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There was so much going on that it was hard to understand everything.
A little over a year ago, Alex Allen moved across the country to San Francisco. He had landed a job as a software engineer, fulfilling his dream of working in a city at the heart of the technology industry. At 24, he loved the open culture of the region and its mild and uniform climate. He wanted to make the most of his adopted city.
But socialization inevitably poses a problem. Sometimes having dinner with new friends meant that he was drinking water by watching them lower.
In the last two years, he had started a fasting diet – 16 hours of fasting, then food every day within eight hours. It had been an awakening for his body. By the end of his teens and early twenties, he regularly lifted weights, but he also carried a lot of fat. He weighed over 200 pounds and he was fed up.
So he tried a 16-hour fast, a popular method called 16: 8. He experimented with another popular diet, 20: 4, in a four-hour window. As a bodybuilder shifts to heavier bars, Allen ends up getting involved with fasting days in his routine. His weight dropped to 166 pounds in four months.
He remained faithful to his diet in San Francisco but realized that he would simply have to miss this part of the session to have a meal with people. "It was a bit strange at first," Allen says. "But I do not mind doing it anymore. It starts a lot of conversations.
Fasting started as a way for him to lose fat. It's quickly become a way of life. "Nowadays, I do it for other health benefits and just because it makes me feel good," says Allen. These benefits are more energy, inner calmness and mental clarity. "I can not imagine that fasting is not part of my routine for the rest of my life."
Allen is part of a growing trend that began several years ago, when fasting drew public attention as a weight loss strategy. Lawyers say the practice is easier to follow than other plans. But that's not enough to explain his ability to stay. Fasting also has its share of clinical studies to support.
Research shows that it is an effective weight loss strategy and that it can also improve the health of people of normal weight. Regular practice can delay the onset of age-related diseases, such as cancer, type 2 diabetes, and neurodegenerative diseases, such as Alzheimer's disease. It also seems to improve learning and memory, and can increase lifespan.
In addition, fasting is being studied as a complementary treatment for brain damage, various cancers and the metabolic syndrome. Most of these results are preliminary and many of them are derived from animal studies findings.
Nonetheless, Valter Longo, a cell biologist and fasting researcher at the University of Southern California, says fasting is the body's integrated fixative. He has the power to heal. "But now, because we eat all the time, this inner repair has been eliminated," he says. "We no longer benefit from this ability."
Fasting is not the first food approach to excite researchers. Before the fast, there was caloric restriction, or CR. The methods have a lot in common. Overall, they significantly reduce energy intake and provide similar health benefits. In a way, they resemble brothers and sisters, especially since studies on fasting have emerged from the work on CR. And now, many former CR researchers are exploring fasting, often establishing a contrast between the two in the lab.
Although CR has never caught the public's attention as fasting, it remains an important food experience for scientists studying the biology of aging. To better understand the fascination of fasting today, we first need skinny CR.
Scientists have been studying CR for 100 years. During this time, they realized that laboratory animals with a daily energy intake of 20-40% were living longer and were less likely to suffer from chronic diseases. It was a disconcerting revelation: eating less than what the body apparently needs is a healthy strategy.
In the 1980s, researchers conducted most CR experiments only on yeasts, flies, mice and rats. An important question remained: would the CR work in humans?
This opportunity came by chance in 1991, when eight scientists entered Biosphere 2, a closed artificial ecological system located near Tucson, Arizona. Their mission was to live for two years with domestically grown foods in order to gather information for future biosphere space colonies.
In 1991, eight scientists wanted to live two years in Arizona's Biosphere 2, surviving food produced in domed facilities. Joe Sohm / Visions of America / Getty Images
The doctor Roy Walford was one of the scientists. He also happened to be a follower of CR and had recently written a book about life until he was 120 years old by following the diet. Shortly after she entered, the team realized that the food she had collected in the dome would not be enough to feed them. Walford has therefore implemented an unplanned CR experience. The four men and four women reduced their approximate caloric intake up to 30%. It was essentially the first human study on CR and its effects.
In a 2002 article on pseudo-experience, Walford and his colleagues reported that Biosphere staff were in excellent health. Almost all of them lowered their blood pressure, blood sugar, cholesterol and other health measures. Despite everything, their skeletal appearance was shocking. "They were malnourished and did not look healthy," says Eric Ravussin, a metabolic researcher at the Pennington Biomedical Research Center in Baton Rouge, Louisiana.
