Dangers of keto diet

Wondering how safe keto is and whether doing it puts you at risk of any side effects? Here’s what you need to know.
Published 16 September 2019 | Updated 6 June 2024

The keto diet continues to be as high in popularity as it is in fat, with its status as a buzzword showing no signs of fading. But just how well does its trendiness translate to safety?

According to U.S News & World Report’s 2024 diet rankings and assessments, the answer might be ‘not very well at all’. Considered the global authority in rankings and consumer advice, the expert panel awarded the keto diet 25th place overall in a field of 47 diets.

One of the main concerns the judging panel had was that, not only is keto nutritionally incomplete, it’s also very high in fat and doesn’t differentiate between the quality or health-rating of fats, either.

It’s the foundation of the diet – practically eliminating carbs and filling up on fats instead, triggers something called ketosis. That’s where your body burns fat for fuel instead of the glucose from carbohydrates that it’d usually use.

The long-term health effects of keto are still being investigated, and while it’s generally considered a no-go zone for people with a kidney or liver condition, the jury also remains out on whether keto offers more of a risk or benefit for people living with a heart condition or type 2 diabetes.

But in addition to a 2018 study which found a link between low-carbohydrate diets and shorter lifespans, research has already confirmed some facts about the potential dangers of the keto diet. Here’s what we know.

Keto diet side effects

Keto flu

Embarking on the keto diet can temporarily trigger a range of flu-like symptoms, including headaches, fatigue and nausea, which may last days or weeks. While it doesn’t affect everyone, keto flu is an immediate side effect of the impact switching to a very-low carbohydrate diet has on the body, and is one explanation why people often find sticking with it in the early days pretty challenging.

Nutritional deficiencies

Keto requires eliminating a variety of nutritious, carbohydrate-rich foods from the diet, like wholegrains and certain fruits and vegetables. As a result, research confirms that experiencing risky vitamin and mineral deficiencies is a very real concern for people doing keto.


When the body goes into that state of ketosis which we mentioned earlier, it starts to produce things called ketones from stored fat, and the body uses these for energy in the absence of glucose. While healthy people typically produce enough insulin to prevent excessive ketones from forming, there is a small risk that ketone levels can climb too high, causing a dangerous condition called ketoacidosis, where acid levels in the blood reach toxic levels.

Blood vessel damage

A small study published in 2019 indicates that having a day off when you’re on keto might be a bad idea, suggesting that in terms of both metabolic effects and delivering results, this isn’t a diet that allows for flexibility.

The study found that after following a low-carbohydrate, high-fat diet for just seven days, a single 75-gram dose of glucose – the equivalent of eating a serve of fries – can cause damage to blood vessel walls, thanks to the sudden spike in blood glucose it creates. In the long term, sustained blood vessel damage can increase the risk of organ damage.

An increased risk of bowel cancer

Being high in fat, and low in fibre on account of the lack of carbohydrates, keto may equal a higher bowel-cancer risk if it’s used long term. While high-fat diets have been shown to encourage colon cancer growth in lab-based studies, research also shows how fat-rich, low-carbohydrate patterns of eating alter the makeup of gut bacteria and reduce the production of short-chain fatty acids that may help protect against bowel cancer.

Irregular heartbeat

The results of a large 20-year study released in early 2019 show that people who consistently eat low-carbohydrate diets are significantly more likely to develop atrial fibrillation. It is an irregular heart rate that can increase the risk of stroke and other heart-related complications. It may be the result of eating fewer vegetables, fruits and grains in order to restrict carbohydrate intake, or the fact that high-fat diets lead to something called oxidative stress, which is a known risk factor for atrial fibrillation.