A 16-year study of more than 400,000 U.S. adults tied swapping 3% of daily calories from animal to plant protein to 10% lower mortality. But when researchers turned from the heart to the biceps, the picture flipped.
A separate meta-analysis of randomized trials found animal protein modestly beat most plant proteins for building muscle, with one notable exception. Plant and animal protein are not interchangeable, and the better source depends on your goal.
For the heart, plant protein has the edge
The mortality data come from the NIH-AARP Diet and Health Study, which followed 416,104 U.S. men and women for 16 years and recorded 77,614 deaths.
The analysis in JAMA Internal Medicine, published in July 2020, tied replacing 3% of dietary energy from animal protein with plant protein to 10% lower mortality in both sexes. Cardiovascular disease mortality fell 11% in men and 12% in women.
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The source of the animal protein mattered. Swapping plant protein for egg protein was linked to a 24% lower mortality risk in men and 21% in women.
Substituting plant protein for red meat protein was tied to 13% lower risk in men and 15% in women.
Because this is a large observational cohort, it shows strong associations but cannot prove cause and effect. The findings, summarized by the National Cancer Institute, fit a broader body of research tying plant-forward eating patterns to lower cardiovascular risk.
For muscle, the answer depends on which plant
Building muscle is a different biological question. A systematic review in Nutrition Reviews, published in January 2025, pooled 30 randomized trials with 1,538 participants comparing plant and animal protein for muscle outcomes.
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Overall, animal protein produced slightly more muscle mass than plant protein, a small but statistically significant effect. The gap widened when the plant protein was rice, chia, oat, or potato, where animal protein clearly outperformed across five trials.
Soy stood apart. Across 17 trials directly comparing soy protein with milk protein, the researchers found no meaningful difference in muscle mass gains. For strength and physical performance, plant and animal protein looked equivalent.
What this means on your plate
The practical picture is not either-or. For heart health and longevity, moving some daily protein from animal sources to plants like beans, lentils, and nuts is consistently linked to lower risk in large cohorts.
For building muscle, milk, whey, and soy protein appear to do the job. Single-source rice, oat, chia, or potato protein may not match dairy, though a blend can bridge the gap.
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Total intake still matters. Researchers continue to debate how much protein people actually need to build muscle, and why the RDA falls short for anyone training hard.
Hitting that daily target from a mix of plant and animal sources fits both the mortality data and the muscle trials. Anyone planning a significant change to their diet, especially with a chronic condition or on medication, should talk it through with their doctor.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.