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Your Guide to Intermittent Fasting

Updated: Mar 19, 2021

Intermittent Fasting or IF, is one of the latest buzzwords now in the health and fitness world with online searches for it having increased 10,000% since 2010!!

However, like many 'new' trends they have their roots in much older or ancient times. Such as the Christian 40 day Lent period before Easter, which used to be more strict until now, when people simply 'give up chocolate' for 40 days, and also the Muslim practice of Ramadan where the faithful fast from daybreak until dusk for one month in order to deepen self-discipline and spiritual reflection. The notion of fasting extends back to the days of Ancient Greece and Roman times. Hippocrates, (460-370BC) the father of modern medicine championed the practice of fasting and wrote:

" To feed when you are ill is to feed your sickness".

Fasting, whether you realise you are doing it or not, seems to be a universal human instinct during times of illness. How much do you feel like eating with the 'flu for example? Furthermore, when you are not are fasting!

So what exactly is IF?

Intermittent fasting is away of eating, or a pattern involving moving between periods of eating and fasting for specific blocks of time.

When we eat, food is broken down into its component parts with carbs being broken down into a simple sugar known as glucose. These molecules of glucose are then linked together to form glycogen which is stored in the liver or muscle. If there is excess glucose the liver then turns this into fat in a process called de-novo lipogenesis, literally making new fat. There is no limit on the amount of fat that can be created and we all know where that gets stored!

With IF, during a fasting period, insulin levels drop therefore sending a signal to the body to start burning stored energy. Blood glucose now starts to fall therefore the body will pull glucose out of storage to use for energy. Basically, IF allows the body time to use up stored energy.

Tick tock it's Fasting O'Clock

IF does have many variations and may or may not include calorie restriction or exclusion of certain food groups. Some of the more well known ones are mentioned below.

The 5:2 Diet. On this diet you can follow a normal, healthy diet for five days out of the week. On the other two days calorie intake must be dropped to 500/600 calories per day.

Alternate Fasting Day Diet. Is as the name suggests a diet where you fast every other day by reducing calories or not eating at all.

16/8 Diet.This type of fasting entails limiting your food intake to an eight-hour window where you can eat. You can customise the fasting hours based on your own schedule, most people find it easiest to simply stop eating after dinner and skip breakfast the next morning.

There are many 'alleged' benefits to IF, and it is not suitable for everyone, but more on that later.

It can support healthy weight maintenance. Studies in normal and overweight human subjects have demonstrated efficacy for weight loss and improvements in multiple health indicators including insulin resistance and reductions in risk factors for cardiovascular disease, however further research needs to be carried out to establish the efficacy of IF in improving general health, and preventing and managing major diseases of ageing.

Boost Brain Health. The present data may provide an insight on how a modest level of short term IF with caloric restriction, imposed in middle age, can slow down or prevent the age-associated decline and impairment of brain function and promote healthy ageing, however, this study was done on mice and not humans so further research is needed.

Many other benefits have body been reported such as body fat loss, possible reversal of diabetes type 2, increased energy, better cholesterol profile, reduction in inflammation and so on, however, much of the research/evidence at the moment at best is moderate to weak.


While IF does have some benefits in certain sections of the population there are several groups for whom it is not advisable.

Pregnant women and children under 18

IF is not recommended for pregnant or breastfeeding women as it could potentially increase the risk of nutritional deficiencies or problems with foetal growth and development. Like wise with children and young adults.

Not suitable for diabetics

IF is not suitable for those with insulin dependant Diabetes as it may interfere with the medications and lead to hypoglycaemia. Please do consult your GP before embarking on any fasted regime.

Females in reproductive years

More research is warranted but there is some to suggest that caloric and energy restriction in this group of females may interfere with normal hormonal functioning, disrupting menstrual cycles and with longer term consequences of fertility problems and bone density concerns.


As a Nutritional Therapist I am trained with the philosophy that there is no 'one size fits all approach" to wellness and health. Intermittent Fasting may have benefits for some people however, the bottomline is that there is no replacement for moderation nor a substitute for a healthy and balanced, whole food diet with moderate exercise. IF is not for everyone, but if you find it works for you then that is fantastic. However, if you feel you would like to try it but don't know where to start then my advice would be to seek the advice of a nutritional therapist trained in diet and lifestyle medicine, who can tailor make a plan, based on your own medical history and current lifestyle.

I am registered with BANT, the British Association of Nutritional Therapy and Lifestyle Medicine, so you can be assured thatI have been trained to a high level of academic and clinical training and adhere to strict and ethical National Occupational Standards.

Patricia Alexander-Bird, Registered Nutritional Therapist, Dip NT, BANT


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