Intermittent fasting - is it safe?

There are many eating plans out there to help people lose weight, with their own individual strengths and weaknesses, and to varying levels of success. Some may involve changing the type of food people eat, while others may restrict meal sizes and portions. One of the options available is intermittent fasting (IF), which is becoming an increasingly common choice amongst dieters.

IF involves significantly restricting how much you eat on certain days, while eating normally on the rest of them. Huge claims have been made regarding the success of this eating plan, and even suggestions that it can improve cognitive function, reduce the risk of disease and help people to live longer.

How does IF work?

IF can be approached in different ways, with certain factors affecting your own eating plan. These include the amount you eat on a fasting day and how many days per week you choose to fast on.

The 5:2 IF plan is one of the most popular. This involves eating largely as you normally would for five days a week, although preferably eating healthy foods, and fasting on the remaining two days. However, on the fasting days you don't have to completely go without food, as it allows men to consume 600 calories while women can consume 500 to get through the day. The plan also states that the days you choose to fast should not be consecutive.

What does the evidence say?

IF's supporting evidence is still unclear, as findings from clinical trials are very limited. In fact, most research is based on animals and the data available on humans is quite old.

With that said, the research findings that we have, whether they be based on animals or humans, do consistently support the popular health claims - including faster rates of weight loss. Add to this the huge volume of positive anecdotal reports from those who have tried IF, and this new approach to weight loss does appear to be worthy of consideration.

The risk factors of IF

At this stage, there isn't a lot of information about the possible side effects of IF as, once again, formal studies in this area are lacking. There are anecdotal reports though, and these include:

To establish how prevalent these side effects are, further studies will have to be taken but here is enough information though to know that IF isn't suitable for everyone. Pregnant women, people with insulin-treated diabetes and anybody who has an eating disorder should not undertake an IF plan.

What to consider when thinking about IF

You're obviously going to feel some degree of hunger and even some lack of energy on the fasting days, so you should carefully consider how this will affect your life.

Fasting on days when you're busy can be a good idea so that you don't have too much time to think about eating. Exercising on a fasting day however is not advisable, as your energy levels will be lower and you're likely to feel even hungrier for the rest of the day.

Stay hydrated on fasting days with plenty of water and fruit or herbal teas. This will prevent dehydration while it can also help dampen some of the hunger pangs, as well as have a mild detoxifying effect.

And finally, if you have any medical conditions whatsoever that may be affected by changes to your diet, then you should talk to your GP first before starting.


1. NHS Choices:

2. BBC Health:



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