Protein and muscle: fasting without losing strength

When you eat in a shorter window, you usually eat fewer meals. That's often the point: fewer meals, fewer calories. But it also makes one nutrient easy to fall short on: protein. And protein is what helps you keep your muscle while you lose fat, and stay full while you do it.

Why protein matters more when you eat less

When you eat fewer calories, your body takes some of the energy it's missing from fat and some from muscle. How much comes from each depends partly on protein. A meta-analysis of 24 weight-loss trials compared diets with the same calories but more or less protein. On average, the higher-protein diets led to a little more fat loss and protected more lean mass, and resting metabolism dropped less ¹.

How much do you need?

The official minimum for adults is set to prevent deficiency, not to protect muscle during weight loss or training. Research points to higher targets for those goals. A meta-analysis of 49 trials found that protein boosted muscle gains from strength training up to about 1.6 g per kilo of body weight per day, with no further benefit beyond that on average ². For older adults, a European expert group recommends at least 1.0 to 1.2 g per kilo a day, and more for those who are active or ill ⁴.

Can your body use a big serving at once?

You may have heard that your body can only use about 20 to 30 g of protein per meal and the rest is wasted. That idea came from short studies of fast-digesting protein on its own. Reviews of the wider evidence suggest some of the extra is still used for building tissue ⁵.

Putting it into practice

• Work out your daily target: 1.2 to 1.6 g per kilo of body weight is a good range for most active adults who are losing weight.
• Build every meal around a protein source: eggs, fish, meat, tofu, tempeh, Greek yoghurt, cottage cheese or legumes.
• Break your fast with a protein-rich meal, so you start your window well fed.
• If you train, try to eat a protein-rich meal within a few hours of your session.
• If you struggle to reach your target, a protein shake within your eating window can help.

MYTH

Anything over 30 g of protein in a meal is wasted.

FACT

Studies following labelled protein show the body keeps using a larger dose for many hours ³. Very large single servings may not be quite as efficient as spreading protein out ⁶, but they're far from wasted.

Sources

1. Wycherley TP, Moran LJ, Clifton PM, et al. 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):1281-98. doi.org/10.3945/ajcn.112.044321
2. 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.org/10.1136/bjsports-2017-097608
3. Trommelen J, van Lieshout GAA, Nyakayiru J, et al. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Rep Med. 2023;4(12):101324. doi.org/10.1016/j.xcrm.2023.101324
4. Bauer J, Biolo G, Cederholm T, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013;14(8):542-59. doi.org/10.1016/j.jamda.2013.05.021
5. Schoenfeld BJ, Aragon AA. How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. J Int Soc Sports Nutr. 2018;15:10. doi.org/10.1186/s12970-018-0215-1
6. Areta JL, Burke LM, Ross ML, et al. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Physiol. 2013;591(9):2319-31. doi.org/10.1113/jphysiol.2012.244897