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‘Fasting 12 or 13 hours every day improves metabolism and sleep quality’

Valter Longo – the director of the University of Southern California’s Longevity Institute – has spent years studying the effects that intermittent fasting can have on the human body

Valter Longo
Valter Longo, a molecular biologist at the University of Southern California, during the interview.Álvaro García
Nuño Domínguez

Contrary to popular belief, going without food for many hours – or even several days – may have some beneficial effects. Studies have shown that, while fasting, the body can adapt to the lack of food. The multiplication of cells slows down, while autophagy – your cellular recycling system – is activated, which allows the body to eliminate old cells and, for a time, sustain itself with its own reserves.

Valter Longo is an Italian-American professor of gerontology at the University of Southern California. For decades, he has studied the biological aging process. Specifically, he has tried to understand how the benefits of fasting can be reproduced in diets, so as to improve health and extend life expectancy. “It matters what you eat, but also when you eat,” he says.

The 55-year-old Longo is a controversial figure in his field. His studies don’t reveal the exact composition of the diets he feeds test subjects to mimic the benefits of fasting. His “fasting-mimicking diet” is trademarked by L-Nutra, a company that he partially owns.

While visiting Madrid for a conference being held at the Spanish National Cancer Research Center (CNIO), Longo spoke to EL PAÍS about nutrition and fasting.

This interview has been edited for clarity and brevity. The views expressed by Dr. Longo do not necessarily represent the position of EL PAÍS. His comments in this interview are not intended as medical advice.

Question. How solid is the scientific evidence behind the benefits of fasting?

Answer. Very solid. Six or seven years ago, the connection was made via experiments with mice. It’s now been confirmed in people. Many clinical trials have proven the benefits of fasting, as well as the benefits of diets that mimic the physiological processes of fasting.

Some studies also point out that the hours in which you eat are key. Fasting 12 or 13 hours every day – for example, eating breakfast, lunch, and dinner before 8:00 p.m. and not eating again until breakfast – improves metabolism and sleep quality. But you don’t have to go overboard, because if the fast is prolonged to 16 hours – if you skip breakfast – there are no longer any beneficial effects. In fact, you could actually have some metabolic problems.

Q. Why does intermittent fasting have these beneficial effects?

A. For thousands of years, our species ate a lot in the summer, when food was more easily available. That saved us during the scarcity of winter. But now, winter doesn’t impact nutrition. As the days get shorter and cold, we eat more than necessary – this can cause insulin resistance, which can lead to diabetes. Fasting or fasting-mimicking diets put us back in our ancestors’ winter mode, which eliminates insulin resistance.

Q. What benefits can fasting have?

A. I advocate going on a special diet that mimics fasting for five days, about three times each year. There are clinical trials that show how a diet like this can reduce blood pressure, glucose, cholesterol and fat levels. A small study that [USC] conducted with the University of Heidelberg showed that this diet makes it possible for people with diabetes to reduce the amount of medication they need to take.

Q. What is the fasting-mimicking diet like?

A. It’s low in calories – about 60% less than the average diet – protein and sugar. It’s very plant-based and high in fats, which come from olive oil, walnuts, almonds, etc. The first time I described this diet in one of my books, it caused problems, because a lot of people basically did what they wanted – they didn’t follow the instructions. That’s why it’s important to always consult at least one nutritionist before beginning this kind of diet.

Q. Can dieting help us live longer?

A. Without a doubt. We’ve done a large review of studies, analyzing data from two million people around the world. It’s clear that, by eating a lot of vegetables, whole grains and nuts, while avoiding red or processed meats, you can lengthen your life. If you add intermittent fasting to the mix, I think we can live 20 years longer.

Q. If you’re very old, is it too late to benefit from a change in diet?

A. Not at all. If you change your diet at age 20, you can extend your life expectancy by more than 10 years. If you start at 60, you gain up to eight years. But, if you switch at 80, you can still lengthen your life by about three years.

It’s also important to remember that this isn’t just about life expectancy, it’s about quality of life. In the US, the average 55-year-old already takes two medications to treat chronic conditions. By 65, they’re usually taking at least three. We see more and more people who are already sick by the age of 30. They’re kept alive with surgery and very expensive drugs: 20% of US GDP is spent on medical treatment, which is also becoming more expensive. It’s an unsustainable situation. We need a nutritional revolution.

Q. Can you speak about the connection between diet and cancer?

A. A couple of decades ago, we began to study the effect of fasting in cancer patients. We realized that cancer cells are unruly: they aren’t affected in the least by hunger or lack of food, they keep multiplying. However, in both animal and patient studies, we found that fasting or fasting-mimicking diets can make oncological treatments more effective.

Q. Can changing your diet prevent cancer?

A. There are no diets that can prevent cancer. It’s not possible to change the effects of a genetic mutation with what you eat, for example. The biggest risk factor for cancer isn’t smoking or being obese… aging is the main concern. For instance: 30 years of life is 50 times more harmful than smoking. High cancer rates are mostly due to the fact that people are simply living longer; the vast majority of cancer patients are well into their sixties. So, while improving your diet can’t help you avoid cancer, it can help you grow older in a healthier way – this protects your immune system, prevents tumors, etc.

Q. What do you think about the option of creating medications that mimic the beneficial effects of fasting or exercise?

A. When you give drugs to someone who has diabetes or cancer, you assume that a small percentage of patients will suffer from side effects. But it’s trickier to distribute medication to the healthy population if some consumers are going to experience side effects. That’s why I advocate the diet we’ve invented, which mimics the effects of fasting.

Q. The diet you’re referring to is sold by L-Nutra, a company you founded that sells boxed, ready-made meals… but can that same food be purchased in a grocery store?

A. Sure it can. But it won’t be the exact same diet, because we’ve patented it. In any case, I donate everything I earn [from L-Nutra].

We’re currently trying to get the medical authorities in the United States and Italy to include this diet as a treatment for people living with diabetes or hypertension. We believe that, in a year, with the support of nutritionists, we can significantly reduce the percentage of the population living with diabetes, along with the associated medical expense, which is in the hundreds of billions of dollars.

Q. Do you think that some food products should be banned?

A. No. We studied the diet of Italian children — everyone said that high obesity rates were due to sugary drinks. But we found that the problem wasn’t soda or juice… it was based almost entirely on diet. Pasta, pizza, potatoes, beef – kids were eating heavy starches and three to four times more protein than the recommended amount. Banning things isn’t the solution, health education is.

Q. How do we tackle this problem?

A. With more and better nutrition professionals who can accompany and support doctors. Many doctors, surprisingly, know very little about this field. They need to be further exposed to the subject of nutrition, so that they can help their patients.

Right now, most nutritionists just do three-year-long certifications. We need more graduate degrees in the field, more specialization, so that they can work hand-in-hand with doctors. Together, they can help patients live longer, healthier lives.

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