Understanding the Impact of Body Composition on Longevity
Updated: Sep 17
Body weight is a blunt predictor of how long people live. Two people of the same weight can carry very different amounts of muscle and visceral fat, and those differences matter more than the scale. This article looks at three measures a modern scan reports, skeletal muscle mass, visceral fat and phase angle, and asks what recent research says about each as a predictor of mortality, how large the associations are, and who the data describe.
The evidence
Wang and colleagues (2023, PLOS ONE) pooled 16 prospective cohorts with 81,358 participants and 11,696 deaths on low skeletal muscle mass index and all-cause mortality. Li and colleagues (2025, Frontiers in Medicine) pooled 11 cohorts with 130,079 middle-aged and older adults on low lean mass and mortality, with a dose-response analysis. Saad and colleagues (2022, Frontiers in Endocrinology) systematically reviewed 12 cohorts on abdominal visceral adipose tissue, mostly measured by computed tomography, and all-cause mortality. Xia and colleagues (2025, Scientific Reports) followed 6,338 adults aged 18 to 49 from NHANES for a median of 214 months to test phase angle against mortality.
What happened
Low muscle mass is associated with higher mortality. The pooled relative risk for the lowest versus normal skeletal muscle mass index was 1.57 (95 per cent confidence interval 1.25 to 1.96), and the association strengthened with body mass index: 1.34 in the normal range, 1.91 in overweight and 2.58 (95 per cent confidence interval 1.20 to 5.54) in obesity.
The relationship is graded. In the 2025 meta-analysis, low lean mass carried a pooled relative risk of 1.30 (95 per cent confidence interval 1.16 to 1.47), with a non-linear inverse dose-response in which each additional kilogram of lean mass corresponded to roughly 1 per cent lower mortality risk.
Visceral fat predicts mortality mainly through metabolism. In cohorts with a mean age of 65 or under, higher visceral fat area carried an 11 to 98 per cent relative increase in mortality, but the association lost significance once glycaemic markers, body mass index or other fat measures were adjusted for. In older cohorts the results were inconsistent.
Phase angle predicts mortality in younger adults. Each one-degree increase in phase angle was associated with a hazard ratio of 0.73 (95 per cent confidence interval 0.59 to 0.91) after full adjustment, and high versus low phase angle with 0.67 (95 per cent confidence interval 0.46 to 0.98), with the association stronger in non-smokers.
The current answer
The most recent syntheses agree that muscle matters: low skeletal muscle or lean mass is consistently associated with a 30 to 60 per cent higher risk of death over follow-up periods of three to fourteen years, the association is graded rather than a threshold, and it is strongest in people who carry excess fat alongside low muscle. Visceral fat is associated with mortality too, but the 2022 review found the effect largely explained by the metabolic disturbance it produces, which is a reason to treat it as a warning marker rather than an independent cause. Phase angle, which reflects cell mass and membrane integrity, is a newer candidate; a single large cohort shows a clear association in younger adults, but it has not yet been pooled across studies. Certainty is moderate for muscle, low to moderate for visceral fat and low for phase angle. All of this is observational and describes populations, not individuals.
How certain is this?
Moderate for muscle mass, because two independent meta-analyses of large cohorts agree and show dose-response. Low to moderate for visceral fat, where adjustment removes much of the effect. Low for phase angle, which rests on one cohort. The samples are mostly middle-aged and older general-population adults; transfer to trained athletes is not established and sex-specific results were not reported. A pooled analysis of phase angle, and cohort data in resistance-trained adults, would change the picture most.
Muscle mass is the body-composition measure with the clearest link to longevity in current data; visceral fat and phase angle are useful flags whose independent weight is still being worked out.
What this means in practice
Treat skeletal muscle mass as the most informative single number on a body-composition report for long-term health, particularly in people who are also carrying excess fat.
Read the dose-response as an argument for maintaining muscle across decades rather than reaching a cut-off; studies observed lower risk with each kilogram, without a plateau in the ranges reported.
Treat a high visceral fat estimate as a prompt to check blood sugar, lipids and blood pressure, since those are where the risk appears to run.
Use phase angle as a trend marker between scans rather than a prognosis; the evidence is promising but early.
Remember who was studied: mostly middle-aged and older adults in general-population cohorts. The size of these associations in trained adults or in women specifically is not established.
Discuss any concerning result with a clinician who can see the whole picture; none of these numbers is a diagnosis.
Ohana Performance Institute measures skeletal muscle mass, visceral fat and phase angle on every InBody 970 scan and explains what each does and does not tell you about long-term health. Book a scan.
References
Last reviewed: 4 September 2026. Re-review if a meta-analysis of phase angle and mortality in the general population is published, or by September 2028.
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