19th June 2020

What’s So Good About Intermittent Fasting?

What is intermittent fasting?

Fasting normally means going without any food for a period of time, but intermittent fasting (IF) is a new, easier to stick to form where you stop eating for a part of each day, or restrict your calorie intake for a few days each week.

Two methods of IF are incorporated into The Fast 800 programme: a 5:2 system where you restrict your calorie intake to 800 calories on two days a week, and eat a healthy diet on the other five days; and Time Restricted Eating (TRE) which encourages you to extend your normal night time ‘fast’ by eating an early supper, or skipping breakfast, to condense your eating period into an eight, ten or 12-hour window.

Does it mean going hungry?

No. Many people think fasting means nothing but water, but new studies1 show you can achieve all the health and rapid weight loss benefits on an 800 calorie fast – 800 is the magic number when it comes to ensuring you can eat enough to get the nutrients you need and to feel satisfied, but to put your body into ‘fasting’ mode. Studies also show health benefits by simply extending your night-time fast each day.2

How does IF work?

These days food is freely available 24/7 and we have developed a habit of grazing all day – eating between meals and late into the evening. This means the digestive process never stops – or only briefly while we sleep – and your body is forced to work continually to process the nutrients and toxins in your food, with little break. However, if you stop eating, or drastically cut back the amount you eat and/or the window in which you eat, your body gets a chance to rest and repair as it should – and this allows your body and brain to have the ‘down time’ it needs. It is only when we are not eating or drinking that our bodies can be freed up to begin the process of repair.

The health benefits of Intermittent Fasting

1.  IF burns fat

We all use two different types of fuel to function:  glucose and fat. If you eat and snack and eat continually throughout the day, your body gets a continual source of glucose from food to fuel your muscles. Any excess (if you eat more calories than you burn off through exercise) is then stored as fat. However, when you spend some time fasting, the glucose supply temporarily runs out, and your body has to switch to taking fat from your fat stores to burn as fuel. Scientists call this fuel transfer ‘flipping the metabolic switch’.

Flipping the metabolic switch’ is a bit like a hybrid car flipping from using electricity to using petrol when the battery begins to run low, and it is great news if you want to lose weight, and particularly fat.

This has significant implications for our health if it means we are losing the metabolically active (and therefore dangerous) ‘visceral fat’ which lurks in and around the abdomen. This fat is associated with high cholesterol and high blood sugar levels.3

2.  IF reduces your diabetes risk

We now know that type 2 diabetes occurs when we tip over what diabetes expert, Professor Roy Taylor calls your ‘personal fat threshold’. Everyone is put together differently, and everyone has a tipping point, beyond which excess fat will start to impact the function of the liver and the pancreas, so affecting your ability to produce the hormone insulin. Insulin plays an essential role in converting the glucose in our blood into energy that our cells can use. Without enough insulin, your blood sugar levels rise and fat stores increase, ultimately putting you at risk of type 2 diabetes. But when you are fasting, you will be reducing the size of your fat stores, and effectively bringing yourself back from your ‘personal fat threshold’.4

3.  IF helps you live longer

 There are communities of people around the world who severely restrict their food intake and fast for days on end because they believe it will extend their life span. There is, indeed, evidence to suggest that fasting can help you live longer, but few of us have the willpower to starve indefinitely. Luckily IF has the same effect – you don’t have to give up eating well or starve yourself permanently to live a long and healthy life.5 Short term fasting activates a process within the body called ‘autophagy’ whereby dead, diseased or worn-out cells are broken down and gobbled up (autophagy means ‘self -eat’) to make way for the shiny new cells that keep us young.

