What a calorie deficit is
Your body burns energy all day: to stay alive, to move and to digest what you eat. When you eat less than you burn, it draws on its reserves, and the main one is fat. That gap between what you burn and what you eat is the deficit.
Eating the same as you burn is called maintenance. It is the starting point of any calculation: first you find your maintenance, then you take the deficit off it.
How big a deficit to aim for
A bigger deficit is not better. In a study of athletes, those who lost about 0.7% of their body weight per week kept more lean mass and strength than those who lost it twice as fast (Garthe et al., 2011). That is why recommendations for people who train sit at 0.5% to 1% per week (Helms et al., 2014).
| Rate | Per week | Who it suits |
|---|---|---|
| Slow | Under 0.5% of your weight | You are close to your goal or want to perform at your best |
| Moderate | 0.5% to 1% of your weight | Most people |
| Fast | Over 1% of your weight | Short stretches, with a higher risk of losing muscle |
Mobbe's calorie calculator uses 0.75% per week as the recommended rate and also shows you the slow and the fast one.
How to work out your deficit in 3 steps
- Find your maintenance. From your age, height, weight and activity. The calorie calculator uses the Mifflin-St Jeor equation, one of the most accurate for healthy adults (Frankenfield et al., 2005).
- Take off the deficit. Multiply your weight by 0.005 (0.5%) or 0.01 (1%) to get how many kilos to lose per week. A kilo of fat is worth about 7,700 kcal, so divide by 7 to turn it into calories per day.
- Adjust every two weeks. Weigh yourself several mornings a week and look at the average. If it has not moved in two weeks, take off another 100 to 200 kcal.
Example: if you weigh 70 kg and your maintenance is 2,400 kcal, losing 0.5% per week is about 0.35 kg. That is roughly 400 fewer calories a day, so you would eat about 2,000 kcal.
The 7,700 kcal per kilo figure is an approximation. Over time your body burns a little less and weight loss slows down, which is why step 3 matters (Hall, 2008).
How to keep your muscle
- Eat enough protein. 1.6 to 2.2 g per kilo of body weight per day covers most people who train (Morton et al., 2018). Work out yours with the protein calculator.
- Keep lifting. Strength training is the signal that tells your body to hold on to muscle while it loses fat. See the fat loss routines.
- Do not go faster than 1% per week. A slower rate keeps more lean mass and is easier to stick to.
Common mistakes
- Cutting too much at the start. A very large deficit brings hunger and fatigue, and it is the quickest way to quit after two weeks.
- Looking at a single day's weight. Weight goes up and down with water, salt and digestion. What counts is the weekly average.
- Not adjusting. As you lose weight, your maintenance drops too. Recalculate every few kilos.
Questions
How big a calorie deficit is safe?
For most adults, a deficit that takes off up to 1% of body weight per week. Diets under 800 kcal a day are only recommended with medical supervision (Jensen et al., 2014).
Can you build muscle in a calorie deficit?
Yes, especially if you are new to training or carry more body fat (Forbes, 2000). With more experience, the usual outcome is keeping muscle, not gaining it.
Why did I stop losing weight if I am still in a deficit?
Because a lighter body burns less, so what used to be a deficit is now close to your maintenance. Recalculate your calories with your current weight and take the deficit off again.
Do I have to count calories every day?
Not necessarily. You can work out your target once, build meals that hit it and repeat them, and use your weekly average weight to see whether you are on track.
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. doi:10.1093/ajcn/51.2.241
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789. doi:10.1016/j.jada.2005.02.005
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20. doi:10.1186/1550-2783-11-20
- Garthe I, Raastad T, Refsnes PE, Koivisto A, Sundgot-Borgen J. 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
- Hall KD. What is the required energy deficit per unit weight loss? Int J Obes. 2008;32(3):573-576. doi:10.1038/sj.ijo.0803720
- Morton RW, Murphy KT, McKellar SR, 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 in healthy adults. Br J Sports Med. 2018;52(6):376-384. doi:10.1136/bjsports-2017-097608
- Forbes GB. Body fat content influences the body composition response to nutrition and exercise. Ann N Y Acad Sci. 2000;904:359-365. doi:10.1111/j.1749-6632.2000.tb06482.x
- Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults. Circulation. 2014;129(25 Suppl 2):S102-S138. doi:10.1161/01.cir.0000437739.71477.ee
This guide is for information only and does not replace advice from a health professional.
