20-Gram Protein Dose Failed to Boost Muscle Building in Older Men

This is a randomized, double-blind trial in people. It enrolled 45 healthy men with an average age of 69. Each man was assigned to one of three groups and took a single protein dose.

One group ingested 20 grams of a plant blend, made of 12 grams of soy protein and 8 grams of pea protein. A second group had the same blend with 2 grams of free leucine added. Leucine is an amino acid thought to help trigger muscle building. The third group had 20 grams of whey, a milk protein often used as the benchmark for muscle-building quality.

The researchers infused a labeled form of the amino acid phenylalanine and took blood and muscle samples for up to four hours. This let them measure how fast the body was making new muscle protein.

The blood results followed the expected pattern. Whey raised blood levels of essential amino acids more than either plant version. The incremental area under the curve, a measure of total rise over four hours, was 135 for whey, compared with 99 for the plant blend and 105 for the plant blend with leucine.

The muscle results did not differ. Muscle protein synthesis rates were similar across all three groups (treatment P = 0.828). None were higher than the men's fasting, or postabsorptive, values. In other words, the protein dose did not measurably speed up muscle building in any group.

The authors conclude that 20 grams of protein alone, regardless of its quality, is not enough to increase muscle protein synthesis in older men. They write that more work is needed to define the best combination of protein quality and quantity for older people.

For you

For personal health, the practical reading is cautious. If these results hold up, a 20gram portion may fall short for older adults, and choosing a better protein source may not make up for a small amount. The study did not test larger doses, so it cannot say how much is enough.

There are limits. The trial tested one dose, in healthy men only, and measured a short-term rate over about four hours. It did not measure muscle mass or strength over time. The weakest point is the leap from a four-hour measurement to what older adults should eat at each meal.

Next to watch: trials that test larger single doses of plant and animal protein in older men and women, and studies that track whether higher per-meal protein intakes actually preserve muscle over months.

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