About the Author
Dr. Michael Mosley is the author of The Clever Gut Diet, The 8-Week Blood Sugar Diet, and the coauthor, with Mimi Spencer, of the #1 New York Times bestseller The Fast Diet, which has been published in over thirty-two languages around the world. He is also coauthor, with Peta Bee, of Fast Exercise and wrote the foreword for The Fast Diet Cookbook by Mimi Spencer and Dr. Sarah Schenker. Dr. Mosley trained to be a doctor at the Royal Free Hospital in London before joining the BBC, where he has been a science journalist, executive producer, and, more recently, a well-known television personality. He has won numerous television awards, including an RTS (Royal Television Award), and was named Medical Journalist of the Year by the British Medical Association.
Excerpt. © Reprinted by permission. All rights reserved.
Mimi Spencer is a feature writer, columnist, and the author of 101 Things to Do Before You Diet.
Peta Bee is an award-winning journalist and qualified running coach with degrees in sports science and nutrition.
The FastLife CHAPTER ONE
The Science of Fasting
FOR MOST ANIMALS OUT IN the wild, periods of feast or famine are the norm. Our remote ancestors did not often eat four or five times a day. Instead they would kill, gorge, lie around, and then have to go for long periods of time without having anything to eat. Our bodies and our genes were forged in an environment of scarcity, punctuated by the occasional massive blowout.
These days, of course, things are very different. We eat all the time. Fasting—the voluntary abstaining from eating food—is seen as a rather eccentric, not to mention unhealthy, thing to do. Most of us expect to eat at least three meals a day and have substantial snacks in between. In between the meals and the snacks, we also graze: a milky cappuccino here, the odd cookie there, or maybe a smoothie because it’s “healthier.”
Once upon a time, parents told their children, “Don’t eat between meals.” Those times are long gone. Recent research in the United States, which compared the eating habits of 28,000 children and 36,000 adults over the last thirty years, found that the amount of time between what the researchers coyly described as “eating occasions” has fallen by an average of an hour. In other words, over the last few decades the amount of time we spend “not eating” has dropped dramatically.1 In the 1970s, adults would go about four and a half hours without eating, while children would be expected to last about four hours between meals. Now it’s down to three and a half hours for adults and three hours for children, and that doesn’t include all the drinks and nibbles.
The idea that eating little and often is a “good thing” has been driven partly by snack manufacturers and faddish diet books, but it has also had support from the medical establishment. Their argument is that it is better to eat lots of small meals because that way we are less likely to get hungry and gorge on high-fat junk. I can appreciate the argument, and there have been some studies that suggest there are health benefits to eating small meals regularly, as long as you don’t simply end up eating more. Unfortunately, in the real world that’s exactly what happens.
In the study I quoted above, the authors found that compared to thirty years ago, we not only eat around 180 calories a day more in snacks—much of it in the form of milky drinks, smoothies, carbonated beverages—but we also eat more when it comes to our regular meals, up by an average of 120 calories a day. In other words, snacking doesn’t mean that we eat less at mealtimes; it just whets the appetite.
Do you need to eat lots of small meals to keep your metabolic rate high?
One of the other supposed benefits of eating lots of small meals is that it will increase your metabolic rate and help you lose weight. But is it true?
In a recent study, researchers at the Institute for Clinical and Experimental Medicine in Prague decided to test this idea by feeding two groups of type 2 diabetics meals with the same number of calories, but taken as either two or six meals a day.2
Both groups ate 1,700 calories a day. The “two meals a day group” ate their first meal between 6:00 a.m. and 10:00 a.m. and their next meal between noon and 4:00 p.m. The “snackers” ate their 1,700 calories as 6 meals, spread out at regular intervals throughout the day. Despite eating the same number of calories, the “two meal a day” group lost, on average, 3 pounds more than the snackers and about 11/2 inches more around their waists.
Contrary to what you might expect, the volunteers eating their calories spread out as 6 meals a day felt less satisfied and hungrier than those sticking to the two meals. The lead scientist, Dr. Kahleova, believes cutting down to two meals a day could also help people without diabetes who are trying to lose weight.
So, simply cutting out snacks and one meal a day could be an effective weight-loss strategy. Yet eating throughout the day is now so normal, so much the expected thing to do, that it is almost shocking to suggest there is value in doing the absolute opposite. When I first started deliberately cutting back my calories two days a week, I discovered some unexpected things about myself, my beliefs, and my attitudes to food.