Biosphere 2 helped lay the groundwork for an unprecedented study. In 2008, Ravussin and his collaborators developed the first rigorous clinical clinical trial on CR in humans, called Calerie.
Scientists at Biosphere 2 soon realized that the available reserves would not last and would reduce their daily caloric intake by 30%, during the first quasi-impromptu experiment on humans. Roy Walford, a resident of the biosphere, led the effort. His weight has gone from 150 (right) to 119 (left). Walford et al./The Revues of Gerontology Series A, June 1, 2002
The trial, which aimed to examine the impact of food deprivation on the aging process, involved 218 men and women aged 21 to 51, both normal and slightly overweight. On this group, 143 of them were tasked with taking substitution treatment, consuming 25% less calories than usual – a reduction deemed feasible based on animal studies. They had to keep this diet for two years with the help of a behavioral intervention team and dietitians to make sure that they were receiving basic nutrition.
Most members of the CR group completed the trial, but their average calorie drop was only 12%. It did not matter, though. Blood pressure, cholesterol, glucose, insulin and other biomarkers have dropped, which has probably reduced their risk of heart disease, cancer and diabetes.
After the trial, another research group incorporated Calerie biomarker data into age estimation algorithms; they wanted to see if CR could have an effect on longevity. The conclusion is striking: during the study period, subjects following CR had aged more slowly than those in the control group.
This reflected some of what the researchers discovered in non-human primates. Rhesus monkeys share 93% of their genetic heritage with humans and generally live around 26 in captivity. In a study of 76 rhesus monkeys in progress at the Wisconsin Primate Research Center in 1989, monkeys receiving a 30% reduction in calories lived an average of two to three years longer than control monkeys. Another ongoing study, launched in 1987 by the National Institute of Aging on 121 rhesus monkeys, did not detect the same increase in longevity. But CR worked remarkably well for the 10 men who started the diet later in life. At least four of them have passed the age of 40, including one at age 43 – a record for the species.
Despite the data from the studies, scientists still do not know how and why CR works. It could be an adaptation developed billions of years ago by microorganisms trying to survive while food was scarce. Studies on E. coli Show that when you go from a nutrient-rich broth to zero nutrients, bacteria live four times longer.
It seems that the limitation of calories activates the genes that direct cells to preserve resources. Rather than growing and dividing, famine cells are actually stuck. In this state, they generally resist disease and stress and go into autophagy, a process of cleaning dead or toxic cells and repairing and recycling damaged components.
In addition, in several mammals, the production of a key hormone for cell growth, called IGF-1, decreases with several items. The hormone helps young people grow and grow, but in the adult, it increases the risk of cancer and accelerates aging if it is not removed.
Cell Cleansing Team Fasting and calorie restriction can both speed up autophagy, a kind of cellular household. When the cells are in starvation mode and do not need to break down food, they suspend their usual tasks and stop dividing. Instead, they work on repairing and recycling damaged components and cleaning dead or harmful cells. Alison Mackey / Discover
Jeffrey Peipert was not necessarily after potential anti-aging benefits when he enrolled in the Calerie trial. And it was not just about advancing cell aging research. He especially wanted to lose weight.
Peipert was 48 years old, 5 feet 5 inches tall and 174 pounds tall. During the trial, he reduced his daily intake from 3,300 to 2,475 calories and his weight dropped to 147 pounds. His biomarkers of health, especially his blood pressure, were excellent. "It was a remarkable drop in blood pressure. This has taught me that for our health, if we were a little thinner, we would not be any better, "says Peipert, a gynecologist and researcher at the University of Medicine's Faculty of Medicine. Indiana.
According to Longo, the big advantage of Calerie is that biomarkers of health are controllable by weight loss. "So, if your doctor tells you that you need medication to control these things, that's not true," he says.
Although CR can be a metabolic magic, it is not a miracle solution. Some mice raised to carry certain genes for laboratory research purposes do not benefit from them, and this in fact shortens the life of genetically modified mice. Deprivation can weaken the immune system of very young and very old animals, making them more vulnerable to disease. And while reducing calories by 25% is the norm, it is unclear if this is the best for animals and humans.
