We looked, and the evidence does not back the claim: either it was tested and did not hold up, or nobody has tested it and nothing that was tested supports it.
Hardly. Peanuts' glycemic index averages about 14 of 100 in the published tests, and in 8 trials pooled in 2022, fasting blood sugar with peanuts came out about 0.5 mg/dL higher than on the comparison diets, a range that includes no difference. What to watch is the jar: reduced-fat peanut butter carries more carbohydrate.
No. In the controlled trials, testosterone on finasteride rose modestly, about 8 to 10% in two large trials and more in men who started low, or did not change significantly; DHT, the hormone made from it, fell about 70%. Sexual side effects are a separate question: about 4 in 100 men on the hair dose reported one in the first year, against 2 in 100 on a dummy pill.
Peanuts and peanut butter showed no clear rise in LDL in nine randomised trials pooled in 2022, three of which gave peanut butter. The pooling's chart puts LDL about 2 mg/dL lower than on the comparison diets; with two of its rows entered as their trials report them, it comes out about even, and both ranges include no difference. In place of saturated fat, LDL fell about 14%.
The warning was in a national magazine by 1888 and selling a coffee substitute in 1900. Since then, 81 girls followed to 18 and 1,769 premature babies given caffeine or a dummy drug had heights not significantly different, and those measured at 11 still did. The signals the other way come from the very young and the poorly fed, mostly at far bigger doses per pound.
Six randomised trials set creatine taken just before training against creatine taken just after, for four to 32 weeks; none found a statistically significant difference in muscle or strength. Morning against evening was tested once, with no significant difference. Sugar alongside it makes muscle store more creatine; the four trials that tested it directly against creatine alone found no significant difference in performance, and one eight-week trial leans toward sugar without a direct test in the part we could read. Rest days are the open question.
Creatine HCl dissolves 38 times better in water. In eight small studies against monohydrate, seven found no significant advantage and one found HCl ahead on sprints and jumps; none found more muscle or strength. The absorption claim rests on a patent's two-hour blood test.
Caffeine makes you pass a little more urine for a few hours: about 3.7 fl oz on average across 16 studies. At ordinary intakes the cup brings more water than that. In 50 men drinking four mugs of coffee a day for three days, body water, measured in 25 of them, was not significantly different from three days on water. Big doses at once are another matter.
There is no official upper limit for protein. In 28 trials, adults without kidney disease ate 1.8 against 0.9 g per kilogram a day, about twice the recommended amount, for up to two years; in the 18 that measured filtration before and after, the change was not significantly different, and no consistent sign of damage appeared. Decades are untested in trials, the long studies of ordinary eaters point both ways, and damaged kidneys are a different question.
Calcium supplements raise bone density by 1 to 2%, once. In the largest, least biased trials of adults living at home, fractures were not clearly fewer; the trial that cut hip fractures was done in French care homes. The heart-attack worry is contested, the kidney-stone risk is measured, and calcium from food goes with fewer stones, not more.
In studies of thousands of people, recreational runners did not have more knee arthritis than people who did not run; in a US study that X-rayed the knees of 2,637 adults, the difference shrank to one chance could explain once age, weight and past injury were allowed for. Former elite athletes are a less clear story, and the claim that running protects the knee rests on weaker evidence than the headlines suggest.