To Stay Younger for Longer, Make This Change to Your Diet

Recent research suggests that if we fast for 16 hours out of the day, we can expect a dramatic increase in lifespan. Still, the long-term implications of confining our calorie intake to an eight-hour period are still not clear. Israeli scientists weigh in

Asaf Ronel
Asaf Ronel
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איור: עמרי כהן

The Western world is in the throes of an epidemic. It’s sparking an incidence of disease on a frightening scale, spreading low self-esteem and shortening life expectancy among millions of people. The whole world is now preoccupied with the coronavirus, but its the obesity epidemic that continues to claim victims apace, and in spectacular numbers. The culture of abundance may offer nutrition security, but it also exacts a steep price.

Staying on a diet to reduce one’s weight is difficult; results are hard to achieve and maintain in the long term. But the problem runs deeper: It is very tough to improve scientific knowledge about obesity, because it entails carrying out research over many years involving documentation of what people consume.

But what if there is another way to confront the problem of overeating? What if there’s a method of nutrition that can increase one’s life expectancy by 30 percent, as has already been seen in hundreds of studies on animals? Moreover, what if scientists could show that this method not only facilitates weight loss but improves cognitive abilities and can slow down the development of a host of diseases, ranging from diabetes and multiple sclerosis to cancer and cardiac ailments? And what if this whole method is summed up in a simple rule: to limit the time frame for eating to eight hours daily and to abstain from food for the rest of the day?

In December, neuroscientist Mark P. Mattson and gerontologist Rafael de Cabo, from Johns Hopkins University, published a seminal article in the New England Journal of Medicine, the world’s most prestigious medical journal. The two offered a survey of two decades of research on the habit of fasting for part of the day, and found a solid scientific basis for a diet that has become increasingly popular in recent years: to concentrate meals into an eight-hour period and refrain from eating for the other 16 hours.

In the article, entitled “Effects of Intermittent Fasting on Health, Aging, and Disease,” De Cabo and Mattson went beyond presenting the health-related advantages of such a regime. Indeed, they called for revamping existing nutrition recommendations for the general public. Whereas today people are being urged to adopt a so-called Mediterranean diet and eat small meals scattered throughout the day, the two scientists from Baltimore propose the conducting of a long-term study on intermittent fasting, as well as the integration of such a diet into the recommendations of modern medicine. The benefits could be dramatic.

In recent weeks, Haaretz spoke with leading researchers, veteran physicians and nutrition experts on the subject. Most objected to the idea of undertaking drastic changes in suggestions regarding proper nutrition, for various reasons. However, they did agree that the findings in support of fasting for most hours of the day are well grounded in science. Apparently, the currently accepted recommendations in this realm suffer from an underlying, fundamental problem.

Hunger as natural

The approach supporting partial fasting on a daily basis stems from a basic truth that has been forgotten over the years: Hunger is actually man’s natural state. Jared Diamond described the situation well in his 2012 book “The World Until Yesterday.” It sums up the knowledge Prof. Diamond gleaned in decades of anthropological and geographical research among traditional societies, and explains how these insights can show us the way to a healthier life. Diamond relates that he found it difficult to understand why, for example, the main topic of conversation of the Fore culture in Papua New Guinea was food, even if everyone had just eaten their fill. Similarly, among the Sirioni Indians in Bolivia, fear of a food shortage is so acute that the two most common expressions in the language are “My stomach is empty” and “Give me some food.”

Illustration: Omri Cohen.
Illustration: Omri Cohen.

“The significance of sex and food is reversed between the Siriono and us Westerners,” Diamond writes. “The Sirionos’ strongest anxieties are about food, they have sex virtually whenever they want, and sex compensates for food hunger, while our strongest anxieties are about sex, we have food virtually whenever we want, and eating compensates for sexual frustration.”

The other side of hunger is gorging. When members of traditional societies have an abundance of food, they devour it wildly. Four Sirionos are capable of wolfing down a 30-kilogram (66-pound) animal, Diamond notes, and similar examples of gorging are documented in many anthropological studies. “These anecdotes illustrate how people accommodate to the pendulum of feast and famine,” he sums up.

Today, when food is usually available to us on demand, the leap from prolonged hunger to gobbling down kilograms of meat sounds fantastical. But we are all offspring of humans who survived the swings of that pendulum.

