5 2 Diet Scientific Research Paper

The body is a temple. In January, for the most part, it is a rather large and overfed temple. This year, under the pressure of constant lifestyle and dietary advice, I decided on a remedy: the intermittent fasting diet.

The regime, which instructs dieters to feast for five days a week and fast for the remaining two, originally took the States by storm in 2013. It has gradually crept over the pond, with numerous bestselling books (The Fast Diet: Lose Weight, Stay Healthy, Live Longer and The Fast Diet Recipe Book) and celebrity adherents (Benedict Cumberbatch). In fact, it’s not just contemporary ‘celebs’ who are singing its praises: Plato once said ‘I fast for greater physical and mental efficiency’; Aristotle was said to be a faster, too. Martin Luther announced: ‘It is right to fast frequently in order to subdue and control the body.’

So what is it? The diet — more commonly known as the 5:2 diet — dictates that you only need acknowledge it twice a week. On these ‘fasting days’, dieters are advised to consume 25 per cent of the recommended daily calorie intake (that’s 500 calories a day for women, and 600 for men). The 5:2 was originally championed by TV medic Dr Michael Mosley and journalist Mimi Spencer.

There are, famously, two golden rules of dieting: never crash diet and never skip meals. Yet the 5:2 seemingly encourages the former, and, it would seem, does not reject the latter. A website claims that ‘it’s easy to comply with a regime that only asks you to restrict your calorie intake occasionally. It recalibrates the diet equation, and stacks the odds in your favour’. So far, so easy.

Five hundred calories a day seems shockingly restrictive, yet Mosley and Spencer’s book suggests it is easily possible to divide such a meagre allowance into three meals. Combinations include a breakfast of two Ryvitas spread with two teaspoons of Marmite, a ready-made vegetable soup for lunch, and a supper of a small steak or fish fillet with mixed leaves. Dieters are encouraged to split their ‘fast days’; black coffee, Diet Coke, green tea and water (go crazy) are all allowed.

Little is known about the long-term effects of intermittent fasting (IF). The NHS guidelines state that ‘despite its increasing popularity, there is a great deal of uncertainty about IF with significant gaps in the evidence,’ and that possible side effects include difficulty sleeping (it’s true — I woke up regularly with severe hunger pains), bad breath (quite likely), irritability (the most prominent), anxiety, dehydration (thank goodness for the water allowance) and daytime sleepiness.

So far, so unappealing. Yet there is evidence to support intermittent fasting — we don’t have to take Plato’s word for it. A study in 2010 found that intermittent fasters experienced reductions in a number of biological indicators that suggest a diminished risk of developing chronic diseases such as type-2 diabetes. Two years later, a similar investigation produced evidence that the 5:2 diet may help lower the risk of certain obesity-related cancers such as breast cancer.

The science behind intermittent fasting is simple: if you don’t consume enough energy, your body burns off your fat reserves. The more complex explanation is that regular intermittent fasting activates a gene called SIRT1, more commonly known as the ‘skinny gene’, which repairs cells during times of scarcity of nutrients. The average intermittent faster loses one pound a week.

The 5:2 diet does, in truth, totally enervate its disciples. Restricting oneself to 500 calories a day is not easy — despite promises of three meals, it was preferable to stick to sushi for lunch and a bowl of baked beans for supper, washed down with endless glasses of tap water. I found myself eschewing all humans, all conversation, and any thought process that didn’t involve food, so obsessed did I become with the following day when I could eat normally again. Counting calories leaves one morose and forlorn. Life’s great pleasures are suddenly stripped away. But, lo, the weight fell off. Two days of pain began to seem like a reasonable sacrifice — particularly when one considers alternative restrictive options that dominate every day of the week.

I’m not quite in Plato’s league yet — but I certainly felt better after the Christmas slump.


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Many diet and exercise trends have origins in legitimate science, though the facts tend to get distorted by the time they achieve mainstream popularity. Benefits are exaggerated. Risks are downplayed. Science takes a back seat to marketing.

One needn’t look any further than the emerging trend of intermittent fasting for a prime example. Advocates for taking periodic breaks from eating — for up to 24 hours once or twice a week — tout it as an effective and research-backed means of losing weight and improving health. That message has been reaching more and more ears of late.

“Right now, we are at a really important juncture for fasting,” says Brad Pilon, an expert on intermittent fasting and author of the book Eat Stop Eat. “It’s becoming extremely popular.”

So popular, in fact, that it is quickly moving into fad territory, suggests Pilon. And when something becomes a fad — intensely popular but only for a short period — several problems typically ensue. For one, he says, many doctors and nutrition experts are prone to dismissing fads out of hand. So their patients and clients, while shielded from the ridiculous claims of overzealous dieting evangelists, may also lose out on the legitimate benefits of fasting done right. You know, the baby and bathwater thing.

