Many people have witnessed it within their families, workplaces or social circles. Two individuals may follow similar diets, lead comparable lifestyles and yet experience very different changes in body weight over time. While eating habits remain an important factor, modern medical research shows that weight gain is shaped by a complex combination of biological, hormonal and lifestyle-related factors that go far beyond the number of calories consumed.
India has been witnessing a steady rise in obesity and overweight cases across various age groups. According to the National Family Health Survey (NFHS-6), nearly one in four Indian adults is now classified as overweight or obese. Excess body weight significantly increases the risk of developing several health conditions, including type 2 diabetes, hypertension, cardiovascular diseases, fatty liver disease, sleep disorders, joint problems and certain types of cancer.
As obesity becomes a growing public health concern, experts say understanding the reasons behind weight gain is crucial for both prevention and effective treatment.
Weight Gain Is More Complex Than Calories Alone
The traditional principle of “calories consumed versus calories burned” continues to hold scientific validity. However, the way each person’s body processes, stores and expends energy can vary significantly.
According to health experts, multiple biological systems influence body weight, meaning that two people eating similar meals may still experience very different outcomes over time.
Everyday Movement Plays a Bigger Role Than Many Realise
One of the lesser-known contributors to weight management is Non-Exercise Activity Thermogenesis (NEAT). This refers to the calories burned through everyday activities such as walking around the house, standing, climbing stairs, changing posture, fidgeting or performing routine household tasks.
Research suggests that some individuals naturally engage in more of these spontaneous movements throughout the day, leading to greater energy expenditure. Others may remain relatively inactive despite following the same exercise routine, making them more likely to store excess calories as body fat.
Hormones Influence Hunger and Fat Storage
Body weight is regulated by a sophisticated network of hormones that control hunger, satiety and energy balance.
Some of the key hormones involved include:
- Leptin, which signals fullness and helps reduce appetite.
- Ghrelin, often referred to as the hunger hormone, which stimulates appetite.
- Insulin, which regulates blood sugar levels and influences fat storage.
- GLP-1, which affects appetite control and slows stomach emptying.
The brain, particularly the hypothalamus, continuously interprets these hormonal signals. Variations in how these hormones function can make some people feel hungry more often, crave food more intensely or experience reduced feelings of fullness after meals.
Over time, these subtle differences can contribute significantly to weight gain.
Resting Metabolism Can Make a Difference
A large portion of the calories burned each day is used simply to keep the body functioning while at rest. This is known as the Resting Metabolic Rate (RMR).
Several factors determine an individual’s metabolic rate, including:
- Muscle mass
- Age
- Gender
- Thyroid function
- Organ composition
- Genetic factors
People with higher muscle mass generally burn more calories throughout the day, even when they are not physically active. Conversely, individuals with a slower metabolism may find it easier to gain weight despite consuming similar amounts of food.
Genetics Also Play a Significant Role
Scientists have identified several genes associated with obesity and weight regulation. These genes can influence appetite, food preferences, fat storage patterns and energy expenditure.
While genetics alone do not determine a person’s weight, they can affect how efficiently the body stores calories and how strongly hunger signals are experienced.
This helps explain why two people following similar diets may see very different long-term results.
Food Quality Matters as Much as Quantity
Not all calories are processed by the body in the same way.
The body expends energy digesting and metabolising food, a process known as diet-induced thermogenesis. Protein-rich foods generally require more energy to digest than fats or refined carbohydrates.
Several dietary factors can influence weight management, including:
- Protein intake
- Fibre consumption
- Level of food processing
- Meal timing
- Sugary beverages
- Hidden fats and oils used during cooking
As a result, two meals containing similar calorie counts may have very different effects on satiety, metabolism and fat storage.
The Growing Importance of Gut Health
Researchers are increasingly studying the role of the gut microbiome — the trillions of microorganisms that live within the digestive system.
Emerging evidence suggests that gut bacteria may influence:
- How efficiently the body extracts energy from food
- Appetite regulation
- Inflammation levels
- Fat storage
Although this field of research is still evolving, scientists believe gut health may play a meaningful role in weight management and metabolic health.
Sleep Deprivation Can Contribute to Obesity
Sleep has emerged as another critical factor influencing body weight.
Insufficient sleep can disrupt hormones responsible for regulating hunger and fullness, increase cravings for high-calorie foods and reduce overall energy expenditure.
Poor sleep has also been linked to insulin resistance, a major risk factor for type 2 diabetes and metabolic disorders.
Adults who consistently fail to get adequate restorative sleep often face greater challenges in maintaining a healthy weight compared to those with healthy sleep habits.
Hidden Lifestyle Factors Often Go Unnoticed
Experts note that many everyday habits can quietly contribute to gradual weight gain over time. These include:
- Frequent snacking
- Weekend overeating
- Alcohol consumption
- Sugary drinks
- Certain medications
- Stress-related eating
- Sedentary jobs and lifestyles
Even a small daily calorie surplus can accumulate over months and years, eventually leading to significant weight gain.
Weight Gain Is the Result of Multiple Interacting Factors
Medical experts emphasise that weight gain is rarely caused by a single factor. Instead, it reflects a complex interaction between genetics, hormones, metabolism, sleep quality, physical activity, dietary choices and lifestyle habits.
Understanding these biological differences can help move conversations about obesity beyond simplistic assumptions and encourage a more informed approach to weight management and overall health.
Disclaimer: The views expressed are those of the author, Dr. Pankaj Aneja, Director, Department of Diabetes and Metabolic Disorders, Max Super Speciality Hospital, Shalimar Bagh, Delhi.