What is Intermittent fasting?

What is Intermittent fasting?

In simplified terms, anytime that you are not eating,you are intermittently fasting. In real life terms we do it every day when we go to sleep for 6-8 hours, we are not eating and therefore this is known as a form of intermittent fasting or everyday life. However, success has been brought about by refining this approach to varying degrees.

At a basic level intermittent fasting allows the body to use its stored energy. For example, by burning off excess body fat when the body has no other access to direct energy from food.

The theory is that our body fat is merely unwanted food energy that has been stored away. If we don’t eat, then our body will simply “eat” its own fat for energy.

When we eat, more food energy is ingested than can immediately be used. Some of this energy must be stored away for later use. Insulin is the key hormone involved in the storage of food energy.

When we eat, our insulin levels rise, helping our body to store the excess energy in two separate ways. Carbohydrates are broken down into individual glucose (sugar) units, which form glycogen, which is then stored in our liver or muscles. Our body has a limited storage space for carbohydrates; and once that is reached, the liver starts to turn the excess glucose into fat.  Some of this new fat is stored in our liver, whilst the rest is transported to other areas of our body.

When we adopt an intermittent fasting lifestyle the process goes in reverse.  Our insulin levels drop, telling the body to start burning our reserved energy. Our blood glucose levels fall, so the body uses the excess energy stored in our cells.

It is important when adopting an intermittent fasting approach that you:

  • Stay hydrated; this includes drinking teas, coffees and low sugar drinks regularly.  
  • Allow your body to adapt to the new approach – this can take 3-4 weeks
  • Cut back on simple carbohydrates, swap to wholegrain, high fibre option
  • Adopt a healthy balanced way of eating when not fasting

Fasting Options


With this option you consume your meals within a tight 8 hour window, so the body ‘fasts’ for the remaining16 hours.  This option is generally adopted on a daily basis and is applied to a normal balanced eating approach –ie you are not restricted to a low calorie allowance such as 500-1000 calories per day.  You are encouraged to have three meals within this time frame, but because they are closer together the inclination is to eat less. Thus meaning you rarely get hunger pangs that cause you to reach for something to nibble on.


This involves having a four-hour eating window followed by a 20-hour fast. You would only do this one or two days per week and normally consume one larger meal or two much smaller ones.

5:2 fast

Created by Dr. Michael Mosley it has become the most recognised modern day still of intermittent fasting.  It has become very popular as many people find they can fit it in around every day life.  It has also been linked to a reduction in the chances of developing type 2 diabetes.

5:2 involves five regular eating days and two fasting days. However, on these two fasting days, you are allowed to eat 800 calories on each day. These calories can be consumed at anytime during the day – either spread throughout the day or as a single meal.  


Devised by Rosemary Conley CBE.  It involves four regular eating days and three fasting days for the first week, followed by five regular eating days and two fasting days. Once you have reached your target weight you progress to the maintenance plan of six regular eating days and one fasting day.

On these fasting days, you are allowed to eat 800 calories per day. These calories can be consumed at any time during the day and spread across 3-4 smaller meals. With the 3-2-1 plan you are not restricted to the proportion of carbs consumed with the 800 calorie days, but that all foods must fall below a 5% fat rule.  

Intermittent fasting is not suitable for everyone

If you have a low BMI (less than 19), under the age of 18, diabetes, gout, are breast-feeding or taking any medications then you should not adopt this style of eating without first seeking the advice of your GP first

If you have any concerns as to whether this style of eating may conflict with any medical condition you may have then you should seek medical advice prior to changing your eating habits.