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Effect of Dietary Protein on Fat-Free Mass in Energy Restricted, Resistance-Trained Individuals: An Updated Systematic Review With Meta-Regression

Refalo, Martin C., Trexler, Eric T., Helms, Eric R.·2026·Strength & Conditioning Journal
DOI 10.1519/ssc.0000000000000888
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Abstract

Individuals often restrict energy intake to lose fat mass (and body mass [BM]) while performing resistance training (RT) to retain fat-free mass (FFM). Therefore, the aim of the present systematic review with meta-regression was to explore (a) the pattern and strength of the dose-response relationship between daily dietary protein intake and FFM change, and (b) whether intervention duration, energy deficit magnitude, baseline body fat percentage (BF%), and participant sex influence this relationship. Studies were included if they involved a standardized RT protocol with nonobese, energy-restricted (experiencing fat mass loss) individuals with a minimum of 3 months RT experience. Of 916 retrieved studies, data were extracted from a total of 29 studies. Bayesian methods were used to fit linear and nonlinear meta-regression models and estimate effect sizes, highest density credible intervals, and probabilities. Results suggest a >97% probability of a linear dose-response relationship between daily protein intake [g/kgBM: β = 0.07 (95% highest density interval [HDI]: −0.01 to 0.14), and g/kg/FFM: β = 0.06 (95% HDI: 0.01 to 0.12)] and favorable FFM changes. The relationship is stronger when protein intake is expressed relative to FFM, in interventions longer than 4 weeks, in men, and when BF% is lower. Overall, the heterogeneity between studies renders our findings exploratory.

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Figure 1 Mediators and moderators of fat-free mass change during energy restriction investigated in this systematic review with meta-regression. Moderators are conditions under which energy restriction may influence fat-free mass retention, whereas mediators are affected by energy restriction and may therefore influence fat-free mass retention.
Figure 1 Mediators and moderators of fat-free mass change during energy restriction investigated in this systematic review with meta-regression. Moderators are conditions under which energy restriction may influence fat-free mass retention, whereas mediators are affected by energy restriction and may therefore influence fat-free mass retention.CC-BY-NC-ND · From the PDF
Figure 2 PRISMA flow chart. Summary of systematic literature search and article selection process.
Figure 2 PRISMA flow chart. Summary of systematic literature search and article selection process.CC-BY-NC-ND · From the PDF
Figure 3 Key characteristics from each group within the included studies. Data are presented as raincloud plots with each dot point representing a group-level effect included in the meta-regression. Energy deficit magnitude does not include extreme values ( . 2000) that were replaced with the median.
Figure 3 Key characteristics from each group within the included studies. Data are presented as raincloud plots with each dot point representing a group-level effect included in the meta-regression. Energy deficit magnitude does not include extreme values ( . 2000) that were replaced with the median.CC-BY-NC-ND · From the PDF
Figure 4 Best fit linear meta-regression displaying the relationship between daily protein intake (grams per kilogram of body mass) and fat-free mass change across a resistance training intervention in energy-restricted individuals. Dot points represent estimated group-level standardized mean changes, with dot size representing its weight determined by inverse variance weighting. Shaded region around regression line represents highest density credible intervals categorized as 50% (darkest red), 80%, and 95% (lightest red).
Figure 4 Best fit linear meta-regression displaying the relationship between daily protein intake (grams per kilogram of body mass) and fat-free mass change across a resistance training intervention in energy-restricted individuals. Dot points represent estimated group-level standardized mean changes, with dot size representing its weight determined by inverse variance weighting. Shaded region around regression line represents highest density credible intervals categorized as 50% (darkest red), 80%, and 95% (lightest red).CC-BY-NC-ND · From the PDF
Figure 5 Best fit linear meta-regression displaying the relationship between daily protein intake (grams per kilogram of fat-free mass) and fat-free mass change across a resistance training intervention in energy-restricted individuals. Dot points represent estimated group-level standardized mean changes, with dot size representing its weight determined by inverse variance weighting. Shaded region around regression line represents highest density credible intervals categorized as 50% (darkest orange), 80%, and 95% (lightest orange).
Figure 5 Best fit linear meta-regression displaying the relationship between daily protein intake (grams per kilogram of fat-free mass) and fat-free mass change across a resistance training intervention in energy-restricted individuals. Dot points represent estimated group-level standardized mean changes, with dot size representing its weight determined by inverse variance weighting. Shaded region around regression line represents highest density credible intervals categorized as 50% (darkest orange), 80%, and 95% (lightest orange).CC-BY-NC-ND · From the PDF
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Citations

Cites

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Metadata

Authors
Refalo, M. C., Trexler, E. T., & Helms, E. R.
Affiliations
  • Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Geelong, Australia;
  • Department of Evolutionary Anthropology, Duke University, Durham, North Carolina;
  • Sport Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, Auckland, New Zealand; and
Venue
Strength & Conditioning Journal
Publisher
Ovid Technologies (Wolters Kluwer Health)
Published
2025-01-22
Volume
48
Issue
4
Pages
398-412
ISSN
  • 1524-1602
  • 1533-4295
DOI
10.1519/ssc.0000000000000888
Cited by
5
References
18
Language
en
Licence
creativecommons.org/licenses/by-nc-nd/4.0/ (unspecified)
Funders
Renaissance Periodization, LLC, Reg. U.S. Pat. & Tm. Off.

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