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Intermittent fasting: healthy without eating

Intermittent Fasting

Three meals a day, interspersed with three snacks, seven days a week. This is what we have always been advised to do, so it is the best for health. But what if it were otherwise, especially when you are overweight or obese? Light on intermittent fasting and its possible effects on health, a subject of research in full expansion.

Does fasting have a therapeutic effect?

Mark Mattson doesn’t have lunch. Besides, he doesn’t dine either. Around noon, when hunger begins to be felt, he leaves for exercise. It is not until early or mid-afternoon that he takes his first meal of the day.

To eat this meal and the other two of the day, Mark Mattson gives himself a six-hour window of time. And the other 18 hours of the day, he doesn’t take any snacks. Not even a small bowl of cereal, fruit, rice chips? Nothing except green tea and water. And his body is fully used to this diet: he has been following it for more than 10 years.

Mark Mattson is head of the Neurological Sciences Laboratory at the National Institute of Aging, a US federal research center from the National Institutes of Health. In fact, he is putting into practice in his own life a field of research that has animated his laboratory for 20 years and which is increasingly fascinating scientists: that of fasting and its possible health benefits.

If health practitioners remain cautious about fasting, citing the lack of scientific data in humans, the interest that researchers have in the world is growing. “It’s really an explosion of research in several fields,” says Dr. Martin Juneau, cardiologist and director of prevention at the Montreal Heart Institute, who says he is “very careful” about the approach.

Fasting studies have been conducted in the vast majority of laboratory animals, but in the past decade, particularly the past five years, controlled studies have also been performed in humans.


More than 3000 clinical trials in humans have been launched since 2005 to test the therapeutic effect of fasting in a variety of areas: weight loss, inflammation, immune system, cholesterol, sensitivity to insulin, effectiveness of medical treatments against cancer, etc.


The most popular fast is the so-called “intermittent” fast, similar to that practiced by Mark Mattson: short (2 p.m., 6 p.m., sometimes 24 h) fast, but repeated.

Mark Mattson’s laboratory is interested in a possible and rather unusual benefit of intermittent fasting: the maintenance of cognitive functions.

“In rats and mice, it is very clear: when they follow an intermittent fast, their nerve cells and the regions of the brain, particularly those involved in learning and memory, are more active when they fast. We see it. ”

The work of his laboratory has shown that intermittent fasting protects, in animals, nerve cells relevant to Alzheimer’s disease, Parkinson’s disease and strokes.

Obviously, rats and mice that follow an intermittent controlled fast consume fewer calories. But this reduction in energy intake and the ensuing weight loss is not the only mechanism involved in explaining the benefits observed. “There is, at least in animals, a beneficial effect that goes beyond what happens when you restrict your calories,” the specialist, told Baltimore, Maryland, told La Presse.

Metabolic shift?

In fact, he says, fasting would lead to a “metabolic turnaround.” Mark Mattson explains, “Every time we eat, the energy stored in the liver is regenerated,” he says. Energy from the liver – mostly glucose – is always used first when fasting. It takes about 10 to 12 hours to deplete the glycogen from the energy stored by the liver. ”

Once these reserves are used up, he says, the “metabolic turnaround” sets in. “What happens next is that fats are released from the body’s fat cells and are moved to the liver, where they are converted to ketones. And these ketone bodies become a major source of energy for cells, particularly nerve and muscle cells. ”

According to researchers’ theory, the brain triggers an adaptive response to this metabolic shift. Her goal: to better manage stress and – ultimately – to help her find food.

From an evolutionary point of view, says Mark Mattson, this theory is full of meaning: individuals whose body and brain function well during a fast have the energy and the presence of mind necessary to find their next meal. . “So we have evolved to function very well during the fasting period,” believes the researcher.

Unlike regular diets, which lower the basal metabolism while dieting (and which explains the difficulty in losing weight!), Fasting would increase this metabolism, studies conclude.


And in humans?

