Why do some people gain weight even when they eat little? Harvard-trained doctor explains

Causes of weight gain: Those who gain weight easily mostly have slower metabolism, low muscle mass, hormonal imbalance, high cortisol, poor sleep, and post-diet metabolic adaptation (Image: Pexels)

• Weight gain depends more on metabolism than food intake
• Higher muscle mass boosts calorie burn even at rest
• Hormonal imbalances can slow metabolism and promote fat storage

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People who gain weight quickly despite “eating little” often complain about those who eat all day long yet don’t put on even a kilo. While it may seem frustrating, the fact of the matter is that weight gain has very little to do with how much you eat and more to do with how your body burns what you eat.

Addressing this in his recent Instagram post, Dr Saurabh Sethi, a Harvard- and AIIMS-trained gastroenterologist, explained that everyone’s body is different. “Your Basal Metabolic Rate (BMR) is the energy your body burns just staying alive, breathing, thinking, digesting, and pumping blood,” he wrote.

Role of metabolism

The gastroenterologist shared that people with faster BMR tend to burn more calories even at rest due to genetics, thyroid function, hormones, or higher muscle mass. This is not the same for those with slower BMR.

Also read | Weight gain: Avoid these unhealthy diet and lifestyle habits to stop unwanted weight gain

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A post shared by Saurabh Sethi MD MPH | Gastroenterologist (@doctor.sethi)

Why muscle mass matters

There’s a reason why muscle mass matters. Dr Sethi said, “People with less muscle burn fewer calories at baseline. This happens after crash diets, long calorie restriction, or muscle loss with age.”

So when you have more muscle, you burn 3 to 5 times more calories than fat even while resting. Hence, those who have higher muscle mass enjoy more food without the worry of gaining weight.

Influence of hormones

Hormones have an impact on your body weight, so imbalances like insulin resistance make it easier to store fat and harder to burn it. This is more so in case of fatty liver, PCOS, pre diabetes, and diabetes.

So those who gain weight easily mostly have slower metabolism, low muscle mass, hormonal imbalance, high cortisol, poor sleep, and post-diet metabolic adaptation. It is different from those who stay thin despite eating anything they want. They mostly have higher metabolic rate, better insulin sensitivity, more daily movement, and more muscle mass.

Dr Sethi concluded that the goal should not be eating less, but working on optimising the body for better gains.

Disclaimer: This article, including health and fitness advice, only provides generic information. Don’t treat it as a substitute for qualified medical opinion. Always consult a specialist for specific health diagnosis.