Another concern is that promoters of intermittent fasting will, perhaps unintentionally, encourage extreme behaviour, such as bingeing. This is reflected in the photos accompanying many recent new articles on “the fast diet” or the “5:2 diet.” Often, they depict people eating heaps of high-calorie, high-fat foods, such as hamburgers, french fries and cake. The implication being that if you fast two days a week, you can devour as much junk as your gullet can swallow during the remaining five days.

There is a large body of evidence that suggests fasting can benefit both the body and brain, but most research has been conducted on animals, such as mice. Researchers studying fasting are calling for more human studies.

Image courtesy of © 2013 Thinkstock

Not so, say more moderate proponents of fasting. Their take on intermittent fasting: eat sensibly most of the time, eat nothing for an extended period every now and then, indulge only on occasion (perhaps once a week, say, on a designated “cheat day”). There is research, they claim, to back up the health benefits of sensibly incorporating fasting into your lifestyle.

There is indeed a large body of research to support the health benefits of fasting, though most of it has been conducted on animals, not humans. Still, the results have been promising. Fasting has been shown to improve biomarkers of disease, reduce oxidative stress and preserve learning and memory functioning, according to Mark Mattson, senior investigator for the National Institute on Aging, part of the US National Institutes of Health. Mattson has investigated the health benefits of intermittent fasting on the cardiovascular system and brain in rodents, and has called for “well-controlled human studies” in people “across a range of body mass indexes” (J Nutr Biochem 2005;16:129–37).

There are several theories about why fasting provides physiological benefits, says Mattson. “The one that we’ve studied a lot, and designed experiments to test, is the hypothesis that during the fasting period, cells are under a mild stress,” he says. “And they respond to the stress adaptively by enhancing their ability to cope with stress and, maybe, to resist disease.”

Though the word “stress” is often used in a negative sense, taxing the body and mind has benefits. Consider vigorous exercise, which stresses, in particular, muscles and the cardiovascular system. As long as you give your body time to recover, it will grow stronger. “There is considerable similarity between how cells respond to the stress of exercise and how cells respond to intermittent fasting,” says Mattson.

Mattson has contributed to several other studies on intermittent fasting and caloric restriction. In one, overweight adults with moderate asthma consumed only 20% of their normal calorie intake on alternate days (Free Radical Bio Med 2007;42:665–74). Participants who adhered to the diet lost 8% of their initial body weight over eight weeks. They also saw a decrease in markers of oxidative stress and inflammation, and improvement of asthma-related symptoms and several quality-of-life indicators.

In another study, Mattson and colleagues explored the effects of intermittent and continuous energy restriction on weight loss and various biomarkers (for conditions including breast cancer, diabetes and cardiovascular disease) among young overweight woman (Int J Obesity 2011;35:714–27). They found that intermittent restriction was as effective as continuous restriction for improving weight loss, insulin sensitivity and other health biomarkers.

Mattson has also researched the protective benefits of fasting to neurons. If you don’t eat for 10–16 hours, your body will go to its fat stores for energy, and fatty acids called ketones will be released into the bloodstream. This has been shown to protect memory and learning functionality, says Mattson, as well as slow disease processes in the brain.

But perhaps it isn’t so much the fasting that produces health benefits, per se, as the resulting overall reduction in calorie intake (if, that is, you don’t overeat on nonfasting days, which could create a caloric surplus instead of a deficit). That appears, at least, to be the case in slowing diseases such as cancer in mice, according to Dr. Stephen Freedland, associate professor of urology and pathology at the Duke University Medical Center in Durham, North Carolina.

“Caloric restriction, undernutrition without malnutrition, is the only experimental approach consistently shown to prolong survival in animal models,” Freedland and colleagues stated in a study on the effects of intermittent fasting on prostate cancer growth in mice (Prostate Cancer Prostatic Dis 2010; 13:350–5). In the study, mice fasted twice a week for 24 hours, but were otherwise permitted to eat at liberty. During nonfasting days, the mice overate. Overall, they did not lose weight, counteracting whatever benefits they might have seen from fasting. Intermittent fasting with compensatory overeating “did not improve mouse survival nor did it delay prostrate tumor growth,” the study concluded.

To improve health, the goal should be to lose weight by reducing the total amount of calories consumed, suggests Freedland, rather than focusing on when those calories are consumed. “If you [don’t] eat two days a week, and limit what you eat the other five days, you will lose weight. It’s one approach to losing weight,” he says. “I’m not sure it works any better than cutting down slightly seven days a week.”

People should also be wary of books written for broad audiences that explain the science behind fasting or any other health trend, he says. One purpose of writing a book for the consumer market, after all, is to sell as many copies as possible. Authors tend to present only evidence supporting their point of view, suggests Freedland, while ignoring evidence that contradicts it. “It’s a lot of spin when you write a book.”

Editor’s note: This is a follow-up to a previous news story at cmaj.ca: “Intermittent fasting: the next big weight loss fad.”

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