I discovered that I often eat when I don’t need to. I do it because the food is there, because I am afraid that I will get hungry later, or simply from habit.
I assumed that when you get hungry, it builds and builds until it becomes intolerable, and so you bury your face in a vat of ice cream. I found instead that hunger passes, and once you have been really hungry, you no longer fear it.
I thought that fasting would make me distractible, unable to concentrate. What I’ve discovered is that it sharpens my senses and my brain.
I wondered if I would feel faint for much of the time. It turns out the body is incredibly adaptable, and many athletes I’ve spoken to advocate training while fasting.
I feared it would be incredibly hard to do. It isn’t.
Why I Got Started
Although most of the great religions advocate fasting (the Sikhs are an exception, although they do allow fasting for medical reasons), I have always assumed that this was principally a way of testing yourself and your faith. I could see potential spiritual benefits, but I was deeply skeptical about the physical benefits.
I have also had a number of body-conscious friends who, down the years, have tried to get me to fast, but I could never accept their explanation that the reason for doing so was “to rest the liver” or “to remove the toxins.” Neither explanation made any sense to a medically trained skeptic like me. I remember one friend telling me that after a couple of weeks of fasting, his urine had turned black, proof that the toxins were leaving. I saw it as proof that he was an ignorant hippie and that whatever was going on inside his body as a result of fasting was extremely damaging.
As I wrote earlier, what convinced me to try fasting was a combination of my own personal circumstances—in my midfifties, with high blood sugar, slightly overweight—and the emerging scientific evidence, which I list below.
That Which Does Not Kill Us Makes Us Stronger
There were a number of researchers who inspired me in different ways, but one who stands out is Dr. Mark Mattson of the National Institute on Aging in Bethesda, Maryland. A few years ago he wrote an article with Edward Calabrese in New Scientist magazine. Entitled “When a little poison is good for you,”3 it really made me sit up and think.
“A little poison is good for you” is a colorful way of describing the theory of hormesis—the idea that when a human, or indeed any other creature, is exposed to a stress or toxin, it can toughen them up. Hormesis is not just a variant of “join the army and it will make a man of you”; it is now a well-accepted biological explanation of how things operate at the cellular level.
Take, for example, something as simple as exercise. When you run or pump iron, what you are actually doing is damaging your muscles, causing small tears and rips. If you don’t completely overdo it, then your body responds by doing repairs, making the muscles stronger in the process.
Thinking or having to make decisions can also be stressful, yet there is good evidence that challenging yourself intellectually is good for your brain, and the reason it is good is because it produces changes in brain cells that are similar to the changes you see in muscle cells after exercise. The right sort of stress keeps us younger and smarter.
Vegetables are another example of the power of hormesis. We all know that we should eat lots of fruits and vegetables because they are chock full of antioxidants—and antioxidants are great because they mop up the dangerous free radicals that roam our bodies doing harm.
The trouble with this widely accepted explanation of how fruit and vegetables “work” is that it is almost certainly wrong, or at least incomplete. The levels of antioxidants in fruits and vegetables are far too low to have the profound effects they clearly do. In addition, the attempts to extract antioxidants from plants and then give them to us in a concentrated form as a health-inducing supplement have been unconvincing when tested in long-term trials. Beta carotene, when you get it in the form of a carrot, is undoubtedly good for you. When beta carotene was taken out of the carrot and given as a supplement to patients with cancer, it actually seemed to make them worse.
If we look through the prism of hormesis at the way vegetables work in our bodies, we can see that the reasons for their benefits are quite different.
Consider this apparent paradox: Bitterness is often associated in the wild with poison, something to be avoided. Plants produce a huge range of so-called phytochemicals, and some of them act as natural pesticides to keep mammals like us from eating them. The fact that they taste bitter is a clear warning signal: “keep away.” So there are good evolutionary reasons why we should dislike and avoid bitter-tasting foods. Yet some of the vegetables that are particularly good for us, such as cabbage, cauliflower, broccoli, and other members of the genus Brassica, are so bitter that even as adults many of us struggle to love them.
The resolution to this paradox is that these vegetables taste bitter because they contain chemicals that are potentially poisonous. The reason they don’t harm us is that these chemicals exist in vegetables at low doses that are not toxic. Instead they activate stress responses and switch on genes that protect and repair.
