15 Oct 2026

What is a calorie deficit? Eating less energy than you use, in a way you can keep up

Two plates on a wooden table with broccoli, tomatoes and grilled chicken breast, alongside nuts, dried fruit and tea in clear mugs — Photo: Zifeng Xia / Pexels (Pexels License)

A calorie deficit means taking in less energy from food and drink than your body uses in a day. It is the basic principle behind weight loss.

This article summarises guidance from the NHS, CDC, WHO and Thailand's Department of Disease Control on how much to cut, how fast to lose weight, what is different for Asian and Thai adults, and how to plan meals that still give you the nutrients you need.

1. What is a calorie deficit?

A bowl of fresh vegetables on a digital kitchen scale beside tomatoes and a tape measure — Photo: Gustavo Fring / Pexels

The energy in food and drink is measured in calories (kcal). If you eat and drink fewer calories than your body uses, it draws on energy stored as fat, so you are likely to lose weight. If you take in more than you use, the extra is stored as fat.

Reference: [1] NHS · [2] NHS calories

2. How much energy does your body use?

The NHS gives averages of around 2,000 kcal a day for women and around 2,500 kcal a day for men, but individual needs vary with age, weight, height and activity.

For a personal estimate, try NIDDK's Body Weight Planner: enter your weight, height, activity and goal to see roughly how many calories to eat. Results are estimates; if your metabolism is low or you are very sedentary, the values may be too high.

Reference: [1] NHS · [2] NHS calories · [4] NIDDK

3. If you are Asian or Thai: what is different

A WHO expert consultation found that Asian populations have a different relationship between BMI, body fat and health risk than European populations. A substantial share of Asian people are at high risk of type 2 diabetes and cardiovascular disease at BMIs below 25, so WHO proposed additional public health action points at BMI 23 and 27.5.

Thailand uses the criteria in the table below (Department of Disease Control).

Topic	Criteria for Thai adults
Healthy BMI	18.5–22.9
Overweight or obesity class 1	BMI 23–24.9
Obesity class 2	BMI 25–29.9
Obesity class 3	BMI 30 and above
Waist (measured at the navel)	No more than your height (cm) divided by 2, e.g. 160 cm tall means a waist of no more than 80 cm
Daily energy to manage weight and waist	Women 1,600 kcal, men 2,000 kcal

The 2,000 / 2,500 kcal averages in section 2 are UK figures from the NHS. Smaller people use less energy, so Thai readers should use Thai figures or a calculator with their real weight and height
Always measure your waist alongside BMI to check belly fat
The recommended rate of loss (0.5–1 kg a week) and the warning about very low calorie diets apply to Asian people too

A BMI of 23 or more is a signal to start managing your weight, not a diagnosis. If you have other risk factors, get a health check with a doctor.

Reference: [7] WHO Asian BMI · [8] Thai DDC · [1] NHS

4. How fast should you lose weight?

Topic	Guidance
Recommended rate	About 0.5–1 kg a week (NHS) or 1–2 lb a week (CDC)
Why go gradually	The CDC says people who lose weight gradually are more likely to keep it off than those who lose it quickly
A first goal	Losing just 5% of your body weight may improve blood pressure, cholesterol and blood sugar; for someone weighing 70 kg, 5% is 3.5 kg

Reference: [1] NHS · [3] CDC

5. Don't cut calories too hard

The NHS says very low calorie diets (under 800 or 1,200 kcal a day) are not suitable or safe for everyone; they are usually for people whose weight affects other conditions, with dietitian support
Cutting too hard makes it harder to get enough nutrients and to keep going
The right deficit is one you can keep up every day without being unbearably hungry

Reference: [1] NHS

6. Build the deficit through food, practically

A meal box with steamed rice, cooked vegetables, broccoli and shredded meat — A plate with vegetables, protein and rice in sensible portions · Photo: David Balbino / Pexels

Read nutrition labels: check the energy (kcal) per serving and how many servings are in the pack
Eat at least 400 g of fruit and vegetables a day; they fill you up without much energy
Keep free sugars (sugar added to food and drinks, including fruit juice) below 10% of daily energy; sugary drinks are an easy place to cut
Limit total fat to 30% or less of daily energy and salt to under 5 g a day
Build plates with vegetables, protein and rice or starch in sensible portions instead of skipping meals

Cut energy, but still get all your nutrients. Don't drop whole food groups without professional advice.

Reference: [2] NHS calories · [5] WHO diet

7. Move more

A woman in a pink T-shirt walking for exercise on a path in a lakeside park — Brisk walking counts as moderate activity · Photo: Hiep Nguyen / Pexels

Moving more increases the energy you use and helps your overall health. You don't need to start hard: brisk walking or taking the stairs counts.

Activity (adults 18–64)	WHO guidance
Moderate-intensity activity	At least 150 minutes a week; up to 300 minutes for extra benefits
Or vigorous activity	At least 75 minutes a week, or an equivalent combination
Muscle strengthening	Major muscle groups on 2 or more days a week

Reference: [6] WHO activity

8. Who should talk to a doctor first

People with conditions such as diabetes, kidney or heart disease, and people on regular medication
People who are pregnant or breastfeeding
Children and teenagers
Anyone with a history of eating problems or who wants to lose a lot of weight

This article is general information, not medical advice. Results differ from person to person. If you have a medical condition or are unsure, talk to a doctor or dietitian.

References

Image credits

Cover image: Zifeng Xia / Pexels ↗ (opens in a new tab) · licence Pexels License ↗ (opens in a new tab)
Image in section 1: Gustavo Fring / Pexels ↗ (opens in a new tab) · licence Pexels License ↗ (opens in a new tab)
Image in section 6: David Balbino / Pexels ↗ (opens in a new tab) · licence Pexels License ↗ (opens in a new tab)
Image in section 7: Hiep Nguyen / Pexels ↗ (opens in a new tab) · licence Pexels License ↗ (opens in a new tab)

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