A rumor about Adele turned the sirtfood diet into a hot trend. Here's how it works.

• The "sirtfood" diet took off last year when a rumor linked it to pop star Adele.
• It involves eating nutrient-rich foods that boost a protein called sirtuin, including berries, red wine and dark chocolate.
• But the diet also restricts calories to 1,000 - 1,500 a day, which nutritionists say isn't sustainable.

After Adele made headlines last year for her weight loss, rumors linked the British pop star to a diet trend called "sirtfoods," rich in dark chocolate, red wine, and green juice.

Adele said in a recent Vogue interview that she hasn't followed any particular diet, and "inside sources" claiming to have spoken to her were unreliable.

"All these other people have come out saying that they trained me," she told Vogue. She called them "weirdos," adding, "I've never met them in my life!"

But her rumored attachment to the diet still prompted immense interest, spiking Google Trends for sirtfoods each time Adele made waves on social media.

The concept was popularized in 2016 in a book titled "The Sirtfood Diet" by the pharmacist Aidan Goggins and the nutritionist Glen Matten.

It involves eating foods that activate a protein called sirtuin, hence the name, and cutting calories for weight loss.

But, while the foods included in the diet are healthy, it could have some drawbacks by restricting what and how much you can eat, potentially making it tricky to follow in the long term.

There's plenty of evidence that sirtfoods are good for you

Blueberries, strawberries, red wine, and dark chocolate are just a few examples of the most appealing sirtfoods you can enjoy on the diet. Other foods that boost sirtuin are green tea, onions, celery, parsley, arugula, and kale, walnuts, buckwheat, and citrus fruits.

There's some research that sirtuin-boosting foods can help mediate the metabolism and could have benefits for extending your life, though there's not yet enough data for fully understand how that might work.

Proponents of sirtfoods have also cited the fact that many of them (such as wine and leafy greens) are common in so-called Blue Zones, areas of the world where people tend to live the longest.

Many of these foods high in healthy compounds, including vitamins and micronutrients called polyphenols, substances found in plant foods that research suggests can have antioxidant and anti-inflammatory effects, helping to reduce the risk of many chronic illnesses and ailments associated with aging.

But a strict diet of fewer than 1,500 calories a day can be risky and isn't sustainable, experts say

While these foods are individually health and fine to include in your diet, there's no evidence that specifically eating only sirtfoods is good for you. Plus, there's a lot of foods and nutrients that are left out of that list, including protein sources from chicken to beans, healthy fats, and whole grains.

And the calorie limitations of the diet could be a problem, too. The plan follows a seven-day cycle of just 1,000 calories a day for the first three days and 1,500 calories a day for days four through seven.

Fewer than 1,500 to 1,200 calories can put you at risk of malnutrition, according to Harvard Health. Any diet that cuts calories so strictly is also very difficult to follow in the long term, the nutritionist Rachael Hartley previously told Insider.

"A thousand calories is under the daily amount recommended for a 2-year-old. So for an adult eating that and expecting to fuel their day, you might not keel over, but you're not going to have the energy to perform at your best," Hartley said.

It can also be risky for people with a history of eating disorders or who otherwise have a fraught relationship with food.

So, while it's fine to include a little more green tea, berries, and yes, even wine with your daily meals, it's still best to consult a nutrition expert, such as a registered dietitian, before jumping into the latest fad diet.

• Read more:
• The science behind Adele's 'sirtfood' diet and 24 other bizarre celebrity weight-loss plans
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