- Weight gain varies due to biological processes beyond calorie intake and expenditure
- Non exercise activity thermogenesis (NEAT) affects daily calorie burning significantly
- Hormones like leptin, ghrelin, and insulin regulate hunger and fat storage differently
It is a common observation within families, workplaces and social circles. Two people may appear to eat similar meals, share comparable lifestyles and experience very different changes in body weight over time. While food intake remains an important factor, modern research has shown that weight gain is influenced by several biological processes that extend beyond what is visible on the plate.
India is witnessing a steady rise in overweight and obesity rates across age groups. According to the National Family Health Survey 6, nearly one in four Indian adults is either overweight or obese. Excess weight is associated with a higher risk of type 2 diabetes, hypertension, heart disease, fatty liver disease, sleep disorders, certain cancers and joint problems. Understanding why weight gain occurs differently in different individuals is therefore important from both a preventive and clinical perspective.
The traditional concept of calories consumed versus calories burned remains scientifically valid. However, the way the human body processes, stores and expends energy can vary considerably from person to person.
Differences in everyday movement
A major contributor to weight regulation is non exercise activity thermogenesis, commonly known as NEAT. This includes activities such as standing, walking around the house or office, changing posture, climbing stairs, fidgeting and other forms of spontaneous movement throughout the day.
Research has shown that some individuals naturally engage in higher levels of these unconscious activities, leading to greater energy expenditure. Others may remain relatively sedentary despite participating in the same planned exercise routine, resulting in a greater tendency to store excess calories as body fat.
The Role of Hormones
Body weight is closely regulated by a network of hormones that influence hunger, fullness and energy balance.
Key hormones include:
- Leptin, which signals satiety and helps regulate appetite
- Ghrelin, which stimulates hunger
- Insulin, which influences glucose metabolism and fat storage
- GLP 1, which affects appetite control and gastric emptying
The brain, particularly the hypothalamus, continuously receives and interprets these signals. Variations in hormonal responses can make some individuals feel hungry sooner, crave food more frequently or experience reduced feelings of fullness after meals. Over time, even small differences in appetite regulation can contribute to gradual weight gain.
Resting metabolism matters
A significant proportion of daily calorie expenditure occurs while the body is at rest. This is known as the resting metabolic rate.
Several factors influence resting metabolism:
- Muscle mass
- Age
- Sex
- Thyroid function
- Organ size and composition
- Genetic factors
Individuals with greater lean muscle mass generally burn more calories throughout the day, even when not physically active. In contrast, a relatively lower metabolic rate may predispose certain individuals to gain weight more easily despite similar food intake.
The Influence of Genetics
Genetics can affect appetite regulation, food preferences, energy expenditure and fat storage patterns. Scientific studies have identified several genes linked to obesity risk.
Genetic predisposition does not guarantee weight gain, nor does it make weight management impossible. However, it may influence how efficiently the body stores energy and how strongly hunger signals are experienced.
This helps explain why two individuals consuming similar diets may have different long term weight outcomes.
- Food quality is as important as quantity
- Meals that appear similar may not have identical metabolic effects.
The body uses energy to digest, absorb and process food, a phenomenon known as diet induced thermogenesis. Protein rich foods generally require more energy to metabolise than fats or refined carbohydrates.
Several dietary factors can influence weight regulation:
- Protein content
- Fibre intake
- Degree of food processing
- Meal timing
- Sugar sweetened beverages
- Hidden cooking fats and oils
As a result, two meals with comparable calorie counts may affect satiety, metabolism and fat storage differently.
The Emerging Role of Gut Health
Scientists are increasingly studying the gut microbiome, the trillions of microorganisms that reside within the digestive tract.
Evidence suggests that certain microbial patterns may influence:
- Energy extraction from food
- Appetite regulation
- Inflammation
- Fat storage
Although research in this area continues to evolve, growing data indicates that gut health may play a role in determining how efficiently calories are utilised by the body.
Also Read: 30.7% Of Women In India Are Obese Or Overweight, Reveals NFHS-6; Key Contributing Factors Explained
Sleep and Weight Gain
Poor sleep has emerged as an important contributor to obesity and metabolic disorders.
Insufficient sleep can disrupt hormones involved in hunger regulation, increase cravings for calorie dense foods and reduce energy expenditure during the day. Sleep deprivation has also been associated with insulin resistance and a higher risk of developing type 2 diabetes.
Adults who consistently obtain inadequate sleep often face greater challenges in maintaining a healthy weight compared with those who achieve adequate restorative sleep.
Hidden contributors are often overlooked, many factors that influence weight gain may not be immediately apparent.
These include:
- Frequent snacking
- Weekend overeating
- Alcohol consumption
- Sugary beverages
- Certain medications
- Stress related eating
- Sedentary occupations
Even small daily calorie surpluses accumulated over months or years can result in substantial weight gain.
Weight gain is rarely explained by a single factor. It reflects a complex interaction between biology, behaviour, metabolism, sleep, hormones, genetics and lifestyle patterns. Recognising these differences can help move discussions about obesity away from oversimplified assumptions and towards a more informed understanding of how the human body regulates weight.
(By Dr. Pankaj Aneja, Director, Department of Diabetes and Metabolic Disorders, Max Super Speciality Hospital, Shalimar Bagh, Delhi)
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