LIFE IN THE FAST LANE

Fasting has transitioned from science-journal fodder to mainstream slimming tool. As it escalates among the health-conscious, we ask if the research stacks up, or is intermittent fasting simply starvation rebranded?

Intermittent fasting: recipe for health or disaster?

We suspect you first heard about fasting from that one friend who discovers and trials all new health trends just before they reach peak take-up, no doubt over a late dinner at a restaurant with counter seating 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.

Since 5:2 came into our lives in 2012, intermittent fasting – the concept of shunning calories for hours or days at a time – has been touted as a way to reduce your 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 500 calories two days a week) and the 16:8 (eating all your day’s food within an eighthour 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 we first learnt about in 2015, but is now garnering mainstream interest as fasting rises in popularity, is a fiveday programme 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 calorie-controlled, scientifically developed diet. But it doesn’t come cheap – it’s £225 for the five-day kit, devised by Dr Longo and sold nationwide by a company called Prolon.

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 the product of scientific developments – or is the diet industry having the last laugh?

RUN 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 calories 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, too.

A short period of severe calorie-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 Dr Longo insists you bear with. 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 water-only diet – something no dietitian would recommend without close monitoring. In this way, Dr Longo’s fast offers a system clean-up that promises to torch fat while also boosting general cellular health and getting nutrients via the food.

HUMAN NATURE

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 quickly replaced with new ones.

But you’re not a mouse. In humans, studies comparing short-term fasts – the likes of 5:2 and 16:8 – with calorie-controlled diets consistently suggest they are 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 Dr Longo’s lab showed findings of a 3% average body fat reduction, lowered blood glucose and lower levels of inflammatory markers. But the evidence for autophagy was circumstantial at best.

Dr 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 both fasting and getting your sweat on put 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 that many people boast of during a fast and, indeed, after exercise.

NIL BY MOUTH

Should you have confessed to friends a few years ago that you were starving yourself, 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 Dr 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.

And even controlled fasts can induce an emotional fallout.

YOUR BODY HAS NO OPTION BUT TO START BURNING FAT

Deprivation studies have consistently found that drastically culling calories can lead to an unhealthy relationship with food. As Duane Mellor, senior lecturer in human nutrition at Coventry University, points out, you only have to look at the gluttonous attitude of some 5:2 dieters on non-fast days to understand how fasting can affect your eating. ‘If you haven’t got your calorie intake under control when you’re not fasting, you could be vulnerable to a binge pattern,’ he says.

OFF YOUR FOOD

So should we be falling for the hype? Epidemiologist Dr Benjamin Horne, who conducted a recent review of 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 know the risks – fainting, dehydration, and malnutrition. ‘No study that 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, diabetics, pregnant and breastfeeding women and anyone with a BMI under 18.5

– if your goal is to burn fat, then studies suggest following a short-term fast can be effective. As for the longevity-boosting potential of the FMD, more research is needed. The only thing that’s really clear about fasting is that its benefits – and results – are subjective. Yes, it can be safe, but that doesn’t mean it’s the healthiest option. Try it, by all means, but also ask yourself if your efforts wouldn’t be better spent on another Bdnf-booster – a gym pass.