Losing 1 kg of body fat takes an energy deficit of roughly 7,700 calories. The figure is an approximation and a useful starting point. A deficit that is truly maintained still produces fat loss. What often shrinks is the realised deficit: as resting metabolic rate decreases, the same daily intake no longer creates the same deficit. The NHS describes reducing daily calorie intake by around 600 calories as a safe and sustainable approach to weight loss.
- Roughly 7,700 calories of deficit is the standard approximation for 1 kg of body fat, derived from a rule first published in 1958.
- A 2014 analysis in the Journal of the Academy of Nutrition and Dietetics concluded that the rule overestimates weight loss when it is applied over months.
- A study in the International Journal of Obesity found resting metabolic rate fell by around 101 calories a day in adults who lost around 8 kg over a year.
- The NHS describes reducing daily calorie intake by around 600 calories as a safe and sustainable approach to weight loss.
- A planned deficit that produced steady weight loss in the first month often shrinks by the sixth, because energy needs fall as weight falls and the same intake no longer creates the same deficit.
- The scale cannot show whether the deficit is removing fat or muscle, and repeated body composition measurements help track both.
Many people track their calorie deficit and find that, after a few months, the scale no longer matches the arithmetic.
How many calories are in 1 kg of body fat?
One kilogram of body fat corresponds to roughly 7,700 calories of energy. Adipose tissue, the tissue that stores body fat, is mostly fat by weight, with the remainder water and other components. Each gram of fat stores around 9 calories of energy, which is where the approximation of 3,500 calories per pound, or around 7,700 calories per kilogram, comes from.
The figure assumes that every kilogram lost is adipose tissue. In practice, the weight lost in the first weeks of a calorie deficit includes glycogen, the water stored with it and some protein, which carry less energy per kilogram than fat. Early weight loss on the scale is therefore faster than the 7,700 calorie figure predicts, and later weight loss is slower.
Where does the 7,700 calorie figure come from?
The rule was proposed by Max Wishnofsky in 1958, who calculated that one pound of body weight lost or gained corresponds to around 3,500 calories. A 2014 analysis published in the Journal of the Academy of Nutrition and Dietetics traced how the rule spread into textbooks and websites, and concluded that it is inaccurate when used to predict weight loss over time.
The authors explain that the rule assumes a constant calorie intake, an unchanging energy expenditure and a constant energy content of the weight lost. None of these holds over months: energy expenditure falls as weight falls, and the composition of the weight lost changes between the early and later phases. As a result, the rule overestimates how much weight a given deficit produces as time goes on.
Why does the arithmetic drift as you lose weight?
Your resting metabolic rate falls
Resting metabolic rate decreases as you lose weight, regardless of how quickly the weight is lost. A study in the International Journal of Obesity measured a decrease in resting metabolic rate of around 101 calories a day in adults who lost around 8 kg over a year. It attributed roughly 60% of that decrease to the loss of energy-expending tissue and roughly 40% to metabolic adaptation. A deficit of 600 calories against your old energy needs becomes a smaller deficit against your new ones.
You may move less without noticing
During a calorie deficit, some people move less in everyday life without noticing, for example standing, walking and fidgeting less. This can reduce the energy they use by an amount that a food diary does not show.
Tracking has a margin of error
Food labels, portion estimates and calorie-tracking apps all carry a margin of error, and fitness trackers can overestimate the energy used in exercise. Small errors repeated every day can remove much of a planned deficit. Liquid calories can easily add to your daily intake. Karak, juice and flavoured coffees are common examples that can contain more calories than people realise.
What size of calorie deficit is sensible?
The NHS describes reducing daily calorie intake by around 600 calories as a safe and sustainable approach to weight loss. A larger calorie deficit does not necessarily lead to better or more sustainable results. This means eating around 600 calories less than your usual daily intake, not limiting your total intake to 600 calories a day.
The US Centers for Disease Control and Prevention states that people who lose weight at a gradual, steady pace of around 0.5 kg to 1 kg a week are more likely to keep it off than people who lose it faster. A larger calorie deficit can increase lean-mass loss and is generally harder to sustain over time. Our article on a weight loss diet plan covers how to build that deficit into meals you can sustain.
