Apart from epilepsy, there are a number of conditions that may benefit. Studies are being done into the potential impact of a ketogenic diet on some cancers and Type 2 diabetes. A study published in the Journal of the American Medical Association found that a low-carbohydrate diet helped cut blood-sugar levels in people with pre-diabetes, though the results hung on patients self-reporting their food intake (notoriously unreliable) and could be explained by the fact that by cutting carbs, most people lose weight, which helps the body respond better to the insulin it makes.
“Yes, a keto diet might initially be marginally better for blood-sugar control than just eating healthily. But after six to 12 months, that’s not supported by the evidence,” says Thomas.
Other areas of investigation include Alzheimer’s disease. A very small pilot study by the University of Kansas suggested an improvement in the cognitive scores of mild sufferers after three months on a ketogenic diet, which declined once they had resumed their regular eating habits. Researchers considered the results significant enough to warrant further study.
Thomas agrees that caution is necessary “because of question marks over the sustainability of the diet and how it can predispose people to disordered eating. I would never start with it as a possible treatment for any condition,” she says.
A 2023 study, presented at an American College of Cardiology conference and using data from the UK Biobank, suggested that keto diets could be linked to higher levels of LDL (low-density lipoprotein) or “bad” cholesterol and may therefore double the risk of cardiovascular events, such as angina, heart attack and stroke. As it was an observational study, the researchers concluded there was an “association” rather than a causal link and further research would be required to spell out the reason for the apparent rise in LDL cholesterol.
But keto-specific research is in its infancy. “We don’t have enough data on long-term keto consequences because not many people can sustain it in the long term,” says Spector.
Thomas outlines the more immediate risks: “Whenever we enforce rules and restrictions around our diet, it can quite easily turn into a preoccupation. It can start to consume our thoughts and interfere with our enjoyment of daily life,” she says. “You might find yourself constantly thinking about food because you’re hungry and scrolling for keto-friendly food on social media – it can become very obsessive very quickly, to the detriment of your relationships and friendships. If it interferes with your social life, we would consider that to be a red flag for disordered eating.”
There’s also, she adds, a potential physiological response. “When there isn’t enough available energy for the body, it starts to shut down what are considered to be non-essential functions. So the first thing that kind of goes offline might be reproduction – women can become amenorrheic and their periods stop. There is some evidence that there might be an increased risk of kidney stones and osteoporosis, and an increased level of uric acid, which is a risk factor for gout. It can have consequences for the whole body.”
Because the keto diet cuts out food groups containing vitamins, minerals and fibre, it is not recommended for pregnant and breastfeeding women, or those with health conditions such as IBS because the high fat content can worsen symptoms. The diet is also not good for anyone with osteoporosis, as it decreases the body’s ability to build new bone and could increase bone breakdown. And it’s a no for anyone with kidney problems, which may be exacerbated by the high levels of protein.
Your gut may not thank you. “A keto diet often results in people eating even less fibre than we already do,” says Spector. “The risks are constipation, heartburn, low mood, unhealthy changes in blood fats and a lack of sustainability, which inevitably leads to yo-yo dieting. It’s an unpleasant short-term fix that negatively impacts our fibre intake and likely our gut microbiome health.”
There is also, says Thomas, some evidence that suggests restriction and dieting might reduce serotonin levels – and could therefore impact our mood. Some experts also believe that keto can lead to irritability.
“Sometimes strict regimens like the keto diet can help people feel more in control of their lives. But what I have seen in my practice is that this effect is usually short-lived and only happens when life is otherwise smooth sailing,” Thomas says. “When life throws a curveball, that seems to be where we see big mental health impacts: the stress and anxiety of trying to maintain the diet while seeing friends and family, the anxiety of not eating the ‘right’ things or being ‘tempted’. Then, if you do ‘slip up’, there’s a lot of shame and guilt. Clients often tell me that when they stop dieting they have far more headspace.”
There are also some potential nutrient deficiencies, she explains, such as B vitamins and minerals like iron, magnesium and zinc which are typically found in wholegrains. These deficiencies can have unfortunate consequences.
“On the keto diet, hair can fall out or become weaker, nails may not grow as fast and could break more easily, and skin can look dull and take longer to heal. This happens because you may not be getting all the nutrients your body needs and, what’s more, these are fairly typical responses we see when people are in an energy deficit – ‘non-essential’ functions tend to be shut down.”
Other side effects may include headaches and brain fog. Many keto dieters also report a metallic or “nail polish” taste in the mouth, leading to bad breath, in the initial stages of the diet as the body adjusts to fewer carbs. This is because your body is breaking down fat for energy through ketosis, and ketones are being expelled by your body through urinating and exhalation.