“Our metabolism is built for short episodes of plentiful food and lengthy periods of hunger,” says Prof. Yuval Dor of the Hebrew University medical school, who studies diabetes. This can explain the fact that in times of distress, people can survive many weeks without food. According to Prof. Elliot M. Berry, an expert on nutrition and former director of the Hebrew University-Hadassah School of Public Health and Community Medicine, “We are programmed to store food and be metabolically efficient, because our forebears didn’t know when the next meal would come.”

The basic ability of a human body to endure periods of hunger originates at the level of the individual cell. As long as the cell has food available (especially glucose), it undertakes a biochemical process that is responsible for growth: protein production and inducement of cellular division. The “logic” of the cell is identical to the biological “logic” of the entire organism: Take advantage of the food as long as it’s there. But there’s a fly in the ointment: When the process responsible for cellular growth is active, the process that breaks down defective elements is inactive.

“While the body ingests food, the cell’s maintenance system is rendered inoperative,” says Eitan Okun, an expert in neurodegenerative diseases at Bar-Ilan University. Eating at all hours of the day over a period of many years, Prof. Okun explains, causes an accumulation of defective proteins and organelles (tiny structures with specialized functions) in the cells, spurring degenerative processes. This is particularly relevant when it comes to brain cells, because in most regions of the brain neurons are not renewed, so the damage only accumulates.

The fact that we do not eat during the night does not solve the problem, because the maintenance system of brain cells does not function when we sleep. A key role of sleep, Okun explains, is to transform short-term memories into long-term ones. In order to establish memories, the brain cells reinforce the connections between them utilizing the process responsible for building cells – and while that process is going on, the cells do not do maintenance work on themselves. The results of this cumulative damage become apparent later in life.

“There would be no problem if everyone lived to the age of 50,” he says. “The difficulty is to reach the age of 95 with a lucid mind. In the modern world, we enjoy a long lifespan along with high food consumption, which prevents the body from looking after itself.”

Incidentally, Okun himself practices a severe form of intermittent fasting: He eats during two hours a day only, and fasts for the remaining 22 hours. “It suits my way of life,” he explains.

Endless noshing

The cell’s maintenance system is not the only mechanism activated by fasting. According to Oren Froy, a professor of biochemistry at the Hebrew University’s agriculture faculty who specializes in nutrition and food science, avoidance of eating sets in motion alternative processes for producing energy – mainly dissolving fatty acids to produce ketone bodies. The latter have been drawing increasing attention lately as an energy source for cells, by virtue of their beneficial effects on laboratory mice.

There are three ways to raise the ketone level in the blood. The first is to go on a ketogenic diet, based on consumption of proteins and fats and abstaining from sugar and carbohydrates. The second possibility is to consume ketogenic drinks, which, for example, significantly improve performances of professional bicyclists. “Ketogenic drinks taste terrible,” warns Dor, the diabetes expert. “It’s like acetone, I’ve tried it myself.”

The third possibility is simply to fast.

“In a state of fasting, the body passes from a carbohydrate-based metabolism to a metabolism of fatty acids,” Dor explains. “The fat dissolves and turns into ketone bodies, which are discharged into the blood. These bodies serve as a central source of energy for the body, and especially for the brain.”

In evolutionary terms, this mechanism is intended to allow human beings to cope with lengthy bouts of hunger. However, studies of animals showed that a metabolism based on ketone bodies also prolongs life, improves cognitive functioning, streamlines the body’s metabolic activities and reduces the severity of some diseases.

For his part, Okun notes that the advantages of intermittent fasting have drawn the attention of researchers who have examined the limits of caloric restriction, and that this method reduced by one-third the quantity of food consumed as compared to a situation where organisms can eat as much as they like. In laboratory conditions, animals enjoy an abundance of sustenance that doesn’t exist in nature. When scientists restricted animals’ food intake, they discovered that their health improved significantly and their life expectancy soared.

“These studies led to the conclusion that fattening up of animals is a pathological phenomenon,” Okun says, adding that “in fact, most experiments are conducted on organisms in pathological states.” After limiting the amount of food turned out to be effective, the next stage was to see whether animals derive benefit from limits on the time period allotted for eating. The answer was unequivocal. “It turned out that it wasn’t necessary to cut down on the amount of food given to the mice – it was enough to narrow the time frame in which they eat in order to achieve similar beneficial effects.”

