What Is Intermittent Fasting and Should I Do It?

Written by
The Manual Team
Medically approved by
Dr Earim Chaudry
Last updated
7th January 2022

In 30 seconds

Intermittent fasting is now one of the more popular health trends around. It would be wrong, however, to call it a diet: intermittent fasting is less about what you eat than when you eat and when you don’t. Plans for intermittent fasting differ. Some people fast for 24 hours, whilst others cut the amount they eat on certain days of the week.

Should you do it? The benefits claimed for intermittent fasting are impressive – ranging from weight loss to improved brain health, from insulin resistance to decreased cancer risk. Whilst this might seem like too good to be true, it needn’t be. There is evidence that it works – although more is needed. 

But it is not for everyone. If you have low blood pressure or diabetes, or you are on medication, you should consult a doctor first.

You may have heard of intermittent fasting. As one of the trends that is currently exciting the fitness world, it costs nothing, it is easy to implement, and it promises a lot of benefits.

But can we believe all that is said of it? Can we really fast our way to health and fitness? 

In this article, we’re going to explore the practice and benefits of intermittent fasting – and whether you should try it yourself.

What is Intermittent Fasting?

Intermittent fasting – or “intermittent energy restriction”, as it is alternatively known – is a health practice that involves controlling when you eat and in what quantities, in order to achieve certain associated health benefits.

Rather than being a “diet” in the traditional sense, though, you can pretty much eat whatever you like, as long as it is at the right time. In this way, intermittent fasting is more accurately described as a type of eating pattern or meal scheduling plan, which can be organised across weeks or within single days.

Whilst these days it is seen by some as merely a fad, it actually has ancient roots. Fasting has been a part of religious practice for thousands of years, with health benefits having been long observed

However, with more widespread interest in the practice, science has recently taken this up further, studying the range of benefits that it might offer.

The Benefits of Intermittent Fasting

These benefits result from the changes that occur in your body due to the reduced amount of energy available. As proponents of the practice are quick to point out, humans – like other animals – are not necessarily biologically equipped to eat three meals a day. Rather, early humans wouldn’t always have found food to eat, meaning that a fast would have been a very normal thing.

In this way, our bodies, if not our culture and mindsets, are prepared to go short periods without food. So, here are some of the possible benefits of intermittent fasting.

Weight Loss

Intermittent fasting, whilst not explicitly placing any limits on your calorie consumption, tends to result in reduced calorie intake. Weight loss results from this – and this is, in fact, the primary reason why most people try intermittent fasting.

Studies have seemed to confirm that intermittent fasting is an effective strategy for weight loss. One study found that people on intermittent fasting lost 3-8% weight over 24 weeks. More recently, further research has supported these results, identifying a reduced chance of obesity due to changes in your metabolism.

However, these benefits will not be seen if you fast for the required time and then binge or eat more than you normally would.

Improves Insulin Resistance

The idea behind intermittent fasting and weight loss is that, when fasting, your insulin levels decrease to the extent that you start to use your storages of fat.

Whilst this is useful for those of us without blood sugar problems, intermittent fasting appears to be effective in the treatment and prevention of diabetes too. According to one study, diabetics who fasted were able to come off insulin therapy as a result.

Another study comparing three different methods of intermittent fasting (see below) found that all three improved insulin resistance – a problem associated with the development of diabetes – and seemed to reduce the risk of type 2 diabetes overall.

Further research is required, however, to confirm these results.

Boosts Brain Health

When you’re hungry, you may well feel incredibly distracted. This feeling increases in the early days of intermittent fasting. However, it does not necessarily last.

In fact, according to studies, your brain’s performance and health actually improve as a result of intermittent fasting. Unfortunately, however, studies have so far only been conducted in rodents – so we are still seeking confirmation of the effect of this in humans.

Decreases Risk of Cancer

A reduction to the risk of cancer is one of the major benefits claimed for intermittent fasting. One review of 22 different studies found that there is in fact a promising link here – as, across the studies, fasting was found to suppress the growth of tumours, to improve overall chances of survival, and to counter the side effects of chemotherapy.

Only four of the studies included were carried out on humans, however – so more work needs to be done.

3 Ways to Do Intermittent Fasting

There are three primary ways to do intermittent fasting, which differ in intensity and the length of the period of calorie restriction. Beside the one study identified above, however, there has been little research into the differences between these methods. Just find the one that works for you.

