In 30 seconds
- In a deficit, the reference review in people who do strength training recommends 2.3-3.1 g of protein per kilo of lean mass a day: about 1.8-2.5 g per kilo of body weight.
- In a meta-analysis of 24 trials with 1,063 people, the high-protein diet preserved 0.43 kg more fat-free mass and added 0.87 kg more fat loss.
- In athletes dieting for 2 weeks, those on 2.3 g per kilo lost 0.3 kg of lean mass, compared with 1.6 kg on 1.0 g per kilo.
- With 2.4 g per kilo, a 40% deficit and intense training, a group of young men gained 1.2 kg of lean mass and lost 4.8 kg of fat in 4 weeks.
When you eat less to lose fat, you need more protein, not less. In people who do strength training, the studies point to 2.3-3.1 g per kilo of lean mass a day 1 2. For most people, that is about 1.8-2.5 g per kilo of body weight. With that amount, most of what you lose is fat rather than muscle.
Why protein matters more in a deficit
When you eat less than you use, your body draws on its reserves. Fat is the main one, but not the only one: it can also use protein from muscle.
The reference systematic review sums it up like this: protein needs rise when you restrict energy and the leaner you are 2. That is why the figure for a fat-loss phase is higher than the one for maintenance.
Level of evidence by outcome
| Outcome | Evidence | What the data show |
|---|---|---|
| Preserving lean mass | High | Less lean mass lost with more protein in a meta-analysis of 24 trials and in several trials with athletes. |
| Losing more fat | Moderate | 0.87 kg more fat lost in 24 trials; in some trials with training, the fat lost was the same. |
| People over 50 | Moderate | More lean mass preserved and more fat lost with more protein, in 20 trials. |
| Satiety | Low | Greater feeling of fullness in 3 of the 5 studies that measured it. |
| Going from 1.6 to 2.4 g per kilo | No clear effect | In a 31-day trial, tripling the recommended intake did not protect muscle more than doubling it. |
The rating is our own, based on the number of studies, their quality and the consistency of the results.
The key studies
| Study | Type | Sample | Outcome |
|---|---|---|---|
| Helms et al., 2014 | Systematic review | 6 studies with lean athletes who do strength training | Likely needs of 2.3-3.1 g per kilo of lean mass a day, higher the bigger the deficit and the lower the body fat. 2 |
| Mettler et al., 2010 | Trial | 20 strength-trained athletes | 2 weeks at 60% of their usual intake: 0.3 kg of lean mass lost with 2.3 g/kg a day, compared with 1.6 kg with 1.0 g/kg. 3 |
| Pasiakos et al., 2013 | Trial | 39 adults | 21 days with a 40% deficit: with 1.6 and 2.4 g/kg, less fat-free mass and more fat was lost than with 0.8 g/kg. 4 |
| Longland et al., 2016 | Trial | 40 young men | 4 weeks, a 40% deficit and training 6 days a week: +1.2 kg of lean mass and −4.8 kg of fat with 2.4 g/kg, compared with +0.1 kg and −3.5 kg with 1.2 g/kg. 5 |
| Wycherley et al., 2012 | Meta-analysis | 24 trials, 1,063 people | Compared with a standard-protein diet: −0.79 kg of weight, −0.87 kg of fat and 0.43 kg more fat-free mass preserved. 6 |
| Kim et al., 2016 | Meta-analysis | 20 trials with people over 50 | With higher-protein diets, more lean mass preserved and more fat lost during weight loss. 7 |
Protein in a deficit
How much protein a day, per kilo of body weight
The figure: 2.3-3.1 g per kilo of lean mass
A systematic review brought together 6 studies with lean athletes who did strength training and were dieting. In 9 of the 13 groups, lean mass was lost, between 0.3 and 2.7 kg 2.
One group stood out: with little fat to start with, no new training and a sharp cut, it preserved its lean mass. It was the group with the highest protein intake: 2.5-2.6 g per kilo 2. The authors conclude that the likely need is 2.3-3.1 g per kilo of lean mass a day 2.
Lean mass is your weight without the fat. If you do not know it, work it out from your body weight: for most people, that is 1.8-2.5 g per kilo 1.
| Your weight | Per day (1.8-2.5 g per kilo) | Before and after training (0.4-0.5 g per kilo) |
|---|---|---|
| 60 kg | 108-150 g | 24-30 g |
| 70 kg | 126-175 g | 28-35 g |
| 80 kg | 144-200 g | 32-40 g |
| 90 kg | 162-225 g | 36-45 g |
Based on Helms et al., 2014: 2.3-3.1 g per kilo of lean mass, which with 20% body fat is equivalent to 1.8-2.5 g per kilo of body weight. Figures rounded.
If you want your exact figure, split across your meals, use our protein calculator.
4-week trial
40% less food: 2.4 versus 1.2 g of protein per kilo
What the trials found
Athletes on a diet: less muscle lost
In one trial, 20 strength-trained athletes ate 60% of their usual energy intake for 2 weeks while continuing to train. Half took 1.0 g of protein per kilo; the other half, 2.3 g 3.
| 1.0 g per kilo (15% of the diet) | 2.3 g per kilo (35% of the diet) | |
|---|---|---|
| Weight lost | 3.0 kg | 1.5 kg |
| Lean mass lost | 1.6 kg | 0.3 kg |
| Fat lost | No difference between groups | No difference between groups |
Source: Mettler et al., 2010. 20 strength-trained athletes, at 60% of their usual intake.