What about human beings? Since the 1970s, the industrialized world has been swept up by an epidemic of obesity, accompanied by a surge in the incidence of diabetes and cardiovascular disease.

Okun: “We eat all the time. We get up and eat something, have coffee with sugar, nibble on something while we’re on the computer. Food is with us from the moment we get up until we go to sleep.”

All that endless noshing has a price, as can be seen in the research being conducted by Iris Shai, an expert in nutrition and epidemiology at Ben-Gurion University of the Negev and Harvard. She and her team are leading some of the lengthiest and most complex clinical studies currently underway in the field: Specifically, they are examining the influence different nutrition methods have on brain and heart function, and on adipose (fat) tissue. Although their focus is not on intermittent fasting per se, they have observed in their work the great benefit people derive from a moderate caloric restriction, which significantly slows down the rate of the body’s aging.

Among other studies, Shai’s researchers are conducting genetic tests that will make it possible to predict life expectancy more accurately than in the past. Such tests calculate a subject’s “biological age” (based on a genetic analysis), which might be quite different from his chronological age. According to Shai, the initial and not-yet-published results of these tests show that a consistent calorie reduction of 20 percent to 30 percent over a period of a year and a half at least, lowers one’s biological age by an average of eight months.

“Let’s admit the truth,” Shai says, “we live in an era of calorie excess. The question is how to reduce calories. Fasting is an interesting route – for some people an all-or-nothing approach works. For some, a proper distribution of food intake throughout the day would be good, but [for the first group], a black-and-white approach will be appropriate, because the more they eat the hungrier they are, and the more they fast the more ketone bodies they have, which are themselves suppressors of hunger. The key issue is hormonal, because there are big differences between people.”

Danger of disorders

Although the prime cause of overeating is the culture of abundance, Froy, the biochemist from Hebrew University, suggests that we also shouldn’t underestimate the damage caused by nutrition recommendations that, though now thoroughly debunked, are still widespread among the public.

“One of the solutions that was found for the obesity epidemic is to eat a large number of small meals throughout the day,” Froy notes, referring to habits everyone is familiar with: midmorning snacks, fruit between meals, sweetened tea in the afternoon. “The logic was that this way people won’t be overly hungry when they get to mealtime. In retrospect, however, we realized that this recommendation only caused additional weight gain. People simply ate a lot more. Today we know that it’s not only the excess calories that are harmful, but also their constant availability.”

Ram Weiss, an expert in juvenile diabetes at the Hebrew University’s medical faculty, agrees with Froy. He, too, thinks that the claimed benefits of a five-to-six-meal-a-day regimen – i.e., a few big meals interspersed with smaller ones – lack any scientific foundation. According to Prof. Weiss, intermittent fasting may be of great benefit in treating diabetes, because limiting the hours of eating facilitates a better balance of sugar levels.

But what about the general, non-diabetic public? Most of the experts Haaretz spoke to are not eager to recommend the partial fasting idea – notwithstanding research that suggests that it may be beneficial. Some suggested that such findings should be treated with skepticism, because the bulk of the research has been done on animals. Others claim that people would generally find it difficult to persist in maintaining such a regimen, which requires regular monitoring by medical professionals during the initial period; still others cited the fact that it could encourage eating disorders. All the experts agree that the partial fasting method is not suitable for children and adolescents.

“We must not interfere with the growth of a young person,” Okun says. “Nor is it a method that would be appropriate in pregnancy,” adds Iris Shai.

For one, Yael Latzer, head of the University of Haifa’s School of Social Work, and former director of the eating disorders clinic at the city’s Rambam Medical Center, is concerned about any sort of diet that could contribute to eating disorders.

“I recommend a cautious approach to every study that encourages hunger,” she says. “Every publication that glorifies hunger and fasting contributes to the development of eating disorders.” Even though it is known that such disorders have a genetic basis, Prof. Latzer notes, what trigger their onset is reduced eating.

“We are talking about a serious disease with high mortality rates,” she says. “The tendency today is to try to stop dieting behavior in youth as much as possible, to prevent the development of an eating disorder in those prone to it.”

