⚖️ Weight loss: a scientific approach to healthy slimming without harming the body

Excess weight affects more than two billion adults worldwide. The weight-loss industry offers hundreds of diets, programmes and "miracle cures", yet only a few people achieve lasting results. The reason is simple: most popular methods are built on strict restrictions that cannot be sustained for long. A scientific approach to weight loss involves understanding physiology, balanced nutrition and the gradual formation of healthy habits.

How metabolism works

Metabolism is the sum of all the chemical reactions in the body that keep it alive. The metabolic rate is determined by several components. Basal metabolism (basal metabolic rate, BMR) is the energy the body uses at rest for breathing, circulation, brain function and maintaining body temperature. It accounts for 60–70% of total energy expenditure and depends on age, sex, height, weight and muscle mass.

The thermic effect of food (TEF) – the energy spent on digesting and absorbing food – accounts for about 10% of daily expenditure. Physical activity (including deliberate exercise and everyday activity such as walking, cleaning and gesturing) takes up 20–30%. Non-exercise activity thermogenesis (NEAT) is often underestimated, but in active people it can amount to as much as 800 kcal a day.

Contrary to popular belief, a "slow metabolism" is rarely the true cause of obesity. Larger people generally have a higher basal metabolic rate. However, on strict diets the body really does reduce its energy expenditure – an adaptive mechanism known as metabolic adaptation.

Energy balance and calorie deficit

The fundamental principle of weight loss is creating a negative energy balance: burning more calories than you consume. When the body receives less energy than it needs, it starts drawing on its reserves – above all, fat. The optimal deficit is 300–500 kcal a day, which allows you to lose 0.5–1 kg a week without putting the body under significant stress.

A more aggressive deficit (over 1,000 kcal) leads to rapid weight loss, but mainly through water and muscle mass rather than fat. In addition, sharply cutting calories slows metabolism, intensifies hunger and increases the likelihood of relapses. This is exactly why extreme diets give only temporary results: once they end, the lost kilograms come back, often with "extra".

Body mass index and body composition

Body mass index (BMI) – weight in kilograms divided by height in metres squared – is used for a rough assessment. A BMI of 18.5 to 24.9 is considered normal, 25–29.9 overweight, and 30 or above obese. However, BMI does not take into account the ratio of muscle to fat: a muscular athlete may have an "overweight" BMI with a low body fat percentage.

More informative measures are waist circumference (the risk of metabolic complications rises with a waist of more than 94 cm in men and 80 cm in women), waist-to-hip ratio and body fat percentage. A healthy body fat percentage is 10–20% for men and 20–30% for women. The goal of weight loss is not simply a lower number on the scales, but a reduction specifically in fat mass while preserving muscle.

Why diets fail

Studies show that up to 80% of people who lose weight on a diet regain it within 1–5 years. There are several reasons:

• Excessive restrictions – completely cutting out entire food groups (carbohydrates, fats) is not only physiologically unjustified but also psychologically unbearable
• Metabolic adaptation – during a prolonged calorie deficit, the body reduces its energy expenditure and intensifies hunger
• Loss of muscle mass – without strength training and sufficient protein, muscle is lost during weight loss, which slows metabolism further
• Lack of habits – the diet is seen as a temporary phase, after which the person returns to their old way of eating
• Emotional eating – restrictions create psychological tension, which is relieved by "eating away" stress

Principles of balanced nutrition

Sustainable weight loss is built not on prohibitions but on developing a healthy diet that can be followed for life.

Proteins

Protein is the key macronutrient for weight loss. It provides a lasting feeling of fullness, preserves muscle mass and has the highest thermic effect (up to 30% of the protein's own calories are spent digesting it). The recommended intake during weight loss is 1.6–2.2 g per kilogram of body weight. Sources: lean meat, fish, eggs, cottage cheese, legumes, tofu.

Fats

Healthy fats are essential for absorbing vitamins, producing hormones and supporting brain function. They must not be eliminated. Preference should be given to unsaturated fats: olive oil, nuts, avocado, oily fish (salmon, mackerel, sardines). Limit trans fats (margarine, industrially produced baked goods) and excessive intake of saturated fats. Fats should make up 25–35% of daily calories.

