A key question for advice in a domain is: how are outcomes in this domain statistically distributed?
If extremely good and extremely bad outcomes are rare, you probably can't do much better than just copying the default or median behavior. The value of acquiring information in this domain seems low.
Conversely, if the distribution has a heavy tail, then changing your behavior can avert very bad outcomes and/or lead to very good outcomes. In this case, the value of information in this domain seems comparatively much higher.
Hence the question: Which health & lifestyle interventions have particularly heavy-tailed outcomes?
Toothpaste: Without having looked into this topic, I'd expect commercially available toothpaste to mostly be in the same ballpark in terms of outcomes. In which case there would be little value in optimizing this domain beyond choosing e.g. the most popular brand, or the product with the highest Amazon rating.
Proper Workout Technique: It's very easy to injure yourself with sufficiently bad workout technique. Irrespective of how much better the outcomes for the best technique are than for the median technique, it at least seems worth some effort to avoid the "bad technique" tail of the outcome distribution.
(There's also a discussion thread on the SSC subreddit.)