Protein Intake and Health: Requirements for Muscle Maintenance and Increase

Proteins consist of chains of amino acids, of which nine are essential and must be obtained through the diet. These chains fold into three-dimensional structures, and their shape ultimately determines the function of the protein in the body. (1) Amino acids are therefore often referred to as “building blocks”.

In recent years, protein has gained increasing attention, and its importance is frequently highlighted. However, recommended intake levels often vary, making it difficult to understand how much protein is actually needed.

Although protein has many functions in the body, including supporting enzyme activity (2), immune function (3) and tissue repair (4), this article focuses on its most widely discussed role: the maintenance and increase of lean body mass.

What does the evidence say?

The World Health Organisation suggests a recommended protein intake of 0.83g/kg of body weight per day to sustain muscle maintenance and prevent deficiency. (5) Several systematic reviews have assessed whether a higher intake may be favourable for muscle mass maintenance and increase.

• A 2018 systematic review and meta-analysis of 49 randomised controlled trials examined whether increased protein intake enhances muscle mass when combined with resistance training. The analysis found small but significant increases in lean body mass, with benefits increasing alongside protein intake up to approximately 1.6 g/kg/day, although this was not strongly statistically conclusive and no further gains were observed beyond that. This suggests that protein intake may increase, but not replace, the effects of resistance exercise. (6)

• These findings are further supported by another systematic review published in 2022 that investigated whether higher protein intake supports muscle mass in combination with resistance training in healthy adults. The analysis showed that increasing protein intake can lead to small but significant gains in lean body mass when paired with resistance training. Benefits were observed across intake ranges of approximately 1.2 to ≥1.6 g/kg/day, depending on age. However, the authors noted that resistance training is a key driver of the effects, and we therefore cannot assume that a higher protein intake alone without training would be equally efficient. (7)

• In contrast, another systematic review including 105 randomised controlled trials investigated the dose-response relationship between protein intake and muscle mass. The authors reported a continuous dose-response relationship between protein intake and lean body mass, showing that an increasing protein intake of as little as 0.1 g/kg/day was associated with a greater increase in lean body mass at total protein intake of approximately 1.3g/kg/day or less, but smaller gains at higher total intake levels, therefore indicating diminishing returns beyond 1.3g/kg/day. (8)

• Lastly, a 2020 systematic review including randomised controlled trials with and without resistance training found that an increase in protein intake was associated with small increases in lean body mass. The authors also concluded that the timing of protein intake did not significantly influence these outcomes. (9)

  
  

What does this mean in practice?

• Across systematic reviews, it becomes clear that there is no single “optimal” protein intake that applies to everyone.

• While higher protein intakes are generally associated with improvements in lean body mass, the exact amount at which these benefits occur is difficult to define. This is largely due to differences between studies, including variations in participant characteristics such as age, baseline protein intake, physical activity levels, and overall health status.

• In addition, study designs differ in terms of protein sources, duration, and whether resistance training is included, all of which can influence outcomes. As a result, protein requirements are best understood as a range rather than a fixed number.

• During regular resistance training, a higher protein intake may support increases in lean body mass.

• Without resistance training, a higher protein intake shows smaller and less consistent effects, with less evidence currently present.

  
  
  
  

Key takeaway

Increased protein intake can support lean body mass, particularly when combined with resistance training. However, the effect of protein alone is modest, and no single optimal intake applies to all individuals. Therefore, rather than focusing on a fixed number, a better approach would be to aim for an adequate daily protein intake within a practical range and adapt it to your individual needs.

References:

1. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. Molecular biology of the cell. 4th ed. New York: Garland Science; 2002. The shape and structure of proteins. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26830/

2. Morris R, Black KA, Stollar EJ. Uncovering protein function: from classification to complexes. Essays Biochem. 2022;66(3):255–285. doi:10.1042/EBC20200108

3. Li P, Yin YL, Li D, Kim SW, Wu G. Amino acids and immune function. Br J Nutr. 2007;98(2):237–252. doi:10.1017/S000711450769936X

4. Ozgok Kangal MK, Kopitnik NL. Physiology, wound healing. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan– [updated 2025 Apr 4]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535406/

5. World Health Organization. Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation. Geneva: WHO; 2007. Available from: https://apps.who.int/iris/handle/10665/43411

6. Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, 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

7. Nunes EA, Colenso-Semple L, McKellar SR, Yau T, Ali MU, Fitzpatrick-Lewis D, et al. Systematic review and meta-analysis of protein intake to support muscle mass and function in healthy adults. J Cachexia Sarcopenia Muscle. 2022;13(2):795–810. doi:10.1002/jcsm.12922

8. Tagawa R, Watanabe D, Ito K, Ueda K, Nakayama K, Sanbongi C, et al. Dose-response relationship between protein intake and muscle mass increase: a systematic review and meta-analysis of randomized controlled trials. Nutr Rev. 2021;79(1):66–75. doi:10.1093/nutrit/nuaa104

9. Wirth J, Hillesheim E, Brennan L. The role of protein intake and its timing on body composition and muscle function in healthy adults: a systematic review and meta-analysis of randomized controlled trials. J Nutr. 2020;150(6):1443–1460. doi:10.1093/jn/nxaa049

Disclaimer: This article is for educational purposes only and does not replace medical advice. Individual needs vary, and personalised guidance from a qualified healthcare professional is recommended for tailored support.