SINGAPORE – A low-carbohydrate, high-fat (LCHF) diet may be linked to higher levels of bad cholesterol, doubling the risk of cardiac events, according to new research.

The study by Dr Iulia Iatan and her colleagues was presented on Sunday at a conference in New Orleans, United States, organised by the American College of Cardiology and World Heart Federation.

“Our study found that regular consumption of a self-reported diet low in carbohydrates and high in fats was associated with increased levels of low-density lipoprotein (LDL) cholesterol – or ‘bad’ cholesterol – and a higher risk of heart disease,” said Dr Iatan, an attending physician-scientist at St Paul’s Hospital and University of British Columbia in Vancouver, Canada.

The study defined an LCHF or a “keto-like” diet as one where no more than 25 per cent of total daily energy or calories is derived from carbohydrates, and more than 45 per cent of that from fats.

Dr Iatan’s research team studied data from UK Biobank, a large-scale biomedical database, and participants were mostly followed for at least 10 years.

Upon enrolling in the biobank, participants completed a self-reported diet questionnaire and had their blood drawn to check for cholesterol levels.

The study matched 305 participants whose questionnaire responses showed that their diet met the study’s definition of an LCHF diet, while 1,220 others reported they followed a standard diet. Seventy-three per cent of each group were women, and the average age of participants was 54.

After a follow-up over an average of 11.8 years, Dr Iatan and her team found that 9.8 per cent of those on an LCHF diet experienced a new cardiac event – such as blockages in the arteries that needed to be opened with stents, heart attacks and strokes – compared with 4.3 per cent of those on a standard diet.

Dr Reginald Liew, a senior consultant cardiologist at Mount Elizabeth Novena Hospital, said Dr Iatan’s study is useful and “provides additional evidence that the keto diet may be detrimental in some people and increase the risk of a heart attack or stroke”.

Generally, a ketogenic diet may comprise 70 per cent to 80 per cent fats, 10 per cent to 20 per cent proteins and 5 per cent to 10 per cent carbohydrates. The high-fat diet forces the body to burn fats from food instead of carbohydrates, producing ketones as fuel.

“The keto diet does appear to help people lose weight in the short term and can improve blood glucose control, but it also often increases the LDL cholesterol level, which is bad for the body,” Dr Liew said.

“As a result, many doctors and cardiologists are reluctant to recommend the keto diet due to the potential increased cardiovascular risk.”

The effect of keto diets may differ depending on what followers eat, said Assistant Professor Huang Zijuan, a consultant at the National Heart Centre Singapore’s department of cardiology.

In an observational study such as Dr Iatan’s, the fats that participants on LCHF diets are likely to consume come more from unhealthy sources with higher amounts of saturated fat, which raises bad cholesterol, Prof Huang pointed out.

Food with saturated fat includes butter, coconut milk, sausages and bacon.

She added that people on keto diets generally consume more animal-based products than plant-based ones.

“Multiple lines of evidence show that consuming healthier plant-based products, compared with animal-based products, is associated with less risk of cardiovascular disease and cancers, and longer lifespan,” said Prof Huang.

“Overall, in scientific literature, there is evidence for ketogenic diets helping in weight loss and sometimes, improving selected cardiovascular risk factors. However, the devil is always in the details.”

She advised people already on a keto diet or planning to adopt one to consult a dietician for a personalised plan, and also for them to involve a doctor to monitor cardiovascular risk factors and keep them under control.

Dr Liew said those who are on a keto diet ought to go for a cardiac check-up, especially if they have hypertension, diabetes or a family history of cardiovascular disease.

“I also do not recommend people to take this diet for a prolonged period of time or more than six to 12 months, as the long-term effects of this diet on the body and future cardiovascular risks are not well known,” he said.

In the short term, a keto diet may be useful for obese individuals to achieve weight-loss targets, said Prof Huang, but there are better means to maintain good cardiometabolic health for the longer term.

Dr Iatan’s research also acknowledged that not all people respond to a keto-like diet similarly.

“On average, cholesterol levels tend to rise (for those) on this diet, but some people’s cholesterol concentrations can stay the same or go down, depending on several underlying factors,” she said.

“One of our next steps will be to try to identify specific characteristics or genetic markers that can predict how someone will respond to this type of diet.”