, often face unique challenges depending on what they are their goal is.

An individual who is on the heavier side and wishes to cut may find himself unable to lose weight easily despite eating less. At the same time, the person on the slimmer end of the scale who is trying to bulk often discovers that no matter how much he eats, hardly anything gets added to their frame.

Taking to Instagram on 20 February, Dr Saurabh Sethi, California-based gastroenterologist trained in AIIMS, Harvard, and Stanford Universities, explained the science behind this phenomenon.

How BMR affects body weight

According to Dr Sethi, the loss or gain of weight because of the diet is influenced by an individual's basal metabolic rate, or BMR. He defined it as the energy that is utilised by the body simply to stay alive and perform basic metabolic functions such as breathing, thinking, digesting food, and pumping blood.

"Everyone's engine is different," stated Dr Sethi. Some people are born with a faster BMR, which can be a result of genetics, thyroid function, hormones, or higher muscle mass. They burn more calories. Others who have a slower BMR burn fewer calories at rest.

When it comes to burning calories, muscles have a major role to play. Muscle tissues burn three to five times more calories than fat while the body is at rest. Therefore, more muscles result in higher burn round the clock. Muscles can be developed with regular exercise. People with more muscle can eat more without gaining weight.

"People with less muscle burn fewer calories at baseline," pointed out Dr Sethi. "This happens after crash diets, long-term calorie restriction, or muscle loss with age."

Apart from muscles, hormonal imbalances like insulin resistance make it easier to store fat and harder to burn it. This is common in individuals who have fatty liver, PCOS, prediabetes, and diabetes.

Differences between the two groups

Dr Sethi highlighted the common differences between people who gain weight despite eating less and those who eat more yet stay lean.

People who gain weight "eating little" often have:

• Slowed metabolism

• Low muscle mass

• Hormonal imbalance

• High cortisol / hidden stress

• Poor sleep

• Post-diet metabolic adaptation

Those who "eat anything" but stay lean usually have:

• Higher metabolic rate

• Better insulin sensitivity

• More daily movement

• More muscle mass

"Small daily movement adds up more than people think," shared the gastroenterologist. "The goal isn't to eat less, but to optimise how your body burns through more muscle, stable hormones, better sleep, and consistent movement."