Weight Gain: Why It Happens? and How to Control It ?- A Comprehensive Health Guide.

Dr JK Avhad MBBD MD [ Last updated 12.12.2025 ]

Obesity has become one of the most complex and rapidly growing public health challenges worldwide. It is no longer viewed as just excess fat or the result of poor lifestyle choices. Instead, it is now understood as a chronic, relapsing, multifactorial disease influenced by biological, behavioral, environmental, socioeconomic, and even genetic factors. The World Health Organization (WHO) estimates that global obesity rates have nearly tripled since 1975, with more than 1.9 billion adults overweight, of which 650 million are classified as obese (World Health Organization, 2021).

Understanding obesity requires shifting away from the outdated belief that it is solely about willpower or calorie counting. It involves a dynamic interplay among the brain, hormones, metabolism, gut microbiota, food systems, socioeconomic determinants, and modern lifestyle patterns. This detailed analysis explores causes, health risks, and evidence-based management strategies for weight gain and obesity.

Defining Weight Gain and Obesity

Body Mass Index (BMI)

BMI = weight (kg) / height² (m²)

The WHO classification:

Normal weight: 18.5–24.9
Overweight: 25–29.9
Obesity Class I: 30–34.9
Obesity Class II: 35–39.9
Obesity Class III: ≥40

In Asian populations, metabolic risk begins at lower BMI levels, so:

Overweight: ≥23
Obesity: ≥25

Table: WHO Classification of Adult Weight Status

Category	BMI Range (kg/m²)
Normal Weight	18.5 – 24.9
Overweight	25.0 – 29.9
Obesity Class I	30.0 – 34.9
Obesity Class II	35.0 – 39.9
Obesity Class III	≥ 40

How the Body Regulates Weight

The body maintains weight through a dynamic interaction among metabolism, appetite hormones, and the central nervous system. Energy homeostasis is modulated by multiple signaling pathways involving leptin, ghrelin, insulin, peptide YY, and neuropeptide Y (Hall & Kahan, 2018 ).

The set-point theory proposes the brain defends a certain level of body fat, resisting intentional weight loss by slowing metabolic rate and increasing hunger (Rosenbaum & Leibel, 2010).

These adaptive responses make obesity a relapsing condition.

Body fat distribution matters: Not all fat is equal

Visceral fat [ around visceral organs ]: highly inflammatory, strongly associated with metabolic disease.
Subcutaneous fat: less harmful, more of a storage depot.

Waist circumference is an important marker:

Men: >102 cm (90 cm for Asian men)
Women: >88 cm (80 cm for Asian women)

Obesity a Chronic Disease

Obesity involves dysregulation of:

Appetite hormones
Metabolic homeostasis
Adipose tissue inflammation
Brain reward pathways
Insulin signaling

Because of these deep biological changes, sustainable management requires long-term strategies, not quick therapies.

Etiology of Weight Gain and Obesity

Obesity develops through a combination of biological, behavioral, environmental, and socioeconomic contributing factors.

Biological Causes

Genetic factors

Genetics contribute 40–70% to an individual’s susceptibility to obesity.

More than 100 genes are associated with body weight regulation.
Variants like FTO, MC4R, and LEP influence appetite, satiety, and fat storage.
Children of obese parents have a 3-4 times higher risk of obesity even when raised in different environments.

Epigenetics

Environmental exposures, maternal nutrition, stress, and early-life trauma can genetically program metabolism.
Examples:

Maternal malnutrition → thrifty metabolism → obesity in adult life
Chronic stress → DNA methylation changes the way fat storage genes express

Hormonal Dysregulation

Hormones controlling appetite and metabolism can malfunction:

Leptin resistance: brain does not sense fullness
Insulin resistance : increased fat storage
Ghrelin called hunger hormone, increases with sleep deprivation and stress
Cortisol is a stress hormone, promotes visceral fat

Age- and Sex-Related Factors

Aging leads to sarcopenia, reduced basal metabolic rate, and increased fat mass.

Women often experience weight gain during pregnancy and menopause due to hormonal shifts (Lovejoy et al., 2008).

Set-Point Theory

The brain maintains a set point for body fat. When a person diets:

Metabolism slows
Hunger increases
Body tries to regain weight

This explains why most dieters regain weight without targeted strategies.

