Calorie deficit: how much to eat to lose fat and still function

Most people who come to me have heard about the calorie deficit already. The problem is somewhere else. Either they cut so little that almost nothing happened in three months, or they cut so much that they fell apart in week five and ate the whole pantry. This article is about setting the number so you can live with it.

Short answer: Take your estimated daily energy use (TDEE, total daily energy expenditure) and subtract 15 to 20%. For someone with a TDEE of 2,000 kcal (calories) that is about 1,600 to 1,700 kcal. The goal is to lose 0.5 to 1% of body weight per week, which at 70 kg is 350 to 700 g.

What a calorie deficit is

A calorie deficit means you take in less energy than you use. Your body gets the difference from its stores, and you lose weight. A kilo of body fat holds about 7,700 kcal. If you are 500 kcal under your energy use every day, you lose about half a kilo a week: 7 days at -500 kcal = -3,500 kcal = about 0.45 kg of fat.

Thermodynamics does not fail here. Sleep, stress, sweeteners or hormones change how easily you hold the deficit and how much you eat, but they don't get around the rule itself. That is why I start with this number with clients, and we deal with supplements only when the base is in place.

How much to cut so it makes sense

Take your estimated daily energy use (TDEE, the total energy you burn in a day) and subtract 15 to 20 percent. A woman with a TDEE of 2,000 kcal ends up at about 1,600 to 1,700 kcal. For a man with 2,600 kcal it comes out at about 2,080 to 2,210 kcal (2,600 x 0.80 = 2,080 and 2,600 x 0.85 = 2,210). You can get your own TDEE estimate from the calculator.

Why not cut more? A Norwegian study of 24 elite athletes compared two paces of weight loss: slow at 0.7% of body weight per week against fast at 1.4%. Both groups lifted four times a week and both lost a similar amount, about 5.5% of body weight. What differed was what they lost. In the slow group fat-free mass went up 2.1%, in the fast group it stayed unchanged. Fat mass fell 31% in the slow group against 21% in the fast group. The slow group cut its intake by about 19%, the fast group by 30% (Garthe, 2011, PMID 21558571).

They were trained athletes, so these numbers don't transfer one to one to a beginner. But the direction is clear. The faster pace cost more muscle and less fat.

A practical conversion: aim at 0.5 to 1% of body weight per week. At 70 kg that is 350 to 700 g. On paper this looks slow. In three months it is 5 to 8 kg, and you don't look gaunt.

Protein keeps muscle when you cut energy

Once you cut intake, your body decides where to take energy from. Protein and strength training are the two levers that tell it to leave muscle alone.

A review of six studies on trained, lean athletes in caloric restriction ended with a recommendation of 2.3 to 3.1 g of protein per kg of fat-free mass (body weight without fat). The harder the deficit and the leaner the person, the higher in that range (Helms, 2014, PMID 24092765). For a client who is not a competitive bodybuilder, converted to total body weight, that comes to roughly 1.6 to 2.2 g per kg. That is what I use as the standard. Sources and portions are in how much protein, and the protein tool ranks foods by protein per 100 kcal.

At some point more protein stops adding anything. A meta-analysis of 49 studies and 1,863 people showed that protein supplementation above a total intake of about 1.62 g/kg a day gave no further gain in fat-free mass during strength training (Morton, 2018, PMID 28698222). Those numbers apply to training in general, not directly to weight loss, but they work as a ceiling of common sense.

Why a deficit 'doesn't work' even when you think you hold it

This I see in clients more often than badly set macros.

In a classic study in the New England Journal of Medicine, researchers followed people with obesity who said they could not lose weight although they ate under 1,200 kcal a day. They measured actual energy expenditure and actual intake. Total expenditure and resting metabolism came out within 5% of predicted values, so a slow metabolism was not the reason. But the people underreported their intake by 47% on average and overreported their activity by 51% (Lichtman, 1992, PMID 1454084).

None of them lied on purpose. Oil in the pan, bites while cooking, and a weekend that somehow doesn't fit into the weekly average. That is why at the start I insist that a client weighs and logs everything for fourteen days, including what 'doesn't count'. Very often it turns out that there was no deficit at all.

How to set it up this week

1. Weigh yourself five mornings in a row, fasted, and take the average. One reading tells you more about salt and water than about fat.
2. Estimate your daily energy use and subtract 15 to 20%.
3. Set protein to 1.6 to 2.2 g per kg of body weight. Build the rest of the day from carbs and fats the way you like and the way it fits your life.
4. Log everything, including cooking fat and liquid calories. Fourteen days, and only then decide.
5. After two weeks compare the averages. If nothing moved, cut another 5 to 10%. If you are dropping faster than 1% a week, add some back.

The rest is repetition. Most clients it worked for didn't have a cleverer plan. They kept it for longer.

Frequently asked questions

Do I have to count calories forever?

Counting is a tool to calibrate your eye. After two to three months most clients estimate decently and weigh only the foods they keep getting wrong, typically sides, nuts and sauces.

What if my weight does not move for a week?

One week alone doesn't mean much, and for women the cycle and water retention also play a role. Decide from two or three week averages. If nothing changed in three weeks and you log honestly, cut 5 to 10% of energy or add daily steps.

Is it better to cut carbs or fats?

For fat loss the total deficit decides, so cut from what you will miss least and keep protein high. With clients who love bread I keep carbs high and cut fat. The other way round works just as well.

Sources, so you can check:

1) Pace of weight loss and body composition: Garthe I, et al. Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. Int J Sport Nutr Exerc Metab. 2011;21(2):97-104. DOI: 10.1123/ijsnem.21.2.97 | PMID: 21558571

2) Protein in caloric restriction: Helms ER, et al. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes. Int J Sport Nutr Exerc Metab. 2014;24(2):127-138. DOI: 10.1123/ijsnem.2013-0054 | PMID: 24092765

3) Ceiling for protein intake: Morton RW, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. Br J Sports Med. 2018;52(6):376-384. DOI: 10.1136/bjsports-2017-097608 | PMID: 28698222

4) Underreporting of intake: Lichtman SW, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med. 1992;327(27):1893-1898. DOI: 10.1056/NEJM199212313272701 | PMID: 1454084

Martin Barna

Online nutrition and fitness coach. Since 2013 I have helped 600+ people lose fat and keep the result. Science, not crash diets.

Apply for coaching

This article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.