Cutting carbs is a popular and often effective way to lose weight. But scientists have recently discovered that eating low amounts of carbohydrates may take its toll on the heart.

A study to be presented at the upcoming American College of Cardiology’s 68th Annual Scientific Session (March 16–18) found that individuals who significantly restricted their carb intake were more likely to develop atrial fibrillation (afib). This heart rhythm disorder, or arrhythmia, can cause the organ to beat too rapidly and impair the function of its upper and lower chambers.

“Because low-carbohydrate diets were associated with increased risk of afib, regardless of the type of protein or fat used to replace the carbohydrate, this popular weight control method should be recommended cautiously,” says lead study author Xiaodong Zhuang, MD, a cardiologist at the hospital affiliated with Sun Yat-Sen University in Guangzhou, China.

Dr. Zhuang and his colleagues analyzed data on nearly 14,000 individuals who did not have afib when they originally signed up for a National Institutes of Health study, which ran from 1985 to 2006. During an average follow-up of 22 years, about 1,900 participants developed the heart rhythm disorder.

A CARBO BENEFIT

Based on participants’ self-reported daily food consumption and related data, investigators estimated their daily carbohydrate intake. They noted that, on average, participants were getting about half their daily calories from carbs. The Dietary Guidelines for Americans recommends that carbohydrates make up 45 to 65 percent of your total daily calories.

The authors then divided the individuals into three groups, based on their carb consumption being low, moderate, or high. Carbs accounted for less than 44.8 percent of daily calorie intake in the low group, from 44.8 to 52.4 percent of calories in the moderate group, and more than 52.4 percent in the high group.

The results revealed that participants with low-carb consumption were 18 percent more likely to develop afib than those with moderate-carbohydrate intake and 16 percent more likely to develop afib than those with high-carb consumption.

AN ANTI-INFLAMMATORY EFFECT

Zhuang says that several potential mechanisms may explain the results. By eating fewer vegetables, fruits, and grains, people potentially reduce their intake of vitamins along with their anti-inflammatory effects.

“The link between a pro-inflammatory state and incidence of atrial fibrillation has been extensively demonstrated,” says Zhuang.

In addition, those eating far fewer carbs may be eating more protein and fat, which can stimulate oxidative stress, a factor linked to a higher incidence of afib.

“Complex carbs like whole grains, fruits, and vegetables are critical sources of antioxidants—vital nutrients that are in limited supply in trendy diets like paleo, keto, and Atkins,” says Sarah Samaan, MD, a cardiologist with Baylor Scott & White Legacy Heart Center in Plano, Texas. “These antioxidants are anti-inflammatory, whereas fat, especially animal fat, tends to promote inflammation. The theory is that higher levels of inflammatory substances in the blood may put an individual at higher risk for heart rhythm disturbances.”

KEEPING THE HEART HEALTHY

Laurence Epstein, MD, system director of electrophysiology at Northwell Health in Manhasset, New York, believes that going on a low-carb diet intermittently or fasting for a day or two could be beneficial and not affect the risk for afib. Overall, he calls for moderation.

“I think in the long term that any extreme is not in people’s best interest in either eating too few or too many carbs,” says Dr. Epstein.

Dr. Samaan emphasizes that avoiding highly processed carbs is generally a good thing.

“That’s one thing a low-carb diet gets right,” she says. “Avoiding sugars and starchy foods means that insulin levels tend to be more stable, which can help curb the appetite.”

The problem is that carbs come in different forms and some are better than others. “Lumping all carbs together is like throwing the baby out with the bathwater,” says Samaan, meaning you may eliminate something good by trying to eliminate something bad.

To optimize heart health, cardiologist Samaan endorses a Mediterranean diet, rich in whole grains, fish, olive oil, green leafy vegetables, and fresh fruit.

Epstein’s advice for reducing the risk of afib is not only to eat a healthy, balanced diet but also to exercise on a regular basis (without overdoing it because too much exercise poses a risk).

“Also, many people don’t realize the negative effect of sleep apnea,” he says. “People should be tested for that and treated appropriately because it’s a known cause of atrial fibrillation.”

Zhuang anticipates that future research will involve a randomized control trial to confirm the findings of this research and examine exactly how carbs affect the heart.

“The long-term effect of carbohydrate restriction is still controversial, especially with regard to its influence on cardiovascular disease,” he says.