Cutting carbs, minimising protein and boosting intake of high fat foods doesn’t sound like a healthy balanced diet, but that’s exactly what the ketogenic, or keto, diet advocates…and it’s proving popular.

A Harris Interactive poll by The Grocer in February 2019 revealed that 35% of consumers see keto as an ‘on-trend’ diet. The interest is clear. In 2018, Google data also revealed that keto was the most Googled diet…


Normally, our bodies use sugar (glucose) from carbohydrate foods to supply energy.  

But if we significantly reduce carbohydrate intake to less than 50g a day (that’s roughly equivalent to a hamburger bun or two apples) the liver begins to break down fat stores to produce energy, in the form of ‘ketone’ molecules. 

This metabolic state is called ‘ketosis’, and the aim of a keto diet is to sustain ketosis throughout the day. Once carbs are restricted it can take anything from 2-4 days to enter ketosis, depending on the individual.

Following a high-fat, low-carb diet can enable rapid weight loss and help to control blood-sugar. In one study by the University of Cincinnati, people on a keto diet lost 2.2 times more weight than those on a low-calorie, low-fat diet.

There a number of variations on the keto theme, but the standard keto diet typically comprises 70-75% fat, 20% protein and 5-10% carbs. 

So say goodbye to potatoes, pasta, rice and beans…

A keto diet relies on increasing the intake of high fat foods such as butter, meat, fish, eggs and cheese, and swapping high carb vegetables, such as sweet potatoes and corn, for low carb alternatives such as cauliflower and leafy greens.

Fruit intake must also be limited, as many are high in carbs. At one end of the scale are watermelons, peaches and oranges, for example, which are relatively low in carbs (7-9g per 100g). Yet at the other end are bananas, boasting a whopping 20g of carbs per 100g. Raisins and dates also score highly.


Equally, overdoing the protein can bring the body out of ketosis, by causing the liver to start converting protein into glucose.

Experts urge those on keto diets to eat a selection of foods, including as many different ‘allowed’ food groups as possible, in order to minimise the risk of missing out on essential nutrients. For example, many types of seafood are carb-free or very low in carbs, yet are also a good source of vitamins, minerals and omega-3s.

Indeed, one of the main concerns related to the keto diet is the severe restriction of certain foods such as fruit, vegetables and grains, which can lead to a deficiency in fibre, and certain vitamins, minerals and phytochemicals.

It is also important to be mindful of the less desirable side-effects as the body switches energy sources. From headache and weakness to nausea and vomiting, a collection of side-effects known as ‘keto-flu’ is not uncommon for a couple of weeks. 

Other less than welcome temporary impacts can include bad breath, fatigue, constipation, decreased bone density and poor sleep.

Increased urination is also common, as the body produces ketones while burning fat, and these are removed through urination. This leads to loss of electrolytes, such as sodium, magnesium and potassium, which can exacerbate the flu-like symptoms.

Dehydration can also lead to lightheadedness, kidney injury, or even kidney stones if not monitored. 


But while a keto diet might not instinctively lend itself to athletes, think again.

Typically, athletes looking to build muscle usually load up on carbs and protein shakes, but there is a school of thought that a keto diet will optimise the body changes seen in weight lifters…

One 2018 study in the Journal of Strength and Conditioning Research followed 25 men on a resistance training program. Some were on the keto diet while others were on a standard diet. Lean body mass increased and fat mass decreased in both groups during the first 10 weeks, yet only those on the keto diet showed more of an increase in lean body mass during the final week, when carbs were reintroduced.

What about HIIT?

In 2018, researchers in the Czech Republic set out to determine how the keto diet impacts high-intensity interval training (HIIT). The results showed that high-intensity performance wasn’t found to be compromised, while the group on the keto diet also demonstrated increased fat oxidation rates – or greater levels of fat burning – than the control group.

So far, studies into the long and short term effects of the keto diet have been small, and more research still needs to be carried out. For example, too much butter and bacon has been linked to increased risk of colorectal cancer, while a diet high in fruit and vegetables has often been linked to a lower risk of cancer and heart disease. 

For all its claims, does a keto diet fly in the face of good sense?

A study presented at the American College of Cardiology earlier this year, showed that people getting a low proportion of their daily calories from carbohydrates are significantly more likely to develop the heart rhythm disorder, atrial fibrillation. Hence, experts continue to debate how long people can safely stay on the keto diet.

One thing’s for sure – the keto diet is effective at promoting weight loss, but it’s not an easy choice. It requires huge discipline and is very restrictive. One single banana could quite feasibly throw you out of ketosis. 

And remember, weight is not the sole determinant of health.

*Be sure to consult your doctor before you try a keto diet.