Calorie Deficit Diet: A Guide for Losing Fat, Not Muscle
A calorie deficit means eating less energy than your body uses, so it draws on stored fat. Here's how big a deficit makes sense, what to eat in one, and how to make sure the weight you lose is fat and not muscle.
What is a calorie deficit?
Your body uses a certain amount of energy every day, your maintenance. Eat less than that and the difference, the deficit, comes from your energy stores, mostly fat. A common estimate is about 7,700 kcal per kg of body weight lost, an approximation that overstates loss over long periods. Every diet that works for fat loss creates a deficit, whatever it's called.
How big should your deficit be?
Size it to a rate of loss rather than a round number. A review on contest preparation for natural bodybuilders suggests about 0.5–1% of body weight a week to keep muscle. For a 30-year-old man at 180 cm and 90 kg who trains four days a week, our calorie deficit calculator estimates maintenance at about 3,008 kcal; losing 0.5% a week means about 2,513 kcal a day, a deficit of 495. Use the calculator for your own numbers.
What to eat in a calorie deficit
Start with protein: about 1.6 g per kg of body weight a day in our calculators, spread over three or four meals. Build each meal around a protein food such as meat, fish, eggs, dairy, tofu or legumes, add vegetables or fruit for volume, then carbs and fats you like with whatever calories are left. Here's an example day built that way.
Example day in a calorie deficit (foods only, not a meal plan)
| Meal | Protein food | Vegetables or fruit | Carbs and fats |
|---|---|---|---|
| Breakfast | Greek yogurt or eggs | Berries | Oats |
| Lunch | Chicken breast | A big salad | Rice, olive oil |
| Snack | Cottage cheese or a protein shake | An apple | A handful of nuts |
| Dinner | Salmon or tofu | Broccoli or green beans | Potatoes |
It's an example, not a meal plan to follow. How much of each depends on your own calories and protein: swap in foods you like and log them to see how the day adds up.
How to keep muscle in a deficit
Three things carry it: keep lifting with the loads you already use, keep protein high, and lose at a moderate pace. In a randomized trial of people training hard in a deficit, a higher-protein diet kept lean mass and lost more fat. Watching your estimated 1RM on the main lifts tells you whether strength is holding while the scale goes down.
Why your deficit changes over time
As you lose weight, your maintenance drops, so the same calories make a smaller deficit; a clinical review on plateaus adds lower resting energy use and more hunger. If your weekly average weight stops falling for two to three weeks while you log accurately, it's time to re-estimate, not to give up.
Risks of going too low
A bigger deficit isn't always faster in practice: it's harder to keep, makes training worse and puts more muscle at risk. Our calculators never suggest less than 1,200 kcal a day or 1.2 times your resting energy (BMR), whichever is higher. If you're considering very low intakes, have a medical condition, are pregnant or breastfeeding, or have a history of disordered eating, speak to a doctor or a registered dietitian first.
Let your deficit be re-estimated each week
The BodyMacros app sets your starting calories and protein from the same formulas as our calculators, then re-estimates them every week from your weight trend and the days you train, and tells you why in plain words. Your lifting log sits next to your food, so you can see that the weight you lose is fat.
FAQ
How do you do a calorie deficit diet correctly?
Estimate your maintenance, set a deficit for a moderate rate of loss such as 0.5% of body weight a week, and keep protein high. Log what you eat, weighing food at first, keep lifting, and judge progress from weekly average weight. Re-estimate as your weight drops, because the same intake makes a smaller deficit over time.
If I eat 2,000 calories and burn 500, will I lose weight?
It depends on your total burn, not on the 500 from exercise alone. Your body also uses energy at rest and through daily movement. If your maintenance, including that exercise, is above 2,000 kcal, you're in a deficit and should lose weight over time. Our TDEE calculator estimates your maintenance from your height, weight, age and training days.
Is 1,500 calories a day too little?
It depends on the person: for a small, less active adult it may be a moderate deficit, for a tall or very active one a steep one. Work from your own maintenance estimate and a moderate rate of loss instead of a fixed number. If you're unsure, or planning to eat much less, talk to a doctor or dietitian.
How do I calculate how many calories I should eat a day to lose weight?
Estimate your maintenance from your height, weight, age, sex and training days, then subtract enough for a moderate rate of loss, such as 0.5% of body weight a week. Our calorie deficit calculator does both and shows the estimated weekly loss. Treat the result as a starting point and adjust it from your weight trend.
Track this in the app
Log your food and your lifts in one place. Your estimates adjust each week to how you eat and train.
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