Behavioral and Lifestyle Causes

Excess Calorie Intake & Ultra-Processed Foods (UPFs)

Modern food systems promote overeating.
UPFs:

Are hyper-palatable
High in sugar, refined carbohydrates, trans-fats, unhealthy fats
Low in fiber and protein
Stimulate dopamine reward pathways
Delay satiety signals

People consuming high-UPF diets often eat 300–500 extra calories/day without realizing it. (Hall et al., 2019).

Sedentary Lifestyle

Physical inactivity reduces calorie burn and weakens metabolic flexibility.
Sedentary behaviors (Owen et al., 2010)

Desk jobs
Excess screen time
Low daily step count
Lack of resistance training
Work from home culture
IT jobs

Poor Sleep

Less than 6 hours of sleep:

Increases ghrelin
Decreases leptin
Elevates cortisol
Slows metabolism
Increases cravings for sugar and high-fat foods (Taheri et al., 2004)

Stress and Emotional Eating

Chronic stress triggers:

Cortisol elevation → visceral fat
Reward-based overeating
Compulsive or binge eating tendencies (Adam & Epel, 2007).

Psychological and Behavioral Factors

Emotional regulation difficulties, binge-eating behavior, reward-driven overeating, and disrupted eating patterns contribute significantly to weight gain (Volkow et al., 2017).

The dopamine reward pathway plays a central role in motivating consumption of high-calorie foods.

Environmental Causes

Food Environment

We live in an obesity favourable environment:

Fast food everywhere
Low availability of healthy foods in urban areas
High marketing of junk foods
Aggressive advertising of fast foods

Urbanization

Modern urban life is associated with:

Less physical activity
Car-dependent lifestyle
Limited access to parks/green spaces (Swinburn et al., 2011).

Chemical Exposure

Certain environmental or industrial chemicals disrupt metabolism:

BPA (plastics)
Phthalates
Pesticides
Flame retardants

These interfere with hormones and encourage fat accumulation.

Socioeconomic Determinants

Income Level

Lower-income groups face:

Cheaper unhealthy foods
Limited healthcare access
Higher stress
Food insecurity –binge cycles (Drewnowski & Specter, 2004).

Education Level

Lower awareness leads to:

Poor dietary choices
Less understanding of nutrition labels

Social and Cultural Factors

Traditional high-calorie diets
Overeating as hospitality in some cultures
Lack of emphasis on preventive health

Medical Causes

Hypothyroidism

Low thyroid levels decrease metabolism.

PCOS

Insulin resistance à hormonal imbalanceà weight gain in women.

Cushing’s Syndrome

Excess cortisolà central obesity.

Medications

Some drugs lead to weight gain:

Corticosteroids
Antidepressants (SSRIs, TCAs)
Antipsychotics
Insulin
Beta blockers

Health Risks Associated with Obesity

Obesity is not merely a cosmetic issue, it significantly increases morbidity and mortality.

Metabolic and Endocrine Complications

Type 2 Diabetes

Obesity is the strongest risk factor.
Mechanisms:

Insulin resistance
Chronic inflammation
Ectopic fat in liver and muscle

Metabolic Syndrome

A combination of:

High blood pressure
High glucose
Elevated triglycerides
Low HDL
Increased abdominal fat

Fatty Liver Disease – Nonalcoholic fatty liver disease [ NAFLD ]—Nonalcoholic Steatohepatitis [ NASH ]

Obesity → liver fat accumulation → fibrosis → risk of liver cirrhosis (Hruby & Hu, 2015 )

Cardiovascular Diseases

Hypertension

Excess fat increases blood volume and vascular resistance.

Coronary Artery Disease

Inflammation and lipid abnormalities increase plaque formation.

Stroke

Heart Failure

Obesity increases cardiac workload and can lead to cardiomyopathy.

Respiratory Problems

Obstructive sleep apnea
Obesity hypoventilation syndrome
Reduced lung capacity

Musculoskeletal Problems

Osteoarthritis (especially knees and hips)
Chronic back pain
Reduced mobility

Reproductive and Hormonal Issues

Women

PCOS
Infertility
Gestational diabetes
Pregnancy complications

Men

Low testosterone
Erectile dysfunction

Gastrointestinal and Other Risks

GERD
Gallstones
Increased risk of some cancers: breast, colon, pancreas, liver, endometrium
Chronic inflammation
Increased infections
Reduced immune function

Psychosocial Impact

Body image issues
Stigma and discrimination
Depression and anxiety
Low self-esteem
Reduced quality of life

Management of Obesity

Obesity management requires a multidimensional, long-term, customized approach. No single intervention works for everyone.

