Is Intermittent Fasting Safe? We Investigate the Truth

Is Intermittent Fasting Safe?

Intermittent fasting has been around for a while, and it has a bit of a mixed reputation. Some believe that intermittent fasting is the solution to all life’s problems, while others feel that it is overrated and possibly dangerous. But, what’s the truth? Is intermittent fasting safe?

Intermittent fasting is perfectly safe. Humans evolved to survive periods of low food availability and provided you are not prolonging the periods of fasting, you should be in no danger. However, it is not universally safe. Diabetics may be at risk of hypoglycaemia if their blood sugar gets too low. People at risk of eating disorders should also avoid intermittent fasting.

In this article, we will be taking an in-depth look at what intermittent fasting is, and whether it is safe.

What is Intermittent Fasting?

Fasting is avoiding food on purpose, this purpose could be health-based, social, or it can be for spiritual purposes. Every year, Muslims purposefully fast during daylight hours during the month of Ramadan.

What constitutes fasting is up for debate. If you refuse a large chocolate bar at 11 am because you don’t want to spoil your lunch, you are technically fasting. You are purposefully avoiding foods that are easily available.

Every night when you go to bed, you are fasting. Breakfast literally means breaking your fast.

But none of the examples above would normally be considered fasting, even though they technically are. Intermittent fasting is a strange term, that can describe three different forms of fasting for the purposes of weight management and health:

  • Periodic Fasting (AKA the 5:2 diet) – You eat for a certain number of days and avoid food for the others. The 5:2 diet has you eating five days each week and fasting for two days. A 6:1 diet would also be considered periodic fasting.
  • Alternate Day Fasting – You eat one day, avoid food the next, and alternate indefinitely. This is basically the same as periodic fasting but is quite a bit more extreme as 50% of your days are spent fasting. Some variants of this diet allow you to consume a certain number of calories on fasting days, but the total is often very low.
  • Daily Fasting – This is where you avoid food for large periods of each day. Fasting during Ramadan is a form of daily fasting where you avoid foods from sunrise to sunset. Though, obviously, the reasons for fasting are different. Common daily fasting techniques involve avoiding lunch or breakfast.

There is a discrepancy between what intermittent fasting can do, and what it is claimed to do. The fact is that intermittent fasting can help with weight loss by making it slightly easier to reduce your caloric intake. But many of the claims surrounding intermittent fasting are made up or exaggerated.

Is Intermittent Fasting Safe?

When performed correctly, intermittent fasting (IF) is perfectly safe for the vast majority of people who follow it. Most of the arguments surrounding IF focus on whether it is better than other dieting techniques, rather than whether it is safe or not.

There are some circumstances where IF may not be safe. But if you are generally healthy, and follow the protocols correctly then there is no reason why you should worry about your safety. As we stated earlier, all of us follow some form of fasting every day, intermittent fasting just takes things a step further.

Is Intermittent Fasting Safe for Diabetics?

Intermittent Fasting is an effective way to lower body fat, so theoretically it could actually be beneficial for many diabetics. However, it does affect blood sugar levels and could lead to hypo or hyperglycaemia. As you get more experienced with IF these risks can be reduced.

But you should talk to your doctor first, and be hyper-vigilant about checking your blood sugar levels. You should also pay attention to your mood and fatigue levels.

Is Intermittent Fasting Safe for People with Eating Disorders?

This depends on the person in question, and their relationship with their particular eating disorder. What is certainly true, is that many people with eating disorders should avoid intermittent fasting. Not only does it add in a lot of (fairly pointless) rules and regulations, which can cause stress, but it can also be used to mask eating disorders from others.

Skipping meals, and then eating lots of food during small periods of time, can be quite unsafe for some people. We offer the same advice as for diabetics, talk to your doctor or a therapist before considering this diet. There are many other (safer) ways to diet.

Is Intermittent Fasting Safe for Women?

You should not follow an intermittent fasting diet while pregnant or breastfeeding. Intermittent fasting may also affect the menstrual cycle, but this is usually only in extreme cases. If you are a healthy woman who is not pregnant or breastfeeding, then intermittent fasting is perfectly safe, provided you follow it properly.

Is Intermittent Fasting Safe for the Elderly?

Provided you are healthy and have discussed it with your doctor, there should be no additional risks to following an intermittent fasting diet as you age. If you are underweight (very common for elderly people) then intermittent fasting is not ideal and should be avoided.

Is Intermittent Fasting Effective for Weight Loss?

Weight loss is caused by a long-term calorie deficit. This is where you consume fewer calories than you expend. If you consume 1,900 calories and burn 2,400 then you have a calorie deficit of 500. Maintain this deficit for 10 days and you will have burned 5,000 more calories than you have eaten.

Initial weight loss is fairly easy, the trick is to find a dieting method that leads to long-term weight loss and weight maintenance. Otherwise, you will regain weight over time. So, the question is not so much whether you can lose weight following IF, the question is whether you can lose weight and keep that weight off following IF.

The answer is that some people can follow IF diets indefinitely, and it will suit them well. But the majority of people will not be able to continue this diet for very long. That doesn’t mean that it can’t be used successfully.

The best option for most people who want to follow IF would be to create a strategy. Follow IF for 12 weeks, and then have a simpler plan that you can implement afterwards.

12 weeks is the average time it takes to see good weight loss results, but it is also around this time that many people begin to struggle. Switching to a high-protein diet where you eat normally 3 x per day would be a great option for weight management or further weight loss.

Is Intermittent Fasting Effective for Building Muscle?

Carb-cycling is very popular with bodybuilders and people who want to build muscle. This is where you eat fewer carbs on non-training days, and then higher carbs before/after your workouts. A similar approach could be made with intermittent fasting, however, you would want to ensure you are getting enough protein on recovery days.

Realistically, there are better options out there for diets while trying to build muscle.

Should I Use Intermittent Fasting?

Does the idea of intermittent fasting excite you? Do you want to follow it? If you do, then it is a perfectly good short-term dieting option. You may find that you like it so much that you continue to do it indefinitely.

If you do not like the sound of it, then you should avoid it. Intermittent fasting can work, but it is no magical diet that outperforms regular diets. In fact, meal replacement shake diets have been shown to be much more effective. A 2010 study found that meal replacement shakes were significantly effective at aiding weight loss in both the short and long term [1].

Intermittent Fasting Pros & Cons

Here are some pros and cons of intermittent fasting, to help you get an idea of whether it is the right diet for you or not:


  • Effective for short term weight loss
  • Simple rules to follow
  • Lots of different IF diets to follow


  • Not enjoyable – low long-term success rate
  • Difficult to integrate with friends and family
  • No more/less effective than easier diets

Alternatives to Intermittent Fasting

A meal replacement shake diet is a good option or a simple high-protein diet which places emphasis on eating more fruit and vegetables. Any calorie controlled diet which requires you to increase your protein will be just as effective as an IF diet.

Is Intermittent Fasting Safe? Final Thoughts

As with any diet, different people will react differently to intermittent fasting. Some people may find it easy to follow and highly effective. Others may find it easy at first, but struggle in the long term. While some people may find the IF diet affects their physical or mental health. If you have any form of health condition, please talk to a professional before embarking on an intermittent fasting diet.