It’s clear why this diet is so popular (see: wine, chocolate), but is it too good to be true? Here’s everything you need to know.

What It Is

The authors of The Sirtfood Diet advise eating foods rich in sirtuins, a type of plant-based protein that has shown some promise in clinical studies to improve metabolic health. “The eating plan itself is designed to ‘turn on’ the sirtuin genes (particularly SIRT-1), which are believed to boost metabolism, increase fat burning, fight inflammation, and curb appetite,” says Edwina Clark, R.D., head of nutrition and wellness for Yummly.

Early studies suggest that calorie restriction and reservatrol (a polyphenol found in foods like grapes, blueberries, and peanuts), activate the SIRT-1 gene, and these two principles underpin the Sirtfood approach to eating.

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How It Works

The diet lasts a total of three weeks and is divided into two phases. During phase one, you limit yourself to three Sirtfood green juices (containing kale, arugula, parsley, celery, green apple, lemon juice, and green tea) and one Sirtfood-rich meal per day, totaling about 1,000 calories each day, says Caroline Apovian, M.D., director of the Nutrition and Weight Management Center at the Boston Medical Center.

For the next four days, you drink two Sirtfood green juices and eat two Sirtfood-rich meals, which brings your calorie total to about 1,500 per day.

Phase two, or the maintenance stage, lasts 14 days. During those two weeks, you’re supposed to have three Sirtfood-rich meals and one Sirtfood green juice daily.

Once those three weeks are up, there’s no set plan to follow. To continue on the Sirtfood path, all you have to do is tweak each of your meals to include as many Sirtfoods as possible. Exercise is also encouraged (30 minutes of activity, five days a week), but getting sweaty isn’t the main focus of the weight-loss plan.

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Pros And Cons

The Sirtfood Diet includes many nutritious foods that are beneficial for weight loss, such as celery, kale, green tea, Medjool dates, lean chicken, lean red meat, and parsley, says Apovian. The diet also restricts or eliminates many foods that are known to cause weight gain, such as refined flours, added sugars, and processed foods with little to no nutritional value. And thanks to that ridiculously low calorie intake, followers will likely lose weight provided they stick to the plan, she says.

“Evidence to date suggests that caloric restriction and intermittent fasting can be an effective strategy for weight loss and improving metabolic health,” says Clark. “However, this may not be appropriate for everyone,” she says.

The long-term sustainability of this plan is questionable. Once you’re past the first few weeks, there’s no eating strategy to follow other than adding more Sirtfoods to each meal. This makes the diet much more flexible than most, which is a huge perk, but a three-week long stretch of deprivation could easily lead to overeating during phase two, ultimately placing you back at square one.

Even if you’re uber-disciplined, this is still a tough diet to follow. “A mere 1,000 calories will leave most people feeling very hungry,” says Apovian. And if you’re not a fan of green juice, a staple of the first week, that will make you even hungrier, she says. Also, since most of the weight loss in phase one is water weight, it will come right back on once you resume normal eating, she says.

Plus, following any diet that doesn’t include a healthy amount of protein, i.e. the first week of the Sirtfood Diet, will result in muscle loss and a slower metabolism, says Apovian. To lose weight and keep it off, building muscle through eating plenty of protein and working out with weights is paramount.

On top of all that, research on SIRT-1 activating foods is still very much in its infancy, so it’s unclear whether consuming polyphenol-rich foods has a substantial impact on weight in everyone. “Weight is a multi-faceted concept, involving complex interactions between our unique genetic makeup and our diet, movement patterns, sleep habits, and emotional state,” says Clark.

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Bottom Line

The approved foods in the Sirtfood Diet are low in calories and high in nutrients, which is great for weight loss. However, nutritionally speaking, this particular diet is too restrictive, says Apovian. “Ultimately, eating a diet rich in a variety of healthy foods, including lean protein sources, different fruits and vegetables, and whole grains is a healthier, more sustainable way to lose weight and keep it off,” says Apovian.