Dr. Zhuang and his colleagues drew their conclusions from data that the National Institutes of Health had collected during a decades-long study of arthrosclerosis, a disease in which fatty deposits cause the heart’s arteries to narrow and harden.
None of the 13,852 participants had Afib when they joined the study. However, 1,892 were later diagnosed with the abnormality.
During the project, the participants reported how much of 66 different foods they ate. Researchers then used a nutrient database to estimate how much carbohydrates the participants ate each day, and what percentage of the total calories they consumed came from that energy source.
The researchers found that carbohydrates accounted for about half of the daily calories, which is within the range that federal dietary guidelines recommend.
They then divided participants into three groups — low, moderate, and high — according to how many of their daily calories were from carbohydrates.
Those in the low-intake group consumed about 44 percent of their calories in the form of carbohydrates.
The moderate group consisted of individuals who derived about 44 to 52 percent of their calories from carbohydrates.
The remainder had diets in which carbohydrates comprised more than 52 percent of the calories.
What the researchers found is that the low-carb group was the most at risk for developing AFib — 18 percent more likely than those who ate a moderate amount of carbohydrates and 16 percent more likely than members of the high-intake group.
Whether low-carb diets actually cause AFib remains uncertain.
One of Zhuang’s theories is that people trying to avoid carbohydrates often cut back not only on grains but also fruits and vegetables. These foods reduce inflammation in the body, and inflammation has been with AFib.
Alternatively, Zhuang said that the additional proteins and fats people eat when they’re on low-carb diets could be the culprit. These two nutrient sources might be causing oxidative stress, which has also been to AFib.
Oxidative stress occurs when there’s an overabundance of molecules containing atoms with an odd number of electrons, so-called free radicals that seize electrons from other molecules to form more stable pairs.
Without enough antioxidant molecules to neutralize these marauders, the highly reactive free radicals can damage proteins, lipids, and DNA by stealing their electrons, resulting in a wide array of diseases.
Although diet is an important predictor of disease, medical science doesn’t yet understand exactly how that works, said Raj Khandwalla, MD, a cardiologist and an assistant professor of medicine at Cedars-Sinai Medical Center in Los Angeles.
Dr. Khandwalla told Healthline that the medical conditions that prompt some people to adopt low-carb diets — diabetes and obesity, for example — could be the real cause of AFib rather than their choice of foods itself.
Zhuang acknowledged that his team’s work doesn’t prove that significantly cutting back on carbohydrates leads to an abnormal heartbeat.
To know for certain would require following up with a randomized controlled study, he said.
These types of clinical trials are designed to eliminate biases that can influence the outcome.
Zhuang also noted that the study didn’t determine what type of AFib participants developed, so it’s not known if they experienced occasional heart palpitations or had a chronic condition.
Furthermore, researchers didn’t consider any changes that participants might have made to their diet after filling out the questionnaire.
For health-conscious people wondering what they should do until the findings are more clear, Andrew Freeman, MD, a cardiologist and co-chair of the ACC’s Nutrition & Lifestyle Workgroup, advises loading up on fruits and vegetables that have undergone little or no processing, and to add some sugars and fats to their diets.
Do people follow this recommendation?
“It’s a big ask,” Dr. Freeman told Healthline, but he noted that more people seem to be willing to give this kind of diet a try.