Two new studies are offering insights into the long-term effects of intermittent fasting on human health. The research suggests fasting for just one day a month over many years can lengthen lifespan and enhance cardiovascular health, but as always, the new studies are riddled with caveats.

Fasting diets are undeniably all the rage these days. From the conservative 5:2 diet to more extreme multi-day fasting strategies, the anecdotal health benefits of these diets seem impossible to ignore. A burgeoning body of research is slowly uncovering the underlying biological mechanisms behind the effects of these diets but there is still a great deal scientists do not understand.

And one of those key unanswered questions surrounds the long-term effects of fasting diets on the human body. While there have been a number of animal studies exploring the biological effects of fasting, and several short-term human studies looking at the acute effects, scientists do not know what happens to a human body when it consistently undergoes intermittent fasts over several years.

To try to tease out the long-term effects of fasting on a human body, a team of scientists from Intermountain Healthcare Heart Institute in Salt Lake City, Utah, tracked over 2,000 patients for nearly five years. The patients were enrolled into the study during the course of a cardiac catheterization procedure, and then followed for several years to ascertain long-term cardiovascular health and overall mortality.

The unique part of the research was the fact that a large portion of the cohort were members of the Church of Jesus Christ of Latter-day Saints. One typical behavior of the church is to fast for up to 24 hours across the first Sunday of every month. While not all modern Latter-day Saints regularly engage with what many call "Fast Sunday," the research was able to home in on 389 subjects in the cohort reporting routine monthly fasting for over five years.

Benjamin Horne, one of the researchers working on the project, says the results were more profound than anyone expected. After five years of follow-ups, those routine monthly fasters revealed a 45 percent lower mortality rate than the non-fasters.

"It's another example of how we're finding that regularly fasting can lead to better health outcomes and longer lives," says Horne.

A second investigation into the long-term effects of fasting on myocardial infarction (MI) and heart failure (HF) revealed interestingly discordant results. The data showed no difference in incidences of myocardial infarction (otherwise known as a heart attack) between the fasters and non-fasters. However, the fasting group strikingly revealed a 71 percent lower rate of heart failure compared to the non-fasters.

"We think that long-term fasting of about one day, once a month, over a period of decades is making the body activate those beneficial mechanisms for a few hours each day between dinner and breakfast when it usually wouldn’t,” says Horne. “Those hours build up over long periods of time and provide the benefits.”

The research, of course, attempted to adjust for the various factors that could underpin these differences, including lifestyle behaviors such as smoking. But, the key element that makes the study somewhat novel is also the factor that limits the broad applicability of its conclusions. Krista Varady, a nutritionist from the University of Illinois at Chicago, who did not work on this current research, notes the problem with using a cohort of fasting subjects who are primarily Latter-day Saints.

"They lead a very different lifestyle compared to the average American," says Varady. "For instance, they don't smoke, don't drink alcohol and are slightly more physically active. It just makes sense they're going to live longer and have a lower chance of heart disease."

Horne fairly recognizes the limitations of his team’s research, accepting the purely correlational results and suggesting there possibly are secondary psychological effects from intermittent fasting that could be leading to the positive health benefits seen in the data.

"Some people who've started fasting say they unexpectedly feel they have more self-control over their appetite," says Horne. "Potentially, there's a direct result between fasting and the strengthening of the mind so people are able to eat a better diet."

Further work is necessary to better tease out the long-term effects of intermittent fasting on human health, but one of the intriguing implications raised by this research is the possible health benefits of such a minimal intervention as fasting one day a month. While many other intermittent fasting strategies suggest either fasting several days per week, or fasting 16 to 20 hours each day, this research suggests from a perspective of overall mortality and cardiovascular health, simply fasting one day a month may be significantly useful.

"With the lower heart failure risk that we found, which is consistent with prior mechanistic studies, this study suggests that routine fasting at a low frequency over two thirds of the lifespan is activating the same biological mechanisms that fasting diets are proposed to rapidly activate," says Horne.

The findings from the heart health and mortality fasting studies were presented at the 2019 American Heart Association Scientific Sessions in Philadelphia earlier in November, abstracts have been published in the journal Circulation.

Sources: American Heart Association, Intermountain Healthcare Heart Institute