Intermittent Fasting: What It Is and the Main Methods

Intermittent fasting is a way of eating that focuses on when you eat rather than exactly what you eat. It has become popular in the UK, and there are several different approaches. This guide explains the main methods in plain terms, who should not try fasting without medical advice, and how food supplements fit around an eating window.

What is intermittent fasting?

Intermittent fasting means alternating between periods of eating and periods of not eating, or eating very little. It is a pattern, not a specific diet. What you eat during your eating periods still matters, and a varied, balanced diet remains the foundation.

The main methods

16:8 (time-restricted eating)

You eat within an eight-hour window each day, for example 12 noon to 8 pm, and do not eat for the remaining 16 hours. Many people find this the easiest method because much of the fasting time happens overnight. Some start with a gentler 12:12 or 14:10 pattern.

5:2

You eat normally on five days of the week, and on two non-consecutive days you eat much less, often around a quarter of your usual intake.

Alternate-day fasting

You alternate between normal eating days and fasting or very low intake days. This is more demanding and is not suitable for everyone.

24-hour fasts

Some people fast for a full 24 hours once or twice a week, for example from dinner one day to dinner the next. This is the most demanding approach and should not be attempted without considering whether it is right for you.

Who should not fast without medical advice

Speak to your GP before trying any form of fasting if you:

• are under 18
• are pregnant, trying to conceive or breastfeeding
• have a medical condition or take any medication
• have a history of disordered eating
• are underweight

Practical tips

• Drink water regularly, including during fasting periods.
• Make meals in your eating window balanced, with protein, fibre, fruit and vegetables.
• Start gradually rather than jumping straight into long fasts.
• Stop and seek advice if you feel unwell.

Taking food supplements around an eating window

Many supplement labels advise taking a product with a meal or with food, and fat-soluble vitamins such as vitamins A, D, E and K are generally taken with a meal. The simplest approach is to take supplements during your eating window, following each label's directions.

If you choose a daily multivitamin, our Multivitamin Complex is a one capsule a day product. It contains vitamin A, so do not take it if you are pregnant or may become pregnant without medical advice. For magnesium, magnesium contributes to a reduction of tiredness and fatigue; our Magnesium Glycinate 650 mg provides 130 mg of elemental magnesium per capsule. You can browse more everyday options in our Daily Foundations collection.

Frequently asked questions

What is the most common intermittent fasting method?

The 16:8 method, where you eat within an eight-hour window each day, is one of the most widely used.

Can I drink water while fasting?

Yes. Water is encouraged during fasting periods.

Should I take supplements during a fast?

Follow the label. Many products should be taken with food, so the eating window is usually the best time.

Is intermittent fasting suitable for everyone?

No. It is not suitable for under 18s, during pregnancy or breastfeeding, or for people with certain medical conditions or a history of disordered eating, without medical advice.

Important information

Food supplements should not replace a varied, balanced diet and a healthy lifestyle. Do not exceed the recommended daily dose stated on the label. Not intended for anyone under 18. If you are pregnant, breastfeeding, taking any medication or under medical supervision, speak to your doctor or pharmacist before taking any food supplement. Keep out of reach of children.