Here's the unusual fat-shredding diet David Haye and Adele swear by
David Haye is a two-weight boxing world champion out to conquer the heavyweight division once more.
Adele is a knock-out singer and millionaire global icon who has the world at her feet.
The two Brits couldn't be more different - except for they both got in incredible shape using the same diet.
Haye went vegan during his three-and-a-half year injury lay-off, but now at the core of his nutrition plan is something called the Sirtfood Diet.
The 36-year-old boxer's performance nutritionist Aidan Goggins created the diet he eats every day around training - which we look at in-depth here.
But while Haye uses it for performance benefits to make him a better, stronger and more powerful fighter, Adele has seen the body composition benefits of it - losing 14kg in weight.
So what is it?
The Sirtfood Diet is based around foods that are high in special polyphenols which activate specific proteins in the body called 'sirtuins'.
These sirtuins supposedly protect cells in the body from dying when they are under stress - like doing hardcore boxing training.
They are thought to regulate inflammation, metabolism (calorie burning) and even the ageing process.
Researchers think sirtuins help the body burn fat and speed up the metabolism - and co-author of the Sirt Diet book Glen Matten says they “mimic the effects of exercise and fasting.”
Although studies in humans are still limited, scientists believe these foods could also play a role in the prevention of Alzheimer's disease and protecting against things like type 2 diabetes, cardiovascular diseases and even some cancers, according to Laura Thomas PhD.
It must be noted that there have been criticisms from some quarters that this is just another in a long line of fad diets - including Thomas, who points out that the select few nominated 'sirt foods' aren't the only plant-based phytonutrients to stimulate sirtuin production.
But on this hallowed list there are around 20 foods including apples, walnuts, kale, parsley, turmeric, blueberries, capers, apples, green tea and, wait for it, red wine.
The diet claims to be able to shift 7lbs in seven days, while retaining muscle, although we imagine this is probably water weight.
It's basically split into two phases - a 1,000 calorie phase for the first three days based around sirt food juices and meals and then four days on 1,500 calories.
This is followed by a maintenance phase over 14 days, where weight loss steadies, based around as many sirt food-rich meals as you want.
Haye obviously has to eat a lot of calories to sustain his size, 16st muscle mass and heavy training volume.
The sirt foods in his diet are designed to give him better muscle function and muscle adaptation which gives Haye better recovery from training and increased muscle mass.
While research still needs to be done on sirt foods, the health benefits of eating more plant-based foods rich in polyphenols, bioflavonoids, carotenoids, retinols and isoflavones is clear.