Diagnosis and Assessment

Clinical assessment includes:

· BMI for general classification

· Waist circumference to evaluate visceral fat

· Body composition analysis

· Laboratory tests (lipid profile, fasting glucose, HbA1c, liver function, thyroid function)

BMI alone is insufficient; combining anthropometric and metabolic markers gives a clearer risk profile (NHLBI, 2013).

Lifestyle and Behavioral Interventions [ First Line of management ]

Nutrition

Principles

Focus on sustainable eating, not dieting.
Calorie deficit of 300–500 kcal/day is enough for steady weight loss.
Emphasize whole foods, not ultra-processed foods.

Evidence-Based Dietary Approaches

High-Protein Diets (Westerterp-Plantenga et al., 2009)

Increase satiety
Reduce cravings
Preserve muscle mass

Mediterranean Diet (Estruch et al., 2018)

Rich in healthy fats, fruits, vegetables, whole grains
Improves metabolic health

Low Carbohydrate or Ketogenic Diet

Aids rapid weight loss
Improves insulin sensitivity

Intermittent Fasting

· Improves metabolic flexibility (Patterson & Sears, 2017)

Low-Fat Diets

Useful for some patients
Less effective long-term than balanced diets

What to Minimize

UPFs
Sugary drinks
Refined carbohydrates
Trans-fats
Unhealthy fats

Physical Activity

Aerobic Exercise

150–300 minutes/week
Walking, cycling, swimming

Resistance Training

2–3 times/week
Increases muscle mass
Boosts resting metabolic rate

NEAT (Non-Exercise Activity Thermogenesis) (Levine, 2002)

Small habits accumulate:

Taking stairs
Walking meetings
Standing desks

Behavioral Therapy

· Cognitive Behavioral Therapy (CBT) (Butryn et al., 2011)

· Food journaling

· Mindful eating

· Stress management

Pharmacotherapy

Medications help when lifestyle efforts alone are insufficient.

Indications

BMI ≥30
BMI ≥27 with comorbiditie

Approved Medications

· GLP-1 agonists [ semaglutide, liraglutide ]: highly effective (Wilding et al., 2021)

· Tirzepatide [ dual GIP/GLP-1 agonist ]: strongest evidence so far

· Orlistat

· Phentermine topiramate

· Naltrexone, bupropion

These drugs reduce:

Appetite
Cravings
Food reward behavior

Weight loss ranges from 5% to 20% depending on medication.

Bariatric Surgery

Indications

BMI ≥40
BMI ≥35 with comorbidities

Types

Gastric bypass
Sleeve gastrectomy
Adjustable gastric band

Benefits

Weight loss 20–35%
Diabetes remission (Schauer et al., 2017)

Emerging Therapies

Gut Microbiome Targeting

Probiotics, prebiotics
Fecal microbiota transplantation [ In research stage ]

Gene-Based Precision Medicine

Brown Fat Activation

Cold exposure
Certain drugs under research

Prevention Strategies

At Individual Level

Healthy meals
Physical activity
Good sleep
Stress management

At Community & Policy Levels

Tax on sugary beverages
Urban planning for walkability
Regulating junk food advertising (Swinburn et al., 2019)

Conclusion

Obesity is a complex, multifactorial chronic disease, not simply the result of overeating. It results from intertwined biological, environmental, and social influences that shape behavior and metabolism in powerful ways. The consequences are far-reaching, affecting nearly every organ system and quality of life.

The most effective approach is holistic, long-term, and individualized. Sustainable lifestyle changes remain the cornerstone, but modern obesity care increasingly includes behavioral therapy, evidence-based medications, and, when necessary, bariatric surgery. Understanding the complexities behind obesity helps reduce stigma and encourages comprehensive, compassionate care.

This article is for informational purpose only and does not substitute for professional medical advise. For proper diagnosis and treatment seek the help of your healthcare provider.

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