Once you start looking at the world in this way, you realize that many activities we initially find stressful—eating bitter vegetables, going for a run, intermittent fasting—are far from harmful. The challenge itself seems to be part of the benefit. The fact that prolonged starvation is clearly very bad for you does not imply that short periods of intermittent fasting must be a little bit bad for you. In fact the reverse is true.
This point was vividly made to me by Dr. Valter Longo, director of the University of Southern California’s Longevity Institute. His research is mainly into the study of why we age, particularly concerning approaches that reduce the risk of developing age-related diseases such as cancer and diabetes.
I went to see Valter, not just because he is a world expert, but also because he had kindly agreed to act as my fasting mentor and buddy, to help inspire and guide me through my first experience of fasting.
Valter has not only been studying fasting for many years, he is also a keen adherent of it. He lives by his research and thrives on the sort of low-protein, high-vegetable diet that his grandparents enjoy in southern Italy. Perhaps not coincidentally, his grandparents live in a part of Italy that has an extraordinarily high concentration of long-lived people.
As well as following a fairly strict diet, Valter skips lunch to keep his weight down. Beyond this, once every six months or so he does a prolonged fast that lasts several days. Tall, slim, energetic, and Italian, he is an inspiring poster boy for would-be fasters.
The main reason he is so enthusiastic about fasting is that his research, and that of others, has demonstrated the extraordinary range of measurable health benefits you get from doing it. Going without food for even quite short periods of time switches on a number of so-called repair genes, which, as he explained, can confer long-term benefits. “There is a lot of initial evidence to suggest that temporary periodic fasting can induce long-lasting changes that can be beneficial against aging and diseases,” he told me. “You take a person, you fast them, after twenty-four hours everything is revolutionized. And even if you took a cocktail of drugs, very potent drugs, you will never even get close to what fasting does. The beauty of fasting is that it’s all coordinated.”
Fasting and Longevity
Most of the early long-term studies on the benefits of fasting were done on rodents. They gave us important insights into the molecular mechanisms that underpin fasting.
In one early study from 1945, mice were fasted for either one day in four, one day in three, or one day in two. The researchers found that the fasted mice lived longer than a control group, and that the more they fasted, the longer they lived. They also found that unlike calorie-restricted mice, the fasted mice were not physically stunted.4
Since then, numerous studies have confirmed, at least in rodents, the value of fasting. Not only does fasting extend their lifespan, but it also increases their “healthspan,” the amount of time they live without chronic age-related diseases. Postmortems on rodents that have been calorie restricted show they have far fewer signs of cancer, heart disease, or neurodegeneration.
A recent article in the prestigious science journal Nature points to the wealth of research on the benefits of fasting, while at the same time noting sadly that so far “these insights have made hardly a dent in human medicine.”5 But why does fasting help? What is the mechanism?
Valter has access to his own supply of genetically engineered mice known as dwarf or Laron mice, which he was keen to show me. These mice, though small, hold the record for longevity extension in a mammal. In other words, they live for an astonishingly long time.
The average mouse doesn’t live that long, perhaps two years. Laron mice live nearly twice that, many for almost four years when they are also calorie restricted. In a human, that would be the equivalent of reaching almost 170.
The fascinating thing about Laron mice is not just how long they live, but that they stay healthy for most of their very long lives. They simply don’t seem to be prone to diabetes or cancer, and when they die, more often than not it is of natural causes. Valter told me that during an autopsy, it is often impossible to find a cause of death. The mice just seem to drop dead.
The reason these mice are so small and so long-lived is that they are genetically engineered so that their bodies do not respond to a hormone called IGF-1, insulin-like growth factor 1. IGF-1, as its name implies, has growth-promoting effects on almost every cell in the body. In other words, it keeps your cells constantly active. You need adequate levels of IGF-1 and other growth factors when you are young and growing, but high levels later in life appear to lead to accelerated aging and cancer. As Valter puts it, it’s like driving along with your foot flat down on the accelerator pedal, pushing the car to continue to perform all the time. “Imagine, instead of occasionally taking your car to the garage and changing parts and pieces, you simply kept on driving it and driving it and driving it. Well, the car, of course, is going to break down.”
Valter’s work is focused on trying to figure out how you can go on driving as much as possible, and as fast as possible, while enjoying life. He thinks the answer is periodic fasting. Because one of the ways fasting works is by making your body reduce the amount of IGF-1 it produces.
The evidence that IGF-1 plays a key role in many of the diseases of aging comes not just from engineered rodents like the Laron mice, but als...
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