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Are we Pulling a Fast One? What does Intermittent Fasting Really Do for our Health?

Posted on July 02 2018

Keto, Paleo, Vegan, Atkins, no-carbs, macro-counting …… there are so many different eating plans that it’s sometimes hard to know which genuinely offer health benefits. Some are, at best, a fad and some are potentially dangerous. 

There is currently a lot of enthusiasm about intermittent fasting (IF).  This describes an eating pattern which cycles between periods of eating and periods of fasting or severe calorie restriction.  IF diets include the 5:2 diet, alternate day eating, and the 16:8 plan, when individuals eat for eight hours during each 24-hour period.

I became interested in learning more about the health effects of IF when I came across an article published in Nature Reviews Cardiology, an extremely well-respected and scientifically rigorous medical journal.  The article, Interventions to promote cardiometabolic health and slow cardiovascular ageing1 (available at, gives a comprehensive overview about what we can do to lead a long and healthy life.  In addition to emphasising the importance of physical activity and reducing psychological stress, the paper also described the tremendous impact of IF and calorie restriction.

Intermittent Fasting and Meal Timing

Calorie restriction has been shown to be an incredibly powerful means of slowing ageing and reducing the risk of multiple chronic diseases in rodents1. Similarly in monkeys, reducing calorie intake by 30 per cent led to a halving of deaths due to cardiovascular disease and cancer reviewed in 1.  It also slowed the processes of age related hearing loss, brain shrinkage and loss of muscle bulk.  In human studies, calorie restriction without malnutrition has been found to result in improvements in cholesterol levels, blood sugar levels, inflammation and blood pressure reviewed in 1.

There is growing evidence that meal timing and diet quality both have a vital role in promoting cardiovascular and metabolic health.In mouse models, intermittent fasting can increase lifespan by up to 30 per cent, and it can also protect the mice from obesity, high blood pressure, diabetes, inflammation and the clinical progression of heart disease reviewed in 1.  In humans, there is data suggesting that alternate day fasting or fasting for any two non-consecutive days throughout the week can reduce body mass, fat mass, waist circumference, levels of unhealthy cholesterol in the blood and blood pressure reviewed in 1.

Diet Quality

However, it’s not just when we eat, but what we eat that is important.  I was surprised to learn that restricting protein or specific amino acids can have an effect in increasing health span and metabolic health reviewed in 1.  In mice, both restricting consumption of the amino acid methionine, and reducing the protein: carbohydrate ratio resulted in an increased lifespan of up to 30 per cent reviewed in 1.

In humans, it has been shown that limiting our consumption of saturated fatty acids from animal sources can lower the unhealthy cholesterol in our blood and reduce the risk of heart disease reviewed in 1.  An ideal approach is probably to follow a Mediterranean diet, and focus on eating food rich in fibre, vitamins and phytochemicals1, which are chemical compounds found in plants.  If we aim to eat a small amount of animal products but have a high intake of vegetables, grains, nuts, seeds, fruits and olive oil, we would achieve a diet high in antioxidants and anti-inflammatories.  This in turn could reduce our risk of heart disease1.

How does intermittent fasting work?

Intermittent fasting affects a multitude of molecular processes in our bodies.  Some of the key effects it has are to reduce the unhealthy accumulation of lipids in the blood, to prevent chronic inflammation, to reduce immune activation and to improve insulin sensitivity, which helps to reduce the risk of Type 2 diabetes.  Furthermore, intermittent fasting reduces oxidative-stress induced damage to lipids, proteins and DNA, and it reduces activation of the sympathetic nervous system.  It can also alter hormone systems and energy-sensing pathways in the body and can diminish the accumulation of substances that can interfere with normal cell function reviewed in 1.  Intermittent fasting also affects the bacteria which live in our guts -  we will look at this in another article.

A Word of Caution

If you’re thinking about trying intermittent fasting, it’s always advisable to discuss your choices with a medical professional before making any significant changes to your diet.  As with any eating plan you must always choose the option which is best suited to you as an individual.  Although intermittent fasting does seem to confer many health benefits, it may not be appropriate for everyone, particularly those with certain illnesses. 


Intermittent fasting appears to be an effective way of improving health, in particular cardiovascular and metabolic health.  It may confer benefits such as improvements in cholesterol levels, blood sugar levels, inflammation and blood pressure.  In addition to timing when you eat, it is also necessary to consider what you are eating.  In the words of the famous physician, Sir Muir Gray2:

Another bit of advice is to eat nothing your great grandmother would not have been able to recognise; less food, less animal food, more grains and vegetables, and more walking, the cavemen had no car.

  1. Fontana L (2018).  Interventions to promote Cardiometabolic health and slow cardiovascular ageing Nat Rev Cardiology Epub ahead of print

Thank you to author Dr. Emma Short for this blog post.

1 comment

  • Jamie: July 06, 2018

    Great article! I loooove fasting. Anyone interested in this stuff should definitely check out the book Everyday Roots. It teaches you how to replace all the toxic chemicals in your life with healthy organic alternatives. Its completely changed my life and how I feel everyday! :)

    Heres a great review of everday roots:

    Keep up the great content!

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