Ginger

Systematic reviews of randomised trials consistently find that ginger reduces nausea and vomiting in early pregnancy compared with placebo. Unusually for a spice, the studied dose — roughly one gram of dried ginger a day — is within reach of ordinary food and drink, though it is still more than most people would use casually. Anyone pregnant should confirm the approach with their midwife or doctor.

Strong evidence. Consistent findings across multiple good-quality human studies.

Some trials report reduced nausea after surgery and during chemotherapy, and reviews generally find a small favourable effect. Results are less consistent than in pregnancy, doses vary widely between trials, and much of the research uses standardised capsules rather than ginger as eaten.

What may be going on: Gingerols and shogaols act on gut serotonin 5-HT3 receptors and may speed gastric emptying.

Moderate evidence. Several human studies point the same way, with real caveats.

A handful of trials of ginger powder in knee osteoarthritis report small reductions in pain scores. The trials are small and short, several used standardised extracts rather than the spice, and dropouts for stomach upset complicate the results.

Limited evidence. Early human work, or mostly lab and animal research.

Ginger is widely marketed for fat loss, often as a tea or shot. The trials that measured body weight are small, brief and inconsistent, with average differences too small to be meaningful, so there is not enough dependable evidence to support that use.

Insufficient evidence. Not enough human research to say anything useful yet.