The keto diet is low carb and high fat - and is often used for weight loss.
It involves drastically reducing carbohydrate intake and replacing it with fat, putting your body in ketosis.
In fact, many studies show that this type of diet can help you lose weight and improve your health and conditions including diabetes.
Dr Michael Mosley is most famous for his keto diet plans with the aim of helping more people lose some extra weight.
The TV presenter and dietician book - 21-Day Keto Magic: Eat Healthy, Burn Fat, Lose Weight, And Keep It Off - looks at "a diet high in fat and protein and very low in carbs".
The aim of Dr Mosley's previous diets has been to start the process of ketosis, an already established way of losing weight.
But Dr Michael Mosley says a low-carb diet doesn’t mean you can’t indulge in meals which are just as satisfying as dishes with flour and potatoes.
So, what foods are important for this process?
What is ketosis?
Ketosis is a process that happens when your body doesn't have enough carbohydrates to burn for energy. Instead, it burns fat and makes things called ketones, which it can use for fuel. Ketosis is a word you'll probably see when you're looking for information on diabetes or weight loss.
According to Diabetes.co.uk, Ketosis can be beneficial for a number of people but there are certain groups, such as people with type 1 diabetes, that need to be more careful. In these groups, very high ketone levels would lead to diabetic ketoacidosis, a dangerous situation caused by a lack of sufficient insulin.
What foods are good for ketosis?
Certain foods are good for encouraging ketosis within your body, according to Michael Mosley.
Our bodies are usually powered by a combination of fat and sugar, but burn fat when they are low on glucose.
Michael told the Mail: "Your body does this by releasing fatty acids from your fat stores and converting them into chemicals called ketone bodies. These can be used by most cells in your body as fuel.
"The process is known as 'flipping the metabolic switch'. Because so many of us top up our sugar stores by nibbling and snacking from first thing in the morning till last thing at night, we rarely get to flip the switch, so we seldom do a serious dive into our fat stores."
Diets such as Mosley's Fast 800 are useful for losing weight, though people with medical conditions, or who are pregnant or breastfeeding, should consult their doctor before trying it.
Here are some useful foods that can be part of the keto diet.
Pizza
Pizza can be made carb-free using cauliflower rice or almond flour - and of course, cheese!
Writing in the Mail, Dr Mosely said: "I’m a convert to cauliflower rice, deliciously doughy pizza made from almond flour and no-carb cheesy biscuits — there’s no reason to miss classic carbs at all."
Fish
Dr Mosley said: "Although fat is an important part of the diet plan, we recommend eating healthy fats (olive oil, oily fish, nuts and avocados), and only in calorie-counted moderation."
Fish fillets like cod or haddock can be steamed with things like tomato and pepper sauce, olives and green beans.
Cheese
One way to make sure enough protein is being consumed is to add nuts, Greek yoghurt or a piece of cheese to meals.
Recipes in Michael Mosley's new book include Goat’s Cheese Frittata, Keto Pancakes with cream cheese and Cheesy Asparagus Prosciutto Bites.
Eggs
Eggs are a really important part of the keto diet and can be eaten on their own or used to make other foods.
Scrambled eggs can be eaten with moderations of avocado, feta and smoked salmon, or used in a goats cheese frittata dish.
Pancakes
We may not associate pancakes with healthy food, but details are in how the pancakes are made.
'Keto pancakes' can be made from ground almonds, cream cheese, eggs, vanilla extract or lemon, butter, berries and full-fat Greek yoghurt.
These pancakes are low in carbs and are a good way of having a tasty treat, while keeping the calorie count down.
Nuts and berries
Nuts and berries are good sources of protein and a useful switch for those hoping to avoid eating meat.
Dr Mosley explained that it also helps which time of day a person eats a a high-protein meal.
He said to GHP: "It is well known that moderately increasing the amount of protein in your diet can help you to feel more satisfied after meals. What is less well known, though, is that the time of day that you eat protein also matters.
"To deliver enough protein to make the difference, breakfast doesn’t have to be meaty – nuts and seeds are good sources of protein, as are eggs, dairy and quinoa-based foods."
Spinach
Mosley has gone as far as to say that certain vegetables can be counted as 'free food'. One of those foods is spinach, as well as kale and broccoli.
Mosley said: "To deliver enough protein to make the difference, breakfast doesn’t have to be meaty – nuts and seeds are good sources of protein, as are eggs, dairy and quinoa-based foods."
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