Here's What Dietitians Think About the Sirtfood Diet—Made Famous by Adele

Trigger warning: Diet culture and disordered eating.

If you’ve been reading Byrdie for a while, you know we’re skeptical of many weight loss trends and not very into the idea of dieting. While weight can tell us important information, it isn’t the only indicator of health. Being overweight or obese is associated with a number of health risks, but weight and body mass index (BMI) aren’t perfect measures of health. Someone can be healthy even if BMI standards indicate that they’re overweight. So if you’re feeling pressured to lose weight, it's important to understand that weight may not be the best indicator of your overall health.

That said, we know our readers are always hearing about the latest diet trends. And since we want to keep you informed, we thought we’d do a breakdown of one of the trendiest diets of the moment—the Sirtfood Diet. This diet is said to promote fat loss and prevent disease while still allowing you to consume chocolate and red wine. That alone is enough to lure many people in, but does the Sirtfood Diet work? And is it safe? Below, dietitians share everything you need to know about the Sirtfood Diet.

What Is the Sirtfood Diet? 

The Sirtfood Diet has grown trendy over the past few years, thanks in part to its popularity among celebrities, including Adele. The diet is based around a group of proteins in the body called sirtuins, which play a role in regulating metabolism, inflammation, and other important bodily functions. Sirtfoods, which are the foods encouraged in the Sirtfood Diet, are claimed to be high in sirtuins activators, which may increase the amount of sirtuins in the body. The idea here is that the more sirtuins, the better our bodies will be able to regulate metabolism, decrease inflammation, and more.

"The diet focuses on consuming a low calorie diet of foods rich in SIRTs (sirtuins) —a family of proteins that have been shown to play a key role in keeping cells healthy and may reduce inflammation and slow aging," says Izquierdo. "The thought is that by eating these foods, certain genes will be turned on which boost metabolism and burn fat."

How Does the Sirtfood Diet Work?

The Sirtfood Diet is based around calorie restriction and eating from a specific list of foods. If you decide to try the diet, you'll see that it's split into two phases that extend over 21 days—the first phase is seven days and the second phase lasts 14 days. 

During the first three days, you’re encouraged to consume just 1,000 calories each day, including one meal and three Sirtfood green juices (for context, calorie needs vary from person to person, but adult women are typically discouraged from eating less than 1200 calories/day minimum).

On days four through seven, the daily calorie intake is upped to 1,500, and you're encouraged to consume two green juices and two meals per day. The diet's second phase allows for three Sirtfood meals and a green juice each day. If you decide to continue beyond the first 21 days, there's no longer a calorie restriction, but you’re encouraged to eat three meals rich in sirtfoods each day, along with a green juice.

Sirtfood-Approved Foods

• Green tea
• Kale
• Red wine
• Dark chocolate 
• Apples
• Citrus fruits
• Parsley
• Walnuts
• Turmeric
• Onions
• Arugula
• Blueberries
• Capers
• Strawberries
• Soy
• Extra virgin olive oil
• Buckwheat
• Medjool dates
• Coffee
• Red lettuce
• Bird’s eye chili

The Sirtfood green juice consists of arugula, kale, parsley, celery, half of an apple, matcha, and lemon juice.

Is the Sirtfood Diet Safe?

Registered dietitians say that for the most part, the Sirtfood diet is reasonably safe, with the caveat being the diet's calorie restriction. “Phase one includes severe calorie restriction with as little as 1,000 calories per day, which may negatively impact blood sugar levels in those with diabetes,” says Gillespie.

Izquierdo says the rapid weight loss this diet suggests is unrealistic. She also points out that 1,000 calories per day is not nearly enough for an adult. “Restricting calories to this extreme may cause fatigue, extreme hunger, lightheadedness and could lead to destructive eating habits long-term, including eating disorders,” she says.

The Pros

A huge pro of the Sirtfood Diet is that the recommended foods generally have a bunch of health benefits, whether or not they’re consumed as part of this diet. “The top 20 sirtfoods recommended on this diet are all foods that would be recommended for a healthy, balanced diet, and most people can benefit from eating more of them,” Izquierdo says.

Kenney points out another benefit: the Sirtfood Diet encourages people to include polyphenol and antioxidant-rich foods into their diet.

The Cons

One big drawback of the Sirtfood Diet is that it’s relatively new, so there isn’t much research to support (or disprove) its effectiveness. “More research is needed to support the benefits of sirtuins on human fat loss and metabolism,” Izquierdo says.

Most of the research on sirtuins is done in animal models, and isn’t yet robust enough to support the diet’s claims, Kenney says. “It would be an over-extrapolation to assume that laboratory research conducted on human stem cells, mice, and yeast has any bearing on real-world health outcomes,” she adds, but she says we do have research that shows eating a diet rich in polyphenols and antioxidants has been associated with better health and longevity.

It’s also important to keep in mind that restrictive diets are rarely sustainable in the long-term. “Most evidence shows that while weight loss occurs in the short-term on very low-calorie diets, most, if not all, of the weight will be regained once the diet is stopped,” Izquierdo says.

The Takeaway

The Sirtfood Diet may be effective in helping people lose weight, but this weight loss is likely due to calorie restriction, rather than specific foods the diet encourages you to eat. Additionally, most dietitians we spoke to find the diet's calorie restriction concerning, particularly in the first phase where you're encouraged to limit calories to 1,000 per day. "This is an inappropriate recommendation to the general population," Kenney says.