Intermittent fasting: what to know

Intermittent fasting is a tailored eating schedule that restricts the opportunity to eat within specific timeframes. In this article, medical weight management specialist Dr Philip Bazire explains the benefits and possible drawbacks of intermittent fasting.

What is intermittent fasting and what can it do?

In intermittent fasting we limit eating to specific time periods and don’t eat outside those periods. There are various ways to do this, such as only eating on certain days, or eating all our meals within a given number of hours each day.

The aim of intermittent fasting is not so much to limit overall calorie consumption, though this is likely to occur to some extent, but rather to ensure a prolonged period without eating any food, as this has notable health benefits for the body.

Being in the fasting state, which typically starts between 8 and 10 hours after your last meal, leads to a number of metabolic changes that promote health:

The body starts to draw on its stores of sugar and fat for energy, which aids weight management and improves the control of cholesterol and sugar levels in the blood.
The body can get round to clearing out the waste products of metabolism and any damaged cellular components (autophagy). These systems only really get going after about 12 hours of fasting, but then accelerate if given more time.
The hormones that control how food is handled are allowed to return to baseline levels. This is known to make them more effective when they become active again the next time food is eaten.

Intermittent fasting has other potential benefits, such as improving gut health, lowering blood pressure, and improving the quality of sleep (if fasting commences a few hours before going to sleep).

People with type 1 diabetes are not recommended to adopt intermittent fasting if not advised to do so by their doctor, but research has shown that this method has promising results in patients with type 2 diabetes, with decreased levels of fasting glucose, fasting insulin, and leptin, and even remission.

How is intermittent fasting done?

There are several ways to perform intermittent fasting, and it is worth trying different approaches to see which one works best for you as an individual. Some popular intermittent fasting plans include:

5:2 – restricted eating of around 600 calories on two days each week, and a normal diet for the other five days. The two low-calorie days can be sequential or separated.
Time-restricted eating – a plan in which all meals are eaten within a given window, which is usually of 8 or 10 hours. No food is eaten in the other 14 or 16 hours, though you can drink water and other non-calorific clear fluids.
Whole-day fasts – also known as eat-stop-eat, where one day (or more) is completely without food, though fluid intake should be maintained. Fasting can vary from 1 day a week to alternate-day fasting, and other options in between, with 2 or 3 days fasting each week.

Are there downsides to intermittent fasting, and what can you eat when not fasting or restricted?

Starting intermittent fasting can be daunting, and as the body adjusts to the new eating plan, it is not uncommon to struggle with hunger pangs until the body becomes accustomed to the new system. Other possible downsides and struggles for those starting with intermittent fasting are feeling lightheaded or weak, a lack of energy, or difficulty concentrating. It is important to eat a healthy diet that covers nutritional requirements to prevent these symptoms and to ensure the preservation of muscle mass.

The following recommendations will help you if you want to try intermittent fasting:

Stay hydrated and drink plenty of water and calorie-free drinks like teas and infusions
Keep yourself occupied with work, tasks, hobbies and crafts to divert attention away from food and eating.
Avoid junk food and refined carbohydrates, as this will make it harder to stick to intermittent fasting plans and will also reduce the health benefits.
Incorporate nutrient-dense foods that are high in fibre, protein, and unsaturated fats like eggs, fish, pulses, fruit and vegetables to ensure that meals are balanced and impactful.
When fasting, don’t expend too much energy by doing intensive physical activities. Brisk walks and yoga are more suitable than intensive workouts on fasting days.
If you want to try the more intensive whole-day fasts, you should speak to your doctor before starting.

If you are struggling with weight management, you can consult with Dr Bazire on his Top Doctors profile.