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Fitness & Health

26th May 2016

How this fasting diet burns fat, cuts weight and boosts your brain power

Ben Kenyon

Food is everywhere these days.

You can get 24-hour McDonald’s, Burger King delivers, supermarkets are open around the clock, and there’s an all-you-can-eat joint in every town.

TV and the internet is saturated with food porn that makes us want to stuff our faces with sticky, chocolatey junk. What a time to be alive!

Although it’s no wonder one in four of us in the UK is now overweight or obese.

But there’s one thing that’s making a quiet comeback – it’s the lost art of fasting.

Going without food is as old as time – and millions of Muslims, Christians, Hindus and Buddhists regularly fast for religious reasons.

Even when you go without food overnight between eight and 12 hours, you’re considered in a ‘fasted state’ (that’s why cardio in the morning before you eat is so effective at burning fat).

But adding a regular period of ‘fasting’ into your daily or weekly diet can bring some truly incredible benefits to your body, brain and general health.


Hormone changes

When you stop eating for a period, hormones in your body are quick to react. With no food in the system, insulin levels drop and this makes your body more likely to tap into fat reserves.

Over time this can make your body more sensitive to insulin – so better able to deal with glucose (sugar) and less likely to develop metabolic diseases like diabetes.

When your calories are cut your body also releases more growth hormone in the blood, according to Authority Nutrition. Studies say GH levels can increase up to five fold. The hormone helps burn fat and build muscle.

Prolonged fasting was found to reduce an enzyme called PKA, which is linked to ageing, and a hormone which increases cancer risk and tumour growth in a University of Southern California study.


Lose weight and fat

Obviously eating fewer calories means you’re going to lose some weight – certainly in the short term. Although just cutting your calories drastically and keeping them low over weeks and weeks will slow your metabolism down and increase your hunger, and you’ll more than likely put more fat back on.

But with intermittent fasting it’s a double-edged sword. On one side you’re reducing the amount of meals you have during the day – so more than likely reducing your overall calorific intake.

Interestingly, fasting also gives a short-term boost to your metabolism – meaning the amount of calories your body burns off increases.

This study showed that weight loss could be anywhere between 3 to 8 percent up to 24 weeks.

Dangerous ‘visceral fat’ – the kind you get on your belly that forms around your organs – is also reduced.


Cell repair

When you go for a period without eating, something incredible happens. Your cells start to repair and regenerate themselves.

One thing that happens is waste is removed from cells and some damaged cells are replaced in order to save energy. It literally switches on your DNA repair genes.

But the University of Southern California found recently that fasting for just three days could completely reboot your immune system, kick starting stem cells into producing new white blood cells which fight off infection.

This could have profound benefits for the elderly and cancer patients.


Good for brain

As we get older our bodies age, but so does our brain. The world is on the precipice of an epidemic in dementia – with 1 million people in the UK projected to suffer from such incurable brain conditions by 2021, the most common of which is Alzheimer’s.

But fasting just two days a week is shown to improve cognitive function. A study in Cell Metabolism on fasted mice showed that the animals retained more of their mental acuity, beating control mice in different memory tests, according to Science Mag.

There is some research it can help humans too. This fascinating TED Talk looks deeper at how reducing energy intake can help reduce brain conditions like Alzheimer’s, Parkinson’s, and other neurodegenerative diseases.

One thing is when your body starts burning fat during fasting, you produce ‘ketone bodies’ which is an alternative source of energy your that fuels the brain more efficiently than glucose.

Fasting also has an effect on the brain similar to the impact of resistance training on the muscles – it causes a stress response that increases the number of mitochondria in neurons which mean more energy can be produced.

Puzzled man thinking looking up at junk food and green vegetables shaped as light bulbs making decision isolated on gray background. Diet choice right nutrition healthy lifestyle wellness concept

Live longer

Restricting calories every day is proven to prolong life in all sorts of different organisms from yeast and worms, to mice and monkeys, according to Science Based Medicine.

Scientists have evidence that intermittent fasting (with 40 per cent calorie deficit) can forestall and even reverse cancer, cardiovascular disease, diabetes, and neurodegenerative disorders in mice.

A study in Cell Metabolism on rodents saw the fasted mice live an average of three months longer (this is significant) while shedding fat and being 45 per cent less likely to develop cancer.

Scientific evidence in humans is limited, but there is research to suggest calorie restriction can help to lower obesity, hypertension, asthma, and rheumatoid arthritis

Evening jogging walk with a dog silhouettes

So, how do you fast?

There are many different kinds of fasts you can do, according to Dr Mark Mattson, who is a professor of neuroscience at Johns Hopkins University.

There are long fasts, with water only, that can include two full days fasting per month, or even two full weeks fasting once a year.

Or there are shorter ‘intermittent fasts’ which seem easier to handle for us 21st century creatures – such as fasting every other day or two days a week on (The 5:2 Diet) on 500-600 calories only. The rest of the five days you can eat normally.

Some people even do just between 16 and 20 hours fasting over the course of a day (so just eating in a 4-8 hour window) to get the health benefits.


The best foods to eat on your calorie-restricted days are foods high in protein and fibre, that keep you fuller for longer – so meat, fish and green vegetables.

You can still drink water, coffee and tea or anything with no calories – but avoid calorie-dense food, sugars and junk food.

You can still exercise while fasting, and there’s evidence you burn more fat in a fasted state. There’s a full list of information here on how to get started.

You can watch this fascinating documentary by British scientist and TV personality Dr Michael Moseley on the BBC called Eat, Fast and Live Longer…