JOHN YANG: News about food safety and can be hard to keep straight.

Take aspartame, the artificial sweetener that's been around for decades.

It was headline news this summer when the World Health Organization said aspartame could possibly cause cancer in humans although the U.S. Food and Drug Administration disagrees.

Pushback quickly popped up on social media, much of it from dieticians.

But their post didn't make clear that they were being paid by the American Beverage Association, a lobbying group whose members include Coca Cola and Pepsi.

Both marketers are products containing aspartame .

It's just one of the instances uncovered by a joint investigation by the Washington Post and the nonprofit newsroom The Examination which specializes in public health around the world.

Washington Post health columnist Anahad O'Connor worked on the investigation.

Tell us the scope of what you found.

How widespread is this?

ANAHAD O'CONNOR, The Washington Post: Yeah, so we analyzed thousands of posts on TikTok and Instagram and Facebook that were posted by registered dieticians, and found that it's actually quite common for them to post ads on behalf of food companies, beverage companies, and dietary supplement companies.

And in many of these ads and posts, we were quite surprised to see dietitians, promoting and defending artificial sweeteners encouraging people to eat ice cream and candy and other junk foods and dietary supplements and just basically promoting advice that runs counter to, you know, decades of scientific research on proper nutrition.

JOHN YANG: Obviously, the food and beverage industry has been around for a long time and they've been trying to influence what people eat and drink for a long time.

How is this different?

ANAHAD O'CONNOR: So what we found is that the food industry is really turning to social media because it's a very effective way of getting their message across to consumers.

There are many influential dieticians on TikTok and Instagram who have very large followings.

And people who follow them develop what are called parasocial relationships with them, they're very trusting of them because they're following them day in and day out, for example, compared to you know, a large advice from a large, faceless organization.

But we found that the food industry oftentimes will pay dieticians to promote industry friendly messages and you know, promote their products and, you know, promote this advice to eat foods.

That's pretty surprising.

JOHN YANG: Does the professional organizations of dietitians, do they have anything to say about this?

ANAHAD O'CONNOR: So the Academy has a code of ethics that says that dietitians should always disclose conflicts of interest and that they should refrain from accepting gifts or partnerships that can influence their professional judgment.

But so far, to our knowledge, the Academy has not penalized any dietitians for this sort of activity on these social media sites.

JOHN YANG: And what does the food and beverage industry say, how do they justify this?

ANAHAD O'CONNOR: So they say that, you know, they pay these dietitians because they are credentialed experts, and that in many cases, they disclose that they're engaged in paid partnerships.

But oftentimes, you know, what we found is that it's very difficult for consumers to know when the videos they're watching posted by these particular dietitians are ads, because they may say, you know, paid partnership down at the bottom of the video and you know, very small letters, or it may say hashtag ad somewhere buried in the caption.

But in the video itself, there are no audible disclosures, and they may not say the specific company or industry that is paying them.

So on these, you know, posts, where dietitians were paid by the American Beverage group to promote and defend artificial sweeteners.

Oftentimes, they did not say that specifically that they were paid by this industry, trade and lobbying group.

JOHN YANG: And the Federal Trade Commission, police's false claims on labels on in ads and so forth.

Do they have any power over this?

ANAHAD O'CONNOR: So the experts we talked to said that, you know, this social media landscape is really the Wild West, you know, there are, you know, countless influencers who are posting thousands if not millions of videos a day and the FTC does try to regulate and monitor it definitely requires influencers to disclose when they're being paid to promote products, but it's very difficult for them to regulate and to monitor this activity and they occasionally bring cases but, you know, it's very few and far between.

JOHN YANG: What prompted you to look into this?

ANAHAD O'CONNOR: So the Academy of Nutrition and Dietetics, which is the group that oversees dieticians, they've been criticized for years for their ties to big food companies like Nestle and Coca Cola, Pepsi, Hershey, they've taken millions of dollars in donations from these companies and they even allowed food companies to provide continuing education courses to their dieticians which they've had faced a lot of criticism for.

But we wanted to look at the very influential dietitians on social media with large followings to see, you know, is the advice that they're giving people influenced at all by the food industry.

And we were very surprised.

We found, you know, dozens of these posts is paid advertisements, essentially thinly veiled advertisements, we found 35 videos in which dieticians and health influencers were paid by the soda industry to, you know, defend aspartame and our other artificial sweeteners and criticize the World Health Organization for its recommendations.

JOHN YANG: You say it's hard to tell these things that they're their ads, what advice do you give people?

What should they look for?

ANAHAD O'CONNOR: So I think consumers have to be very skeptical.

If you see a dietitian or someone else, you know, promoting advice that sounds dubious or sounds questionable.

You should, you know, wonder or check, you know, is this -- essentially a thinly veiled ad is this person being paid to push an industry friendly message to me.

JOHN YANG: Anahad O'Connor, a health columnist for the Washington Post, thank you very much.

ANAHAD O'CONNOR: Thank you.