The ultimate guide to fasting: from limited eating hours to total food abstention

It’s currently all the rage in health circles, but fasting has been around for centuries. People have been periodically restricting their food intake for health, spiritual and dietary reasons for many years.

We’re used to hearing health advisors telling us not to skip meals, to eat little and often and never let ourselves go hungry, but fasting diets are turning this logic on it’s head. From the 5:2 to the Warrior Diet, fasting-based diet plans are everywhere. But are they really good for us?

In short, yes.

We are now learning that going for extended periods of time without food can actually provide us with a variety of health benefits. For example, fasting has been proven to promote health and longevity by reducing disease risk factors and promoting cell regeneration.

What’s more, while previously linked to reduced metabolic rate resulting in ‘rebound weight gain’, if carried out correctly, fasting diets can also be an effective tool to support weight loss. It’s all about finding the right fasting method for you.

Here I’ve rounded up four of the most popular fasting strategies, outlined the pros and cons and how they work on a practical level.

Intermittent Fasting


One of the diet buzzwords of 2018, Intermittent Fasting is all about alternating 24-hour periods of fasting with periods of eating normally. Fast days involve either consuming water only, or significant calorie restriction.

The most popular take on this is the 5:2 diet, which has been in the press for almost a decade now. Studies have shown that intermittent fasting is as effective as ongoing calorie restriction for improving weight loss, insulin sensitivity and other health markers.


The 5:2 diet requires an understand of the calorific values of the foods being consumed, which can often result in an increased awareness and positive influence on food choices on non fasting days. You can also choose which days to fast, in order to allow this method to work around your lifestyle.


Whenever you restrict your food intake, you also limit the opportunity to consume vital nutrients such as vitamins, minerals, antioxidants, essential fats and fibre. It’s wise to consider taking a good quality multivitamin and omega 3 supplement, and also to be mindful that your general diet is based on whole, natural, nutrient-dense foods.


Intermittent Fasting involves reducing calorific intake for one or two non-consecutive days per week. This could mean consuming nothing but water for the day, or, more commonly, doing two days for just 500 calories for women, 600 for men, and then eating normally on the other five days.

(Dan Gold)

Time Restricted Eating (or Time Restricted Feeding)


This is all about limiting your eating hours to a smaller time period in the day, so that your body experiences a period of fasting each day. Typically, this involves eating all your food in an eight-hour window.

Research has shown that time restricted eating is clinically relevant for preventing and treating obesity and metabolic disorders, including type 2 diabetes. One study with overweight individuals showed that when their daily eating window was reduced from over 14 hours, to between 10–11 hours daily for 16 weeks, their body weight was reduced, and they reported being energetic with improved sleep. This was despite not consciously changing what they were eating. Only when.


This is a great strategy for people who don’t usually feel like eating breakfast. It doesn’t involve going for extended periods of time without food or require calorific restriction.


It won’t be easy if you’re a constant grazer, as you’ll have to either get used to delaying breakfast or eating an early dinner and cutting out any evening snacking.


Eat all of your food during an eight-hour window every day. For example, have your first meal at 11am and finish your last by 7pm, and then consume only water between 7pm and 11am. This can be done by eating just two main meals a day (skipping either breakfast or dinner) or just by adjusting the timings of your meals

Periodic Fasting


This is the most traditional form of fasting, which involves abstaining from food completely and consuming nothing but water for a period of at least three consecutive days. Leading experts believe that to achieve the full range of fasting health benefits, prolonged fasts of more than three to four days are required.

Prolonged fasts induce autophagy, a process that helps maintain healthy cellular function, encouraging cells to repair and regenerate. Periodic fasting can also induce ketosis, with the body switching from using glucose (found in carbohydrates) to burning stored body fat.

This can produce excellent results if you’re looking to reduce body fat.


Along with the weight-loss benefits, traditional periodic fasting triggers cell renewal through autophagy, which other methods may not.


Along with the obvious difficulty of going long periods without food, there is the risk of side effects such as headaches, low blood sugar and fainting. Cutting out vital nutrients including protein, fats, vitamins and minerals can result in deficiency if not carefully managed.

Extended fasts should only be carried out under expert supervision, and will not be suitable for people with certain medical conditions.


The first step in a water-only fast is to speak to a healthcare professional to plan your programme. It is advisable to have blood tests carried out in advance to rule out any underlying health issues or nutritional deficiencies. Plan to drink between two and three litres of water spaced out throughout the day and avoid strenuous activity.

(Brooke Lark)

Fast Mimicking Diets


FMDs (Fast Mimicking Diets) were developed by Professor Valter Longo and his team at the University of Southern California to provide the benefits of water-only fasting but with a special plant-based diet plan to sustain you throughout the fasting period.

This diet plan does not trigger nutrient sensing pathways, so the body goes into fasting mode. Studies showed that FMDs reduced risk factors for ageing and diseases including diabetes, cancer and cardiovascular diseases.


FMDs provide the benefits of periodic fasting without having to go without food altogether for long periods. The body will still receive essential nutrients while remaining in a fasted state, meaning the individual can go about their normal life for the duration. There is also a reduced risk of certain contraindications as compared to water-only fasts.


It is still advisable to complete a FMD under the supervision of a healthcare professional, as it is unsuitable for people with certain conditions. It is also unsuitable for those allergic to ingredients in the programme including nuts and soya.


It is recommended that three FMD cycles be completed over three months, with 25 days off in between. After that, it is advised that you complete the programme three times a year. I often recommend ProLon, the world’s first fasting mimicking diet, to my clients.

It includes plant-based energy bars, soups and a variety of snacks, drinks and supplements. If you think it might be right for you, you can get in touch with my team to find out more.

It’s important to note that one or all of these methods of fasting might not be right for you. For example, anyone with an active infection or disease, a history of fainting, taking regular medication or pregnant women should not fast unless specifically recommended to by a qualified and experienced practitioner.

But there is plenty of evidence to suggest that when done correctly, fasting diets can not only be effective for weight loss, they have a host of other health benefits, too.


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