Putting a swimmer on the cover of a magazine about health influencers might raise a few eyebrows, I’ll admit. I mean, if you wanted to improve your times in the 200-meter butterfly, you wouldn’t call a shrink, would you? I guess it depends on who the shrink is, and who the flier is, too. But that’s what the advent of the influencer has wrought.

Used properly, influencers can be extremely powerful tools to help raise awareness — of brands, issues, causes. Witness Michael Phelps’ work to raise awareness about the value of tending to your mental health. The Olympic star had the courage to stand up and admit he had emotional problems, and that he had sought therapy to help overcome them. That he did so on behalf of Talkspace, an app that connects users to licensed therapists, was beside the point.

Phelps wasn’t promoting himself as the therapist; he was saying that it was OK to seek help. By doing so, he has helped remove the stigma from seeking help for emotional issues. Having someone of Phelps’ achievements stand up for a cause drew massive amounts of attention to the issue. And for that work, and his courage, we put Phelps at the top of our list of the most influential people in health marketing.

I wish that all celebrities used the platform their fame provides them to such admirable ends. I don’t need to name names here, but there are plenty of well-known people who have decided to use their fame — some of it achieved through naked ambition — to promote bogus causes such as anti-vaccination or the completely unfounded powers of, say, a juice cleanse.

Apart from the utter lack of valid, scientific proof, these types of influencers often pass themselves off as experts in the field. When that’s combined with the nature of celebrity — they’re famous, so they must be smart, right? — influencers can really mess things up.

I’m not immune to influencers, but I take them for what they are. Two of my favorites on this list are David Goggins and Jocko Willink. Goggins’ Instagram feed often shows him in the middle of a 50-mile run. I get tired driving 50 miles, so I know I’m not going to Be Like David. But I can appreciate his message: have a goal, a plan for how to achieve it and go after it, no matter what you’re trying to do. I need to hear that once in a while. We all do. Which is why Goggins makes the list.

Click here to view the Health Influencer 50