Talk about mystery meat.

As plant-based protein makers like Impossible Foods and the newly public Beyond Meat take the food industry by storm, the question of whether their products are better for consumers than actual meat is still very much open, says former U.S. Agriculture Secretary Dan Glickman.

"We can't really market it ... as necessarily better for you, because we don't know," Glickman, who now runs the Aspen Institute's Congressional Program, said Tuesday on CNBC's "Fast Money."

"Some people eat it. It certainly won't hurt you. It can be very tasty. But it doesn't mean it's better for you," he said.

Glickman, who recently co-authored an op-ed in the New York Times titled "We Need Better Answers on Nutrition," cited the "lack of nutrition science" in the United States as a major issue when it comes to understanding what's in the food we eat.

When it comes to plant-based meats, for example, "I think we know enough to know that it's healthy, and we know that it has some protein in it," he said. "But as a general rule, apart from the plant-based meat, we do not know enough about what's in our food."

That lack of understanding manifests itself much more broadly than people think, Glickman said. Diet-related diseases are the No. 1 cause of mortality in the U.S., with poor eating habits leading to nearly 1,000 deaths per day, according to Tufts' Friedman School of Nutrition Science and Policy.

"There's an old expression, 'You are what you eat.' But nutrition has never been a serious study of science in the National Institutes of Health," said Glickman, whose New York Times piece called for the NIH to establish a new institute devoted specifically to nutrition research.

"We study major diseases like heart disease, cancer, arthritis, Alzheimer's, but we don't do enough study in how you can prevent disease from happening. And food is a big part of that," he said. "So, I certainly support plant-based meat, but I don't think anybody should look at that as the nirvana or the only solution to the problem. We need to look at this across the board to try to help people make intelligent food choices based on good science."

Part of the solution will be more funding from the federal government, Glickman said. According to a 2015 study, federal funding for nutrition research is roughly $1.5 billion per year. For comparison, U.S. residents spent over $50 billion in January of 2015 eating at restaurants, according to the American Enterprise Institute.

"I think the federal government should spend a lot more money and effort investigating the science of nutrition generally," Glickman argued. "A lot of folks are very confused about what's good for you. We change all the time: should you drink whole-fat milk or low-fat milk?"

And while some segments of the National Institutes of Health do conduct nutritional research of their own, the efforts are largely piecemeal considering how much we still don't know about our food, Glickman said.

"There's certainly a lot of people who worry about meat for a lot of reasons including environmental issues, but meat is a very important part of the diet," Glickman said. "Plant-based meat does provide some protein in there. You've got pea additives and other things [like] legumes that add protein to your diet. But whether it's better for you than meat is really something we just really don't know yet."

At the end of the day, "we do know it's safe, and those consumers who are vegetarians will probably go that route," Glickman told CNBC. "That's the great thing about the food industry today. There are all sorts of options out there. It's just that we need to do more research to figure out what is really good for you."

Beyond Meat's initial public offering has proved to be one of the best-performing IPOs of 2019 so far, with the stock up over 230% since its May 2 debut. The still-private Impossible Foods has raised over $750 million in funding so far and struck a partnership with Burger King parent Restaurant Brands International to create an Impossible Whopper.

Analysts at Barclays predicted Wednesday that alternative meat will become a $140 billion industry in the next 10 years.