A keto diet plan involves eating a diet full of high fat, high protein foods.
Cutting out carbs is key in the plan, which aims to shift the metabolic state of the dieter.
The body usually uses carbohydrates for energy.
A man recently used the keto diet plan to lose just 15 stone in a year.
Ketosis is when the body shifts to using fats as its main source of fuel.
This state encourages rapid weight loss, which is why the plan has become so popular.
The keto diet was initially devised to help those with epilepsy or who suffer with seizures.
What is the keto diet?
The usual breakdown for a keto diet is to get 70 per cent to 80 per cent of your daily calories from fat.
Twenty to 25 per cent should come from fat and five – 10 per cent from carbs.
How can you tell if you are in ketosis?
Suzannah Robin, who is behind a new device to test whether someone is in ketosis, revealed how to tell if you are in ketosis.
How can you tell without using a device?
She said: “There are a variety of ways to tell whether your body is in ketosis. Some methods are more reliable than others as they depend on physical signals that aren’t always consistent and could be indicative of something else, such as bad breath.
“The most obvious signal, of course, is weight loss. Appetite suppression and increased focus and energy will also tell you if the keto diet is working for you. However, these signs alone won’t tell you exactly when you are burning body fat and, if so, at what rate.
“Knowing this will help you to optimise the keto diet and your exercise regime, and tailor them accordingly.”
However, there are more accurate tests you can use.
She added: “There are three methods of testing for ketosis – blood, urine and breath.
“In the last few years some breathalyser manufacturers have tried to adapt electronic breathalyser semi-conductor sensors to detect the acetone that is produced during ketosis.
“However, these devices, while relatively cheap, are generally inconsistent, are inaccurate at lower levels and can’t be calibrated, so have a fairly short lifespan.”
The Ketoscan Mini is the world’s first portable cartridge-based analyser, which can tell if you are in ketosis using your breath.