The truth behind what intermittent fasting does to your body

"Your blood sugar is constantly high. Your insulin levels are constantly high. You have type two diabetes, which is a huge epidemic. These high levels of blood sugar cause damage to the interior of our arteries. The kidneys close up. People go on dialysis. It's a disaster fundamentally. "

A century of IF research, in humans and in animals, illustrates its claims. Studies show that IF can lead to weight loss, stabilized blood glucose, reduced inflammation, improved memory and resistance to stress, slower aging, longer life expectancy, and a longer life span. blood sugar stabilization – these are promising health benefits in exchange for significant lifestyle changes.

What is intermittent fasting?

Unlike some complex diets, IF requires minimal effort: you simply do not eat or eat only very limited amounts for hours at a time. No meal preparation, calorie calculation or riddles at the restaurant.

But there are many ways to feed. Some supporters of the FI maintain eat limited in time, pressing all their meals in a period of eight to ten hours, followed by a night fast from 14 to 16 hours. Other people are crazy about Diet 5: 2, which involves eating normally five days a week, and then consuming 25% of the daily caloric intake for two days (between 500 and 600 calories for most people). Others simply limit the consumption of food completely some days of the weekrelying on water, black coffee and tea to avoid hunger signals.

There are no nutritional guidelines or suggestions for "sure days "when to eat is unrestricted. But doctors and dieticians suggest eating a diet rich in nutrients, rich in plants and protein, to help you during periods of fasting.

What happens during intermittent fasting?

To understand SI, you must first understand what is happening when you eat.

"Insulin is a hormone that is released when we eat, but it's not supposed to be released all the time," says Tello. "Intermittent fasting is simply about leaving your insulin level at a near normal level to unlock your fat stores. So no one will lose weight unless they lower that level of insulin. And that's why eating very small meals throughout the day does not really help you lose weight. "

People did not have KIND bars.

Waiting a little longer than usual between meals is perfectly normal, she says, despite what society tells us.

"Historically, we did not have access to things like snacks even a hundred years ago," says Tello. "People did not have KIND bars. People, nowadays, keep the food in their glove compartments, for God's sake. It's like people can not stand hunger for a second. It's not normal, it's not healthy.

"During exercise, the cells are stressed. They do not grow up and do not become stronger and bigger during exercise, but during the rest period. So we think that with intermittent fasting – during the fasting period, cells enter a sort of stress resistance mode. And then, when you eat, they are prepared to quickly absorb nutrients, proteins and to grow. "

How to start

On IF's first attempt, the transition can be difficult, admits Mattson.

Many fasting people report an uncomfortable, even painful feeling of hunger, when they refrain from eating. Mattson suggests people slow down and try different types of IS to see what works with their goals and routine. He advises first to reduce the "window of food" from an initial unrestricted period to 12 hours, then 10 hours, then 8 hours before finding a window of sustainable food .

During the first week or two of the IF, fasting people may notice that their stomachs are moving or feeling empty. Some people are exhausted, dizzy or shaky because of a decrease in their blood sugar on days of fasting. Others have low concentration, irritability, mood swings and even vertigo. In particular, people who work long hours or with heavy machinery should pay more attention to staying hydrated, rested and alert when fasting.

After about a month, people generally feel better and are less hungry, says Mattson.

Tello agrees: "The longer you can stay between meals, the less hungry you are. I think that many people are hungry, unlike the very low calorie diet, where you are constantly eating small amounts of food. It's like a tease all day. "

Mattson encourages the fasters to be patient and wait for these side effects to go away.

"Many people will say," Well, I tried. I'm too hungry, I'm irritable and I can not focus, but they have to stick to that, "he says. "It's a bit like an exercise. If you are in bad shape, your body and brain take a while to adjust. But once you get used to it, you feel better. And if you stop doing it, you feel worse. "

To make fasting manageable, Tello suggests an overnight fast, which can more easily fit into the routine of the world. Research shows that it has been shown that limiting diet to the hours of the day, an approach that aligns dietary habits with circadian rhythms, has benefits for metabolism and weight loss. .

"Eating at night is horrible," says Tello. "Nighttime snacks are like the worst. Eat at night then go to bed, it goes straight to the fat; it's the safest way to gain weight and it's so bad for your blood sugar. "

Can you lose weight with intermittent fasting?

One of the main reasons why many people start and keep up with the SI is to lose weight. A practice-based Reddit group with more than 380,000 members is brimming with photos before and after spectacular fasts, some of which have lost more than 150 pounds using the weight loss approach. Most people are ecstatic about their results: thinner bodies, more energy, and happier prospects.

