Intermittent fasting: what's all the hype?

Emma Brown - Nutritionist | 06 Jan, 2020

Dr Michael Mosley first introduced the 5:2 fasting idea on a TV show back in 2012. Since then, fasting has grown in popularity and there are many variations in terms of the length of fasting window and calorie intake on the fasting days. Fans of fasting point to the health benefits - which extend beyond weight loss or maintaining a healthy weight. But is one fasting regime better than another? Let's discuss!

Weight loss

Intermittent fasting can help with weight loss, simply because it's a way to restrict calorie intake. Whether it's significantly reducing your intake for two days of the week or minimising your eating times to an 8 hour window every day – these approaches inevitably lead to a reduced calorie intake. Research comparing weight loss in individuals who fasted for two days of the week compared to those who reduced their calorie intake by 20% every day, found no difference in the amount of weight lost. This suggests intermittent fasting is no better for weight loss than simply reducing your calorie intake a little each day.

Health benefits

There are countless studies looking into the effect of intermittent fasting on the health of rats, with very promising results. Some research has been conducted in humans, showing similar effects on blood pressure and insulin resistance. However, in order to improve the quality of the evidence base, long term studies in humans are needed to establish whether intermittent fasting produces lasting results and positive effects for longevity.

That said, some research has found that intermittent fasting can result in:

  1. Increased insulin sensitivity
  2. Reduced blood pressure
  3. Reduced bad cholesterol levels
  4. Better blood sugar control
  5. Improved appetite hormones regulation
  6. Increased growth hormone secretion

Many of these factors will result in a reduced risk of chronic diseases such as diabetes and heart disease.

While the evidence for the health benefits of intermittent fasting in humans isn't yet concrete, there's little evidence to suggest it could be particularly harmful if conducted sensibly. So if a particular fasting approach suits you and your lifestyle, by all means give it a try and potentially you could be benefiting your health in multiple ways too!

Which fast is best?

There are various intermittent fasting approaches being popularised right now, but is any one more effective than the others?

Let's quickly outline how each works:

  1. 5:2 fast – the original and very well known approach to intermittent fasting requires you eat normally for 5 days and restrict calories on 2 days each week. Originally it was suggested women restrict to 500 calories on fasting days and men to 600 calories. However this has been revised in recent years to recommend 800 calories on fasting days. There is also a 'rapid weight loss' phase to this diet, which recommends having just 800 calories per day for 2-12 weeks. This should only be done under the guidance and approval of a medical professional.
  2. 16:8 – this approach requires you to fast for 16 hours a day and only eat during an 8 hour window. So for example, eat your evening meal by 7pm then don't eat anything else until 11am the following day.
  3. Alternate day fasting – this requires you to fast every other day for an entire day. Some versions allow 500 calories to be consumed on the fasting days, while others require a complete fast.
  4. Warrior diet – this approach suggests eating raw fruit and veg during the day, then eating a huge meal in the evening during a 4 hour window.

Some approaches don't require you to monitor your calorie intake, but rather rely on you naturally consuming fewer calories across the course of the day or week. The premise is that if there are less hours in the day when you can eat, you will consume fewer calories, and when you do eat, there's only so much food you can manage in one meal. This means they can all be effective approaches for weight loss.

Not all approaches have been rigorously studied – in fact, despite it having the most spotlight, the 5:2 approach hasn't been subjected to much long term research in humans especially. It's mostly backed by research in rats and the general idea and proposed benefits of intermittent fasting – but currently there is nothing to say this fasting approach is any better than the others highlighted.

Does when we eat matter?

There is much research to support the idea of eating more food earlier on in the day, and gradually reducing our intake until early evening. One study found that women who ate their largest meal at the start of the day, lost twice as much weight as those who ate their largest meal at the end of the day. This is believed to be due to our body's natural circadian rhythms and when it is most geared up to receive and metabolise food.

On top of this, research involving prediabetic men found that if they ate all their calories within an eight hour window (between 7am and 3pm), their blood pressure reduced and insulin sensitivity increased – when compared to eating the same amount over 12 hours.

These findings highlight the importance of meal timings and general dietary patterns for maintaining good health and weight loss.

Bottom line...

If your goal is to lose weight, intermittent fasting may not produce any better results than a standard calorie reduction diet. That said, it's about finding an approach that allows you to stick to a reduced intake most easily. Some people prefer to have two very strict days in the week and then 5 days more relaxed eating, others find that limiting their eating window helps to prevent excess evening snacking for example, whilst others find it preferable to moderately reduce their food intake every day.

At the end of the day, it all comes down to finding a sustainable approach that works for you. While the evidence may suggest sleeping for 8 hours, then eating a healthy breakfast at 7am, followed by additional healthy meals until 3pm, then fasting for 16 hours until the following morning, may be the best approach for weight loss success, general health and longevity – that's not a particularly realistic lifestyle for many of us.

We're social animals, and much of our socialising or family time is in the evenings, or over dinner. There is no need to give this up in order to be healthy. Eating good quality calories and staying a healthy weight are most important, however you achieve this. A regular eating pattern also seems to help. You may decide to follow a moderately reduced calorie intake each day. Or you could try the 16:8 approach but have your eating window later in the day – there may still be the same health benefits from the period of fasting no matter when it is carried out.

Take home!

Find an approach that suits you and that you can stick to – that's the best way to achieve long term success.

One final thing...

The Nutracheck App has a setting to support the 5:2 diet; select your 2 fasting days of the week and set your calorie target - either 500 calories or 800 calories. To find the 5:2 diet setting, open the App, tap the white icon top right on the screen, then scroll down the page.

Nutritionist Emma Brown (ANutr), MSc Human Nutrition is passionate about how food science applies to the human body, and how the nutrients in what we eat affect us and ultimately have an impact on our health.