Noticing that the waist circumference on average went down on the peppermint group (85.17 -> 84.61) while the placebo group it went up (88.33 -> 88.65)? Also the resting heart rate dropped for the peppermint group. My initial suspicion is that the peppermint group coincidentally was also the 'got in better shape' group. Maybe the peppermint helped, but for relatively small groups that also seem to be improving waist circumference and heart rates likely due to good diet and exercise, I'm not convinced the peppermint did jack shit. More investigation needed! Would be awesome if it helped though!

There has been some research on spearmint suggesting anti-androgen effects in PCOS, which is a bit unexpected to me as I wouldn't expect mint-family herbs to have much hormone modulating effect at all. I would imagine there to be similarities in profile between spearmint and peppermint so perhaps a related mechanism is involved, although I would probably expect the opposite outcome as a naive layperson. But I haven't closely evaluated the paper nor do I know whether there's been much else suggesting this

It is important to remember that herbs are difficult to study in this setting compared with isolated compounds -- likely because their pharmacological and chemical compositions are sensitive to many factors: hour and season of harvest, form consumed (raw powder, alcohol extract, cold water infusion, fat emulsion, hot water infusion, combustion, pyrolysis, essential oil), part consumed (leaf, root, flower, seed), among staggeringly many others. Anyone with experience consuming cannabis or coffee can probably testify to the above

Not to mention that the pharmacologically active compounds in many plants are far from being comprehensively understood, let alone their interactions and dynamics

This isn't to say that every claim about herbs is to be taken seriously. My point here is more that there is no good reason to dismiss the herb itself as a cause yet simply because it's an herb and a fairly mundane one at that. There are easy examples of herbs which have pronounced physiological effects, used for recreation, performance enhancement, as literal poison, to induce labor, to thin the blood -- among others.

https://pubmed.ncbi.nlm.nih.gov/19585478/

But weight/mass didn't change one bit (okay exaggeration, but not by much), so maybe peppermint helps relieve gas. Who knows? There's a lot that this data could mean, and no simple way to figure it out.

Peppermint oil has traditionally been used in India for digestion, so you may be on to something. I remember this particular brand growing up: https://www.amazon.com/clp/B001NQ7S9G (no relation).

Nothing but blood pressure and heart rate was significant, and heart rate only barely so. I wouldn't read anything into the other numbers. It was a 20 day study, you aren't going to get long term outcomes from that.

I'd think weight could be causal for hypertension result or sentiment over health measurement could have been causal for weight or the study could just be too small.

Maybe it helps with weight loss (I wish)

Wild-ass guess: maybe the aftertaste of peppermint oil twice daily leaves people who are already unhealthy wanting to snack less, leading to minor weight loss.