What Exactly Is the Sirtfood Diet, and Why Is Pippa Middleton On It? (Spoiler: You Can Drink Red Wine!)

In news that will shock no one, Pippa Middleton reportedly is hitting the gym hard and strictly adhering to a diet in advance of her May 20 wedding. According to E! News, the 33-year-old, set to marry hedge fund manager James Matthews, has been attending hour-and-15-minute Pilates classes at the exclusive KX Gym in London’s Chelsea, and sticking to the Sirtfood diet, created by “health consultants” Aidan Goggins and Glen Matten. (Adele and a bunch of other Brits we’ve never heard of also reportedly are fans.)

So what is the Sirtfood diet, anyway? And should you be doing it? Here's the lowdown.

What is the Sirtfood diet?

Research shows that certain foods contain chemicals called polyphenols, which stress out cells so much they stimulate your sirtuin genes, which go into “fasting mode” and control metabolism and trigger weight loss. Such foods include kale (of course), blueberries, capers, extra virgin olive oil, onions, and walnuts, to name a few, but also indulgences like dark chocolate and red wine (!).

OK, you had me at red wine. How does it work?

For the first three days of the diet, you are only allowed Sirtfood green juices and one full meal made up of approved Sirtfoods, for a grand total of 1,000 calories a day. After the initial phase, you can increase caloric intake to 1,500 calories by having two green juices and two Sirtfood-rich meals a day.

Sounds doable. What’s the catch?

The diet not only restricts calories, it also limits what you can eat. “I never recommend completely removing foods from my client’s lives because it never ends well,” says Tracy Lockwood, a celebrity registered dietitian and founder of Tracy Lockwood Nutrition in New York. She recounts how whenever her clients complete a “quick fix” diet, they tell her how they celebrated their success with pizza and fries. “Now, that doesn’t make sense!” she says.

Still, I’ll lose weight on the Sirtfood diet, won’t I?

Any weight loss you do experience on this diet likely isn’t real, Lockwood says. “The initial weight loss may be related to fluid loss, so it’s going to eventually come back—and then some—when people go back to their regular eating patterns,” she says.

But how bad could eating kale, blueberries, and walnuts all day every day really be? Is the Sirtfood diet safe?

Not at all, says Lockwood. “Anyone who is looking to lose weight won’t effectively and safely do so by putting themselves in such a severe caloric deficit,” she says. “And this diet can cause disordered eating habits due to the restrictive nature of the calories and lack of essential macronutrients.”

What’s more, maintaining such a diet long-term is near impossible for most folks, unless your sister is a princess and you’re about to marry a millionaire. Instead, Lockwood advises, “I would encourage people to simply incorporate foods that are high in sirtuins in their existing balanced diet rather than adopt this one.”

It seems Middleton herself would even agree. “I grew up with the belief that good health is about moderation in all things,” she wrote for Britain’s Waitrose Weekend magazine back in 2014. “So I’ll be celebrating healthy living through exercise, a balanced diet, and a little of the naughty stuff sprinkled in.”