The low-carb ketogenic (keto) diet has skyrocketed in popularity in recent years among those looking to lose weight.
A new study, however, suggests that a "keto-like" diet could trigger a spike in "bad" cholesterol, which can lead to a buildup of plaque in the arteries and a significantly greater risk of heart attacks, strokes and other cardiovascular events.
Findings from the study were presented on Sunday in New Orleans, Louisiana, at the American College of Cardiology’s Annual Scientific Session Together With the World Congress of Cardiology.
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"Our study found that regular consumption of a self-reported diet low in carbohydrates and high in fat was associated with increased levels of LDL cholesterol — or ‘bad’ cholesterol — and a higher risk of heart disease," said lead author Iulia Iatan, M.D., PhD, in a press release about the findings.
Iatan is attending physician-scientist at the Healthy Heart Program Prevention Clinic, St. Paul’s Hospital and University of British Columbia’s Centre for Heart Lung Innovation in Vancouver, Canada.
"To our knowledge, our study is one of the first to examine the association between this type of dietary pattern and cardiovascular outcomes," she added.
While there are different variations, the ketogenic diet generally includes very low carbs, typically less than 50 grams per day.
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The target ratio is usually around 75-80% healthy fats, 10-20% protein and 5-10% carbohydrates, according to Harvard’s School of Public Health.
By default, the body’s metabolic system will try to burn carbohydrates for energy.
With the keto diet, because carb intake is so low, the body starts looking for fat to use for energy instead of carbs (or glucose).
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The liver then breaks down the fat and creates an alternative fuel source called ketones, which is where the keto diet gets its name.
For the new study, researchers looked at data for those who ate a low-carb, high-fat (LCHF) diet containing 25% or less carbs and more than 45% fat.
(This wasn’t quite as low-carb as the standard keto diet, which is why it was dubbed "keto-like.")
For comparison, they looked at participants who ate a more standard, balanced diet as well.
The data was pulled from the UK Biobank database, which includes more than 500,000 U.K. residents who were monitored for at least a decade.
A total of 1,525 people were included in this study; 305 ate an LCHF diet and 1,220 ate a standard diet. The participants were the same gender, age group (averaging 54 years old) and body mass index range.
Those who were on an LCHF diet were found to have markedly higher levels of LDL ("bad") cholesterol and apolipoprotein B (apoB), a protein that attaches to LDL and can help measure the risk of heart disease.
"After an average of 11.8 years of follow-up — and after adjustment for other risk factors for heart disease, such as diabetes, high blood pressure, obesity and smoking — people on an LCHF diet had a more than two times higher risk of having several major cardiovascular events, such as blockages in the arteries that needed to be opened with stenting procedures, heart attack, stroke and peripheral arterial disease," the American College of Cardiology’s press release noted.
A total of 9.8% of participants who were on an LCHF diet experienced a new cardiac event within the course of the study, compared with 4.3% of those on a standard diet.
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Kim Kulp, a registered dietitian in San Francisco, California, who was not involved in the study, was not surprised by the findings.
"Previous research has shown that a higher intake of saturated fat can increase levels of LDL cholesterol, or the type of cholesterol that raises the risk of heart disease," she told Fox News Digital via email.
"Saturated fat is what’s found in higher amounts in popular foods like butter, ice cream, cheese and fatty meats such as bacon and sausage. This is why the American Heart Association recommends limiting total fat intake to no more than 35% of daily calories, and saturated fat to less than 7%."
Iatan wrote that before anyone starts a low-carb diet, it’s important that he or she consult with a doctor.
"While on the diet, it is recommended [patients] have their cholesterol levels monitored and … try to address other risk factors for heart disease or stroke, such as diabetes, high blood pressure, physical inactivity and smoking," she added.
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Lindsay Allen, registered dietitian nutritionist and owner at Back in Balance Nutrition, LLC in Tampa Bay, Florida, was not involved in the study but warned that many people who go on a keto diet do not balance the fats appropriately.
"If you're eating 60-80% of your calories from fat, you must ensure you are getting plenty of monounsaturated fats and omega-3 fatty acids (specifically EPA and DHA from fish), and are not overdoing saturated fats like meat, cheese and bacon," she told Fox News Digital by email.
"Most people unintentionally over-consume saturated fat without balancing a healthy ratio of all the other fats, and when they do this, they run into issues with cholesterol."
Some experts believe that it's healthier to cycle on and off the keto diet instead of following it long-term.
"Eating too low carbs for too long can greatly diminish the antioxidants, phytonutrients and fiber that are needed to balance our cholesterol levels," Allen said.
The study authors called out some limitations.
The participants self-reported their food intake via a questionnaire at only one point in time, which could impact accuracy.
"With only one day of food choices reported, there could be a lot of variation as to what diet these subjects actually followed on an ongoing basis," said Kulp of San Francisco.
Additionally, because this was an observational study, it shows only an association — and not causation, the authors wrote.
"There's nothing inherently bad about the keto diet, as long as it's for the appropriate person, the consumption of fats are balanced, and the diet is cycled to allow for antioxidants and fiber," Allen told Fox News Digital.
"This study demonstrates that the keto diet definitely is not for everyone, and it would be helpful to seek guidance from a professional to make sure you're a good candidate."
More research is needed on the link between keto-like diets and heart health, Iatan said.
