- Dr Saurabh Sethi, a gastroenterologist trained at AIIMS, Harvard and Stanford University, explains why some people put on weight despite eating very little, while others seem unaffected, pointing to differences in metabolism, muscle mass, and how the body burns energy.
- What metabolism actually means
- Why some people gain weight even when they eat less
- The role muscle mass plays in burning calories
- What can slow your metabolism over time
- How hormones affect weight gain
- Why some people gain weight while others stay lean
- It’s not laziness, it’s how the body works
Dr Saurabh Sethi, a gastroenterologist trained at AIIMS, Harvard and Stanford University, explains why some people put on weight despite eating very little, while others seem unaffected, pointing to differences in metabolism, muscle mass, and how the body burns energy.
We all know that person. Barely eats, watches every bite, yet keeps gaining weight. And then there’s the other one. Snacks all day. Never gains a kilo. It feels unfair. Confusing. Frustrating too.
But weight gain isn’t only about how much food goes in. It’s also about what the body does with that food. How it uses it. Or sometimes, doesn’t.
What metabolism actually means
This is where metabolism enters the picture. More specifically, Basal Metabolic Rate, or BMR. It’s the energy your body needs just to keep things running. Breathing. Thinking. Digesting. Pumping blood. All the quiet work happening in the background. And this part matters. Everyone’s metabolic engine runs a little differently.
Why some people gain weight even when they eat less
On Wednesday, Dr Saurabh Sethi, MD, MPH, Gastroenterologist trained at AIIMS, Harvard and Stanford University, explained this in an Instagram post. He spoke about why some people gain weight even when they feel they’re barely eating, while others don’t seem affected at all.
According to Dr Sethi, some people are born with a naturally faster BMR. This can be shaped by genetics, thyroid health, hormones, or having more muscle. Their bodies tend to use up more energy even when they’re resting. Others run on a slower baseline, meaning fewer calories are burned through the day, even if food intake is modest.
The role muscle mass plays in burning calories
A lot of this comes down to muscle. Muscle tissue is metabolically active. It needs energy, even when you’re sitting still. Fat doesn’t demand the same. So people with more muscle are quietly burning calories throughout the day. This is why those who move more or train regularly often tolerate higher food intake without seeing the scale climb.
What can slow your metabolism over time
Metabolism isn’t fixed for life. Dr Sethi points out that it can slow down after:
- Crash dieting
- Long-term calorie restriction
- Muscle loss with age
Over time, these changes make the body more efficient at conserving energy. So even when eating habits stay the same, weight can start creeping up.
How hormones affect weight gain
Hormones also play a big role. Dr Sethi explains that conditions such as insulin resistance make it easier for the body to hold on to fat and harder to burn it off. This pattern is often seen in people with fatty liver, PCOS, prediabetes, and diabetes, where weight gain can happen even when food intake feels controlled.
Why some people gain weight while others stay lean
According to Dr Sethi, people who gain weight despite eating little often deal with:
- Slowed metabolism
- Low muscle mass
- Hormonal imbalance
- High cortisol or hidden stress
- Poor sleep
- Post-diet metabolic adaptation
On the other hand, people who seem to “eat anything” and stay lean usually have:
- A higher metabolic rate
- Better insulin sensitivity
- More muscle
- More daily movement
It’s not laziness, it’s how the body works
Dr Sethi makes one thing very clear. “It’s not laziness. It’s physiology.” The aim isn’t just to eat less. It’s to help the body burn more efficiently. Building muscle. Sleeping properly. Managing stress. Moving regularly. Even small, everyday movement adds up more than most people think.
Disclaimer: Tips and suggestions mentioned in the article are for general information purposes only and should not be construed as professional medical advice.
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