Evidence is consistent, with known limits.
Across 139,691 people in 17 countries, each 5 kg of weaker grip went with a 16% higher risk of dying, a better predictor than systolic blood pressure. Whether getting stronger lowers that risk is unproven: trials that counted deaths found no clear difference.
Around 117,000 Japanese adults were followed for years, and those who said their life felt worth living were less likely to die. None of those studies used the four-circle diagram, which was first published in 2012 with a different word in the middle: purpose.
A 2025 meta-analysis linked 7,000 steps a day to 47% lower mortality (14 studies) and 38% less dementia (2 studies). For death the curve bends near 5,400 steps; cancer risk did not move. Whether age changes the number is still open.
Two big analyses of the trials found magnesium lowers blood pressure by about 2 to 3 points, mainly in people whose blood pressure is high. For older adults' night leg cramps, Cochrane found nothing. And the headline sleep result, 17 minutes, comes from two small trials.
Two big trials and a meta-analysis agree that testosterone therapy lifts sex drive in men with confirmed low testosterone; its effects on energy and mood are small. The largest trial found no rise in heart attacks or strokes, but more heart-rhythm problems, lung clots and kidney injury, and the largest trial to count fractures found 43% more of them.
Of 3,334 men, 277 had a normal total testosterone but a low free one, and more sexual and physical symptoms on average; 96 had the reverse and mostly did not. A smaller study disagrees. Plus the three ways a lab gets a free number, and the one the guideline says not to use.
Processed meat goes with an 18% higher colorectal cancer risk per 1.8 oz (50 g) a day. Two 2019 reviews measured a smaller cut, three servings a week, and found about 1 fewer case per 1,000 people over a lifetime. Both are true. Here is why, what IARC's Group 1 actually means, and why steak is a weaker case.
The famous PREDIMED trial was retracted from the New England Journal of Medicine and republished — and the nuts arm did just as well as the olive oil arm. Across 92,000 Americans over 28 years, swapping butter or margarine for olive oil went with lower death rates. Against other vegetable oils combined, no significant difference at all.
Same trial, same 59 people, same 40-gram dose: lactitol caused severe symptoms across the board and maltitol caused no laxative effect at all. Both are labelled sugar alcohols. Europe's regulator set a limit on erythritol for diarrhoea — not clots — and refused to drop the warning label. And the erythritol and xylitol heart scares came from one dataset.
Nineteen people ate 441 calories a day less without being told to, purely from moving protein from 15% to 30% of their meals — with the appetite hormones pushing the other way. But when 38 foods were ranked head to head, the most filling was a boiled potato, and water content predicted fullness better than protein did.