Carbohydrates

Carbohydrates are the main source of energy. The problem is not carbohydrates as such, but their quality. Complex carbohydrates (wholegrain bread, oatmeal, buckwheat, brown rice, vegetables) contain fibre, are digested slowly and provide a steady level of energy. Simple carbohydrates (sugar, white bread, sweets, juices) cause sharp rises and falls in glucose, intensifying hunger. Carbohydrates should make up 40–50% of the diet, with an emphasis on complex ones.

Fibre and water

Fibre (25–35 g a day) slows digestion, creates volume in the stomach and prolongs fullness. Vegetables, fruit, legumes and whole grains are the best sources. Drinking enough water (30–35 ml per kg of body weight) supports metabolism; a glass of water before a meal reduces calorie intake by 75–90 kcal per meal.

Myths about meal frequency

The popular claim "eat 5–6 times a day to speed up your metabolism" is not supported by science. The total thermic effect of food depends on the daily calorie intake, not on the number of meals. Some people are more comfortable with three substantial meals, others with five small ones. What matters is the overall calorie balance and a consistent routine. Intermittent fasting (16/8, 5:2) can help control calorie intake, but it has no magical effect on metabolism.

Physical activity for weight loss

Exercise is a powerful weight-loss tool, but its role is often overestimated. A workout burns fewer calories than it seems: an hour of running burns about 500 kcal, the equivalent of a single burger. The main value of exercise during weight loss is preserving muscle mass, improving insulin sensitivity and overall health.

• Aerobic exercise (walking, running, swimming, cycling) – effective for burning calories and training the cardiovascular system
• Strength training – critically important for preserving and building muscle mass; muscle increases basal metabolism
• High-intensity interval training (HIIT) – short bursts of intense exercise with rest periods; saves time and creates an "afterburn effect" – increased calorie burning after the workout

The optimal strategy is a combination of all three types of exercise, starting at a level that is comfortable for your current fitness and increasing gradually.

Sleep, stress and hormones

Lack of sleep (less than 7 hours) raises levels of ghrelin (the hunger hormone) and lowers leptin (the satiety hormone), leading to an increase in appetite of 300–400 kcal a day. Chronic stress increases the production of cortisol, which promotes the accumulation of visceral fat and cravings for sweet and fatty food.

Hormonal disorders – hypothyroidism, Cushing's syndrome, polycystic ovary syndrome, low testosterone – can make weight loss harder. If there are persistently no results despite proper nutrition and exercise, it is worth seeing an endocrinologist.

Plateaus and how to overcome them

After 2–3 months of weight loss, the weight often "stalls". This is a normal adaptation of the body: with a lower body weight, energy expenditure decreases and the previous calorie deficit stops working. Strategies for breaking through a plateau:

• Recalculate your calorie intake based on your new weight
• Increase everyday activity (walk more, take the stairs)
• Add or step up strength training
• Do a "refeed" – 1–2 days of eating at maintenance level – to normalise hormones
• Make sure your calorie counting is accurate (hidden calories in sauces, oil, drinks)

Maintaining weight after weight loss

Maintaining the result is the hardest stage. The National Weight Control Registry (USA) studies people who have successfully maintained a loss of 13+ kg for more than a year. Their common traits: 78% eat breakfast every day, 75% weigh themselves regularly, 90% do about an hour of physical activity a day, and 62% watch less than 10 hours of television a week.

After reaching the target weight, calorie intake is gradually increased to maintenance level. The habits formed during weight loss remain for life. Regular weighing (1–2 times a week) helps track trends and adjust the diet in time.

Emotional eating and dangerous diets

Emotional eating – eating not out of hunger but to relieve stress, boredom, anxiety or sadness – is one of the main causes of weight gain. Working with a psychologist, keeping a food diary and mindful eating help break the "emotion – food" cycle.

Extreme diets (less than 800 kcal a day, mono-diets, detoxes, fasting without medical supervision) are dangerous: vitamin and trace element deficiencies, loss of muscle mass, menstrual cycle disorders, gallstones, eating disorders. Any significant changes to your diet should be discussed with a doctor or dietitian.

Healthy weight loss is not a sprint but a marathon. A realistic goal is to lose 0.5–1 kg a week, which adds up to 12–24 kg over six months. A combination of a moderate calorie deficit, sufficient protein, regular exercise, adequate sleep and stress management produces lasting results without harming your health. The key is patience and consistency.