Daily Protein and Prebiotic Supplements Boost Memory in Adults Over 60

The researchers set out to protect aging muscle. What they found instead was happening in the brain.

A randomized controlled trial from King's College London, published in Nature Communications in February 2024, tested whether a prebiotic supplement could slow muscle decline in adults over 60. The primary outcome, measured by how quickly participants rose from a chair, showed no significant benefit. But a secondary finding caught the team's attention: the same prebiotic significantly improved scores on a visual memory and learning test, the same cognitive assessment used in early Alzheimer's disease screening.

The PROMOTe trial (effect of PRebiotic and prOtein on Muscle in Older Twins) enrolled 36 twin pairs, all at least 60 years old, in a 12-week double-blind study. Both twins in each pair received identical daily sachets containing 3.32 grams of branched-chain amino acid protein powder. One twin's sachet also included 7.5 grams of a commercial prebiotic blend of inulin and fructooligosaccharides, sold as Darmocare Pre; the other received a placebo of maltodextrin. Because genetic makeup was held constant within each pair, any difference in outcomes reflected the supplement rather than inherited traits.

Gut bacteria shifted measurably. By the study's end, the prebiotic group showed 60 microbiome features changed compared to three in the placebo group. Bifidobacterium, a genus that prior animal studies link to reduced cognitive deficits through gut-brain signaling pathways, rose significantly in the prebiotic group.

"We are excited to see these changes in just 12 weeks. This holds huge promise for enhancing brain health and memory in our aging population," said Mary Ni Lochlainn, a geriatric medicine researcher at King's College London. "Unlocking the secrets of the gut-brain axis could offer new approaches for living more healthily for longer."

The accessibility angle resonated with the team. "These plant fibers, which are cheap and available over the counter, could benefit a wide group of people in these cash-strapped times. They are safe and acceptable too," said geriatrician Claire Steves at King's College London.

What 12 weeks did not prove matters as much as what it did. The cognitive improvement was a secondary endpoint, not the central question the trial was designed to answer, and no specific effect sizes in percentage terms have been released in public reporting. The study involved 72 participants, a sample researchers themselves acknowledged may have been too small to detect the muscle benefit they originally sought. No long-term follow-up data exist. Because both groups received protein powder, the memory benefit is attributable to the prebiotic component, not the protein. And the trial ran entirely by remote video visit and mail-delivered samples, which constrained the precision of physical measurements.

Anyone considering adding inulin or FOS to a daily routine should factor in the specific conditions of this trial before reaching for a bottle. The dose tested was 7.5 grams of inulin-FOS blend daily for 12 weeks. People with irritable bowel syndrome or FODMAP sensitivity should approach with caution: both inulin and FOS are fermentable carbohydrates that commonly cause gas, bloating, and diarrhea, particularly at higher doses. Those managing diabetes with medication should consult a physician, as inulin can enhance blood-sugar-lowering effects. The key questions to bring to a doctor: whether any existing gut or bowel condition rules out fermentable fiber supplements, whether any current medications interact with prebiotic fiber, and whether a 12-week secondary cognitive finding in 72 twins constitutes a strong enough evidence base for a personal health decision.

The King's College team says its next task is testing whether the cognitive effects hold in larger cohorts and over longer periods. Until that data exists, the gut-to-brain signal is promising but not yet a prescription.