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Review
. 2014 Apr;15(4):310-21.
doi: 10.1111/obr.12143. Epub 2014 Jan 22.

Weight loss composition is one-fourth fat-free mass: a critical review and critique of this widely cited rule

S B Heymsfield  1 , M C C Gonzalez, W Shen, L Redman, D Thomas
Affiliations
Review

Weight loss composition is one-fourth fat-free mass: a critical review and critique of this widely cited rule

S B Heymsfield et al. Obes Rev. 2014 Apr.

Abstract

Maximizing fat loss while preserving lean tissue mass and function is a central goal of modern obesity treatments. A widely cited rule guiding expected loss of lean tissue as fat-free mass (FFM) states that approximately one-fourth of weight loss will be FFM (i.e. ΔFFM/ΔWeight = ∼0.25), with the remaining three-fourths being fat mass. This review examines the dynamic relationships between FFM, fat mass and weight changes that follow induction of negative energy balance with hypocaloric dieting and/or exercise. Historical developments in the field are traced with the 'Quarter FFM Rule' used as a framework to examine evolving concepts on obesity tissue, excess weight and what is often cited as 'Forbes' Rule'. Temporal effects in the fractional contribution of FFM to changes in body weight are examined as are lean tissue moderating effects such as ageing, inactivity and exercise that frequently accompany structured low-calorie diet weight loss protocols. Losses of lean tissue with dieting typically tend to be small, raising questions about study design, power and applied measurement method reliability. Our review elicits important questions related to the fractional loss of lean tissues with dieting and provides a foundation for future research on this topic.

Keywords: Body composition; energy expenditure; mathematical model; obesity.

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Conflict of interest statement

Potential Conflicts of Interest: None of the investigators report conflicts of interest for this study.

Figures

Figure 1
Figure 1
Three models describing “obesity tissue” or “excess weight”. Each model proposes a stable composition of weight loss with dieting that includes established values for fractional weight losses as fat and the indicated fat-free mass (FFM) or related adipose-tissue free mass (ATFM) components. The Minnesota model of body mass consists of three parts, a “core” of “normal” (N) size and composition, excess extracellular fluid (H), and obesity tissue (G) with specified proportions of fat, water, and cell solids. Wishnofsky viewed diet-related body mass changes as deriving solely from adipose tissue fat . Webster’s model posits a “core” body mass with zero fat that in women has a FFM index of 15 kg/m2; body mass above this level has a rounded fractional composition of 0.75 fat and 0.25 FFM.
Figure 2
Figure 2
The main recognized or potential contributing factors that influence the fractional loss of FFM (ΔFFM/ΔW) with dieting.
See this image and copyright information in PMC

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