BEYOND THE WAISTLINE: the secrets of intermittent fasting

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Like any other trend, diet fads come and go, while the desire to stay young, healthy, and beautiful remains. Today, no one even remembers the 1970s «sexy pineapple» diet. Or the less exotic options: the potato diet, avoiding acidic foods, eating according to blood type, and so on.

Perhaps the only dietary concept that has managed to avoid oblivion for over a decade is intermittent fasting. It is believed to enhance cognitive function, prevent cancer, and even slow down aging. According to Nature magazine, one in eight adults in the U.S. practices it. So, what accounts for its popularity?

THE INTERMITTENT FASTING REVOLUTION

Much of the popularity of intermittent fasting can be attributed to the ongoing media buzz surrounding it. Celebrities practice it, books are written about it, and it’s frequently featured in the news. Over the past 10 years, more than 100 clinical trials have been conducted, showing that intermittent fasting is an effective strategy for those seeking to lose excess weight — which generally has a positive impact on overall health.

At the same time, intermittent fasting is clearly not a cure-all. There is still no unequivocal scientific evidence that this dietary approach enhances cognitive function, suppresses tumors, or extends lifespan. It’s quite possible that such expectations are rooted in medical myths. Still, that’s no reason to eliminate the experience of hunger from our lives, as it is — evolutionarily speaking — the norm, not an anomaly.

This is the view of American neurobiologist Mark Mattson from Johns Hopkins School of Medicine in Baltimore, who has been studying fasting for 30 years. In his book The Intermittent Fasting Revolution, he demonstrates that humans are biologically adapted to function optimally in a fasted state. After all, during the long era of hunting and gathering, people regularly went without food and evolved in such a way that they could benefit from breaks in eating.

THE DEEP ROOTS OF FASTING

Fasting, practiced in many of the world’s religions, can be considered a form of intermittent fasting. The healing properties of food restriction have been known for a long time. As early as the 5th century BCE, Greek physician and philosopher Hippocrates prescribed fasting to some of his patients. Modern science, however, began studying the effects of calorie restriction only in the 1930s.

As usual, the first to be subjected to fasting were rodents. Surprisingly, this «torment» actually increased their lifespan. The question remained: why? Could it be that a lack of calories slows down growth? Or perhaps it reduces cell damage caused by unstable free radicals? In 1990, Ronald Hart, who studied aging, nutrition, and health at the National Center for Toxicological Research in Jefferson, USA, summarized several of these scientific hypotheses.

Mice once again came to the rescue — they lived longer when fed once a day with a 20-hour interval. In humans, this same miraculous «interval effect» begins to emerge after about 12 hours: the fat stored in adipose tissue starts being converted into ketone bodies, which the body then uses as an alternative source of energy.

THE THREE «MAIN» DIETS

Since then, various systems of intermittent fasting have been developed, all involving recurring periods of zero or very low caloric intake. The most common versions are as follows. The first is time-restricted eating (TRE), where all food is consumed within a 4- to 12-hour window, usually without counting calories. The second is alternate-day fasting (ADF), which involves either complete abstinence from food or limiting intake to 500 calories every other day. The third option is the «5:2 diet,» which restricts intake to 500 calories on two days per week.

Beyond weight loss, some studies have recorded other adaptive stress responses. Among the results of «metabolic switching» are reduced blood pressure and insulin sensitivity, increased DNA repair, and enhanced breakdown and recycling of damaged cellular components.

Unfortunately, such studies are far from universally convincing. They involve many variables that complicate controlled testing: human behavior, differences in genetic background and baseline health, and participants failing to adhere strictly to the experiment’s protocols.

EVERY-OTHER-DAY DIET

But when it comes to obesity, intermittent fasting is undeniably effective — this has been scientifically proven. In 2022, Courtney Peterson, a nutrition researcher at the University of Alabama at Birmingham, confirmed this once again. However, she noted one caveat: most people found it easier to follow a simple rule about when to eat and when not to, rather than counting calories or choosing healthier foods.

That same year, dietitian Krista Varady from the University of Illinois in Chicago found that ADF and the 5:2 diet were more effective — resulting in 4–8% body weight loss in 8–12 weeks, compared to just 3–4% with TRE over the same period. Varady, the author of the book The Every-Other-Day Diet, argues that those who follow ADF don’t need to give up unhealthy food. It’s a more effective way to lose weight than calorie counting or avoiding fatty and sugary foods.

In this way, intermittent fasting is the perfect solution for people who prefer to limit when they eat, rather than what they eat. Still, Varady has her critics among scientists, and even she admits there’s no certainty that the benefits of intermittent fasting are independent of calorie restriction.

BEYOND THE WAISTLINE

And yet, despite many doubts and critical remarks, scientists continue to seek and discover the benefits of fasting that go far beyond the waistline. As early as 1999, Mark Mattson found initial evidence that ADF protects rodents from neurodegenerative diseases and acute brain injuries such as stroke.

Intermittent fasting increased production of β-hydroxybutyrate — a ketone body that protects neurons from damage in rodent models of Alzheimer’s and Parkinson’s disease. It also improved cognitive functions such as working memory, spatial learning, and memory retention. The risk of developing tumors also decreased as the animals aged.

Meanwhile, Satchin Panda of the Salk Institute for Biological Studies in La Jolla, California, studying circadian rhythms, discovered that they affect the condition of mice far more than light cycles. Obesity and reduced lifespan were the result of disruptions to the 24-hour circadian cycles that govern standard biological processes such as «sleep–wake» and «hunger–digestion.»

CIRCADIAN RHYTHMS MATTER — A LOT!

There are signs of a circadian effect in humans as well. A 2024 review of TRE trials noted that participants who ate before 6 p.m. experienced improved blood sugar and insulin regulation. Those who ate later in the day did not see the same benefits, even when following the recommended fasting duration. For most people, blood sugar control is best in the mid-to-late morning, so eating earlier in line with these circadian rhythms leads to lower overall blood sugar levels.

According to Omer Yilmaz from the Massachusetts Institute of Technology in Cambridge, prolonged fasting carries one notable risk: when stem cells begin dividing in the intestine, they can become a source of precancerous conditions. But with intermittent fasting, you’re not abstaining from food entirely or for extended periods.

Essentially, you’re restricting calorie intake by aligning it with specific biological rhythms. Intermittent fasting can truly benefit your body — but if you decide to try it, it’s wise to consult a registered dietitian or healthcare provider first.

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