To verify if the results obtained on rodents apply to humans, Mark Mattson’s laboratory is currently conducting a clinical trial with subjects aged 55 to 70, obese, resistant to insulin and therefore more likely to have cognitive impairment. In Quebec, the Montreal Heart Institute is preparing a clinical study project with a control group to assess, also in obese subjects, the effect of intermittent fasting on the main metabolic factors and cognitive functions.

To date, the available data looks promising, agrees Dr. Martin Juneau. “But is it going to be usable in the clinic?” wonders the cardiologist. This is the big question. Are people going to be ready to fast? And what type of fast? ”

Until research tells us more, very few health professionals in Quebec and Canada recommend or encourage fasting.

“There are some interesting studies, but in my opinion, it will take a lot more to recommend that,” says Dr. Dominique Garrel, endocrinologist and associate professor in the nutrition department of the University of Montreal.

Yes, intermittent fasting “may help some people lose weight,” but the scientific evidence remains “mixed,” said Kate Comeau, dietician and spokesperson for Dietitians of Canada, who represents 6,000 members across the country. The results obtained from rodents, she recalls, cannot be extrapolated to human beings.

Intermittent fasting exists in many forms … and requires certain precautions.

Fasting in a limited time

Another form of intermittent fasting is called time-restricted feeding. People can eat what they want, but only in a limited time window (like four, five, or six hours a day). It is practiced every day or several days a week.

Fasting 5: 2

Popularized in 2013 in the book The Fast Diet by British journalist Michael Mosley, the 5: 2 diet consists of eating little two days a week, not consecutive, i.e. 400 to 500 calories for a woman and 500 to 600 for a man. Some people don’t eat at all on fasting days, from supper to supper, for example. The other five days, we eat normally.

Fasting every other day

Finally, as its name says, fasting every other day (alternate days fasting) consists of eating little (even less than 600 calories per day) or not at all every other day. It is a more intense version of fasting 5: 2.

Water, coffee, broth?

In classic fasting, you only drink water – you have to drink a lot to replace the liquid in food. “There are also variations where you can drink tea, herbal tea, coffee,” says Ontario nephrologist Jason Fung, who operates a fasting clinic. Some also allow themselves bone broths.


People who take medication (diabetes, hypertension …) and who would like to try a fast must be subject to medical monitoring, warns cardiologist Martin Juneau, who does not encourage the practice of fasting in his patients. because of the lack of evidence. Fasting could quickly lower blood sugar and blood pressure.

Not for everyone!

Children, frail elderly, pregnant and breastfeeding women should not fast, insists Dr. Jason Fung. “Those who are under their healthy weight or who may be malnourished probably shouldn’t be fasting either,” he adds.

No long-term studies

In order to maintain the benefits associated with it, at the forefront of weight loss, intermittent fasting should be practiced for the long term, even for life. Is it physiologically possible, but above all psychological? Long-term scientific data is non-existent. Experts question themselves.

The impact on humans

The scientific literature on intermittent fasting has been accumulating for the past twenty years, but the difficulty is that there is no data that assesses the long-term impact of the practice on being human, says Dr. Dominique Garrel, endocrinologist and associate professor in the nutrition department of the University of Montreal. “You should have data for at least a year,” he says. Nutritionist Bernard Lavallée, author of the blog The urban nutritionist, notes the same lack: “It is possible to restrict oneself for a certain time, he says, but it has been well demonstrated that restriction is not a good way to change eating habits. Often, there is a return of the pendulum which is done. ”

Compensatory mechanisms

According to Dr. Garrel, the effect of fasting on compensatory mechanisms – seen in almost all people on diets – remains unknown. “The brain is extremely well structured to prevent the weight from going down or to make the weight go up after it goes down,” he says. For example, he says, in people who follow a severe calorie restriction (700 calories per day) for 6 weeks, there are signs of an increase in appetite hormones … even a year later! On the other hand, people on calorie restriction will generally decrease their involuntary activities (linked to everyday activities) in a completely unconscious way, he adds. Even the effectiveness of muscle contraction increases in people under restriction, which allows you to do the same with less energy.