As with mice, people react differently to starvation. In recent years, scientists have learned that genetics, diet composition (amount of carbohydrate, protein and fat), regular exercise, and other factors play a role in the effectiveness of CR.
The experience of Peipert in the Calerie trial shows these problems well. Despite his biomarkers, he had sleep problems, reduced libido, low energy, and was hungry most of the time. "I loved gardening," says Peipert, who is 57 years old today. But during the trial, "I drove a wheelbarrow full of dirt and I felt weak. I was not myself. "
These types of side effects were not more prevalent in the general population of diet plan members, but many people had to withdraw from the study for safety reasons. The noted side effects of CR are a chronic loss of bone density and lean mass, as well as an excessive weight loss. Some dieters have body mass indexes in adolescents, suggesting malnutrition and frailty, says Longo.
CR can also lead to psychological problems. The Calerie trial was minimal, but Ravussin says it's probably because people have been examined for predispositions: food fantasies, irritability and social isolation, he says. Some Biosphere 2 scientists said they became quibbling and obsessed with food during their 21 months of deprivation.
Kelly Vitousek, a psychologist at the University of Hawaii, who has written summary articles on CR, says that these problems make sense from an evolutionary point of view. food is one of our top priorities. "Do not waste your time with other things," she says. "Think about food, not socialization, not sex. Be concerned about the food. Get it. "
During the Biosphere 2 experiment and the Calerie trial, some researchers hoped that CR would become a viable regimen. But the enthusiasm has been considerably cooled. Side effects were a problem, but the hammer blow was people's inability to stick to a drastically reduced calorie load each day. At this point, fasting was CR's obvious heir: it seems that nothing may be better on the occasion than eating less all the time.
Fasting has deep roots in human culture. It has been a practice practiced in various religions for millennia and the Greeks of the time are amazed by its impact on the body and mind. For centuries, doctors have noticed that it can reduce seizures. Paracelsus, a 16th century German-Swiss doctor, called him "the doctor from the inside".
But it was not until the 1940s that the first experiments began as an extension of RC studies. Researchers began retaining feed from lab animals every other day, says Michelle Harvie, a research dietician in Manchester, England. And in 1946, The nutrition journal published the first study on fasting, showing that rats deprived of food every third day lived longer and were less likely to develop tumors than control animals. Subsequent work has shown that fasting causes metabolic changes similar to those of CR.
In the 2000s, some studies on fasting showed better results than RC. In a 2003 experiment, Mark Mattson, a neuroscientist at Johns Hopkins University and the National Institute on Aging, found that mice fed every other day were healthier than mice at 40% fewer calories. .
In 2012, the idea of fasting was popularized when BBC commentator Michael Mosley aired a popular TV documentary on diet. A successful book, The Fast Diet, followed the next year.
As fasting has grown in popularity, scientists and nutritionists have developed different methods of practice. Some, like Allen, practice a restricted diet over time, like the 20: 4 diet. Some push the approach to 23: 1, placing all their food within an hour of a 24-hour day. Other approaches space the days of fasting throughout the week, such as the 5: 2 method: two days of fasting over seven days. Some amateurs complete their practice with fasts of several days.
Although people generally think that fasting consumes only water, the most popular of these diets, however, provides calories on "fast" days, which is not enough to harm the healthy physiological effects of the diet. practice, says Mattson.
In 2012, Carolyn Corbin, who lives in the Channel Islands, gained first-hand experience with the flexibility of fasting. At 5 feet 2 inches tall and 159 pounds, Corbin was overweight, with a BMI of 29.1. After seeing Mosley's show on the BBC, she adopted the 5: 2 diet, eating 500 calories twice a week and eating normally the rest of the time. She quickly adopted fasting only two days a week. Since he started training, the 65-year-old has lost 20 kilograms and stayed. "Forget the counting of calories, diet foods and diet drinks," says Corbin. "Fasting to lose weight works."
And there is more than an anecdotal experience like Corbin, fasting can help people lose weight. In a one – year study, 100 obese adults aged 18 to 64 were divided into three groups. One group practiced fasting every other day, consuming 75% fewer calories every other day; another group followed CR, with a 25% calorie restriction per day; the others were in a control group. Compared to the control group, the fasting men had an average weight loss of 6%, and those attributed to the CR, about 5%, according to the 2017 paper of JAMA Internal Medicine.
