Like the Atkins, Dukan and Zone diets, eating to a ketogenic plan restricts carbs. Bread, pasta, potatoes, rice and sugar are out; protein is in.

A rigorous keto diet allows 5% – around 20g – of your daily calorie intake for carbohydrate, with a further 25% for protein, and 70% for fat; more relaxed plans involve a carbohydrate intake of up to 50g. To be successful on the ketogenic diet, carb-containing fruit, veg and wholegrains need to be largely avoided.

According to Dr Michael Mosley, BBC presenter and author of the new Fast 800 Keto (Short Books, £9.99): ‘Without sugar, bread, pasta and rice, your body increasingly relies on your fat stores for fuel, converting that fat into “ketone bodies”, which puts your body into a state of “ketosis”.’ The result is fast weight loss, as the body’s water stores empty, with the happy side of reduced hunger (the production of ketones takes the edge off your appetite).

The keto diet is very different to the NHS’s current Eatwell guidelines, which recommend that a third of what we eat should be made up of starchy carbohydrates, fat should only be eaten sparingly, and that we should be eating at least five portions of fruit and veg. Dietitian Helen Bond says: ‘The carbohydrate-containing fruit, veg and wholegrains you need to exclude to do keto are a great source of fibre in our diet. We should be consuming 30g of fibre a day, but only 9% of adults meet that; removing carbs makes it very difficult to get 30g of fibre daily. And we know that wholegrains, which you also avoid on the keto diet, are important for digestive and heart health.’

‘The problem with the keto diet is that people don’t have enough information to do it properly,’ says nutritionist Rob Hobson, author of The Detox Kitchen Bible (Bloomsbury, £14.99). ‘The focus should be on eating minimally processed foods, healthy fats like olive oil, nuts and avocado; fibre comes from non-starchy veg and berries. There are definitely foods that you cannot eat on the keto diet, but this doesn’t mean it’s restrictive or that your options are limited. With a little planning you can still create tasty and nutritious meals using foods such as meat, oily fish, eggs, cheese, nuts, seeds, healthy oils and avocado. It’s a good idea to support your nutrient intake with a multivitamin and mineral supplement, too.’

Studies show that following a well-planned ketogenic diet can help manage type 2 diabetes and improve blood sugar control. Followers often report higher energy and better concentration.

The ultra low-carb approach is not suitable for some people, so it’s vital you check with your doctor before attempting the diet.

Tracking your ‘macros’ (your protein, carbohydrate and fat intake) is important on the keto diet; the easiest way to do this is to enter all the food you eat into a free app like MyFitnessPal or Cronometer.

As your body adapts to the diet, you may suffer nausea, headaches and tiredness among other symptoms; these should only last a few days. You may also find you have bad breath, caused by ketones being released from the body – fortunately, this side effect is usually temporary!