Relationship with food

The principle of intermittent fasting comes up against a philosophy in vogue among nutritionists: intuitive eating, which consists in listening to the signals of hunger and satiety in one’s body, in ceasing to impose external rules (number of calories, banished foods, etc.) and to experience emotions other than using food. “Perhaps, for some people, it’s easier to eat less or even not to eat at all two days a week than to be careful every day about what they eat,” agrees Bernard Lavallée. On the other hand, the fact remains that, for many people, embarking on this type of restriction can have consequences on their relationship with food and with their bodies. Remember that between 30% and 50% of obese people who are undergoing weight loss treatment have the diagnostic criteria for binge eating disorder.

Eating disorders

According to Howard Steiger, head of the Eating Disorders continuum at the Douglas University Institute, fasting has the potential to attract people who suffer from eating disorders. In his practice, he finds that patients justify themselves by citing the possible health benefits of fasting. “Fasting may have positive potential for population health, he agrees, but any indication of control over food or exercise, which in general can be positive, can lead to behavior at risk for someone who is vulnerable, “he says. Does intermittent fasting increase the risk of eating disorders? To date, no study has addressed the issue, said American researcher Mark Mattson. But in his eyes, a diet that involves counting calories at all meals seems more difficult psychologically than intermittent fasting.

The doctor who makes his patients fast

Dr. Jason Fung is one of the few doctors in Canada to use fasting as a treatment for obesity and type 2 diabetes. Interview with this Toronto nephrologist, founder of the Intensive Dietary Management (IDM) program and author of the book The Complete Guide To Fasting.


I am a kidney specialist. And the most common cause of kidney failure is type 2 diabetes. We have always been told that type 2 diabetes is a chronic and progressive disease, but in reality it is a reversible disease : if people lose weight, usually it gets better. And one of the ways used for thousands of years to lose weight is fasting. When they undergo bariatric surgery, people eat very little for months and start to get better.

If the issue is not to eat, then why not just make people not eat? Five years ago, I therefore opened the IDM clinic. We use fasting as therapy, just as we would with medication. Thousands of patients have been treated like this.


Because for years we have been told to eat six times a day. Eating zero times seems like the wrong thing to do. But the reality is that if you don’t eat, you will lose weight! […] There are people who weigh 300, 400, 500 lb. If they don’t lose weight, they’ll get very, very sick. They are going to receive dialysis, have heart attacks, strokes and they will die. Why couldn’t they skip a meal


Yes, it is difficult and it is not pleasant. But it’s not nice to be on dialysis, to have a heart attack, to have a stroke. Anyone who wants to get better should have the option of fasting, but who will help? Her doctor has rather the opposite reaction: “Yes, you have to lose weight, but don’t skip meals and make sure you eat this, eat that, eat six times a day” … So she doesn’t lose weight. I monitor patients, control their blood tests and adjust their medication.


If you think that by eliminating 500 calories per day, you will lose 1 lb per week and therefore 50 lb in a year, it sounds like it should work, but it almost never works. The success rate for this type of approach is around 1% or 2%. Because it’s not just a matter of calories: you have to keep a balance between the state of food and the state of fasting. When you eat, you tell your body to store energy. The time you spend without eating allows you to burn fat.


It depends on the support they get around them. The problem with fasting is that those around you – family, neighbor, doctor – advise to stop. So some stop … and regain the weight. […] We have patients who, after five years, have completely reversed their type 2 diabetes and stopped taking medication.


No. Several factors come into play. For example, you could put a 40-year-old who has 100 lbs to lose on a stricter diet than if he were 75 and overweight. We try different things and patients see what they like, depending on their lifestyle.


Indeed, there is a tendency to eat more when you haven’t eaten all day, but it is very difficult to eat the same amount. People are told to eat as normally as possible [the team also provides nutritional advice for healthy eating]. Most patients who eat too much will suffer from stomach aches and will learn from them.

Originally posted 2020-06-17 17:51:33.

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