Look at the scales: the low-protein group lost twice as much weight, but a good part of it was muscle. The fat lost was the same in both groups, and performance did not change either 3.
A 40% deficit: double is enough
Another trial compared three amounts in 39 adults: 0.8, 1.6 and 2.4 g per kilo. After 10 days of maintenance, they spent 21 days in a 40% deficit and lost about 3.2 kg 4.
With 1.6 and 2.4 g per kilo, a smaller share of the weight lost was fat-free mass and a larger share was fat. With 0.8 g, the muscle's response to a protein-rich meal fell during the deficit; with the higher amounts, it did not 4.
With intense training: building muscle while eating less
In the most striking trial, 40 young men ate 40% less than they needed for 4 weeks. They trained 6 days a week, combining strength work and high-intensity intervals 5.
- With 2.4 g per kilo: they gained 1.2 kg of lean mass and lost 4.8 kg of fat.
- With 1.2 g per kilo: they gained 0.1 kg of lean mass and lost 3.5 kg of fat.
It is a demanding protocol, but it shows what a high protein intake can do alongside training 5.
Meta-analysis of 24 trials
High-protein diet versus standard protein
What the meta-analysis says
In 2012, a meta-analysis brought together 24 trials with 1,063 adults. It compared diets with the same energy, some high in protein and others with standard protein, over 12 weeks on average 6.
With the high-protein diet 6:
- 0.79 kg more weight lost.
- 0.87 kg more fat lost.
- 0.43 kg more fat-free mass preserved.
- A smaller drop in resting energy expenditure and greater fullness in 3 of the 5 studies that measured it.
From 50 onwards
As the years go by, it gets harder to keep your muscle, so protein carries more weight in your plan. A meta-analysis brought together 20 trials with people over 50 who were losing weight. With higher-protein diets, they preserved more lean mass and lost more fat 7.
You will find the complete plan for this stage of life in our guide to losing fat after 40.
How to spread it
The reference review suggests 3-6 meals a day, with a serving of 0.4-0.5 g per kilo before and another after training 1. If you weigh 75 kg, that is about 30-38 g each time.
In practice:
- Include protein at every meal: meat, fish, eggs, dairy or pulses.
- Start with breakfast, which often falls short.
- Use a shake when a meal does not provide enough. Protein contributes to the maintenance of muscle mass 8. A varied and balanced diet and a healthy lifestyle are important.
- If you have kidney disease, check with your doctor before increasing your protein.
You will find how to calculate your calories in calorie deficit: how much to eat.
What about CLA?
With protein and strength training in place, CLA has also been studied. A meta-analysis of 18 trials found 0.09 kg more fat lost per week than with placebo, with 3.2 g a day 9.
Frequently asked questions
How much protein should you eat in a calorie deficit?
The reference review in people who do strength training recommends 2.3-3.1 g per kilo of lean mass a day, about 1.8-2.5 g per kilo of body weight. If you weigh 80 kg, between 144 and 200 g a day, spread across 3-6 meals.
Can you build muscle in a calorie deficit?
Yes, especially if you train intensely and eat plenty of protein. In a 4-week trial with a 40% deficit, young men who took 2.4 g per kilo and trained 6 days a week gained 1.2 kg of lean mass.
Does eating more protein help you lose more fat?
A little. In a meta-analysis of 24 trials, with the same energy intake, the high-protein diet added 0.87 kg more fat loss and preserved 0.43 kg more fat-free mass than the standard-protein diet.
Do I need more protein if I am over 50 and dieting?
Yes, it helps. In a meta-analysis of 20 trials with people over 50, higher-protein diets preserved more lean mass and lost more fat during weight loss.
Sources
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11(1):20. View publication
- Helms ER, Zinn C, Rowlands DS, Brown SR. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. Int J Sport Nutr Exerc Metab. 2014;24(2):127-138. View publication
- Mettler S, Mitchell N, Tipton KD. Increased protein intake reduces lean body mass loss during weight loss in athletes. Med Sci Sports Exerc. 2010;42(2):326-337. View publication
- Pasiakos SM, Cao JJ, Margolis LM, et al. Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial. FASEB J. 2013;27(9):3837-3847. Europe PMC record. View publication
- Longland TM, Oikawa SY, Mitchell CJ, Devries MC, Phillips SM. Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. Am J Clin Nutr. 2016;103(3):738-746. View publication
- Wycherley TP, Moran LJ, Clifton PM, Noakes M, Brinkworth GD. Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012;96(6):1281-1298. View publication
- Kim JE, O'Connor LE, Sands LP, Slebodnik MB, Campbell WW. Effects of dietary protein intake on body composition changes after weight loss in older adults: a systematic review and meta-analysis. Nutr Rev. 2016;74(3):210-224. View publication
- Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods. View publication
- Whigham LD, Watras AC, Schoeller DA. Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans. Am J Clin Nutr. 2007;85(5):1203-1211. Summary by NutraIngredients. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product.
