A deficit of 300 to 500 kcal a day delivers around 0.5 kg of weight loss a week
A calorie deficit of 300 to 500 kcal a day is the most evidence-based strategy for gradual weight loss. At a 500 kcal daily deficit, you build up a cumulative shortfall of 3,500 kcal after 7 days. That corresponds to roughly 0.5 kg of fat mass. This pace is realistic, protects muscle mass and is sustainable.
You can go faster. But faster isn't always better. A deficit of 1,000 kcal a day sounds efficient, but for most people it leads to muscle loss, increased fatigue and a slower metabolism within three to four weeks. Recovering from that costs more time than the extra weight loss is worth.
Below, you'll find how to calculate your maintenance calories, the thresholds you shouldn't dip below, and why protein is the linchpin of any sensible deficit.
How to work out your maintenance calories
Your maintenance calories are the number at which your weight stays stable. This figure is known as your Total Daily Energy Expenditure (TDEE). Working it out takes two steps: first your basal metabolic rate (BMR), then your activity level applied on top.
Step 1: calculate your BMR with the Mifflin-St Jeor formula
The Mifflin-St Jeor formula is currently the most validated method for people with a healthy to slightly elevated weight. It was published in 1990 and has since been tested repeatedly in clinical settings.
- Men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
- Women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161
A concrete example: a woman aged 35, 70 kg, 168 cm. BMR = (10 x 70) + (6.25 x 168) - (5 x 35) - 161 = 700 + 1050 - 175 - 161 = 1,414 kcal/day.
Step 2: multiply by your activity factor
| Activity level | Description | Factor |
|---|---|---|
| Sedentary | Desk job, barely any movement | 1.2 |
| Lightly active | Exercise or walking 1 to 3 times a week | 1.375 |
| Moderately active | Exercise 3 to 5 times a week | 1.55 |
| Very active | Daily intensive exercise or physical work | 1.725 |
| Extremely active | Elite sport or heavy manual labour | 1.9 |
The same woman works at a desk and exercises twice a week. Factor: 1.375. TDEE = 1,414 x 1.375 = 1,944 kcal/day. If she wants to lose 0.5 kg a week, she eats 1,444 to 1,644 kcal daily.
Reference values by profile
| Profile | Weight | Activity | TDEE (estimated) | Target calories (-500) |
|---|---|---|---|---|
| Woman, 30 years, 65 kg | 65 kg | Lightly active | ~1,850 kcal | ~1,350 kcal |
| Woman, 45 years, 80 kg | 80 kg | Sedentary | ~1,900 kcal | ~1,400 kcal |
| Man, 35 years, 85 kg | 85 kg | Moderately active | ~2,600 kcal | ~2,100 kcal |
| Man, 50 years, 95 kg | 95 kg | Lightly active | ~2,500 kcal | ~2,000 kcal |
Want to know which calorie level suits your specific situation? The Bioteïne phase test gives you a personalised starting point based on your weight, activity and goal.
Safe deficit versus going too low
There is a hard lower limit. The Dutch Nutrition Centre (Voedingscentrum) sets 1,200 kcal/day for women and 1,500 kcal/day for men as the minimum during weight loss. Below this threshold, it's nearly impossible to get enough protein, vitamins and minerals from normal food.
What happens with too aggressive a deficit is well documented. The British Dietetic Association describes this as "adaptive thermogenesis": the body lowers its resting metabolism in response to prolonged calorie restriction. In practice, that means you burn less, lose more muscle mass and your weight loss stalls sooner than with a moderate deficit.
| Deficit size | Weight loss/week | Risk | Recommended? |
|---|---|---|---|
| 200 to 300 kcal | ~0.2 to 0.3 kg | Low | Yes, during a plateau or maintenance |
| 300 to 500 kcal | ~0.3 to 0.5 kg | Low | Yes, optimal |
| 500 to 750 kcal | ~0.5 to 0.7 kg | Moderate | Yes, provided protein intake is high enough |
| Above 750 kcal | More than 0.7 kg | High | No, unless medically supervised |
Why you should keep protein high during a calorie deficit
This is the most underrated principle of any fat loss programme. In a calorie deficit, the body doesn't just lose fat. It also breaks down muscle tissue for energy, unless protein intake is high enough to prevent this.
A meta-analysis published in the American Journal of Clinical Nutrition (Helms et al., 2014) showed that an intake of 1.6 to 2.4 g of protein per kg of body weight per day maximises muscle preservation during an energy deficit. For a 70 kg woman, that's 112 to 168 g of protein a day.
That's a lot. More than most people are used to eating. And that's exactly why it's so tricky to achieve this while also watching your calories. Protein has a higher thermic effect than carbohydrates or fat: burning protein itself costs the body 20 to 30% of its calorific value. For carbohydrates, that figure is 5 to 10%. This is known as the thermic effect of food (TEF).
The practical upshot: a 400 kcal meal with 40 g of protein delivers fewer net calories than the same 400 kcal from pasta. And it keeps you fuller for longer. You'll find more on optimal daily protein distribution in the Bioteïne high-protein diet guide.
Worked example: from TDEE to a daily menu
Take a man aged 42, 88 kg, 181 cm, lightly active (desk job, running twice a week).
