Trump claimed diet soda kills cancer, Dr. Oz says. But was it a joke?

President Donald Trump has raised some eyebrows with recent comments about the power of diet soda.

TV personality turned Centers for Medicare & Medicaid Services Administrator Dr. Mehmet Oz shared that Trump, in the latest defense of his junk food-heavy diet that Health and Human Services Secretary Robert F. Kennedy Jr. recently called "unhinged," argues that diet soda can fight cancer.

Oz discussed the president's theory in a recent podcast featuring Trump's son as his guest.“Then comes the diet soda pops, which your dad argues that diet soda is good for him because it kills grass - when it’s poured on grass - so therefore, it must kill cancer cells inside the body," Oz told Donald Trump Jr. on the April 13 episode of his “Triggered” podcast.

"We were on Air Force One the other day, and I walk in there because he wants to talk about something, and he’s got an orange soft drink on his desk,” Oz laughed. “I said, ‘Are you kidding me?'”

Oz continued, “So he starts to sheepishly grin. He goes, ‘You know, this stuff is good for me, it kills cancer cells.’ And then he tells me, ‘It’s fresh squeezed, so how bad could it be for you?'”

"But then maybe he’s on to something," Trump Jr. added about his dad's diet. "Because I will say this. I know a lot of guys pushing 80, not a lot have his level of energy, recall (and) stamina."

While the pair laughed off the comment, Trump, along with Kennedy and Oz, has become known for touting health and wellness advice and theories that range from scientifically contested to widely admonished. Beef tallow,whole and even raw milk, cane sugar and peptides are among the latest recommendations promoted by the administration, while food dyes, vaccines,antidepressants and Tylenol have become the subjects of its criticism.

White House Press Secretary Karoline Leavitt told reporters during an April 15 news conference that the comment was a joke. "As we all know, the president has a very good sense of humor. I have heard him tell this joke before,” she said.

Diet soda and cancer: Is there a link?

No data or evidence suggests that diet soda has a therapeutic impact on cancer cells, treatment or prevention. Some studies have even suggested the opposite: that sweetener replacements used in diet drinks, like aspartame, may be carcinogenic or cancer-causing - at least in test animals like rats and mice who consumed large amounts.

The other impacts of diet soda on your health are less clear, Dr. Travis Masterson, spokesperson for The Obesity Society and assistant professor in the Department of Nutritional Sciences at Penn State, told USA TODAY.

"The links between cancer, liver disease, those kinds of things. There are kind of mixed results," he said. "It's important to note that there's not a ton of human studies done on diet soda. So usually the information that we rely on is broad population kind of studies, it can kind of look for patterns, but it can't tell us exactly what's going on."

So, what's healthier? Diet or regular soda?

Unsurprisingly, the question of whether diet or full sugar soda is healthier has a somewhat unsatisfying answer: It depends.

What is "better" for your health depends on your personal circumstances, said Masterson. While drinking more nutritious beverages like water, milk or whole fruit juice is always preferred over any soda, those trying to improve their habits may use diet soda as a step in the right direction.

"Diet soda intake is often associated with elevated weight and diabetes, those types of chronic diseases. But then you have to consider who's likely to be drinking a diet soda," said Masterson. "It's somebody with elevated weight or with a chronic disease that's probably trying to improve that. And so in the short term, we do see that it does often help people reduce weight, but it's probably not the ultimate long-term strategy."

The biggest difference between most diet and normal sodas is the removal of sugars and the associated calories, he said. While there isn't an overall consensus on the long-term health impacts of other additives in both drinks, no single ingredient commonly found in diet soda is generally considered more "unhealthy" than in the other sodas.

"When we don't have a real clear consensus on something, some people will say, 'Oh, there's no good evidence, I'm going to keep doing it.' And other people will say, 'Well, there's no good evidence it's healthy for you, so why do it?'" said Masterson. "So I think everybody can make their own decision on what they're willing to have their risk profile be."