Question 1

What is a calorie deficit?

Accepted Answer

A calorie deficit occurs when you consume fewer calories than your body burns in a day (below your TDEE). Your body then uses stored energy (primarily body fat) to make up the difference. A deficit of approximately 3,500 kcal is needed to lose one pound (0.45 kg) of fat, based on fat having about 9 kcal per gram and a 7,700 kcal = 1 kg fat approximation.

Question 2

How much of a calorie deficit is safe per day?

Accepted Answer

Most guidelines recommend a deficit of 500-1,000 kcal per day for a weight loss rate of 0.5-1 kg (1-2 lbs) per week. Deficits below 500 kcal/day produce slower weight loss; deficits above 1,000 kcal/day significantly increase the risk of muscle loss, nutritional deficiencies, and metabolic slowdown. Very low-calorie diets below 800 kcal/day require medical supervision.

Question 3

How long will it take to lose 10 kg on a 500 kcal deficit?

Accepted Answer

A 500 kcal/day deficit gives approximately 3,500 kcal/week, which corresponds to roughly 0.45 kg (1 lb) of fat per week (using the 7,700 kcal/kg rule, it is closer to 0.45 kg). At this rate, losing 10 kg would take about 22 weeks (approximately 5 months). However, metabolic adaptation means the rate slows as weight decreases, so real-world results often take 10-25% longer than simple arithmetic suggests.

Question 4

What is TDEE and why does it matter for a calorie deficit?

Accepted Answer

TDEE (Total Daily Energy Expenditure) is the total calories you burn per day including all activity. A calorie deficit is always calculated relative to TDEE, not BMR. Eating at your TDEE maintains weight; eating below it creates a deficit. TDEE is estimated by multiplying BMR by an activity factor (1.2 to 1.9). Because TDEE is an estimate, the actual deficit on any given day may differ from the target.

Question 5

Does a calorie deficit cause muscle loss?

Accepted Answer

Some muscle loss is possible in a calorie deficit, but it can be largely prevented with adequate protein intake and resistance training. Protein recommendations for weight loss range from 1.6-2.2 g per kg of body weight per day. Resistance training provides the stimulus to maintain muscle even in a calorie deficit. A conservative deficit (500 kcal/day) combined with high protein and strength training minimises muscle loss while maximising fat loss.

Question 6

What is metabolic adaptation in the context of calorie deficits?

Accepted Answer

Metabolic adaptation (also called adaptive thermogenesis) refers to the body lowering its metabolic rate in response to prolonged calorie restriction. As you lose weight, your TDEE decreases partly because your body is lighter, and partly because non-exercise activity thermogenesis (NEAT) decreases. This is why weight loss often plateaus after several weeks. Re-feeding periods or "diet breaks" are used by some to temporarily reverse adaptation.

Question 7

Should I eat below my BMR to lose weight?

Accepted Answer

Eating below BMR (basal metabolic rate) for extended periods is generally not recommended. BMR represents the minimum calories for vital organ function. Chronic sub-BMR eating can lead to nutrient deficiencies, muscle loss, hormonal disruption (especially in women), reduced bone density, and significant metabolic slowdown. Most nutrition professionals recommend a minimum intake of 1,200 kcal/day for women and 1,500 kcal/day for men.

Question 8

What is the difference between a calorie deficit and intermittent fasting?

Accepted Answer

A calorie deficit specifies eating fewer total calories over the day or week. Intermittent fasting (IF) specifies the timing of eating (e.g., eating within an 8-hour window each day). IF can create a calorie deficit by limiting eating time, but it does not automatically do so. Weight loss from IF is generally attributable to the resulting calorie deficit rather than any metabolic advantage from the fasting window itself, as shown by controlled trials comparing IF to continuous calorie restriction.

Question 9

How do I track my calorie deficit accurately?

Accepted Answer

Track food intake with a food diary app (weighing food with a kitchen scale is more accurate than eyeballing portions). Track exercise with a wearable or use METs-based estimates. Adjust intake over time based on actual weight change: if you are not losing at the expected rate after 2-3 weeks, reduce intake by 100-200 kcal/day or increase activity. Individual variation in TDEE estimates means that adjusting based on results is more reliable than relying solely on calculator estimates.

Question 10

Can you create a calorie deficit through exercise alone?

Accepted Answer

Yes, but it is difficult. Running 1 mile burns approximately 100 calories for a 70 kg person; to create a 3,500 kcal weekly deficit (1 lb of fat) through exercise alone would require 35 miles of running per week. In practice, people typically combine diet (reduced intake) with exercise (increased expenditure) because the diet component is more efficient per hour of effort. Exercise also provides muscle-protective and metabolic benefits beyond calorie burn.

Goal	Daily change	Weekly calories	Weekly weight change
Lose 0.25 kg/week	-275 cal	-1,925 cal	-0.25 kg
Lose 0.5 kg/week	-550 cal	-3,850 cal	-0.5 kg
Lose 1.0 kg/week	-1,100 cal	-7,700 cal	-1.0 kg
Gain 0.25 kg/week	+275 cal	+1,925 cal	+0.25 kg
Gain 0.5 kg/week	+550 cal	+3,850 cal	+0.5 kg

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