A systematic review of 40 studies published in 2015 in Molecular and Cellular Endocrinology, showed that IF was effective at losing weight, with a typical loss of 7 to 11 pounds in 10 weeks.

But the IF is not necessarily more effective at weight loss than other energy restriction diets, such as simply counting calories or reducing carbohydrates. A one-year study on obese men, published in JAMA Internal Medicine in 2017, showed that fasting over two days did not produce superior adherence, weight loss, weight maintenance or cardioprotection compared to daily caloric restriction.

How to eat healthy during intermittent fasting

If the goal is to lose weight in a healthy way, Tello suggests maintaining a plant-based diet alongside fasting and not using the IF as an excuse to overeat or consume unhealthy foods during off-peak periods In a plant-based diet, plants make up the lion's share of food consumption. Think of vegetarian, vegan or Mediterranean diets.

People do not have to be completely vegan, but they have to eat mostly plants. "

"We have so much evidence, countless evidence on millions of people that a plant-based diet is the healthiest diet," said Tello. "And people do not have to be completely vegan, but they have to eat mostly plants."

Tello suggests that plants produce 80% of your diet. You can always eat steaks, cakes and whole grains occasionally, but the essentials of your diet should come from the ground or grow in a tree or bush.

"You will be a healthier person. It's anti-inflammatory, it's full of fiber. This will lower your cholesterol level. Your digestion will improve, "says Tello.

Will intermittent fasting make you live longer?

In 2012, the BBC Michael Mosley, a radio and television broadcaster, introduced IF to the cinema with the documentary Eat fast, live longer, which draws on research from Michelle Harvie, Ph.D. at the University of Manchester. Journalist Kate Harrison's book followed soon after. The diet 5: 2 in 2013 and Dr. Jason Fung The code of obesity in 2016.

Research on the effects of IF on aging goes back a century. "Nutrition and aging are very closely linked," said John Newman, MD, Ph.D., a geriatrician at the University of California at San Francisco and a researcher at the Buck Institute on Aging. reverse.

"One of the earliest experiences of nearly a hundred years ago has shown that if you give the rats less food, they will live longer until they start starving them. Fasting, dietary restrictions and the ketogenic diet activate the repair routes and help the animals to live longer. "

A century of laboratory research on animals and humans, brought together by Harvie and Anthony Howell, Ph.D., both of the University of Manchester, badociates caloric restriction with the prevention of disease-related diseases. age, including tumors, cardiovascular diseases, diabetes and diabetes. dementia. Research also suggests that this increases the shelf life.

What are the risks of intermittent fasting?

Some dieticians warn that ignoring hunger signals can have unintended consequences. Evelyn Tribole, dietitian and author of The Intuitive Diet Exercisebook, encourages its clients to listen to their hunger and satiety signals when they choose to eat rather than abide by strict dietary rules. Tribole thinks that ignoring these primary signals is a dangerous practice.

"I have a problem when someone really feels a biological hunger and you're going to ignore that," Tribole said. "I think it's a problem, especially for people who have diets or eating disorders; they are more likely to engage in binge eating and emotional eating. "

Anyone with a history of disorderly eating should consult with a health professional to confirm that the IF is suitable for them.

A systematic review published in the journal Stress in 2016, found that the IF can initially increase the stress levels of the fasters. The increase can be reduced after a few weeks of fasting. According to other research, the FI could lead to greater metabolic fluctuations and increased appetite on non-fasting days compared to an intermittent energy restriction, a diet that allows certain foods .

The future of fasting

Mattson, Tello and Newman note that research on IF has its limitations. In particular, a large part of the studies have been performed on rats and animal models, as well as on obese or overweight human subjects.

The impact of the IF on other populations – growing adults, pregnant women, diabetics, existing medical conventions, people taking medications requiring nutrition or people over 65 – remains to be determined.

More randomized controlled studies across a wider range of adult populations would confirm some of the potential health benefits. But for now, it seems like SI is here to stay.

"Intermittent fasting goes far beyond fashion," said Mattson, who criticizes the trend, fearing that this will lead people to discredit the value of evidence of good reputation.

"Fortunately, there is a lot of research on humans and intermittent fasting," says Tello. "There are all these different studies that call for different words, but they look at the same thing, which is prolonged fasting."

"At this point," she says, "I think it's really fair to say that any type of modified fasting diet promotes weight loss and improves metabolic health. I think we're really sure to say that. "