Dr. Melik: This morning for breakfast he requested something called "wheat germ, organic honey and tiger's milk."
Dr. Aragon: [chuckling] Oh, yes. Those are the charmed substances that some years ago were thought to contain life-preserving properties.
Dr. Melik: You mean there was no deep fat? No steak or cream pies or... hot fudge?
Dr. Aragon: Those were thought to be unhealthy... precisely the opposite of what we now know to be true.
Dr. Melik: Incredible.
Is it just as simple as exposing yourself to enough poison/radiation to kill weaker pathogens but not enough to hurt yourself too much?
It just seems like the evidence is back and forth when one tweet summarizes a mendelian randomization study on LDL cholesterol and CVD outcomes, and then the next tweet is a guy with one million followers explaining how butter cures cancer. But it shouldn't be very confusing once you filter out the latter in favor of the former.
You jest, but there's some small (<10%) cohort of cancers for whom minimizing available glucose will significantly slow their growth (obviously not stop or reverse), allowing more time for other treatments. Tumors in general tend to be highly glycolytic, and making the body's fuel mix oriented toward fatty acids and ketone bodies may help in these cases.
People love to find problems with stuff so I'd imagine if there were problems they'd be publicised. My intuition is coffee doesn't actually have much effect on health either way.