If you want protein to maintain muscle while losing weight, the ranges the research actually uses are roughly 1.0 to 1.6 g per kg of body weight per day, spread across three main meals at 25 g or more each. That is the honest number. The honest effect size is smaller than almost anything else you will read on the subject: a higher-protein diet during an energy deficit preserved about half a kilogramme more fat-free mass than a standard-protein one. Protein is worth getting right. It is not the main lever, and anyone telling you otherwise is selling something.

For the full picture of what gets lost, how to measure it and how to train, start with our guide to losing fat without losing muscle. This piece deals with one question only: the number.

Expertise reviewed by James Cooper, Founder and CEO at Body Transformation London. BSc Nutrition, King’s College London.

What does the evidence say about protein to maintain muscle while losing weight?

The headline study is a meta-analysis of 24 trials and 1,063 participants comparing higher-protein diets (around 30% of energy) with standard-protein ones (12 to 18%) during energy restriction. The higher-protein groups lost 0.87 kg more fat mass (95% CI 0.48 to 1.26 kg more) and retained 0.43 kg more fat-free mass (95% CI 0.09 to 0.78).

Read that second figure again. Four hundred and thirty grammes. Less than a bag of sugar. That is the average benefit, across two dozen trials, of eating substantially more protein while dieting.

It is a genuine, statistically significant finding, and the confidence interval sits above zero, so the direction is trustworthy. It is also nothing like the transformation the internet promises. Most content in this space inflates this result by an order of magnitude and never quotes the number.

Is half a kilogramme actually worth bothering with?

Yes, for three reasons, none of them dramatic.

First, it comes bundled. The same dietary shift that preserved 0.43 kg of fat-free mass also stripped 0.87 kg more fat. You are not choosing between the two.

Second, it compounds. Most of our clients are not doing one twelve-week block. They are doing several years of training with occasional deficit phases, and a small consistent bias in the right direction across a decade is a meaningfully different body at 55.

Third, protein is one of the cheapest interventions available. It costs you nothing but the order in which you build a plate.

What it will not do is show up on a scan. ESPEN’s technical review puts changes of less than 1.5 to 2 kg inside the noise of bioimpedance, and on the class of device most gyms run, a change in body fat percentage under roughly 2 to 3 points cannot be confidently separated from noise either (McLester 2020, on the InBody 230, 720 and 770). So a reading that says you gained 0.4 kg of muscle this month is measurement error, not progress.

Does the answer change as you get older?

The direction of the evidence gets slightly stronger. A review of 20 randomised trials in older adults found that higher-protein diets, defined as at least 25% of energy or roughly 1.0 g/kg/day, retained more lean mass and lost more fat mass during weight loss than lower-protein comparisons.

The European Association for the Study of Obesity’s position statement on older adults is the most usable practical guidance we have. It sets a minimum of 1.0 to 1.2 g/kg/day, timed at 25 g or more per meal across three main meals, and pairs it with moderate-to-high-intensity resistance training, which it describes as attenuating lean mass loss during weight loss and preserving bone mineral density.

Note the structure of that recommendation. A daily total, a per-meal floor, and a training requirement. All three, not one of them.

So where does 2.4 g/kg come from?

From one four-week study that is probably the most over-extrapolated paper in fitness.

Forty young men ate at roughly a 40% energy deficit for four weeks while doing near-daily supervised hard training. The 2.4 g/kg/day group gained 1.2 kg of lean mass (SD 1.0); the 1.2 g/kg/day group gained 0.1 kg (SD 1.0).

Look at what that protocol required. Young. Healthy. Male. Supervised almost every day. Four weeks, not four months. An extreme deficit no sensible coach would run for long. And standard deviations of a full kilogramme either side, meaning individual responses varied enormously.

It is a good proof of concept that protein and hard training can shift what is possible under laboratory conditions. It is not a recommendation. It does not license telling a 50-year-old solicitor who trains twice a week between client meetings to eat 2.4 g/kg/day, and the fact that it gets used that way constantly is the clearest sign of how loose this niche is with evidence.

What does 1.0 to 1.6 g/kg look like on a plate?

Do the arithmetic on your own body weight first. At 80 kg, 1.0 to 1.6 g/kg is roughly 80 to 128 g of protein a day. At 65 kg, roughly 65 to 104 g. Divide by three meals and you land near the 25 g per meal floor the EASO statement describes.

In practice, for a busy British professional, that usually means building each meal around a protein source rather than adding one at the end:

• Breakfast, the meal most often skipped or made of toast alone. Eggs, Greek yoghurt, milk-based porridge, smoked salmon, baked beans on wholemeal toast, or cottage cheese.
• Lunch, usually bought and usually the weakest meal of the day. A chicken, tuna, prawn, egg or bean-based salad or sandwich rather than a pastry or a soup on its own.
• Dinner, the one people already get right. A palm-sized portion or larger of chicken, fish, lean mince, tofu, lentils or pulses, with the rest of the plate built around it.

That is the whole method: three meals, each anchored by a protein food, rather than one large protein hit at dinner. If you want exact grams, the back of the packet will tell you. You do not need a supplement to hit these numbers, and we do not sell any.

This is general, population-level guidance. It is not a meal plan, and it is not tailored to you.

Does protein work without lifting?

Not on its own, no. Protein is a raw material, not a signal.

