It seems unfair—some people can eat whatever they want without gaining a pound, while others gain weight just by looking at dessert. Is it all genetics, or is there more to the story? Science offers several explanations for why some people stay lean despite their diet.
1. Metabolism Differences
Metabolism plays a key role in how the body processes food. People with a naturally high basal metabolic rate (BMR) burn more calories at rest than those with a slower metabolism.
- Genetics – Some people inherit a faster metabolism, allowing them to burn calories more efficiently.
- Muscle Mass – More muscle means more calories burned, even when not exercising.
2. Non-Exercise Activity Thermogenesis (NEAT)
NEAT refers to the calories burned from daily activities like fidgeting, walking, or even standing. Some people unconsciously move more throughout the day, increasing their calorie expenditure without structured exercise.
- Fidgeting & Restlessness – Studies suggest that small movements can add up to hundreds of extra calories burned daily.
- Active Lifestyles – People who naturally take more steps or stand more often tend to burn more energy.
3. Gut Microbiome Influence
The gut microbiome—the trillions of bacteria living in our digestive system—can affect how efficiently the body extracts calories from food.
- Different Bacteria Types – Some gut bacteria help store more energy, while others promote calorie burning.
- Digestion Efficiency – Some people’s bodies don’t absorb all the calories they consume due to variations in gut bacteria.
4. Hormonal Regulation
Hormones like leptin and ghrelin regulate hunger and metabolism. Those with a natural balance of these hormones may feel full faster and have a lower tendency to overeat.
- Leptin Sensitivity – Some individuals have a strong response to leptin, the hormone that signals fullness.
- Ghrelin Control – Lower ghrelin levels reduce hunger cravings, making it easier to maintain weight.
5. Adaptive Thermogenesis
Some bodies are more efficient at burning excess calories through thermogenesis, the process of heat production.
- Wasted Calories – Some individuals’ bodies generate extra heat after eating, burning off excess energy.
- Cold Adaptation – Exposure to cold temperatures can activate brown fat, which burns calories to produce heat.
Staying slim despite eating a lot isn’t just about genetics—it’s a combination of metabolism, activity levels, gut health, and hormones. While some people have a natural advantage, lifestyle factors like regular movement, muscle mass, and a healthy gut can also influence weight regulation.
