Mackey, speaking at Fortune‘s Brainstorm Health conference in San Diego, said both involve changing well-established patterns. He gave the example of going out for a run or starting a yoga session for the first time. After a single session, your body hurts and you don’t want to do it again. Eating healthy requires fighting through similar discomfort.

“That’s how it is with food. ‘I tried kale, I didn’t like it,'” said Mackey. “Just like you need to get your body in shape for exercise, you have to get your palate in shape. You have to train it.” Mackey went on to say that he estimates it takes 10 to 15 experiences with a new food to train your palate to learn to like it. “I like everything now and it is just because I taught myself to like it. You might as well re-educate yourself to enjoy the healthiest foods in the world.”

Mackey, a vegan who travels with his own rice cooker, is an executive that loves to talk about healthy food. His appearance at Brainstorm Health comes just after the publication of his new book The Whole Foods Diet: The Lifesaving Plan for Health and Longevity, which was published last month. In that book, he advocates for a diet that leans on whole foods (i.e. no processed foods) and as much plants as possible. That’s a similar stance to the famous quote from New York Times author Michael Pollen: “Eat food. Not too much. Mostly plants.”

Whole Foods now generates nearly $16 billion in revenue annually thanks to Mackey’s push to sell healthier foods, including many organic brands, to consumers. But with success comes copycats: many other retailers, including Kroger (KR) and Walmart (WMT), have entrenched into Whole Food’s turf and put pressure on prices in the process. At Whole Foods, same-store sales decreased by 2.5% in the most recent year as the retailer admits that consumers have more options for how and where they want to buy their food than ever before.

Last month, activist investor Jana Partners disclosed it took a 9% stake in Whole Foods and said it would push for the company to speed up a turnaround plan and consider selling itself. Just a few weeks later, it was reported that privately-held Albertsons was mulling a takeover.

Mackey, speaking to Fortune reporter Beth Kowitt at Brainstorm, wouldn’t say much about the activism or future plans as Whole Foods is reporting earnings next week and is in a quiet period. He did admit that competition is tough due to all the copycats that Whole Foods is combating, but also pointed out that rivals like Kroger are feeling the squeeze in sales as well.

Kowitt asked Mackey to also weigh in on why the United States population continues to face so many health problems, despite the recent push to eat healthier foods. “There’s tremendous misinformation about what a health diet is,” Mackey responded. As an example, he said that organic potato chips are an item that could be perceived as healthy, but they aren’t. A consumer would be better off eating a non-organic real potato rather than processed organic chips.

The disconnect, he explained, is tied to our biology. We crave calorie-dense foods because of how humans evolved. For many years, those foods packed with sugar and fat were scarce. Now they aren’t, but we still want them.

Whole Foods, of course, like all retailers sells a lot of healthy foods—but also some items that aren’t so good for us. With 71% of Americans overweight and over a third considered obese, that might send a mixed message considering Mackey’s personal plea for Americans to eat healthier. But he points out selling a variety of foods and drinks (including some that aren’t healthy) is good business.

“My first store, before Whole Foods Market, was called Safer Way,” he said. It was vegetarian, sold no alcohol and had no foods with sugar or refined grains. “It was very pure and it didn’t do business.” After relocating that store and starting to sell coffee, beer, and meats, it was a natural food store that sold exceptionally well. While Mackey would prefer to stick to the healthier stuff, he says customers need to vote out the bad stuff with their dollars.

“You may have the highest ideals in the world, you try to educate people…but ultimately you need to sell what people want to buy or you don’t have a business,” Mackey said.