Heartbroken over Data: Why the AHA is Wrong about Intermittent Fasting

AHA wrong about fasting

The American Heart Association (AHA) issued a press release last week with a headline liable to give some dieters chest palpitations: 8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death.

The pronouncement came at an auspicious time. Between the 1.9 billion Muslims observing Ramadan and the 2.3 billion Christians called to celebrate Lent, over half the world’s population is currently under at least a nominal religious obligation to curtail their caloric intake.

The religious requirements are especially stringent for adherents of Islam, who traditionally eschew eating from sunrise to sunset during Ramadan.

Less than a week before the AHA statement, a Medical Xpress article highlighted the results of a meta-analysis of the positive effects of faith-based fasting on cardiovascular disease—to much less fanfare. One of the authors of the paper, published in February in Nutrition, Metabolism and Cardiovascular Diseases, summarized their approach and findings:

“[We] explored the potential health effects of different religious and faith-based fasts. By conducting a systematic review of published data from Muslim and Orthodox Christian communities only, our recent analysis showed that both fasting approaches are associated with a reduction in cardiovascular risk—although for different reasons.”

What religious institutions have upheld as a spiritual salve for millennia is now increasingly recognized and embraced by secular and scientific communities as more than a mere balm for the soul—it’s good for the mind, body, and gut as well.

So, do the data really support the AHA’s new bombastic claim?

In a word: no.

First, the findings in question, rather than a peer-reviewed study, were simply preliminary research presented at the AHA’s 2024 Epidemiology and Prevention, Lifestyle and Cardiometabolic Scientific Sessions, held last week in Chicago.

So flimsy was the data on which the headline relied that the press release itself even included the following scathing bit of skepticism from Christopher D. Gardner, Ph.D., FAHA, who was left wanting for more detail:

“One of those details involves the nutrient quality of the diets typical of the different subsets of participants. Without this information, it cannot be determined if nutrient density might be an alternate explanation to the findings that currently focus on the window of time for eating. Second…

…it needs to be emphasized that categorization into the different windows of time-restricted eating was determined on the basis of just two days of dietary intake.”

Dr. Gardner is the Rehnborg Farquhar Professor of Medicine at Stanford University in Stanford, California, and chair of the writing committee for the AHA’s 2023 scientific statement, Popular Dietary Patterns: Alignment with American Heart Association 2021 Dietary Guidance.

While extrapolating long-term health implications from a mere two days’ worth of self-reported eating habits is dubious enough, the study had other notable and considerable abnormalities with its participant population.

To start, the headline-grabbing group of individuals who limited their food intake to an 8-hour window comprised a paltry 2.1% of the total sample. Second, this cohort’s members were considerably more likely to be smokers than the overall sample, at a rate of 27.1% versus 17.9%— a surely relevant detail for cardiovascular consideration. This group also had a higher average BMI than any other segment of the study.

Lastly, given that search traffic for the term “intermittent fasting” was virtually non-existent for the first decade of the study (which began in 2003), the folks who were following this diet were likely placed on it for other confounding health reasons, or at the very least were not apt to be doing so as a healthy lifestyle choice—it simply was not yet in the public zeitgeist.

While the AHA may not have an appetite for intermittent fasting, the popular and versatile modality is worth continued consideration.

A primer on Intermittent Fasting:

Intermittent fasting, a dynamic and flexible approach to eating, is characterized by its variety of protocols, each defined by specific periods of eating and fasting. These regimes, often referred to by their time structures, offer different paths to the same purported health benefits and wellness goals.

16-8 Method

This popular approach to intermittent fasting involves restricting daily food intake to a specific eight-hour window. For example, one might choose to eat only between 11 a.m. and 7 p.m. The remaining 16 hours of the day, which include sleeping hours, are spent fasting. This method is favored for its simplicity and adaptability to everyday life, allowing individuals to reap the benefits of fasting without significant disruption to their schedules.

5-2 Diet

The 5-2 diet breaks the week into two types of days: five days of normal eating and two days of restricted calorie intake (often about 500-600 calories per day for the fasting days). These fasting days don’t have to be consecutive, offering flexibility in scheduling. This regime is praised for its balance, allowing individuals to enjoy their usual meals most days while still experiencing the benefits of reduced calorie intake.

Fasting-Mimicking Diet

A relatively new addition to the fasting world, the fasting-mimicking diet is designed to offer the benefits of fasting while still allowing for food consumption. Over a period of five days each month, participants follow a low-calorie, plant-based diet that claims to trigger some of the same mechanisms as a water fast. Recently published research in Nature Communications suggests this method can reduce markers of aging and disease, even claiming to reverse aging signs by roughly 2.5 years.

Extended Fasting

Extended fasting involves going without food for a longer period—as many as seven days—or even longer in some extreme cases. This approach is more intensive and should be undertaken with medical supervision. Extended fasts are believed to prompt significant cellular and metabolic benefits, including autophagy (the body’s process of cleaning out damaged cells) and improved metabolic markers. This method was highlighted in recent research published in Nature Metabolism, which noted its potential for profound multi-organ health impacts.

Religious Fasting

As mentioned above, fasting is a practice deeply embedded in many religious traditions that serves both spiritual and communal functions. These religious fasts vary in their specific practices and restrictions but are united by their roles in fostering reflection, community, and spiritual growth.

Each of these fasting regimes offers a unique approach to integrating fasting into one’s lifestyle, reflecting the diverse ways individuals can explore the benefits of intermittent fasting. Whether for health, spiritual reasons, or personal challenge, these methods provide a spectrum of options to suit different needs and preferences.

What does this all mean for the food industry?

While a defined period of foregoing food is hardly music to the industry’s ears, the intermittent fasting trend need not—and largely does not—entail ascetic practitioners eating scant bowls of rice.

Human nature being what it is, a period of fasting is likely followed by a large, well, break-fast—at whatever time of day that happens to be.

No matter the reason or precise method of fasting, food brands can cater to consumers’ unique requirements throughout this need state by marketing calorically dense, protein-rich meals to kick-start periods of fasting, followed by electrolyte-laden beverages to sustain periods without food, and macrobiotically balanced fiber-rich meals to gently ease the GI tract back into peristalsis after a fast.


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