How long does 1 kg take?
The table below applies the 7,700 calorie approximation to four daily deficits. The figures describe what the rule predicts. Real weight loss after the first weeks is generally slower than the rule suggests, and the first week is often faster because of water.
| Daily calorie deficit | Weekly deficit | Predicted weight loss per week | Days to 1 kg by the rule |
|---|---|---|---|
| 300 calories | 2,100 calories | Around 0.3 kg | Around 26 days |
| 500 calories | 3,500 calories | Around 0.45 kg | Around 15 days |
| 600 calories | 4,200 calories | Around 0.55 kg | Around 13 days |
| 1,000 calories | 7,000 calories | Around 0.9 kg | Around 8 days |
The 600 calorie row matches the NHS approach and sits within the gradual rate the US Centers for Disease Control and Prevention describes. The table is a general illustration. A personal target depends on your body size, your activity and your medical history.
Why is the scale the wrong tool for checking the arithmetic?
The scale measures total body weight, which includes body fat, muscle, water and the contents of the gut. Water weight can hide fat loss on the scale. You may follow your calorie target closely and see no change one week, then see a drop the next.
The deficit is meant to remove body fat, and the scale cannot show whether it has. A larger calorie deficit can also increase the amount of lean tissue lost alongside body fat, and the scale records that loss in the same way as fat loss. Our article on how much weight you can lose in a month explains what a normal monthly rate looks like.
What does Endocare measure instead?
At Endocare, body composition analysis is included free of charge at every consultation. Body composition analysis estimates body fat, muscle mass and body water. Repeated measurements help your endocrinologist understand how your body is changing beyond the number on the scale. Over repeated measurements, a month in which the scale has barely moved can still show a fall in body fat. A fast fall on the scale can show that muscle is being lost. Your endocrinologist will adjust the advice from that trend.
Endocare does not set a fixed calorie number for every patient. Our lifestyle coaches set and adjust targets from your body composition analysis, your activity and your progress. Our article on the difference between fat loss and weight loss explains why the composition of the loss is important.
Frequently asked questions
How many calories is 1 kg of fat?
One kilogram of body fat corresponds to roughly 7,700 calories. A gram of fat stores around 9 calories, and adipose tissue is mostly fat, which gives the approximation of around 7,700 calories per kilogram.
Is the 7,700 calorie rule accurate?
The rule is a reasonable starting point, although it becomes less accurate over months. A 2014 analysis in the Journal of the Academy of Nutrition and Dietetics concluded that the rule overestimates weight loss over time, because energy expenditure falls as weight falls and the composition of the weight lost changes.
How big should my calorie deficit be?
The NHS describes reducing daily calorie intake by around 600 calories as a safe and sustainable approach. Your own target depends on your body size, activity and medical history, and Endocare’s lifestyle coaches can set it with you.
Why has my deficit stopped working?
The realised deficit often becomes smaller over time even when the plan has not changed. Resting metabolic rate decreases as you lose weight, everyday movement can fall, and small tracking errors add up. We do not recommend responding to a weight loss plateau by immediately cutting calories further. A larger calorie deficit can be harder to sustain and may increase the risk of losing lean mass. Instead, our coaches typically review the plan, maintain adequate protein intake and allow more time before making further adjustments.
Do I need to eat back exercise calories?
We do not recommend eating back every estimated exercise calorie. Fitness trackers can overestimate the energy used in exercise, so eating back every estimated calorie can remove much of the deficit. Your lifestyle coach can set a target that already accounts for your usual activity.
How many calories would I need to cut to lose 2 kg a week?
By the 7,700 calorie rule, losing 2 kg a week would need a deficit of around 2,200 calories a day, which is more than many adults use in a day. MedlinePlus states that losing more than 0.5 to 1 kg a week is not safe for most people. Our article on how to lose 5 kg in a month explains what a faster but realistic target looks like.
If your tracked deficit is no longer matching the scale, a consultation can show what your body composition is doing. Your endocrinologist will review your body composition analysis, your blood tests and your plan, and Endocare’s lifestyle coaches can adjust your targets from what they show.
You can book a consultation at our clinics in Dubai and Abu Dhabi.
