Dieters can tuck into foods such as eggs, avocados, oils, nuts, vegetables, meat and fish.
They should avoid high carb foods such as bread, pasta, rice and even some fruits.
This is thought to help some slimmers lose weight quickly, Daniel Reilly, PT and health and fitness tutor for The Training Room has explained.
He said: “The theory behind the ketogenic diet is that if you deprive your body of its main source of energy – glucose from carbohydrate-containing foods – and bring carbohydrates down to less than 10 percent of a person’s daily caloric intake, it goes into a state of ketosis.
“This is where it burns fat stored in the body for fuel instead.
“During this process, by-products called ketones are produced, which are then used by the body’s muscles, tissues, and brain.”
Does it work?
A study published on the National Library of Medicine found that those on a keto diet lose 2.2 times more weight than those who followed a calorie restricted low fat plan.
Another study revealed slimmers on a keto diet shed three times more weight than those on a plan recommended by Diabetes UK.
The expert explained this diet can be a good way for some people to get into shape.
Daniel said: “This diet works well for so many people because it targets several key, underlying causes of weight gain – including hormonal imbalances, elevated insulin, and high blood sugar levels.”
However, he issued a warning to those considering the plan as it is not suitable for everyone.
He continued: “While restrictive weight-loss diets might work in the short-term, the majority of people using them regain that weight – and often more – partly because restrictive behaviours and eating plans aren’t sustainable.
“The carbohydrate restriction may cause nutritional deficiencies, fatigue, low mood, irritability, headaches, constipation, and brain fog.
“Plus, because the keto diet takes valuable sources of fibre off the table, it may increase your risk of bowel cancer if it’s used long-term.”