Plant and Dairy Protein Shakes Left Blood Chemistry Alike in Adults Over 50

That is the finding of a secondary analysis of a randomised controlled trial, published in 2026 in Metabolomics, the official journal of the Metabolomic Society. The trial was double-blinded and ran for 12 weeks. It enrolled 171 healthy adults aged 50 and over, 100 women and 71 men. The average age was 59.2 years. A secondary analysis means the researchers went back to data from an earlier trial to ask new questions.

Participants were randomly assigned to one of three daily shakes. One was a plantbased protein shake with 23 grams of protein. One was a dairy-based shake with 22 grams. The third was a low-protein shake with 2 grams. Everyone was told to keep their usual diet and physical activity. Fasting blood samples and handgrip strength were taken at the start and after 12 weeks.

The team measured 140 metabolites in plasma, the liquid part of blood. Metabolites are small molecules made or used by the body's chemistry. The researchers asked whether plant and dairy protein changed this profile differently. According to the paper, they did not. There was no significant main effect of group (p = 0.23) and no significant group-by-time interaction (p = 1.00). Time itself did have a significant effect on the profile.

Grip strength did not differ between groups at the start, averaging 27.9 kg. Changes in grip strength over 12 weeks also did not differ significantly between the groups (p = 0.17), according to the paper.

The second question was whether any metabolites tracked with grip strength. Because the shakes made no difference to the profile, the authors pooled all participants for this part. After correcting for the many comparisons made, 26 of the 140 metabolites were significantly correlated with baseline grip strength. The methods also say the researchers examined whether baseline metabolites were linked to later changes in grip strength, but the portion of the results we could review cuts off before those findings, so we cannot report them. Some research cited in the paper has linked circulating branched-chain amino acids, which include leucine and isoleucine, to muscle mass and strength in older adults, but that is background, not a result of this trial.

These are correlations. They do not show that any metabolite causes stronger grip, or that raising it would help. The participants were also healthy and free of chronic or metabolic disease, so the results may not apply to people with such conditions. The paper notes that higher baseline branched-chain amino acid levels have been linked in other research to later type 2 diabetes risk, so the picture is not simple. This is where the argument is weakest: we cannot say from the text available which metabolites matter most.

The authors conclude that the metabolic changes were not related to protein type. They say the links with grip strength suggest the need to evaluate a person's metabolic state before nutritional interventions. In plain terms, the same extra protein may not suit everyone equally. This trial did not test that idea directly.

The findings add a different angle to an earlier piece in The Arising, on a 47-year Swedish study in which aerobic fitness and endurance peaked between 26 and 36. That work tracked how capacity changes with age. This trial asks what blood chemistry might say about strength in people already past 50. They are separate studies.

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Studies that test directly whether a person's baseline metabolic profile predicts who gains strength from extra protein.

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