The clearest evidence sits in a network meta-analysis of 62 randomised trials and 4,429 participants. Caloric restriction alone was the only arm that significantly lost lean mass compared with control. It lost 1.66 kg of lean body mass (95% CI 0.19 to 3.12 kg). Every arm that added training protected lean mass better, although the individual confidence intervals crossed zero, so the robust finding is the negative one: dieting by itself is the approach that costs you tissue.

The British Nutrition Foundation put it plainly in 2025: adequate protein and strength-based activity are essential to help maintain muscle mass. Both halves. If you only have the appetite to fix one thing this quarter, fix the strength training during weight loss side first, then the protein.

If your weight loss is being overseen by a clinician, no authority has established an optimal protein target for that situation, and the ranges being proposed are explicitly borrowed from bariatric surgery practice by authors who state openly that prospective data are lacking. The same range and the same training requirement are the sensible starting point, and anyone quoting you a precise figure is guessing.

Where coaching stops and dietetics starts

“Dietitian” is the only legally protected nutrition title in the UK, regulated by the HCPC. “Nutritionist” is not protected by law and the register is voluntary. BTX coaches are coaches. James Cooper’s background is in nutrition, and none of us are your dietitian.

That means everything above is general and population-level, which is exactly what it should be. Individual meal prescriptions, calorie-specific plans, anything targeting a medical condition, and clinical interpretation of results all sit outside coaching scope, and we refer for those rather than improvise. If you are between 40 and 74, the free NHS Health Check covers height, weight, waist measurement, blood pressure and cholesterol every five years, and is the sensible starting point for the medical side.

If you want this measured and programmed around

Getting protein roughly right is a solved problem you can act on today without us. What is harder is knowing whether your training is actually protecting the tissue you care about, and reading a measurement honestly enough to tell. That is the part we do, in Finchley Road, through nutrition coaching and training built around it. If you want it measured properly and programmed around, book a call and we will tell you what we can and cannot see.

Free InBody scan until 30 September

We are running complimentary body composition scans at our Finchley Road studio, Monday to Friday between 10am and 2pm. Thirty minutes: the scan itself, plus a coach taking you through what your numbers mean and which ones to ignore. No charge, no obligation, one per person.

Book your free scan or see what’s included.

This article is general information, not medical advice. If you have a medical condition, are pregnant, are taking any prescribed medication, or have a history of disordered eating, speak to your GP or a registered dietitian before changing how you train or eat.

Frequently asked questions

How much protein do I need to keep muscle while losing weight?
The literature works in a range of roughly 1.0 to 1.6 g per kg of body weight per day. The EASO position statement on older adults sets a minimum of 1.0 to 1.2 g/kg/day with at least 25 g per meal across three main meals, alongside resistance training. At 80 kg that is roughly 80 to 128 g a day.

Is more protein always better?
There is no good evidence that pushing far above that range helps a normally training adult. The 2.4 g/kg figure comes from 40 young men on a supervised near-daily training protocol for four weeks at an extreme deficit. It is a proof of concept under laboratory conditions, not a target for someone training two or three times a week.

Do I need a protein shake?
No. The daily totals above are reachable from ordinary food across three meals, and we do not sell supplements. A shake is a convenience, not a requirement.

Does protein protect muscle if I am not lifting?
It helps, but it is not the mechanism. In a network meta-analysis of 62 trials, caloric restriction alone was the only arm that significantly lost lean body mass, at 1.66 kg. The British Nutrition Foundation’s 2025 position is that adequate protein and strength-based activity together are what help maintain muscle mass.

Sources

• Wycherley TP et al. Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets. American Journal of Clinical Nutrition, 2012.
• Kim JE et al. Effects of dietary protein intake on body composition changes after weight loss in older adults. Nutrition Reviews, 2016;74(3):210–224. https://academic.oup.com/nutritionreviews/article/74/3/210/1825906
• Di Vincenzo O et al. European Association for the Study of Obesity position statement on nutrition and older adults. Obesity Facts, 2026;19(4):422–437. https://karger.com/ofa/article/doi/10.1159/000549751/940127/
• Longland TM et al. Higher compared with lower dietary protein during an energy deficit. American Journal of Clinical Nutrition, 2016.
• Xie Y, Gu Y, Li Z, Zhang L, Hei Y. Network meta-analysis of exercise and caloric restriction on body composition. Frontiers in Nutrition, 2025;12:1579024. https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2025.1579024/full
• British Nutrition Foundation. Summary statement on weight loss and muscle mass, 2025.
• Spreckley M, Ruggiero CF, Brown A. International Journal of Obesity, 2026;50:265–267. https://www.nature.com/articles/s41366-025-01952-w
• Kyle UG et al. Bioelectrical impedance analysis: ESPEN technical review. Clinical Nutrition, 2004. https://www.espen.org/documents/BIA1.pdf
• McLester CN, Nickerson BS, Kliszczewicz BM, McLester JR. Reliability of the InBody 230, 720 and 770. Journal of Clinical Densitometry, 2020;23(3):443–450.
• British Dietetic Association, what is a dietitian. https://www.bda.uk.com/about-dietetics/what-is-dietitian.html
• Association for Nutrition, registration FAQs. https://www.associationfornutrition.org/register/registration-faqs
• NHS Health Check. https://www.nhs.uk/conditions/nhs-health-check/

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