Demand is rising for Adele's rumored weight loss plan, the sirtfood diet. Here's how it works.

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British popstar Adele was reported to follow the "sirtfood" diet.

It involves eating foods high in a protein called sirtuin, including blueberries, strawberries, turmeric, walnuts, onions, green tea, and even red wine and dark chocolate. 

There's good evidence that these foods are healthy and could even lead to a longer life, thanks to inflammation-reducing compounds called polyphenols.

But the diet also restricts calories to 1,000-1,500 per day, which nutritionists say could be risky and isn't sustainable in the long term.

After Adele made headlines again for her weight loss, there has been an uptick in interest in the eating plan she has reportedly relied on.

The "sirtfoods" diet isn't new, and Adele has not, herself, recommended it over even spoken about it, but Google trends for the term spiked this month as Adele's birthday Instagram post dominated the internet. 

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

It involves eating foods high in 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 high in sirtuin are green tea, onions, celery, parsley, arugula, and kale, walnuts, buckwheat and citrus fruits.

There's some research that sirtuin-rich foods can help mediate the metabolism and potentially have benefits for extending your lifespan, although 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 are also high in other 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, whole grains, and many more. 

And the very low calorie limitations of the diet could be a problem, too. The plan follows a 7-day cycle of just 1,000 calories a day for the first three days and 1,500 calories a day for days 4-7. 

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, 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 nutritionist before jumping into the latest fad diet. 

Slideshow: 44 items from your favorite chain restaurants that are under 500 calories (Provided by Insider) 

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