Everything? Even cigarettes? Of course not, so a better rule of thumb would be to avoid things which are known to cause health problems altogether, at least to an extent which is practical.

Sure, an occasional cigarette probably won't hurt much, all things considered.

Exercise (beyond a point) can cause health problems. I know of a guy who is a quadriplegic because he liked to bike on trails.

But health authorities won't say that; once it gets to the level of advice to laymen, it's been heavily filtered. A quick search returns this page, which claims that "there is no safe level" of cigarette smoke:

http://www.cancer.org.au/preventing-cancer/smoking-and-tobac...

Really? One cigarette per year (per lifetime?) will show up? Of course, what they mean is that, if you're in the population susceptible to nicotine addiction and you're trying to quit, some smoking will make it harder than not at all. But the claim is still false as taken literally.

Nope. Doesn't work in my case. At least in reference to carbohydrates (simple and complex). More carbs = higher blood sugar.

Currently, diabetes type 2 dietitians say I can eat up to 60g carbs per meal. Well, see for yourself and tell me if you think that's a good idea in my case:

https://mega.nz/#!JwcSEAwC!zPqA1zVhA3zcLwLLZRJucc6AtT9zlHfNY...

Pay attention to row 37. I started with 143mg/dL . I made a meal that was much higher than I had anticipated. My high was 182mg/dL and lasted for about 3.5 hours until returning to before food numbers.

And that was just 12g carbohydrates (2/3 sugar, 1/3 complex).