Weight mystery: Why same food affects people differently

Almost all of us are familiar with this phenomenon—some people gain weight despite eating very little, while others eat voraciously throughout the day yet struggle to maintain their weight. This raises the question: why do our bodies react differently to the same food?

Researchers say the reason is not simply the quantity of food consumed; factors involved include metabolic rate, muscle density, hormonal balance and genetic influence.

Basal Metabolic Rate (BMR) differs for each individual. Those with a higher metabolic rate can burn more calories even while at rest. Their bodies absorb energy quickly despite eating more, so weight gain occurs slowly. Conversely, those with lower BMR may gain weight rapidly even with minimal food intake.

Muscles play a vital role not only in energy production but also in burning calories. Muscular individuals can expend calories more quickly. Regular exercise increases both muscle density and strength, helping the body burn excess calories faster. This explains why such people do not gain weight despite eating more.

The human body contains two types of fat—brown fat and white fat. Brown fat helps burn calories and maintain body temperature, while white fat primarily stores calories. Studies have shown that thin people have higher amounts of brown fat, which is why they do not gain weight despite eating more.

The hormone insulin regulates fat storage and energy utilisation. When insulin balance is disrupted, insulin resistance develops, reducing the rate of calorie burning and promoting fat accumulation. As a result, such individuals may gain weight despite eating less.

Genes also determine the risk of being overweight or underweight. Researchers have identified genes such as MC4R, LEP, BSN and NTRK2 as being linked to obesity. Additionally, a gene called 'FTO' increases addiction to high-calorie foods and raises the risk of obesity by nearly 70 per cent when present. The MC4R gene causes the brain to receive satiety signals late, leading people to overeat.

Researchers say that despite genetic or hormonal predispositions, maintaining proper dietary habits and lifestyle discipline can keep weight under control. Healthy food choices, regular exercise and adequate rest help reduce the risk of both weight gain and excessive thinness.

The reasons behind being overweight or underweight are multiple. Metabolic rate, muscle density, fat type, hormones and genes have greater influence than merely the quantity of food consumed. Understanding these factors and making lifestyle changes can help maintain a healthy and balanced body.