What you need to know about intermittent fasting
The last
You may have seen the headlines: “Intermittent fasting linked to 91 percent increase in risk of death from heart disease”; “The intermittent fasting trend may pose risks to your heart.”
The news came from a summary presented Monday at an American Heart Association conference in Chicago. The study has not yet been published in a peer-reviewed journal and experts warned that it has many limitations. Here’s what we know.
The background
Intermittent fasting involves switching between eating and fasting for specific periods of time. For example, a common approach is to eat only within an eight-hour window each day, says Krista Varady, a professor of nutrition at the University of Illinois, Chicago.
Several short-term studies have suggested that this eating style can lead to diabetes some weight loss and can lower and improve blood pressure control of blood sugar levels in certain people, she said.
But the longest intermittent fasting trial lasted only a year, says Victor Wenze Zhong, lead author of the new study and an epidemiologist at Shanghai Jiao Tong University School of Medicine in China. His goal, he said, was to look at longer-term health.
The research
The new study included more than 20,000 adults from the United States. The participants completed two questionnaires, less than two weeks apart, about what time they ate the previous day. The researchers then calculated the participants’ average eating times and assumed this was their usual schedule for the remainder of the study, said Dr. Zhong. The participants were followed for an average of eight years.
During that time, participants who limited their eating to eight hours a day were 91 percent more likely to die from cardiovascular disease than those who ate during a 12- to 16-hour window, the researchers reported.
But there were only 414 people in the eight-hour eating group, said Dr. Zhong. And they tended to be younger; less educated and wealthy; have less access to food; and are more likely to smoke than the other participants.
The researchers took these factors into account in their analysis, said Dr. Zhong. But the study didn’t show that this style of eating caused deaths from cardiovascular disease, only that the two were linked.
The limitations
Because the study has not yet been published or peer-reviewed, it is challenging to fully evaluate it, Dr. Varady said.
A “major limitation” is that they used only two dietary questionnaires to accurately reflect people’s typical eating patterns, said Dr. Varady; and the study did not appear to evaluate what types of foods people ate.
Dr. Dariush Mozaffarian, a cardiologist and professor of medicine at Tufts University, called the study “very problematic.” The eight-hour eating group may have included many people who were very busy or faced other challenges that caused them to skip meals or eat irregularly, he said.
The group could also have included people who were already in poor health — people with eating disorders or an illness that reduced their appetite, for example, which could have led them to eat in a shorter time frame, said Satchidananda Panda, a professor at the Salk Institute. for biological studies in San Diego.
And if intermittent fasting is really harmful, it’s not clear why that is. Dr. Zhong said his research was not intended to answer that question.
What’s next
More research is needed to evaluate the long-term health effects of intermittent fasting, said Dr. Zhong.
Intermittent fasting isn’t for everyone, says Dr. Pam Taub, a cardiologist at the University of California, San Diego. But many of her patients have enjoyed its benefits, such as reduced cholesterol levels.
Now her patients are “confused and scared” by the headlines they read, said Dr. Taub. But she won’t recommend that they change anything based on this research, she said, adding that people should always talk to their doctor before changing their diet or lifestyle.