Mr. Borges, formerly the owner of a chain of gyms in Miami, has worked with the couple for 10 years, since his client Pharrell Williams introduced him to Jay Z. In 2013, Mr. Borges challenged Beyoncé and Jay Z to a week of plant-based breakfasts, and handed over some recipes to their chef. Jay Z started with oatmeal with seeds and berries; Beyoncé with an avocado, tomato and cucumber salad. Jay Z, Mr. Borges said, decided that was easy, so they added in a few all-veggie lunches. (“Jay’s like, ‘O.K., let’s talk to Brandon,’ ” Mr. Borges said, referring to their chef.) In December, they finally decided they were ready for the 22 Day vegan challenge. Though they struggled to adjust, every day “gets easier,” Beyoncé said. The pair quickly felt, it could be said, flawless.

She, for one, saw “a noticeable glow to my skin without having to deprive myself of carbs,” she said. “I even slept better.”

Making cumin-and-turmeric-flecked Baba’s Kidney Beans a go-to meal wasn’t originally Beyoncé or Jay Z’s idea. It was Mr. Borges who founded the company, and three years in he asked them to join.

“I thought, ‘Well maybe this is a long shot,’ but the first words out of Jay’s mouth were, ‘I thought you were going to keep this to yourself,’ and he just kind of started laughing,” said Mr. Borges, who is lean, wiry and seems perpetually on the verge of jumping onto a sofa to demonstrate his passion for all things plant-based. During one conversation, he talked for 23 minutes without stopping. (His enthusiasm is clearly infectious: Jay Z wrote the foreword to Mr. Borges’s 2010 book, “Power Moves”; Beyoncé wrote the one for his just-released “22-Day Revolution,” which contains a recipe for walnut tacos she loves. “It’s hard to believe they’re actually good for you and they taste great,” she wrote in an email. Of Mr. Borges, she said, he “does not talk about something; he lives it.”)

Mr. Borges is often listed as the company’s C.E.O., and he handles the day-to-day affairs, but he said technically none of them have titles and they share equally. “Some days I do the heavy lifting, and some days they do,” he said. “What does that mean? It means we want to put out a press release. I don’t do that. They do that themselves.” In a world where access to the couple is tightly controlled — where it can take more than a month, countless emails and layers of people to get an answer to a question — this partnership works simply because Mr. Borges is “with them all the time,” he said. “It wouldn’t work if it were an email every other week.”

Image Mr. Borges’s new book.

Meetings are frequently spontaneous, often around the breakfast table. Mr. Borges described opening his MacBook once to show Jay Z something unrelated to the company, but his malfunctioning Safari browser coughed up some cached copy with an “old school” design that Mr. Borges had been working on, and that Jay Z decided was “sick.”