Pippa Middleton's New Wedding-Day Diet

Pippa Middleton is an English "socialite" and the sister of Kate Middleton, the Duchess of Cambridge. Her good looks, chic style, and frequent appearances at London's hottest clubs thrust her into the public spotlight and earned her many admirers, as well as critics. In May, Pippa will be marrying her financier fiancé, Jordan Matthews, and to really wow on her wedding day, she is turning to a questionable weight-loss routine — the Sirtfood Diet, based on a book of the same name published in January by British nutritionists Aidan Goggins and Glen Matten.

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So where does the Sirtfood Diet rank in terms of fad diets adopted by wealthy social elites? Researchers believe that a special group of polyphenol-rich foods help activate sirtuins — a class of proteins that have been implicated in a range of cellular processes such as aging, inflammation, and stress resistance. Sirtuins are also believed to affect the body's ability to burn fat, which is why they've suddenly received more attention from the diet/weight-loss community. In an ideal scenario, the Sirtfood Diet leads to a seven-pound-per-week weight loss while preserving muscle mass.

If you're wondering which foods you can eat on this diet, the answer is not many. The ten most common sirtfoods are green tea, dark chocolate, apples, citrus fruits, parsley, turmeric, kale, blueberries, capers, and red wine. These foods are undoubtedly healthy and contain a number of beneficial antioxidants, flavonoids, and other nutrients, but nutritionists are skeptical that they provide enough protein and carbohydrates to make up a healthy eating regimen. The Sirtfood Diet is one part calorie restriction and one part juice cleanse.

The diet involves two distinct phases. The initial phase lasts one week, requires that participants eat no more than 1,000 calories for three consecutive days, and usually involves three sirtfood juices (celery, kale, and lemon are common juice components) and one low-calorie meal per day. For the next four days, calorie restrictions are increased to 1,500 kilocalories, with an extra solid meal added in place of a juice. The second phase is where consistent weight loss takes place. For the next two weeks, dieters eat three meals per day of only sirtfoods and one sirtfood juice.

If this diet stinks of starvation, then your nose is spot on. Registered dietitian Brigitte Zeitlin explained to The Cut that although it's true that a person can initially lose weight on this diet due to its overly restrictive nature, "they'd be starving themselves in the process." Zeitlin argues that eating fewer than 1,200 calories per day is potentially dangerous, and you'll lack the necessary energy to get through the day. Rapid weight loss is usually just water weight, not fat, meaning that after you get off the diet the pounds come right back.