The 5/2 Diet

The 5/2 diet is a plan for every week – and it is probably the least demanding of the calorie reduction programmes. That’s because it doesn’t actually require you to fast strictly speaking – but rather to strict your calorie intake.

On two days of the week – and they shouldn’t be consecutive – reduce your energy consumption to 500-600 calories. Every other day you can eat as normal.

The 16/8 Diet

The 16/8 diet is one of the more popular variations on intermittent fasting. This involves you restricting the times at which you eat everyday to a window of eight hours.

Something like 1pm to 9pm is an effective way to do this. So, skip breakfast and enjoy lunch and dinner as normal within this window. You’ll be fasting for sixteen hours a day.

24-Hour Fasting

Intermittent fasting as a term is most accurately applied to the third method here. This is when, once a week, you have a period of 24 hours in which you fast, or, more specifically, in which you only drink water.

Most people do it from dinner to dinner. So, skip an evening meal on one day and, on the following day, fast throughout the day until your dinner.

Is Intermittent Fasting Right for Me?

Whilst intermittent fasting may have its benefits, it is not a health regime that is suitable for everyone. This is because it impacts upon your body’s systems, chemical balance, and strength.

As such, pregnant women should best avoid intermittent fasting and nor should children be subjected to it. If you are on medication, if you are diabetic, or if you have low blood pressure, we recommend that you talk to a medical professional before you experiment with fasting. Even though studies noted above have shown positive effects of fasting upon diabetes, these are not confirmed.

Similarly, if you work with heavy machinery, it is best that you do not fast whilst on shift, as the changes to your energy levels can cause distraction and weakness.

Key Takeaways

Intermittent fasting is an eating pattern or schedule that may be incredibly powerful for our health. However, not all of the benefits attributed to it have yet been confirmed.

That’s not to say don’t try it – as most people in good health will not face any serious consequences from restricting their energy consumption periodically. However, if you have a medical condition already, it is best to seek professional advice first.


  1. Roger Collier (2013). Intermittent fasting: the next big weight loss fad: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3652955/

  2. Angeliki Persynaki R.D.a, Spyridon Karras M.D., Ph.D.b, Claude Pichard M.D., Ph.D.a (2016). Unraveling the metabolic health benefits of fasting related to religious beliefs: A narrative review: https://www.sciencedirect.com/science/article/abs/pii/S089990071630226X?via%3Dihub

  3. A Johnstone (2015). Fasting for weight loss: an effective strategy or latest dieting trend?: https://www.ncbi.nlm.nih.gov/pubmed/25540982

  4. Adrienne R.Barnoskya, Kristin K.Hoddy, Terry G.Untermana, Krista A.Varady (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings: https://www.sciencedirect.com/science/article/pii/S193152441400200X

  5. Rafael de Cabo, Ph.D. and Mark P. Mattson, Ph.D. (2019). Effects of Intermittent Fasting on Health, Aging, and Disease: https://www.nejm.org/doi/10.1056/NEJMra1905136

  6. Suleiman Furmli, Rami Elmasry, Megan Ramos and Jason Fung (2018). Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6194375/

  7. J LeeW DuanJ M LongD K IngramM P Mattson (2000). Dietary restriction increases the number of newly generated neural cells, and induces BDNF expression, in the dentate gyrus of rats: https://www.ncbi.nlm.nih.gov/pubmed/11220789

  8. Veerendra Kumar Madala Halagappa , Zhihong Guo, Michelle Pearson, Yasuji Matsuoka, Roy G Cutler, Frank M Laferla, Mark P Mattson (2007). Intermittent fasting and caloric restriction ameliorate age-related behavioral deficits in the triple-transgenic mouse model of Alzheimer’s disease: https://www.ncbi.nlm.nih.gov/pubmed/17306982

  9. Lei Sun, Yong-Jiang Li, Xi Yang, Ling Gao, Cheng Yi (2017). Effect of fasting therapy in chemotherapy-protection and tumorsuppression: a systematic review: http://tcr.amegroups.com/article/view/12654

While we've ensured that everything you read on the Health Centre is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. It should never be relied upon for specific medical advice. If you have any questions or concerns, please talk to your doctor.

Further reading

From our health centre. Experts, information and hot topics. See all Daily Health articles

Daily Health by Manual

Daily health supplements

Help your body fight the good fight with our scientifically proven range of nutrients and vitamins. Making healthier easier, every day.