What is 'Intermittent Fasting' and does it work?

What is intermittent fasting (IF)?

There are various versions of Intermittent fasting (IF). As the name suggests, the term simply means going through periods of time fasted, i.e. having not eaten. Fasting dates back centuries and is still commonly practiced for religious reasons, a prime example being Ramadan where no food or water is consumed between sunrise and sunset.

Intermittent fasting

The most commonly used methods of fasting for non-religious practice are:

a) The 16:8 diet

This is a popular example of establishing an ‘eating window’. Food is only consumed between 12 noon and 8pm (8 hour period) and fasting takes place between 8pm and 12pm (16 hours).

b) The 5:2 diet

This method introduces longer periods of reduced or no food intake, whereby you fast for 2 days a week. This method actually allows for 5-600 calories of food throughout each of the fasting days.

There are a number of claimed benefits to fasting, but is there any truth behind these nutritional claims?

Is fasting better for weight loss?

Short answer - no. However, that short statement doesn’t give fasting the credit and consideration it is due. I frequently use fasting protocols with clients and produce excellent results. So why am I saying it isn’t better for weight loss?

Well, in terms of weight loss the evidence is pretty clear. A calorie deficit is a calorie deficit. The only slight caveat to that is that eating less carbohydrate will make you lose weight quicker initially, but this is actually water loss, not fat loss. Additionally not eating enough protein will make you lose weight quicker, but this is lean tissue loss, not fat loss - which I would certainly not recommend.

So, from a physiological perspective fasting is not a superior method of dieting for weight loss. However, for some people it may work from a psychological or behavioral perspective.

How does intermittent fasting compare to other ‘diets’?

How could fasting be easier than eating in moderation, calorie counting, cutting out carbs or going low fat?

It can be less restrictive

If you want to avoid the ‘dieting mentality’, by which I mean feeling restricted or that you are constantly attached to counting ever calories via Myfitnesspal, then intermittent fasting is a straightforward way for you to create a calorie deficit without counting calories or cutting out food groups.

Your perceived feeling of restriction is a big predictor of whether or not a diet will work. As cliché as it sounds, once you have the basics right (energy balance) the best diet for you when it comes to weight loss is going to be the one you can stick to.

Many people enjoy fasting because when they do eat, they don’t have to be as conscious about their food choices or counting calories. For example, if you told someone to start limiting themselves to 600 calories for two days a week and then simply not to over eat on the other days then they would certainly create a calorie deficit and start losing weight.

Many diets use methods like this to almost ‘trick’ you into a deficit. For example, if you cut out gluten and don’t replace all of those gluten containing foods with other foods, then you will be eating less and thus likely begin to lose weight. It was not the gluten that was stopping you losing weight. It was the calories in all the gluten containing foods you were eating.

Are the results of fasting superior to other diets?

  • Physiologically? No. Your fat loss is dictated by energy balance.
  • Psychologically? Possibly. But this is very independent and really depends on whether you feel it is easier to stick to this method of dieting.

Does fasting have other benefits?

The following benefits are not definitive, but have noticed by some people during fasting:

Improved concentration

I find I concentrate far better if I eat less frequently. Some would call this fasting. Others would call it simply missing or pushing back breakfast.

There is also some evidence for improved metabolic and brain function. One of the proposed benefits is that fasting may induce small periods of ketosis. Ketosis is when your body uses ketones for fuel instead of glucose. This switching of fuel from glucose to ketones may offer some benefits but there is no definitive results.

This is largely because diets are notoriously hard to study due to the many factors that would need to be controlled. One small study showed increased glucose clearance after meals in intermittent fasting compared to continuous calorie restriction, despite the same weight loss.

Reduced hunger

Some people find reduced hunger when fasting. You will likely notice that hunger comes and goes around meal times, whether you eat or not. This is because some of your hunger hormones (e.g Grhelin) increase before expected meal times and lower after whether or not you actually have a meal. You may have experienced this if you have missed your usual lunch time and found that you are no longer hungry a few hours later.

It’s flexible

At certain times or periods in your life, different dietary approaches may work better for you. For example, you might not decide to do IF (eating window 12-8pm) every week, but it could work especially well when you are on holiday. You simply push your first meal back until 12pm and then stop eating after your dinner at 8pm.

It curbs snacking

This particular fasting protocol also works well as most people who are actively trying to watch their diet find the evening is where they go off track. A perfect example is snacking in front of the TV after dinner. Having a rule in place where you stop eating after your dinner means you avoid this often mindless additional food consumption which is adding unnecessary calories to your diet and often stopping you losing weight.

5 top tips for intermittent fasting

1) Eat a big dinner

Leave most of your calories until the evening. There is nothing worse than going to bed hungry. Knowing you have a good meal to look forward to when you get home from work is always nice.

2) Choose ingredients wisely

If you choose high volume foods then you can put together 2 fairly large, filling 300 calorie meals. Big salads and lots of veg is always a good bet.

3) Break the fast with protein

When you break your fast, start with some nutritious foods such as fruit and/or veg with a good protein source like eggs.

4) Eat slowly and mindfully

Be present and give meal times your full attention and gratitude, so that you can understand and value the nutritious food that you are eating.

5) Fasting isn’t for everyone

If it doesn’t work for you, then there are many other options. The best methods for nutritional success are the ones you genuinely find easiest to stick to.


I would suggest avoiding methods of fasting if you have binge eating tendencies or a history or eating disorders. If you have any concerns, please talk to a healthcare professional before undertaking fasting.