WILLIAM BRANGHAM: We return now to our video podcast "Settle In."

Geoffrey Bennett recently spoke to Gideon Meyerowitz-Katz.

He's an epidemiologist and writes the Health Nerd blog.

He has spent years helping people understand the data behind the news they see about their health.

They spoke about bad science, misconceptions around what we eat, and Health Secretary Robert F. Kennedy Jr.

's Make America Healthy Again campaign.

Here's a little bit of that conversation.

GEOFF BENNETT: When we talk about the health secretary, RFK Jr., Robert F. Kennedy Jr., what do you make of his personal crusade to reveal, to unearth the cause of autism?

GIDEON MEYEROWITZ-KATZ, Health Nerd: So, when we talk about autism, what we're discussing isn't necessarily the sole cause of autism.

What -- certainly, what RFK Jr., when he speaks, he's mostly discussing the increase in the rates of autism.

So if you look at the number of people who are autistic, if you look at the earliest studies of that, they were conducted in the '60s in the United States and also in the U.K.

And they estimated that around one in 2,000 children had autism, somewhere around five in 10,000 kids, give or take.

If you look at the most recent estimates, the number is now closer to one in 30.

So, somewhere -- it's just under 3 percent of children would be diagnosed as autistic today.

So that's about a 60-times increase between the 60s and 2025.

But if you look at the history of autism, it quickly becomes clear the main thing that's happened there.

So in the '60s, when we talk about autism, it was a term used to describe severely disabled or children with very significant developmental delay who were mostly nonverbal, who required a great deal of assistance in their lives.

And so it was a very specific disease.

And then, as the decades went on, when we talk about autism spectrum disorder, it is very, very broad compared to the 1960s definition of autism.

It includes children who are fully verbal, who are succeeding at school, who are very able to take care of themselves.

And these are all things that, in the 60s, would be considered to be exclusion.

So if you could do any of that, you wouldn't be diagnosed as autistic.

And so we know that a large portion of this increase that RFK Jr.

and co.

are attempting to explain is simply because we have changed the definition of what autism is.

And, I mean, the other big thing that's changed, I don't -- and, again, we're referencing the '90s.

Growing up in the '90s and the '80s, it was very hard to be diagnosed with autism.

And that's because there were very few providers who recognized the term, who were experienced and trained in recognizing autism.

And I remember, when I was a kid you had to go to a special psychiatrist who had monthslong wait to see -- to even get assessed for autism.

These days, you can be assessed online and it takes maybe two appointments to get a diagnosis if you believe that you have autism.

It's very quick.

And so the expansion of the diagnostic criteria and the substantial expansion in sort of the ability to get diagnosed explains the majority of the increase in autism.

And there are studies looking at this.

So there was one study in California that found that just replacing the term mental retardation, which fell out of favor in the '80s, with autism, which became the new diagnosis, explained 25 percent of the increase in rates of autism in California, which is 25 percent just for that one term being removed.

And there was a study in Denmark that found the overwhelming majority of the increase in autism is explained in that country by the change in diagnosis and the improved access to diagnosis.