GEOFF BENNETT: President-elect Trump's nomination of Robert F. Kennedy Jr. to lead the Department of Health and Human Services has raised a number of questions in the public health community about Kennedy's long history of opposing vaccines.

It's also put a spotlight on a number of other comments he's made, including about what millions of Americans eat and drink each day.

For more on those claims and what the science says, here's William Brangham.

WILLIAM BRANGHAM: Robert F. Kennedy Jr. is trained as an environmental lawyer, but in recent years he's focused almost exclusively on public health, and he stirred a great deal of alarm with some of his claims.

So we're going to dive into a few of them here to better understand what the research tells us, what those claims tell us about Kennedy, and what this could mean for Americans should he get confirmed as health secretary.

Let's start with ultra-processed foods.

Kennedy has vowed to remove them from school lunches.

ROBERT F. KENNEDY JR., Health and Human Services Secretary Nominee: We are literally poisoning our children systematically for profit.

WILLIAM BRANGHAM: Ultra-processed means foods that have been altered in a factory with added dyes, sweeteners, or preservatives.

And they tend to be high in calories, sugar, fat, and sodium.

This category contains a lot of things you would expect, sodas, frozen pizzas, hot dogs, but also things you might not expect, like flavored yogurts, plant milks, whole grain breads, and cereals.

The U.S. has been slower than other developed countries to regulate ultra-processed foods, even though the consensus on their health impacts, including from the National Institutes of Health, is quite clear.

LINDSEY SMITH TAILLIE, Nutrition Epidemiologist, University of North Carolina: There's very strong scientific evidence about this link between consuming ultra-processed foods and a wide array of health outcomes.

In addition to that, there's a large body of observational studies that show links between ultra-processed foods and things like type 2 diabetes, cardiovascular disease, and also mental health.

WILLIAM BRANGHAM: Kennedy's attempt to regulate these foods would likely face opposition from well-funded industry groups, politicians, as well as members of the public who may lack access to affordable, healthier food.

And some worry that his approach -- he's vowed to fire anyone at the Food and Drug Administration who stands in his way -- could be counterproductive.

LINDSEY SMITH TAILLIE: We're not doing enough.

That's clear.

I am very concerned about the idea that RFK Jr. would wipe out entire branches of the federal government or kick out the scientists who've been working on these issues for ages, because those are exactly the type of experts that we need.

And if that were to happen, there's a real risk that we could end up worse off in the long run than we are now.

WILLIAM BRANGHAM: Now to raw milk.

That's milk that hasn't been pasteurized, which means heating it to about 161 degrees Fahrenheit for 15 seconds to kill viruses and bacteria.

In recent years, a small online community has argued that raw milk contains good bacteria, and pasteurization kills nutrients that can help prevent asthma, allergies, and illness.

MAN: This is why you should be drinking raw milk.

WOMAN: It is easier for your body to digest.

WOMAN: Raw dairy actually has active and bioavailable enzymes, probiotics.

MAN: Raw milk also contains over 700 species of commensal bacteria in the actual raw milk fluids.

WILLIAM BRANGHAM: Kennedy recently wrote that he will end the Food and Drug Administration's -- quote -- "war on public health," including its -- quote -- "aggressive suppression" of many things, including raw milk.

Yet there's no evidence for any of these beneficial claims about raw milk, while there's plenty of evidence that drinking it increases the risk of foodborne illnesses from things like salmonella, listeria and E. coli, which can be deadly.

JOHN LUCEY, Professor of Food Science, University of Wisconsin: We have 100 years-plus of data showing that there is the potential of pathogens present in raw milk.

So there's a clear risk and no study has yet shown any nutritional benefit from consuming raw milk.

And, in fact, most of these claims can be relatively easily debunked.

WILLIAM BRANGHAM: Children, the elderly, pregnant women and those with weakened immune systems are the most at risk from infection.

And the recent bird flu outbreak presents yet another risk to consider.

While there are no known cases of humans becoming infected from drinking raw milk, scientists warn the virus seems to concentrate in the udders of infected cows.

And at least one raw milk producer in California recently issued a recall after detecting bird flu in its product.

JOHN LUCEY: Fortunately, the pasteurization inactivates it.

So we have a simple technique that kills the pathogens.

And, thankfully, now it kills this avian flu virus that could be present in milk.

And the levels are high.

This is not a trivial amount.

WILLIAM BRANGHAM: Now, could Kennedy change the rules on raw milk?

The federal government doesn't determine whether it's legal to sell.

That's left up to the states.

And most states do allow it to be sold at some level.

But since 1987, the FDA has prevented raw milk from being sold across state lines.

So that's something Kennedy could impact.

JOHN LUCEY: It would lead to increased sales of raw milk, for sure.

And it would increase the amount of food illnesses and outbreaks.

WILLIAM BRANGHAM: Finally, let's talk about fluoride in drinking water.

Just before the election, Kennedy posted this on X, vowing that the Trump administration would advise U.S. water systems to remove fluoride, which he called an industrial waste associated with a number of health conditions.

Backing up a bit, fluoride is a naturally occurring mineral that's commonly found in soils and rocks.

And since 1962, the federal government has recommended adding it to our drinking water to strengthen the enamel in our teeth to help protect against tooth decay.

DR. LEANA WEN, Emergency Room Physician: The CDC has hailed fluoridating public water systems to be one of the greatest achievements in public health in the 20th century.

And that's because having fluoride in water has reduced dental cavities, especially in children.

But, at the same time, it's also true that that value of fluoridating public water is much less now that we do have fluoridated toothpaste.

WILLIAM BRANGHAM: The amount of fluoride is important here.

Since 2015, the CDC has recommended 0.7 milligrams per liter of water.

An NIH review this year showed that at twice that level there are impacts on children's I.Q.

and development.

It's important to note that those studies mostly looked at other countries, where levels are higher.

But there have been higher levels in some communities in the U.S.

The Environmental Protection Agency currently requires that officials keep levels below four milligrams per liter.

DR. LEANA WEN: This is an issue of dosing, but I think it's also an issue of informed consent.

I can understand why there are activists who are saying, well, I just didn't know this.

And had we known that the level of fluoride in our community water system is higher than what's recommended, maybe we would have taken different steps during our pregnancy or with baby formula.

And I think that that kind of nuanced communication needs to happen.

And, without it, that actually breeds distrust.

WILLIAM BRANGHAM: Ultimately, the decision to fluoridate drinking water and how much is left to states and municipalities, which follow federal guidance.

So, there, Kennedy could influence what local authorities ultimately choose to do.

Overall, public health voices say that, on this issue and others, Kennedy has a record of combining good information with bad.

DR. LEANA WEN: But then he also has views on issues like vaccines that simply are disproven by the science.

And I'm very concerned about someone like that, who basically is an activist, and not a scientist, holding the position of overseeing our nation's scientific and medical and public health agencies, because, ultimately, a person overseeing these agencies should be guided by science.

WILLIAM BRANGHAM: In our next explainer, we will dive further into that issue, Kennedy's many years opposing vaccines.

For the "PBS News Hour," I'm William Brangham.