How much should you really eat?

Your calories at rest

I use the Mifflin-St Jeor equation, published by Mifflin, St Jeor and colleagues in 1990. A 2005 review by Frankenfield and colleagues compared the common formulas and found this one the most reliable for healthy adults. For women it goes like this:

10 × weight in kg + 6.25 × height in cm - 5 × age - 161

Your normal day

That number is what your body burns lying still. I multiply it by your activity level to get your maintenance calories, the amount that keeps your weight where it is.

Your goal

To lose fat, I take 20% off maintenance, and never more than 750 kcal a day. A bigger cut costs you muscle, energy and mood, and it is hard to stick to. To maintain, you eat your maintenance. To build muscle, I add 8%. A small surplus is enough to feed your training.

Never below 1500

I never set a target under 1500 kcal. Below that it gets very hard to eat enough protein, fiber and vitamins, and hunger wins in the end. If the math lands under 1500, I add movement instead of cutting food.

Protein, fat, carbs

Protein is 1.8 g per kg of body weight, or 2.0 g when you are losing fat, to protect your muscle while you eat less. A 2018 meta-analysis by Morton and colleagues found the muscle benefit levels off around 1.6 g per kg, and the ISSN position stand recommends 1.4 to 2.0 g per kg for people who train. If your BMI is over 30, I use the weight you would have at a BMI of 25, so the number stays realistic. Fat is 28% of your calories and at least 0.8 g per kg of that same weight. Carbs get whatever is left. They fuel your workouts.

The weekly estimate

I count 7700 kcal for each kg of body fat (3500 for each lb). Real bodies are messier. Water, salt and your cycle move the scale from day to day, so read it as a direction. Track for 2 to 3 weeks, then adjust.