The ketogenic, or ‘keto diet’ for short, is a low carb ‘body hack’ diet that claims to trigger an alternative metabolic state in the body, leading to weight loss. Ketosis is a state your body enters when it isn’t getting enough carbohydrates from dietary sources and switches to burning the body’s fat reserves. This creates something called ketones, which can be used as energy. If someone’s blood ketone levels reach more than 0.5 millimoles per liter then they are in a state of ketosis.
While this sounds like the ultimate body hack and a quick way to shed excess weight, the extreme nature of the diet makes it unsustainable, and many people find that once they switch back to carbohydrates as a source of energy, they regain the weight lost while on the keto diet. This is because the keto diet simply isn’t designed for long term use, being originally designed to support medication-resistant epilepsy in children.
So why is the keto diet so popular? Is there any scientific evidence indicating that it can be used for weight loss? And are there any risks? Read on to discover more.
What is the keto diet?
Laura Clark (opens in new tab), a registered dietician, food therapist and nutrition consultant, broke down the keto diet for us. “For a diet to be officially 'keto' only 5-10% of daily energy should come from carbohydrates,” she explains. “This means less than 50g of carb per day. This shifts the emphasis towards the other macronutrients in the diet, namely protein and fat. All meat and fish are included as is butter, oil, plant-based milks which are low in carbs such as almond and coconut, and cheese. Nuts, seeds and lower carb vegetables are all fine, as are artificial sweeteners and other things that have become synonymous with keto, for example bone broth.”
A study in the British Journal of Nutrition (opens in new tab) found that eating lots of protein may help with feelings of satiety, making the higher protein aspect of the keto diet potentially useful for curbing hunger. Often the problem with restrictive diets is that people lose motivation to stick to them, so keeping hunger levels down with lots of protein may help people to stay consistent with it.
- Related: What are high protein foods?
- Related: Do you need to eat meat to get protein?
Clark added that the keto diet’s low carbohydrate nature cuts out a lot of ‘core’ foods. “This rules out all starchy foods like bread, rice or pasta, fruit, some vegetables, milk and most yogurts, and foods containing added sugar such as biscuits, sweets and cakes,” she says.
How does the keto diet work?
By replacing carbohydrates with fat sources the body goes through a physiological change and enters a state called ketosis. When in ketosis, the body begins metabolizing its stores of fat and producing ketones, which it uses as energy instead of its usual preferred source - carbohydrates.
As the keto diet removes most dietary carbohydrates, including simple sugars, people on the keto diet may be less likely to have ‘sugar crashes’ as their carbohydrate intake is very low. A review in the journal Neuroscience & Biobehavioral Reviews (opens in new tab) indicates that the effect of sugar on mood can be detrimental and cause feelings of fatigue, sometimes as soon as 30 minutes after consuming carbohydrates.
Potential benefits of the keto diet
One review in the International Journal of Environmental Research and Public Health (opens in new tab) indicated that the keto diet could be beneficial in the treatment of obesity when implemented under the supervision of a doctor. The benefits included reduction in hunger in obese adults and potential to improve fat oxidative metabolism, which could reduce overall weight. The review also summarizes that the diet can be useful from a period of a few weeks (to induce a state of ketosis) to several months, but advises caution when reintroducing carbohydrates into subjects' diets.
Clark agrees that the keto diet can be a useful weight loss tool. “Keto diets are associated with quicker initial weight losses, mainly due to the loss of water as carbohydrate stores in the body are used up,” she says. “Some people find the satiation achieved with higher protein and fat intakes useful as a weight management tool. However, 12 months down the line, weight loss results between low carb and low fat approaches are similar.”
So perhaps keto is a good option for those trying to induce extreme weight loss, if under medical supervision, but how sustainable is that over time? Clark indicates that the downside of the keto diet is that it is difficult to follow for any extended period. “Compliance is a key factor - ultimately what is easy to follow for the long term,” she says.
It is also worth noting that the keto diet wasn’t designed to be used for weight loss, although a World Obsesity Review (opens in new tab) study indicates it is increasingly being used for this purpose. “The keto diet was originally developed for the treatment of drug-resistant child epilepsy and was designed to be done under medical supervision,” Clark says, of the keto diet’s original purpose. “It is now being trialed as a treatment for other conditions such as chronic pain, cancer and neurological conditions.”
Have a look at our guide to 'what fruits can you eat on keto' for a list of low-carb, keto-friendly fruits and keto diet foods: what to eat and what to avoid.
Is the keto diet safe?
Clark recommends caution to those with underlying health conditions. “Those with pre-existing medical conditions such as cardiac problems, liver or kidney disease may need to be cautious,” she says. “Whilst we don't have strong evidence that a keto diet would cause adverse events, it's important for a person's medical team to be involved. We still lack robust studies looking at the long term effects of following a keto diet.”
As with any diets that dramatically change the way you eat by cutting out entire food groups, we cannot recommend that you undertake the keto diet without the supervision of a medical professional. Although the keto diet has become popular with weight-loss gurus, it is extreme and it puts the body into an alternative metabolic state which should absolutely be monitored by a doctor.