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Researchers swabbed tongue coating from 62 older adults, 31 with Alzheimer's and 31 without, then ran bacterial DNA and metabolite tests. The Alzheimer's group had a different bacterial mix and dozens of altered metabolites, with one fat-metabolism pathway standing out as most disrupted, a pattern also seen in their spinal fluid. It's a small, one-hospital study, so it shows a link, not proof the bacteria cause the disease.

TL;DR: Alzheimer's patients showed a distinct tongue bacteria and fat-metabolism signature also found in spinal fluid, but it's a link, not proof of cause.

Researchers compared gut bacteria and genetic ancestry in 441 adults to see which better predicts heart and metabolic risk, like blood pressure, insulin, and body fat. Gut bacteria beat ancestry by a wide margin, 0.05 versus just 0.01, with Akkermansia muciniphila linked to lower risk and E. coli to higher risk. It's a cross-sectional (one-time) snapshot, so it shows a link, not proof the bacteria cause the risk.

TL;DR: Gut bacteria beat genetic ancestry at predicting heart and metabolic risk here, though it can't prove bacteria cause it.

A review pooled nine small studies comparing gut bacteria in adults with mild cognitive impairment (431 people) to healthy controls (586). Across them, impairment tracked with fewer SCFA-making bacteria like Ruminococcus and Lachnospira and more inflammatory Bacteroides; in one study, fecal bacteria alone correctly flagged 93% of cases. But the studies are small and cross-sectional, and some microbes, like Prevotella, swing in opposite directions between populations.

TL;DR: Gut bacteria shifts track with mild cognitive impairment and can flag it early, but the evidence is too thin to call it diagnostic.

A review of 143 studies on Lachnospiraceae, a gut bacteria family that turns fiber into immune-signaling fatty acids, found its strongest effects are from mice. The best human evidence comes from 158 cancer patients, where more of one Lachnospiraceae type tracked with more tumor-fighting immune cells in people who responded to checkpoint immunotherapy. That is correlation, not proof the bacteria caused it, and the human data overall stays thin.

TL;DR: Gut bacteria called Lachnospiraceae show a real but unproven link to how well cancer immunotherapy works, with almost all solid evidence still coming from mice, not people.

A four-week trial gave 31 frail older adults a daily fiber supplement (low methoxy pectin) or a matched placebo. The fiber group improved more on a leg strength test and had bigger drops in anxiety and depression, tracking with a rise in one gut bacterium, Coprococcus comes. The catch: the inflammation markers the trial was built to test showed no real difference between groups.

TL;DR: A daily fiber supplement eased anxiety and boosted leg strength in frail seniors, tied to a shift in one gut bacterium, but never touched the inflammation markers the study targeted.

Researchers tracked about 13,700 Chinese adults over nine years, comparing those with and without gastrointestinal disease or heart disease at the start. People with GI disease were 44% more likely to later develop heart disease, and the reverse held too, partly explained by depression. It's observational, so it can't prove one condition causes the other.

TL;DR: Gut disease and heart disease each predicted the other's onset years later in a large cohort, partly through depression, but causation isn't proven.