A PROSPERO-registered umbrella review graded 57 meta-analyses on diet and lung cancer using AMSTAR and GRADE. Only folate reached moderate-quality evidence for lower risk; most other links, including beta-carotene supplements and red meat, remain low or very-low quality, with a real but secondary mention of gut microbial short-chain fatty acids as a possible mechanism.
Pooling 17 studies and 7,371 participants, a PROSPERO-registered meta-analysis finds fecal butyrate, a gut-bacteria byproduct of fiber fermentation, is reliably lower in people with established type 2 diabetes, though the same signal is largely absent in prediabetes and in blood samples.
A decade-long study of 5,388 US adults 50 and older found that people who ate more fiber relative to their calorie intake were significantly less likely to develop new difficulty walking, climbing stairs, or lifting objects, though the link weakened sharply after age 75 and cannot prove cause and effect.
A pooled analysis of 29 studies finds people with periodontitis have measurably different gut bacteria than people with healthy gums, with lower diversity and a shift toward inflammatory microbes. The association is strong. Proof that one causes the other is not there yet.
A large, double-blind, placebo-controlled trial of 428 New Zealand infants found that daily use of the probiotic Streptococcus salivarius K12 did not significantly reduce ear infections, respiratory infections, or antibiotic prescriptions over an 18-month period, contradicting hope built on smaller, earlier studies.
A meta-analysis of 43 studies and 48.7 million people estimates that H. pylori, the bacterium behind most stomach cancer, may also be linked to 22% of colorectal cancer cases worldwide, evidence that is suggestive, not conclusive.
Within a few decades, Inuit communities in the Canadian Arctic went from getting roughly half their calories from seal, caribou, and fish to as little as 2 percent in some communities today. A scoping review of 162 studies traces the fallout, obesity, diabetes, anemia, and food insecurity, and why nutrition scientists suspect the gut plays a role even though this review never measured it directly.
A landmark five-country study of nearly 1,900 adults finds that gut bacteria diversity and its link to obesity depend heavily on where someone lives, not just their biology.
The largest brain-imaging study of irritable bowel syndrome ever run found no meaningful cortical differences between IBS patients and matched controls, even though the IBS group reported significantly more pain, anxiety, and depression. The result challenges over a decade of smaller neuroimaging studies claiming visible brain changes in IBS.
A meta-analysis of over 143,000 people found that eating more nuts, especially around a handful a day, was linked to meaningfully lower hypertension risk, likely via fiber-fed gut bacteria producing blood-pressure-lowering compounds.
