Inside the Sirtfood celebrity diet trend that's taking over the U.S.

Founded by U.K. nutrition experts Aidan Goggins and Glen Matten, the Sirtfood Diet promises to stimulate the “skinny gene,” or the proteins under the SIRT1 gene, to counteract the effects of inflammation and weight gain, as well as aging.

The Sirtfood Diet is based on the principle that certain foods activate sirtuin, a (highly controversial) protein in the body that is alleged to help regulate metabolism and offer cell protection to slow down the aging process. Proponents of the diet say that eating sirtuin-rich foods like green tea, kale, blueberries, salmon, and citrus fruits can give the body a steady metabolic boost, allowing you to lose weight fast. Such foods are also packed with polyphenols, which are antioxidants that better your skin and heart, says Brooke Alpert and author of The Diet Detox.

The Sirtfood Diet is split into two phases. The first phase, which lasts three days, requires you to restrict your daily calorie intake to 1000 calories per day by drinking three green juices and one sirtfood-rich meal per day. (You increase your meal count from days 4 to 7 to two meals and two green juices per day.) The second phase, the “maintenance” phase, lasts 14 days and requires you to eat three sirtuin-rich meals and one green juice per day.

While the promise of the Sirtfood diet is intriguing (Adele and Pippa Middleton are reportedly fans), and while restricting your calories might in fact lead you to lose weight in the short-term, the question remains: is this diet actually healthy, or is it just another silly (and potentially risky) diet trend? For that matter, is it even effective in the first place?

First things first: the Sirtfood diet is admittedly very restrictive. Unlike the Keto or Paleo diets, which emphasize having a balanced diet, the Sirtfood diet focuses heavily on counting calories. It also requires you to cut out some major food groups and downsize portions to an extreme, if only temporarily. So for the first week or so, you might be missing out on lean proteins (beef, poultry, and legumes). While you’re still allowed to eat olive oil and walnut (both of which are sources of sirtuin), the total daily calorie count for the first week is extremely low — less than 50% of what the average active guy needs. It also lacks other essential nutrients, like calcium and iron.

It’s also unclear whether sirtuin can actually cause weight loss to begin with. To date, there have been no human studies definitively linking sirtuin-rich foods to weight loss. It’s more likely that drinking juices that are high in greens and low in sugar for most of the day can easily cause short-term weight loss on its own: if you’re getting fewer calories and staying hydrated, it makes sense that you’ll shed a few pounds. .

Kristen Smith a spokesperson for the Academy of Nutrition and Dietetics, backs this up. “It is difficult to decipher whether the rapid weight loss promised in the first week of the diet is attributed to the significantly low-calorie diet recommended or related to the fat-burning powers of sirtuin-boosting foods,” she says.

Basically, “regardless of the sirtuin-boosting foods, people are going to lose weight on a 1000-calorie diet,” she explains.

Alpert agrees. “The authors say that people can lose up to 7 pounds in 7 days but I wonder how much of this weight actually stays off for longer than one month, if that long,” she explains.

Even if you lose weight during that first week, it could be primarily water weight, which means you might gain it back once you start taking in more calories. In fact, you might even gain more weight: as Men’s Health has previously reported, when you lose a lot of weight quickly, your body’s metabolism actually slows down, because your body is trying to make up for its reduced calorie intake.

As with any diet, the Sirtfood Diet also comes with its own side effects. While it likely won’t do much damage for you to eat so little in the short-term, if you’re not used to eating so little during the day, it can cause fatigue, nausea, impaired mental focus, and headaches, says Smith. It can also lead to unpleasant bowel movements if you’re not getting enough fiber. What’s more, you might get bad breath, which can be a side effect of not eating enough.

There is, however, one positive: If you eat a lot of sirtfoods over a sustained period of time, you might notice improvements in heart health due to the polyphenols in the foods you’re eating, Smith says. If you continue to eat sirtfoods after you end the diet and start to eat more calories, you’ll see the benefits.

The takeaway? While it is likely to lead to short-term weight loss, the Sirtfood diet is ultimately so restrictive that it’s not really sustainable. And if you’ve ever had an eating disorder or a complicated relationship with eating in the past, it’s best to avoid it altogether, says Alpert.

“I wouldn’t recommend such a low calorie intake for anyone. Extreme dieting sets people up for terrible eating habits and overeating when it’s over,” she adds.

That said, eating more sirtuin-rich foods is undoubtedly good for your health, so you can easily introduce them into your diet without limiting yourself to one meal or one juice at a time. There’s nothing wrong with eating more fish, berries, and leafy greens (especially because these foods are packed with fiber and protein), and having a green juice that’s low in sugar could be a great addition to an already balanced diet.

Ultimately, you can probably reap the benefits of the SIRT diet without diving in completely. Just make sure your portions are sensible and you’re getting your calories from a wide variety of healthy sources — no crash dieting or juice fasting necessary.