Losing 7lb (3.2kg) in seven days, being encouraged to eat cocoa and drink red wine and coffee – the Sirtfood diet seems like it could be too good to be true, and there are some who caution that it is.

Created by nutritionists Aidan Goggins and Glen Matten, who co-authored a book of the same name, the way of eating activates a family of proteins called sirtuins, or “skinny genes”. This, in turn, supposedly mimics the effects of exercise and fasting.

Goggins and Matten do recommend performing “moderate activity” for half an hour five times per week, in line with World Health Organisation recommendations.

The diet’s critics cite a lack of evidence that the programme can accomplish what it promises.

Doctor and nutrition specialist Dr Melina Jampolis, based in California, the US, shuts down the notion of “skinny genes”.

“They want to sell books, so they’re saying that there’s something magical about these sirtuin genes, that it activates your skinny genes,” she says. “There are no skinny genes. I mean, you couldn’t activate them. There are people who are metabolically born skinny and can’t gain weight.”

Though she thinks the diet is being oversold, she is a fan of encouraging people to eat more healthful foods. Here’s what you should know about the Sirtfood diet.

What is the Sirtfood diet?

The plan pushes people toward certain foods without focusing on items that should be removed from one’s diet.

Goggins says when the sirtfoods are ingested, “they turn on a recycling process in the body, and that clears out cellular waste [and] improves how our cells function. The consequence of this burns fat.

“When somebody eats a diet rich in these types of foods, the outcome is similar to that same effect of exercise and fasting: a more energetic, leaner, healthier you.”

What is the controversy?

“As far as the science behind the sirtuin proteins and that sort of thing, that’s where the gimmick kind of comes in,” Jampolis says. “The science isn’t there in humans to support some of their claims that it activates the ‘skinny gene’ and can boost metabolism and increase fat-burning.”

She predicts the plan will “likely not” fulfil every promise, but says “if people eat more of these foods, long term they will be healthier.”

According to Goggins, the Sirtfood diet is simply bringing awareness to what he calls “nature’s pharmacy” – “why plant foods are so good for us, and how certain ones are highest in specific nutrients that we know improve how our cells function. Simply, these are the foods we should be incorporating maximally in our diet.”

In their book, Goggins and Matten wrote of an experiment conducted at KX, a fitness centre in London. They report 39 of the 40 members put on phase one of their plan (described in detail below) saw “an average 7lb of weight loss in seven days after accounting for muscle gain”.

Jampolis has concerns about the trial’s validity, as the subjects were all members of the gym: “They’re a motivated population. It’s not the average Joe Shmoe who’s sitting on their couch thinking about losing weight.”

What are the sirtfoods?

The book lists the top 20 sirtfoods as: arugula, buckwheat, capers, celery, chillies, cocoa, coffee, extra virgin olive oil, garlic, green tea, kale, Medjool dates, parsley, red endive, red onion, red wine, soy, strawberries, turmeric and walnuts.

Jampolis endorses most of this list, except for the Medjool dates (she recommends people monitoring their weight avoid dried fruit) and emphasises that the soy should be minimally processed.

The diet is broken into two phases.

Phase one lasts for a week and restricts the amount of calories consumed. For days one to three, those on the diet are allowed a maximum of 1,000 calories per day, and should consume three sirtfood green juices (made of kale, arugula, flat-leaf parsley, celery, green apple, fresh ginger, lemon and matcha) and one meal. For days four through to seven, caloric intake is raised to a maximum 1,500, consisting of two sirtfood green juices and two meals.

The second phase lasts 14 days, in which followers’ daily intake includes three meals high in sirtfoods, one sirtfood green juice and one or two sirtfood bite snacks, which are optional (and consist of walnuts, dark chocolate or cocoa nibs, Medjool dates, cocoa powder, ground turmeric, extra virgin olive oil, seeds of a vanilla pod or extract, and water).

Goggins says phase one can be skipped and people can select “the path that suits them best”.

Jampolis questions a lack of calorie guidelines for phase two. Without any restrictions, she cautions, “you can have too much of a good thing.”

What else should you eat?

Sirtfoods should be accompanied with protein for a meal. The authors recommend oily fish.

“We don’t focus on what foods to cut out,” Goggins explains. “We don’t demonise food groups.” However, he warns against overloading on processed and sugary food, as well as fish that are high in mercury.

In addition to the sirtfoods listed above, Goggins and Matten advise including vegetables, fruits, nuts, grains, beans, herbs and tea in one’s diet. Asparagus, bok choy, green beans, blackberries, goji berries, kumquats, raspberries, chia seeds, peanuts, popcorn, quinoa, cinnamon and ginger are among their suggested foods.

The authors suggest all meals should be consumed by 7pm.