IF also appears to reduce the rate at which your body produces a chemical called ‘insulin like growth factor’ (IGF-1). Although IGF-1 plays an important role in the growth of young people, it appears to accelerate aging and cancer in later life, so the less of it you have at midlife, the better.6

4.  IF boosts your brain power

Fasting has shown to improve brain function because it boosts the production of a protein called brain-derived neurotrophic factor (BDNF) which stimulates the creation of new brain cells and new brain cell connections protecting your brain cells from the changes which might be associated with Alzheimer’s and Parkinson’s disease.7

5.  IF lifts your mood

When fat is released from your fat stores it is converted into fatty acids and ketone bodies. This process happens steadily and consistently with no up and downs, giving you steady energy levels so you feel better and our concentration levels and cognitive function is also higher. BDNF is also a natural anti-depressant, which could explain why so many people find IF surprisingly easy to stick to.

6.  IF boosts energy levels

You might expect to feel tired and lethargic if you haven’t eaten for 12 hours, or you only ate 800 calories the day before, but IF trips your body over into fat burning mode and fat is a highly efficient fuel for your body and brain. This flip makes your metabolism work more efficiently, keeping energy levels stable.

7.  IF cuts your cancer risk

We know that IF reduces insulin levels and this can be enough to reduce your risk of some common cancers, such as breast cancer.8 IF may also enhance the effects of chemotherapy should you need treatment for cancer.9 This is because fasting cleverly exploits the difference between ordinary cells and cancer cells. When you cut off their food supply, normal cells slow their activity levels, but cancer cells continue growing leaving them vulnerable to attack.

8.  IF improves heart health

By helping you lose weight and lowering your blood sugar levels IF can also improve your heart health. Studies10 show it can reduce blood pressure (down by 9% compared to 3%) and make your body more efficient at clearing fat from the blood after a fatty meal so reducing your risk of heart disease.

9.  IF aids better sleep

Healthy sleep can also be compromised by overeating during the day and into the evening, but going to bed with a relatively empty stomach enables internal clocks in your digestive system to align with the clock in your brain so all your systems agree to go offline for sleep. IF also causes levels of the sleep-promoting hormone, melatonin to rise, which can help you fall asleep faster and stay asleep longer. IF also promotes the release of human growth hormone, one of your body’s vital resources for repairs while you’re asleep.11

10.  IF bolsters immune system

IF strengthens immune function in a number of ways. The break from food offers the opportunity for effective ‘rest and repair’ which allows the body to repair cells and damaged DNA and also to deal with unhealthy systemic inflammation which weakens the immune system and acts as a major contributor to aging and disease. IF also encourages the breakdown of white blood cells and triggers stem cell-based regeneration of new immune system cells.12

Intermittent Fasting is not suitable for everyone, particularly those who are under 18, pregnant or breastfeeding or are on medication. We recommend seeking advice from your GP before beginning any diet or fitness regime.


Human trials of TRE at the University of Surrey found eating breakfast 90 minutes later than usual, and dinner 90 minutes earlier each day led to a drop in body fat and falls in blood sugar levels and cholesterol. https://www.surrey.ac.uk/news/changes-breakfast-and-dinner-timings-can-reduce-body-fat

A major study published in 2018 by Professor Roy Taylor of Newcastle University and Professor Mike Lean of Glasgow University, showed that nearly half of those people who followed an 800 calorie rapid weight loss diet not only lost a lot of weight, but by doing so were able to put their diabetes into remission and come off medication. https://www.necsu.nhs.uk/wp-content/uploads/2019/02/2018-01-DiRECTStudy.pdf

VALTER LONGO studies show short term fasting activates a process within the body called ‘autophagy’ Longo, Valter D., and Satchidananda Panda. “Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan.” Cell metabolism 23, no. 6 (2016): 1048-1059.

Studies by Mark Mattson, professor of neuroscience at the National Institute on Aging have shown that mice on an intermittent-fasting diet didn’t develop dementia until they were well into old age. https://www.sciencedaily.com/releases/2019/12/191226084351.htm

A huge US study showed women who fasted for more than 13 hours a night had 36% less chance of a breast cancer recurrence. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4982776/

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