Even with these results, one of the concerns of fasting is that people will gorge themselves on non-fast days. But the results of two-month trials, published in 2018 in the journal Food science and nutrition, showed that dieters, especially those who follow 5: 2, do not stuff themselves. "When you impose a 70% calorie restriction over two days, you consume about 25% less on natural days," says Harvie, one of the study's authors and co-designer of diet 5: 2. "And that's why the diet is so effective."
Popular fasting plans based on water only or low calorie (500-600):
1. Restricted supply in time: Eat in a specific time window in a 24-hour period. The most popular is 18: 6, eating only for a six hour period of a 24 hour day. The other variants are 20: 4, 22: 2 and 23: 1.
2. Alternate fasting: Fast every other day.
3. Intermittent fasting: Fast one day or several days a week. The most popular is 5: 2 – eat normally five days a week, fasting two days a week.
How far can calories go?
People can live days without food and water, and weeks or months consuming only water. In laboratory animals, when caloric intake is reduced by more than 50%, they die as a result of complications due to starvation. In the final stages of starvation, the body, devoid of glucose and fatty acids, turns to muscle proteins for energy. Humans die when their body mass index (BMI) is around 12.
BMI beaches for adults
The body mass index, or BMI, uses height and weight to determine the health status of a person's weight. (To calculate, multiply the weight in pounds by 703, divide by height in inches, then again by height in inches.) Although it does not measure body fat, it has been shown that BMI was in close correlation with the risks of metabolism and disease. In general, health risks increase for people with a BMI greater than or equal to 30 or less than 18.5.
Alison Mackey / Discover
Is fasting better than CR to improve people's health? It's far from clear. However, experiments on rodents suggest that it might be best to improve cognition.
For years, researchers have found that mice and rats do many cognitive tests in case of starvation. While they are fasting, rodents improve their stamina, their senses, their memory, and their ability to learn.
So, what explains this high mental state? It seems that fasting triggers a radical change in the body's metabolism, according to an article by Mattson and his colleagues published in February in the journal of experimental biology FASEB. In humans, fasting for 12 hours or more decreases glycogen levels, a form of cell glucose. Like switching to a backup gas tank, the body switches from glucose to fatty acids, a more efficient fuel. The switch generates the production of ketones, which are energy molecules made in the liver. "When fats are mobilized and used to produce ketones, we believe that it is a key factor for generating health benefits," Mattson said.
One type of ketone that floods the brain is beta-hydroxybutyrate, or BHB. According to an article published in February in Nature Reviews Neuroscience, BHB stimulates memory, learning, and the cellular cleansing process of autophagy in mice. BHB also brings neurons, including those from the hippocampus, a center of brain memory, to release what is called neurotrophic factor derived from the brain, or BDNF, an important protein for the brain. 39, learning, memory and mood enhancement. CR does not generate these levels of ketones because the glucose reserves are never empty.
Mattson emphasizes that, from the point of view of evolution, the brain power generated by fasting makes sense. Mammals usually spend days without food, often hunting on an empty stomach. Half-hungry animals, with improved intelligence and energy, would be more likely to get food and live another day. "If you're that wolf or that lion, now a week without food, you'd better be able to focus and focus on what you need to do to get food," he says.
Ketones may also help to explain several mysteries surrounding brain damage and disorders. According to several studies, for example, fasting rodents recover better from traumatic brain injury and spinal cord injury.
Start a metabolic switch – The body can use three types of fuel: carbohydrates, proteins and fats. Alison Mackey / Discover
But fasting comes with its own drawbacks: a higher risk of excessive consumption of food, low blood pressure, irritability and headaches. The last two tend to disappear after a few weeks because the body adjusts to fewer calories. Nevertheless, long days of fasting can cause fainting. Doctors recommend it only under the supervision of a doctor.
Ravussin, the researcher in CR, is not convinced that fasting offers more benefits than CR, nor that ketones are as powerful as Mattson and Longo say. "Ketones are good for reducing your appetite, but are they good for cell health?" He asks. "I have not seen any convincing data that says yes."