Among the researchers interviewed, Okun is the most ardent proponent of intermittent fasting; he believes it would be beneficial to public health in general. He acknowledges that a change of this scope in one’s everyday life would be challenging, but maintains that an eight-hour time frame is more than enough for eating, and adds that in such a regimen, coffee and tea can be consumed all day as long as no milk or sugar are added.

“People go on all sorts of diets,” he says. “If they are capable of that, they are also capable of eating only within an eight-hour span during a 24-hour period and not sweetening their tea. It’s simpler than counting calories.”

Oren Froy thinks there are different ways to achieve a proper metabolism. It’s clear that reducing the period during which we eat during the day is beneficial to health, he says, but that doesn’t mean it’s necessary to adopt the partial-fasting approach as an overall policy. In his research Froy has showed that three balanced, nutritional meals a day, without in-between noshing, is a generally beneficial to one’s health.

“There are people for whom three meals a day are appropriate, and people for whom 16 hours of fasting are appropriate,” Froy says, adding that one’s ability to implement suggestions is no less important than the results of lab experiments. “When mice are restricted to eating during three-four hours a day, a distinct health benefit is seen, but most people will not stay the course in those conditions. We need to find a dietary regimen that is suitable for humans.”

Prof. Berry, who was involved in drawing up the Health Ministry’s current nutrition recommendations, says their underlying logic is based on the most solidly grounded research available, and as of today, the Mediterranean diet is the most healthful of all regimens. “We are trying to formulate the lowest and most healthful common denominator, one that will be suitable for as many people as possible.”

Berry confirms that intermittent fasting might contribute significantly to health, but he is convinced that people will not be able to sustain it. He points out that a dietary regimen of this sort necessitates close medical supervision and cites the recent article by the scientists from Johns Hopkins, which asserts that someone who opts for fasting must undergo blood and urine tests for at least the first four months. “Although this method is grounded in science,” Berry sums up, “the health system in this country would not be capable of coping with so many tests and follow-ups.”

‘Social eating’

Prof. Elliot M. Berry.
Prof. Elliot M. Berry. “We are programmed to store food and be metabolically efficient."Credit:

Yitshal Berner, an expert in nutrition and geriatric medicine at Tel Aviv University’s Sackler School of Medicine, is among those who would rain on the parade of those supporting intermittent fasting. “People want to skip breakfast and continue to eat like pigs,” he says. “There are no instant solutions. The body creates ketones even in a situation of extreme consumption of alcohol, yet that’s no reason to recommend drinking to excess.”

Prof. Berner explains that as people age, the capacity to absorb the nutritional substances that food provides diminishes – and that decline sometimes justifies consumption of a large number of small meals every day. Moreover, he says, eating relatively large quantities of food at one time within the framework of the fasting regimen increases the burden on the heart.

For those who nevertheless want to shorten the period during which they eat, skipping breakfast would appear to be the easiest route. That is also the recommended method, Prof. Okun says, contrary to the usual recommendation to eat a hearty breakfast. However, the other experts disagree, citing recent studies suggesting that it’s more beneficial to forgo supper. Berry and Berner refer to research showing that children who went to school without breakfast had a harder time learning than peers who ate before their first class. Both quote Maimonides, who recommended eating like a king in the morning, like a prince at midday and like a pauper in the evening.

For her part, Prof. Shai says that based on experiments her team is conducting, she thinks that it’s generally better to eat breakfast and start a fast in the afternoon. “Entering into a state of energy deprivation before sleep can be very helpful in the process of breaking down fat that takes place at night,” Shai says. At the same time, she cautions, different people have different biological clocks, so fasting during the evening may not have the same results for everyone. “In addition, not eating in the evening takes us out of our comfort zone,” Shai says. “For most people, eating in the morning is physiological eating, while in the evening it’s social eating.”

Prof. Weiss comments that the idea of having general recommendations for nutrition is becoming less and less relevant in the modern era, when the emphasis is on more precise and personal medicine. “Today we know that genetics affects the way a person responds to consumption of specific types of food,” Weiss says, adding that nevertheless, the scientific principles supporting the intermittent fasting approach are persuasive. “Food is partly burned up and also partly accumulates, and fasting during the day can prevent the accumulation of harmful substances in the cells.” When thinking about healthful nutrition, he adds, the first consideration is what we eat, then how much we eat and finally when we eat.

