Registered Dietitians Weigh In on the Sirtfood Diet, and Spoiler Alert, the News Isn’t Good

Very few celebrities are spared this, even a multiple Grammy-winning artist like Adele. She's made headlines this year after pictures she's shared of herself have gone viral, with people endlessly speculating over the apparent change in her physique. Frequently, these discussions include interest in something called the Sirtfood diet, the eating plan that Adele reportedly used for weight management.

With their curiosity piqued, many people are googling this diet du jour. And so, we called in two registered dietitians to break down the claims and concerns associated with the Sirtfood diet. Spoiler alert: Most healthy eating experts are not on-board with this particular eating plan.

What is the Sirtfood diet?

The Sirtfood diet was created by two British nutritionists, Aidan Goggins and Glen Matten. According to their book, The Sirtfood Diet, there are specific foods (such as arugula, coffee, and dark chocolate) containing compounds that activate a group of seven proteins in the body called sirtuins. Goggins and Matten dub sirtuins "skinny genes" because activating them, they say, leads to rapid weight loss. These genes are otherwise only activated through exercise and fasting, they say. Emphasis on "they say," as research on the subject is hazy at best—but more on that later.

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Essentially, the Sirtfood diet encourages people to focus specifically on these "sirtfoods" for a three-week period, while also severely restricting calories (much more on that later as well). The diet operates in two phases:

• Phase 1: This is the first week of the eating plan. For the first three days, a person has a calorie cap of around 1,000 per day (far less than the minimum of 1,600 calories per day recommended for the average, non-active adult woman); each day they eat mostly green juices and just one solid meal. For the next four days, a person increases how much they eat to  1,500 calories per day (still less than what is recommended for the average adult) and increases the amount of solid food they eat.
• Phase 2: This 14-day phase is called the "maintenance phase" of the diet. A person eats three meals every day, plus one green juice. All meals (and juices) continue to be high in sirtfoods.

After the 21-day plan, adherents to the diet are encouraged to "sirtify" their meals by continuing to use lots of those foods in their diet and drink lots of green juice, although the two phases of the diet can be revisited "as and when necessary for a health boost," the diet's website claims.

What registered dietitians think of the Sirtfood diet

Registered dietitians Vanessa Rissetto, RD, and Jessica Bippen, RD, both say they have some major problems with the Sirtfood diet. First off, it's very restrictive. Not only is what you eat vastly limited, but also how much you eat—and again, 1,000 calories is far less than what is typically recommended for adult women to consume in a day.

This comes with a lot of potential problems. Rissetto says restrictive diets aren't healthy because often when people are eating off a limited food list—such as the one the Sirtfood diet recommends—they likely will not get all the nutrients the body needs to function. (For example, the Sirtfood diet food list includes very limited sources of protein and healthy fats.) Additionally, for many people, this might not be enough food, period. "Eating only 1,000 or 1,500 calories a day is very extreme," Bippen adds. "For active adults, even ones who want to lose weight, this is very low and makes it challenging to get all the nutrients that are needed."

Both dietitians also say that restrictive diets don't work. "One reason for this is that it often leads to bingeing later," Rissetto says. (This is the body's natural reaction to deprivation, Christy Harrison, MPH, RD, previously told Well+Good.) Then people feel guilt and shame for "falling off the wagon," so to speak, and then restrict again—starting a cycle that is linked to an increased risk of eating disorders. "Restrictive diets are inherently harmful because they can lead to disordered eating," Rissetto says. "Many people who follow restrictive eating plans become overly obsessed with food and calories, and that's not healthy."

Additionally, both dietitians say that the science around sirtuin proteins does not check out. "The idea of sirtuin proteins is a theory with limited research and the research that does exist is inconclusive," Rissetto says. "There's research on mice about these proteins being activated resulting in some changes in metabolism, but that doesn't necessarily translate to humans," Bippen says. Basically, the limited research isn't conclusive enough to support a whole diet with sirtuin proteins as the focus.

Bippen says people who follow the Sirtfood diet will likely lose weight, but it likely doesn't have anything to do with sirtuin proteins—more the fact that you're just eating less food, period. "When you follow a restrictive diet, what you really lose in those first couple weeks is water weight," she says. "People get really excited those first couple weeks because they see the number on the scale going down, but as soon as you start eating normally again, that water weight is going to come back."

The bottom line: There are many, many ways of eating, and it's important to acknowledge that there is no one right eating plan for every single individual. But for these two dietitians, the Sirtfood diet isn't backed by science, likely won't work as advertised in the long-term, and will leave you hungry. So maybe think twice before busting out the juicer.