- BMR: (10 x 88) + (6.25 x 181) - (5 x 42) + 5 = 880 + 1,131 - 210 + 5 = 1,806 kcal
- TDEE: 1,806 x 1.375 = 2,483 kcal/day
- Target calories at a -500 kcal deficit: 1,983 kcal/day
- Protein target: 88 kg x 1.8 g = 158 g protein/day (= 632 kcal from protein)
- Remaining calories for fat and carbohydrates: 1,983 - 632 = 1,351 kcal
This is a realistic schedule. Not easy on paper, but easier with the right food choices. A 200 kcal protein shake with 35 g of protein does more for this goal than a 200 kcal cheese sandwich with 12 g of protein.
| Meal | kcal | Protein |
|---|---|---|
| Breakfast: Bioteïne shake + fruit | ~310 kcal | ~38 g |
| Lunch: Bioteïne meal replacement | ~400 kcal | ~30 g |
| Snack: Bioteïne protein bar | ~190 kcal | ~20 g |
| Evening meal: chicken, vegetables, rice | ~600 kcal | ~45 g |
| Evening snack: Greek yoghurt | ~150 kcal | ~15 g |
| Total | ~1,650 kcal | ~148 g |
Slightly under the 1,983 kcal target, leaving room for an extra snack or a dressing. And 148 g of protein sits close to the 158 g target.
Pitfalls that stall weight loss
The most common reason people stall after three or four weeks isn't that they've got the formula wrong. It's the things that don't get tracked.
Underestimating calorie intake
Research from Cornell University shows that people underestimate their calorie intake by 20 to 40% on average. Oil in the pan, sauces, drinks, a handful of nuts. It all adds up. 30 ml of olive oil is 240 kcal. Invisible, but real.
Eating too little
Eating less than 1,200 kcal sounds like a quick fix. It works for the first week. After that, the body lowers its energy expenditure. Muscle loss increases. Appetite rises. And as soon as you go back to eating normally, the weight returns. This is the well-known yo-yo effect, not the exception but the rule with overly aggressive diets.
Drinking your calories
Fizzy drinks, fruit juice, alcohol, energy drinks. All calories with no fullness to show for it. A glass of orange juice (250 ml) contains 110 kcal and 0 g of protein. A 250 ml protein shake contains 180 kcal and 30 g of protein. The choice is simple once you put them side by side.
Weekend creep
Five days of eating well, then letting go from Friday to Sunday. Most people fully undo their 2,500 kcal deficit (5 x 500) in just two evenings. That's not a moral judgement, it's simply the maths. Consistency beats being perfect during the week and free-for-all at weekends.
Bioteïne meal replacements: making the deficit easy to hit
The hard part of a calorie deficit isn't deciding to eat less. It's that every meal choice becomes a puzzle: low calorie, high protein, filling enough, practical to prepare. That's a balancing act three times a day.
Bioteïne meal replacements were developed for exactly this problem. A shake or meal pack of 200 to 400 kcal delivers 25 to 40 g of protein, all the micronutrients you need and a high satiety value. You don't have to count anything. The maths has already been done.
These products aren't meant as a permanent diet. They work best as a replacement for one or two meals a day, with the third meal being a normal, high-protein evening meal. This gives your day structure and makes it easier to stay within your calorie and protein targets without having to plan every single meal from scratch.
- Protein shakes: quick, portable, 30 to 40 g of protein per serving
- Meal replacements: a complete meal, 300 to 400 kcal per serving
- Protein bars: for between meals, 15 to 20 g of protein, max 200 kcal
- Protein biscuits and snacks: if you fancy something to chew on without blowing your deficit
Want to know which schedule suits your starting point best? Start with the Bioteïne starter pack. It includes a selection of products for the first two weeks, along with a daily schedule.
Frequently asked questions
How many calories a day to lose weight as a woman?
That depends on your weight, height, age and activity level. An average woman aged 30 to 50 has maintenance calories of 1,700 to 2,100 kcal a day. For 0.5 kg of loss a week, eat 300 to 500 kcal less. Don't drop below 1,200 kcal a day.
How many calories a day to lose weight as a man?
Men generally have higher maintenance calories due to greater muscle mass: 2,200 to 2,800 kcal depending on activity. A 500 kcal deficit brings that down to 1,700 to 2,300 kcal a day. The lower limit for men is 1,500 kcal a day during weight loss.
How do I calculate my calorie deficit?
First work out your TDEE using the Mifflin-St Jeor formula: BMR multiplied by your activity factor. Subtract 300 to 500 kcal from that. This is your daily target. Track it for three to four weeks and adjust based on your results.
What happens if I eat too few calories?
The body lowers its metabolism during prolonged restriction. Muscle mass is broken down for energy. Fatigue, difficulty concentrating and increased appetite are common consequences. As soon as you go back to eating normally, weight returns faster because of the lowered metabolism.
How much protein do I need in a calorie deficit?
The recommendation for preserving muscle during weight loss is 1.6 to 2.4 g of protein per kg of body weight per day. For someone weighing 75 kg, that's 120 to 180 g of protein a day. This is considerably more than the standard recommendation of 0.8 g per kg used for weight maintenance.
Is it true I can eat more on training days?
Yes. On days when you burn 300 to 600 kcal extra through exercise, your TDEE is higher. You can then eat a little more and still maintain your deficit. Use your activity factor per day rather than a weekly average for the most accurate calculation.
How quickly can I lose weight?
A sensible pace is 0.5 to 1 kg a week. More than 1 kg a week is almost always accompanied by muscle loss and a slower metabolism in the long run. Starting faster can make sense under medical supervision, but it's not a strategy for going it alone.
Do meal replacements really help with weight loss?
Clinical research shows that structured meal replacement is effective for weight loss, particularly in the first twelve weeks. They remove the daily decision about calories and protein per meal. The effect depends on how consistently you use them within a calorie-restricted plan.