Some questions about fasting – Newsroom

Opinion: “A lie can travel halfway around the world before the truth can get its boots on.”(Anonymous.)

And misinformation can travel at an even higher speed in the deeply connected global world of social media, motivating a mainstream media ever thirsty for alarming, click-bait news.

And so it was with recent publicity that I read “Intermittent fasting linked to high risk of cardiovascular disease, study reveals”. I have received more queries from colleagues and friends on this particular item over the past few weeks than I have had for any other health-related issue for many years.

The news item was based on a poster presentation at a recent conference in Chicago, reporting a statistical association between time-limited eating – eating within an eight-hour window each day (i.e. the equivalent of 16-hour fasting) – and a 91 percent increase in cardiovascular disease, in an observational study of about 20,000 participants.

This report is inconsistent with the existing literature pointing to probable cardiovascular and other health benefits from regular fasting.

A 2020 review of the existing cardiovascular literature published in the American Journal of Medicine concludes that although the exact mechanisms for the benefit have yet to be fully elucidated there is a clear positive impact of fasting on cardiovascular risk factors including obesity, high blood pressure, disordered blood lipids, and diabetic metabolic derangement. Further, intermittent fasting has been shown to improve outcomes following a heart attack.

So why the report of cardiovascular risk in the recent conference poster?

Firstly, the conference poster has not been published in a peer-reviewed journal, which means it has not yet had the benefit of independent scrutiny from experts in the field. Here are some issues I have thought need clarification prior to its publication.

The original study was not focused on the question about cardiovascular risks from fasting. The finding appears to have occurred when a broad statistical analysis was undertaken on the dataset – a ‘fishing trip’.

This research approach risks the finding of false positive results. Although an attempt was made to account for differences in the ‘time-limited eating’ group, the study was observational based on self-report of eating and, importantly, not a randomised controlled trial.

Thus, the methodology utilised was not appropriate to properly answer the question. Further, and critically, it wasn’t clear whether those with ‘time-limited eating’ were actually fasting or limiting their eating for other reasons.

For instance, people who had low appetite might be limiting their eating during the day because they just weren’t hungry, not deliberately limiting their eating as in fasting. Low appetite may have been linked in some to underlying health conditions, which obviously could dramatically skew the results.

Actually, I suspect this is the main reason the association between ‘time-limited’ eating and cardiovascular disease was found; i.e. the researchers were ‘comparing apples with oranges’. Finally, the Statistics 101 mantra that correlation doesn’t imply causation is highly pertinent here.

In the meantime, therefore, I’m going to continue to base my own fasting lifestyle on the existing peer-reviewed published literature which points to strong health benefits from regular fasting; while continuing to be open to new scientifically based findings that broaden and deepen knowledge about fasting, its health benefits, and potential risks. And I encourage others to do the same.

What is known about fasting at this point?

Fasting is a personal health practice that has been around for millennia. Pythagoras, Plato, and Hippocrates are some of the more well-known figures who advocated fasting for physical and cognitive health; and five of the seven major religions of the world encourage fasting for spiritual (and physical) health.

Because fasting is free, there is not the normal funding support from corporations including Big Pharma that is available for medical research testing a saleable product. However, the science of fasting is gathering momentum.

Eighty years ago, 137 laboratory rats were subjected to a randomised controlled trial of four different fasting regimes (Carlson & Hoelzel, 1946) in one of the earliest controlled studies of fasting.

Lifespans increased 20 percent in the fasted males and 15 percent in the females compared with normal ad libitum eaters. No retardation in growth was observed, and the rate of mammary tumours (breast cancer) was reduced in proportion to the amount of fasting.

Longevity through fasting has subsequently been demonstrated across the biological realm, including yeast, nematodes, drosophila, mice, further rat studies, and Rhesus monkeys.

Research is continuing on the mechanisms by which fasting rejuvenates the body, including key metabolic processes of autophagy, apoptosis, and inflammation reduction. There is growing evidence that fasting can help prevent, as well as arrest, common chronic diseases – Type 2 diabetes, cancer, Alzheimer’s disease, and yes, cardiovascular disease.

Readers interested in learning more about intermittent fasting for weight loss and health enhancement are welcome to contact the author for a free booklet: doug.sellman@otago.ac.nz