Nearly every successful weight loss plan, from keto to intermittent fasting, works through the same mechanism: it helps you eat fewer calories than your body uses. Understanding this principle lets you choose an approach you can actually stick with.
What Is a Calorie Deficit?
A calorie deficit means consistently taking in fewer calories than your body burns. To make up the shortfall, your body draws on stored energy, mostly body fat. The old rule that 3,500 calories equal one pound (about 7,700 calories per kilogram) of fat is a useful approximation, but real-world results vary because metabolism adapts and water weight fluctuates.
How Many Calories Do You Burn?
Your total daily energy expenditure (TDEE) has four parts:
- Basal metabolic rate (BMR): Energy for basic functions, about 60 to 70 percent of the total.
- Thermic effect of food: Energy to digest meals, about 10 percent. Protein has the highest effect.
- Exercise: Planned workouts.
- NEAT: Non-exercise movement such as walking, fidgeting and chores, which can vary a lot between people.
A common estimate is the Mifflin-St Jeor equation. For men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age + 5. For women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age – 161. Multiply by an activity factor of 1.2 (sedentary) to 1.725 (very active) to estimate TDEE. Online calculators do this for you, but treat results as a starting point.
How Big Should Your Deficit Be?
For most adults, a deficit of 300 to 500 calories a day, or about 10 to 20 percent below maintenance, leads to a steady loss of roughly 0.25 to 0.5 kg (0.5 to 1 lb) a week. Larger deficits can increase muscle loss, fatigue, nutrient gaps, gallstones and rebound overeating. Women should generally not go below about 1,200 calories and men below 1,500 without medical supervision.
Practical Ways to Create a Deficit
- Cut liquid calories. Soft drinks, sweetened tea and juices can easily add 200 to 400 calories a day.
- Fill half your plate with vegetables. High-volume, low-calorie foods keep you full.
- Prioritise protein. It preserves muscle and reduces hunger.
- Moderate portions of calorie-dense foods. Oils, nuts, fried foods and sweets add up fast, so measure rather than guess.
- Move more. Walking 7,000 to 10,000 steps and strength training twice a week help preserve muscle and raise expenditure.
- Sleep 7 to 9 hours. Poor sleep increases hunger hormones and cravings.
Common Mistakes
- Crash dieting, which leads to muscle loss and rebound weight gain.
- Underestimating portions and overestimating exercise burn.
- Skipping strength training.
- Relying on “diet” packaged foods that are low in nutrients.
- Making the plan so restrictive that it cannot be maintained.
Plateaus Are Normal
As you lose weight, your energy needs fall. If progress stalls for three to four weeks, recheck portions, increase daily steps, adjust calories slightly or take a planned diet break at maintenance for one to two weeks to recover.
Who Should Not Diet Without Medical Advice?
Pregnant or breastfeeding women, children and teens, people with a history of eating disorders, and those with diabetes, kidney disease or other medical conditions should seek professional guidance before cutting calories.
The Bottom Line
A modest, sustainable calorie deficit paired with nutritious food, protein, strength training and good sleep is the most reliable path to healthy fat loss. Go slowly and focus on habits you can keep for life.
This article is for general education and is not a substitute for personalised advice from a registered dietitian or doctor.