Pooled across 15 randomised trials of berberine and barberry, people lost 1.9 lb more than a comparison group. Semaglutide, in the trial that made it famous, beat placebo by 28 lb. Both are measured the same way, from the best evidence available for each.
The trial behind the 2024 headlines was retracted in September 2025, four days after a meta-analysis pooled it, and a year on that meta-analysis still carries no correction. What survives: a real but modest effect on blood sugar after meals, and about 2 lb of weight across twelve short trials, most of it back within a month of stopping in the one trial that checked.
Partially hydrogenated vegetable oil genuinely harmed people: when 11 New York counties restricted trans fat in eateries, hospital admissions for heart attacks and strokes fell an extra 6.2%. The FDA has since banned it. The fear outlived it and reattached to the oil that's left, which is usually soybean, as the ingredient list will tell you.
Eggs raise LDL by about 5 to 8 mg/dL in the pooled trials, so "eggs don't affect your cholesterol" is wrong. Whether that matters for the heart is disputed: in six US cohorts the egg's link with heart disease followed the cholesterol in its yolk, and the big pooled analyses disagree. And two meta-analyses disagree about the one thing the "it's a wash" argument needs.
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.
Pooled across 72 measurements, instant oatmeal scored 75 on the glycaemic index and large-flake oats 53. Regulators have signed off on oats for cholesterol, at 3 g of beta-glucan a day, not for weight. On weight, pooled trials of beta-glucan from oats and barley found about 2 lb at best, and the newest, in overweight adults, found none.
Researchers measured urine pH across citrus juices: orange juice alkalised it; lemon, grapefruit and lime didn't. The ritual picked the wrong fruit. For kidney stones, lemon juice is unproven: the one randomised trial of it that counted new stones could not rule out chance, and one in five got heartburn.
The famous PREDIMED trial was retracted from the New England Journal of Medicine and republished — and the nuts arm did just as well as the olive oil arm.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.
Canola is rapeseed bred low in erucic acid — the name literally means Canadian oil, low acid. The FDA ban people cite was against mustard oil, not this. Erucic acid does fatten animal hearts at high doses, which is why it was bred down to trace levels and is capped by law. And in 13 head-to-head trials, canola lowered LDL more than olive oil did.
In a review of human trials, cutting dietary linoleic acid by up to 90% did not move arachidonic acid in the blood, and three of four later studies we read agree, so the route usually blamed for inflammation mostly fails at step one. But two recovered BMJ trials found no mortality benefit, and in one, more men died on the oil. Here is the whole file, including what's wrong with both halves.