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    Intermittent fasting – a guide

    On this page
    1. What is intermittent fasting?
    2. Does intermittent fasting work for weight loss?
    3. The different types of intermittent fasting
    4. The benefits of intermittent fasting
    5. Can you eat anything whilst intermittent fasting? 
    6. How long should a fasting plan last?
    7. Who shouldn’t fast?
    8. Tips for success with intermittent fasting
    9. Our lifestyle hub 

    Reviewed by our clinical team

    What is intermittent fasting?

    What is intermittent fasting?

    Intermittent fasting is an eating schedule with prolonged periods of not eating (or fasting). The main difference between intermittent fasting and traditional diets is that fasting diets focus on ‘when’ a person should eat rather than ‘what’ they should eat. 

    The reason many people try intermittent fasting is because some researchers claim that the human body is designed to go without food for long periods, for example, when we were hunter gatherers. It is also linked to weight loss, improved metabolic health and decreased insulin resistance. Insulin is a driver of fat storage and is triggered by eating. If released all day over a prolonged period, insulin resistance occurs, and the body has to make more. Fasting provides the opportunity for insulin levels to drop. 

    Does intermittent fasting work for weight loss?

    There is evidence to suggest that people lose some weight when intermittent fasting. However, studies show that there is no significant difference between fasting groups and continuous calorie restriction groups. Calorie restriction is a regimen where calories are reduced from what is ‘normal’ without causing malnutrition. 

    The different types of intermittent fasting

    During the fasting period, it’s important to stay hydrated. Drinking plenty of water is advised – this can be sweetened with a slice of lemon or lime. People often drink tea or coffee in their fasting period too but avoid using milk or sugar. 

    Before starting a fasting plan, if you have a medical condition or special dietary needs, talk to your GP. 

    There are two main intermittent fasting schedules:

    16:8 fasting schedule

    During this type of fast, people fast for 16 hours a day and follow a healthy diet (within the recommended daily calorie allowance) for eight hours. Another version of this is 14/10 where the eating window is two hours longer. 

    5:2 fasting schedule

    During a 5:2 fast a person should restrict calorie intake to 500-600 calories on two days of the week and follow a healthy diet on the remaining five days.

    The benefits of intermittent fasting

    Several benefits have been reported, including:

    Can you eat anything whilst intermittent fasting? 

    Technically, yes. Intermittent fasting focuses on sticking to eating windows rather than prescribing what should be eaten. 

    However, to maximise the benefits of intermittent fasting, during an eating window, we recommend you maintain a healthy and varied diet, which means eating foods across the food groups. For example, make sure you’re getting enough protein, eating fruits and vegetables, wholegrains and avoiding overly processed foods. 

    How long should a fasting plan last?

    If weight loss if the goal, intermittent fasting is not a quick fix. As mentioned above, across 40 studies, participants lost weight gradually over a 10-week period with a typical loss of 7-11 pounds. 

    Who shouldn’t fast?

    Drastically reducing calories and skipping meals can be dangerous for some people, including those people with:

    • Diabetes
    • Digestion issues, for example, stomach ulcers
    • Weakened immune system
    • Cancer
    • Eating disorders
    • Some other chronic conditions. 

    Fasting is also not recommended during pregnancy because of the importance of mother and baby getting the nutrients they need. If you choose to fast whilst breastfeeding it’s important to discuss with a health professional first, such as a GP or midwife. 

    Tips for success with intermittent fasting

    • Start slowly (don't start off straight away with a 16 hour fast. Start with 10/12 hour fast and slowly increase and build up to 16:8)
    • Stay hydrated
    • Plan meals in advance (planning healthy/nutritious meals)
    • Avoid high-intensity workouts during fasting days/period
    • Get enough rest (sleep) and make sure you have time to relax
    • Avoid late night eating
    • During eating window make sure meals are rich in nutrients form all food groups

    Our lifestyle hub 

    To read more expert diet and lifestyle advice visit our lifestyle hub. We’re here for you with simple and clear expert advice on losing weight, stopping smoking and leading a more balanced lifestyle.

    Considering weight loss treatment?

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    References

    https://patient.info/news-and-features/is-intermittent-fasting-a-healthy-way-to-lose-weight
    https://www.diabetes.co.uk/diet/5-2-intermittent-fast-diet.html 
    https://www.hsph.harvard.edu/nutritionsource/healthy-weight/diet-reviews/intermittent-fasting/
    https://diabetesmyway.nhs.uk/keeping-healthy/different-dietary-approaches-for-weight-loss/intermittent-fasting/
    https://www.nejm.org/doi/full/10.1056/NEJMra1905136
    https://www.health.harvard.edu/heart-health/not-so-fast-pros-and-cons-of-the-newest-diet-trend
    https://www.tommys.org/pregnancy-information/im-pregnant/nutrition-in-pregnancy/fasting-pregnancy 

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