Fast track to health
It generates major buzz. But does the research on intermittent fasting stack up, or is it simply starvation rebranded? Read on...
Are fasting diets like the 5:2 all they’re cracked up to be? We get the lowdown
WWe suspect you first heard about fasting from that one friend who never fails to jump on the latest health trend just before it hits peak take-up, no doubt over a late Japenese fusion dinner where she eschewed food in favour of regaling you with the science behind eating intermittently. She’s done the 5:2, tried the 16:8 (“it’s the same science, just easier to follow!”) and is currently evangelising about the five-days-every-three-months fasting mimicking diet. Yep, we’ve been there!
Since 5:2 came into our lives in 2012, intermittent fasting – the concept of shunning kilojoules for hours or days at a time – has been touted as a magical way to reduce the risk of heart disease, diabetes and cancer, while melting belly fat and offering your digestive system a reboot. The premises of the 5:2 (cutting back to 2100kj two days a week) and the 16:8 (eating all your day’s food within an eight-hour window) are basically the same. When you give your body a break from eating, it begins feeding off your fat reserves.
Another iteration, the fasting mimicking diet (FMD) – which first hit headlines in 2015 but is now garnering mainstream interest as fasting rises in popularity – is a fiveday program based on the research of Dr Valter Longo, a biologist at the University of Southern California.
It’s designed to make your body think all it’s being fed is water, while keeping actual starvation at bay via a kilojoule-controlled, scientifically developed diet. But it doesn’t come cheap: it costs $400 to buy the five-day kit devised by Dr Longo and sold as Prolon in the US.
Hang on a minute. Depriving yourself of food goes against all your instincts, not to mention the dietary advice we’re always hearing. So, is this latest nutrition trend really the product of scientific developments – or is the diet industry having the last laugh?
Running on empty
The science is fairly simple. When you put yourself on the 5:2 or the 16:8, you starve your body of the energy it usually gets from food, which forces it to seek its fuel internally. First, you’ll utilise the sugar in your bloodstream. When that’s gone, it’s time to tap into the liver’s glycogen stores. After a day or so of eating fewer kilojoules than your body needs, these too will run out, so your body has no option but to start burning fat.
But proponents of the FMD insist that when you fast for longer than a day or two, the benefits go beyond weight loss. Yes, the five-day plan pushes your body into ketosis – the metabolic state in which the body burns fat for energy, made famous by the Atkins diet (and keto breath) – but something else is going on.
A short period of severe kilojoule deprivation forces the body to save as much energy as possible by beginning to break down and digest its own cells, a process called autophagy. Sounds scary, but Longo insists you bear with it. The body is intelligent enough to start with dead or damaged cells that aren’t worth the energy to sustain – the ones that contribute to ageing and are more likely to turn cancerous. In other words, the body becomes healthier, seemingly younger and at less risk of disease. Until the FMD came along, the only way to trigger autophagy was to go on a wateronly diet – something no dietitian would recommend without close monitoring. In this way, Longo’s fast offers a system clean-up that promises to torch fat while also boosting general cellular health and delivering nutrients via the food.
One important thing to know? Most of the studies that sell fasting as a nutritional win point to results found in mice. Periodic fasting of rodents in a lab setting reduced fat, increased lifespan and cut incidences of cancer and inflammation – linked to everything from heart disease to depression. And where some of the mice’s cells were lost to autophagy in the organs, muscles and bones, they were replaced with new ones.
But you’re not a mouse. In humans, studies comparing short-term fasts – such as 5:2 and 16:8 – with kilojoule-controlled diets consistently suggest they’re no more effective at shifting weight and improving metabolic markers than any other kind of diet. And when it comes to the protective impact of periods of prolonged fasting, the evidence is limited. A recent pilot trial of the FMD on humans in Longo’s lab showed findings of a 3 per cent average body fat reduction, lowered blood glucose and lower levels of inflammatory markers.
But the evidence for autophagy was circumstantial at best.
Longo insists that even healthy people could benefit from a periodic fast. The scientist whose research led to the development of the 5:2 diet is unconvinced. “We have no evidence of benefits for people who are a healthy weight,” says Dr Michelle Harvie, a researcher at the University of Manchester, who first looked into fasting as a way to help women at risk of breast cancer to lose weight. “All the evidence is for weight loss among the overweight.” As for the promise of longevity, we’ll just have to wait and see.
Others point out that fasting isn’t the only way to lure your body into a replenishing state. The alternative
is called exercise, and the theory goes that, just like fasting, getting your sweat on puts the body into a state of mild stress, stimulating it to repair itself. It also gives the brain a boost by triggering the release of a chemical called brain-derived neurotrophic factor (BDNF), which increases the brain’s tendency to make new neurons and create and maintain connections. This might account for the clear head many people boast of during a fast and after a good old sweat session.
Nil by mouth?
If you’d confessed to starving yourself a few years ago, you’d have been met with concern. Today, replace the word ‘starve’ with ‘fast’ and you’re more likely to be met with a knowing smile. But do the two mean the same thing? Yes, according to Longo – and that’s the point. In order for fasting to trigger a system reboot, the body needs to think that it’s starving. “Your body tips over into starvation quite quickly – but that’s a good thing,” he explains. “After a couple of days, it starts killing off cells.” All very well if you’re doing it in a controlled way, like the FMD, but take it too far and it can prove fatal – people have died from doing water-only fasts.
Fasting can also induce an emotional fallout, leading to an unhealthy relationship with food. “This can happen to people who already have a pattern of disordered eating,” says Dr Helena Popovic, an MD specialising in the application of neuroscience to weight management. “If you’ve been a binge eater or chronic dieter, you’re going back to the ‘I just have to hold out’ [mentality] then, when you’re allowed to eat, you overdo it. These people may find that intermittent fasting triggers binge-eating circuits in their brain that might have been dormant for a while.
“I definitely support fasting in whatever way a person wants, as long as they’re the right person for it,” Popovic adds. “We’re all individuals. Fasting works really well for some, and not so well for others in terms of their psychological approach to it.”
Fact versus fiction
The final word? Epidemiologist Dr Benjamin Horne, who recently reviewed the evidence, found that fasting is generally safe when done every other day for a year, or five days in succession once a month. But it’s important to be across the risks: fainting, dehydration and malnutrition. “No study I know of has given us information regarding the threshold for malnutrition, which likely depends on the individual,” he says. And with no research comparing different fasting methods in humans, it’s hard to know which works best. While it’s accepted that there are people who shouldn’t fast – children, pregnant and breastfeeding women and anyone with a BMI under 18.5 – if your goal is to burn fat, then studies suggest a short-term fast can work.
Speaking of short term, Popovic says an overnight fast is really all you need. “If every person on the planet left at least 12 hours between dinner and breakfast, that would lead to huge improvements in health and longevity, gut health, and would lower the risk of obesity,” she says.
As for longevity-boosting, more research is needed. Clearly, fasting’s benefits are subjective. It can be safe, but it may not be the healthiest option. Perhaps ask if your efforts would be better spent on another Bdnf-booster: a gym pass.
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