According to Prof. Shai, who was among the chief formulators of the Health Ministry’s current nutrition recommendations, there is a consensus among most of the world’s health organizations that the Mediterranean diet would be beneficial to most people. “It is a diet that is compatible with our biology and is based on solid, broad science,” Shai says. “But still, on that basis, there is room for various adjustments.”

Fasting, Weiss points out, can be problematic for people who take medication or engage in certain physical activities, and thus “we must find the golden mean between the health recommendations and patients’ quality of life. It’s important to find a recipe for nutrition that people can stick with and that does not significantly impact on their quality of life. It’s also important to remember that because of the difficulty of conducting lengthy experiments with humans, we don’t really know what the long-term consequences are of intermittent fasting.”

In a similar context, Berry says that two long-term studies in which monkeys were put on a fasting regimen did not have the same, clear-cut results as similar research conducted on rodents. However, Okun attributes the inconclusive findings to the fact that, similar to man’s culture of abundance, the lab rodents had relatively free access to food, while monkeys were fed only at fixed intervals.

The body fights back

Examining the long-term effects of an intermittent fasting regimen is important not only to determine its risks but also in terms of the way the body reacts to weight loss. Dror Dicker, director of the obesity clinic at Hasharon Hospital, which is part of the Rabin Medical Center in Petah Tikva, says that his emphasis in treatment is not so much on initial weight reduction as it is on maintaining weight loss.

“The body does not allow us to maintain a reduction in weight over time,” Dr. Dicker says. “After a few months [of dieting], it activates some serious physiological defense mechanisms, which are in effect impossible to overcome.” The first mechanism heightens the feeling of hunger, whereas the second mechanism reduces the amount of energy the body burns up. Thus, people who stick to a diet must keep consuming fewer calories to maintain their lower weight. “That’s why people who lose weight gain it back, not because they have failed or because whoever has treated them has failed,” Dicker notes.

In addition, adds Dicker, recent studies show that weight fluctuations can be hazardous to one’s health and can heighten the risk of diabetes, and of heart and vascular diseases, “which is why, when I start treating a patient, I ask him what he thinks he will be able to maintain for the rest of his life. If you’re not capable of maintaining a particular nutrition regimen for the rest of your life, don’t start on it.”

What about fasting? Dicker says he does not dispute the medical benefits of intermittent fasting for a short period of time, but that he won’t begin recommending the method until he sees studies that present its long-term implications. “The experiments that show that intermittent fasting helps during the first month are great,” he says, “but again, the question is whether a person can continue to eat that way subsequently, as well.”

In terms of treating obesity, says Iris Shai, it is definitely worthwhile to integrate fasting as one strategy among many, particularly in order to motivate people to reduce their food intake and to eat more healthfully.

“In the first month or two, intermittent fasting can be a supplementary tool in a long-term therapeutic process,” she says, adding that the method may be of particular benefit to people who have seen very little change after trying other regimens. “After a certain period of time, the body resumes control, the reduction in weight becomes more moderate, and then you need to add physical activity and consider other strategies.”

According to Shai, as long as they are healthy and not harmful, different types of diets should be used to challenge the body, because “it always responds well in the first months of change, but then returns to the starting point.” What always works, she says, is physical activity. “A morning run – that’s my solution.”

Shai emphasizes that intermittent fasting should not constitute a green light to eat whatever one wants at meal time. “Fasting can disrupt the caloric assessment while we eat, and that could end very badly. It’s necessary always to be meticulous about the quality of food we consume. No sort of fasting will compensate for eating junk food.”

For her part, Latzer still has reservations: “Obesity is a serious medical problem for which no ideal solution has yet been found; research and treatment are still in the process of being examined. I don’t think fasting is the solution to that problem. There are well-grounded findings showing that when non-eating is encouraged or accelerated, one easily enters into cycles of uncontrollable gorging. As I always say to parents in counseling: When we urge a child to refrain from eating, we are effectively encouraging him to eat secretly, in stealth, which may even make him feel humiliated, so that he then denies that he ate anything. Simply put, as soon as you’re told not to eat – you will eat more.”

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