Intermittent Fasting: A Closer Look at the Risks

Intermittent fasting has emerged as a popular dietary trend this decade. It suggests that by tweaking when you eat, rather than what you eat, you can enhance your health—minus the hassle of counting calories or cutting carbs. Many tech leaders and Hollywood celebrities endorse it; for instance, Rishi Sunak, the former Prime Minister of the UK, mentioned once starting his week with a 36-hour fast.

Current research appears to back some of the claims around intermittent fasting. Some studies indicate that lengthening the overnight fasting period could boost metabolism, support cellular repair, and potentially extend lifespan. Still, nutritionists have long cautioned that skipping meals isn’t a fail-proof solution and might pose risks for individuals with pre-existing conditions.

This fasting method typically narrows your eating to an eight-hour window, leaving a 16-hour period without food. Other time-restricted diets, like the 5:2 plan, focus on caloric intake on specific days rather than precise hours.

However, a recent large-scale study has raised some serious concerns. Researchers analyzed data from over 19,000 adults and found that those who limited their eating to under eight hours daily had a 135% higher risk of dying from cardiovascular disease compared to those who spread their meals over 12 to 14 hours.

This elevated risk implies that individuals may be more susceptible to heart-related issues, such as heart attacks or strokes, based on their health and lifestyle profiles.

The connection to overall mortality—deaths from any cause—was weaker and less consistent, but the heightened cardiovascular risk was evident across different age, gender, and lifestyle categories, even after rigorous tests.

Therefore, while the study showed a shaky link between time-restricted eating and total deaths, the data about cardiovascular disease mortality was compelling. The authors emphasize that this research doesn’t establish a direct cause-and-effect relationship. Yet, the implications challenge the idea that fasting is a risk-free approach to improving health.

In this study, American adults were monitored over eight years. Participants provided recall of all foods and beverages consumed on two separate occasions. Based on these “dietary recalls,” scientists estimated each individual’s average eating window, which was treated as their long-term habit.

The findings indicated that those who confined their eating to an eight-hour window had a 91% greater risk of dying from cardiovascular disease compared to those with a wider eating span of 12 to 14 hours.

Interestingly, this heightened cardiovascular risk was consistent across various socioeconomic groups, particularly pronounced among smokers and individuals with diabetes or existing heart issues. This suggests that those groups should approach narrower eating windows with caution. These associations held even after adjusting for diet quality and other lifestyle factors.

I wondered how to interpret the fact that heart-related deaths spiked while overall deaths didn’t—was it a biological issue or data bias?

Victor Wenze Zhong, the study’s lead author, highlighted that since diet significantly influences diabetes and heart disease, it follows that an association with increased cardiovascular mortality isn’t surprising.

Still, Zhong noted that it was unexpected to find that adhering to a narrow eight-hour eating window over an extended time linked to a higher risk of cardiovascular death. This challenges the widely held belief, often supported by short-term studies, that time-restricted eating benefits heart and metabolic health.

Anoop Misra, a key endocrinologist, discussed the advantages and challenges of intermittent fasting in an accompanying editorial. He mentioned the upsides, such as potential weight loss, improved insulin sensitivity, and lowered blood pressure. It could also aid individuals in managing their blood sugar without strict calorie monitoring and conveniently fit into cultural or religious fasting practices.

However, he pointed out the potential downsides, like nutrient deficiencies, increased cholesterol, and cravings, among others. For people with diabetes, unmonitored fasting might lead to dangerous drops in blood sugar, and for older adults or those with chronic conditions, extended fasting could worsen frailty or lead to muscle loss.

This scrutiny of intermittent fasting isn’t new. A previous three-month study found that participants might have only lost a small amount of weight, largely from muscle. Another study reported side effects such as weakness, hunger, dehydration, and trouble concentrating.

As Misra noted, this latest study adds a concerning caveat regarding a potential link to increased cardiovascular risk for certain individuals.

When I asked Zhong what advice he would give to both clinicians and the general public based on the new findings, he recommended caution for those with diabetes or heart disease regarding an eight-hour eating window. He emphasized the necessity for personalized dietary guidance based on health status and evolving evidence.

He concluded that, at least for now, focusing on the quality of food seems more crucial than the timing of meals. People might want to avoid long-term commitment to an eight-hour eating window if they aim to prevent cardiovascular disease or enhance longevity.

Ultimately, the takeaway isn’t necessarily to abandon fasting but to customize it to individual health profiles. Until more conclusive evidence emerges, it may be wiser to concentrate less on when you eat and more on what you eat.