Harvie thinks that fasting could stay, partly because it is flexible. People can choose a fasting practice and a nutrition plan tailored to their lifestyle, she says. "We're chirping to see which diets are the best. But in the end, a plan is as effective as the one that follows it, "says Harvie. "For some people, the 5: 2 will be perfect, and for others, it will be absolutely horrible.
The psychologist Vitousek has already witnessed this kind of enthusiasm – and it was for CR. Caloric restriction never reached the popularity of fasting, but it had its share of lay members in the 2000s, when she had the opportunity to talk with members of a group that practices it. At first, they were enthusiastic and motivated. Then, like most dieters, the majority began to fall. Some who had been doing CR for years just could not do it anymore. "You can pretty much carry that to the bank," says Vitousek about the decreasing enthusiasm of dieters. "That's the reason we have these cyclic waves."
For Peipert, it was a jagged trip. He has always struggled with his weight and obesity is common in his family. A few years after the Calerie trial, he regained all the weight he had lost, plus 6 pounds. "This type of drastic reduction in calories for two years is probably not a sustainable plan or a good plan to lose weight throughout life," he says.
When fasting became a diet, Peipert was skeptical. But in March, he started the 5: 2 diet. It was difficult at first, he says, but by the middle of the summer he had lost 9 pounds. He hopes to lose 10 to 15 others. "It helped me control my hunger," Peipert says. And with his CR experience always in his head, "No side effects."
Even though fasting and caloric restriction can have health benefits, they both require eating less – which is unattractive to most people. Scientists and nutritionists have therefore experimented with ways to mimic the biochemical and physiological effects of prolonged periods of food deprivation.
Ketosis occurs when the body, deprived of food for 12 hours or more, passes its source of energy from carbohydrates and glucose to fatty acids. The process generates ketone bodies that can have beneficial effects on health.
Keto diets, which are low carbohydrate foods, high in protein and high in fat, can also trigger this metabolic shift. Since the 1920s, keto diets are used in medicine to reduce seizures. More recently, diets have completed standard treatments for type 2 diabetes and cancer, with promising results.
In recent years, keto diets have become more popular. Some celebrities and sports stars embrace them, and people who quickly use the diet to push their body more towards ketosis.
But followers are cautious, says nutrition researcher Michelle Harvie. Dieters who go to keto tend to lose weight, but diets are low in fiber and high in saturated fat, posing a risk of cardiovascular disease. "And more and more evidence is showing that its effects on the gut microbiome are rather unfavorable," says Harvie. "The intestinal microbiome is a poorly understood but potentially important part of our metabolic health. And if you make a mistake, you have problems. "
Diet imitating fasting
Valter Longo, a cell biologist at the University of Southern California, has developed ProLon, a five-day diet imitating a five-day fast, but without loss of essential nutrients. It is a fully vegan diet with a high content of unsaturated fats (think almonds, avocados and peanut butter), low in sugar and low in protein.
In a study of 2017 in Science médecine translationnelle, 71 participants ayant terminé le régime imitant le jeûne ont montré des bienfaits pour la santé, notamment une perte de poids, une baisse de la pression artérielle et une baisse du taux de l'hormone IGF-1, qui stimule principalement la croissance mais joue également un rôle dans la régulation de la glycémie. Et selon votre état de santé, vous n’aurez peut-être pas besoin de vous en tenir au régime trop longtemps. Par exemple, Longo affirme qu’un athlète en bonne santé n’aura peut-être besoin de le faire que deux fois par an, tandis que celui qui a un excès de poids peut avoir besoin de continuer jusqu’à ce qu’il voie les améliorations qu’il souhaite.
Des médicaments qui traitent des maladies chroniques, telles que l'épilepsie et le diabète de type 2, sont explorés pour imiter le jeûne. Les principaux acteurs sont la rapamycine, la metformine, le resvératrol et l’hydroxycitrate. Les médicaments sont prometteurs, mais présentent également des inconvénients.
La rapamycine, par exemple, induit les cellules en erreur en leur faisant croire qu'elles sont privées de nutriments, provoquant ainsi le rajeunissement cellulaire observé lors du jeûne, mais elle supprime également le système immunitaire. C’est utile dans des scénarios médicaux, tels que la prévention du rejet d’organes après une greffe ou le traitement de maladies auto-immunes, mais pas très bon pour un diète moyen.