Intermittent Fasting: Is It Just Another Fad Diet?

Debunking The Latest Weight Loss Craze

Many people practice intermittent fasting to lose weight or improve their health. But does fasting actually have any health benefits?

Intermittent fasting is the latest weight loss craze. There are many other perceived health benefits of intermittent fasting too. Also known as 5:2, 1:1, and 8:16, intermittent fasting is becoming a popular way of eating for many health-conscious individuals. But is it actually healthy to practise intermittent fasting? Or is it just another fad diet?

To answer these questions, let’s first define what intermittent fasting actually is.

Fasting is the absence of energy-containing foods or beverages in your body. In other words, it’s when you haven’t taken in any calories for an extended period of time. For example, if you haven’t eaten all morning but have had a milky coffee, you’re not in a fasted state. Why? Because milk contains energy (i.e. calories). Whereas, if you’ve had nothing but water all morning, you’re in a fasted state.

Intermittent fasting is simply when periods of fasting are sandwiched between periods of consuming energy. You’re not fasting 100% of the time — you’re fasting intermittently.

None of us eat 24 hours a day. And, we all fast at night when we’re asleep. So what counts as a significant period of fasting alongside normal eating habits? How long do you need to fast before you can say “I practise intermittent fasting”?

There are many different ways to practise intermittent fasting. For some people, it’s 2 consecutive days of fasting per week and eating normally the rest of the time (i.e. the 5:2 diet) (Jane et al., 2015). For others, it’s alternating between fasting days and unrestricted eating days (1:1) (Jane et al., 2015). You can also practise intermittent fasting by skipping breakfast or dinner, thus narrowing the window during which you eat to 8 hours every day (8:16). These are all types of intermittent fasting.

There are 3 types of intermittent fasting: 5:2, 1:1, and 8:16. This is the ratio of time spent eating normally (the first number) versus fasting (the second number).

Now you know what intermittent fasting is. Why might you want to practise it?

When compared with the traditional weight loss method of cutting calories, intermittent fasting has more promise. This is because your body turns to alternative fuel sources during periods of fasting. It can’t get energy from food so it releases stored energy instead. So, in theory, you burn more fat for energy when you practise intermittent fasting, which results in weight loss.

But does this beneficial metabolic change actually happen? Does intermittent fasting promote weight loss?

If you’re obese, practising intermittent fasting may improve your blood sugar regulation, which can indirectly lead to weight loss — particularly if you have diabetes (Harvie and Howell, 2017).

However, scientific research suggests that there are no such health benefits for normal weight individuals. In fact, intermittent fasting could actually do more harm than good if you’re not overweight.

Why? When your body breaks down fats to make energy, it increases the levels of fatty acids in your blood. If you follow the 5:2 or the 1:1 diet, your fatty acid levels will fluctuate considerably, each time you start and stop fasting. During a fast, your fatty acid levels will be around 3 times higher than someone who isn’t practising intermittent fasting (Harvie and Howell, 2017). These fluctuating levels of fatty acids have the potential to hinder your blood sugar regulation (Harvie and Howell, 2017). This, in turn, may promote weight gain and predispose you to type 2 diabetes.

Intermittent fasting only appears to be beneficial to health in people who are overweight or obese — particularly individuals with type 2 diabetes.

What about the 8:16 method of intermittent fasting? Your fatty acid levels don’t fluctuate as much in 16 hours as they do during a 24 to 36 hour fast. Therefore, the 8:16 pattern (i.e. limiting your window of eating to 8 hours a day) appears to be a much safer way of practising intermittent fasting.

Animal research indicates that following a 16:8 eating pattern might have a positive influence on your metabolism — even if you’re not consuming less calories overall (Peek et al., 2012; Wegman et al., 2015). Animal studies also suggest that intermittent fasting reduces inflammation, slows the aging process, and protects against cancer — perhaps by altering the way that genes are expressed (Wegman et al., 2015; Boutant et al., 2016; Harvie and Howell, 2016). Sounds promising!

However, we don’t know the long-term implications of intermittent fasting on human health (Antoni et al., 2017). Even if you’re overweight or obese, there’s very limited research to support intermittent fasting as being superior to traditional calorie counting when it comes to weight loss (Harvie and Howell, 2017). And, according to rodent studies, if you’re under physical or emotional stress, you’re less likely to experience health benefits from intermittent fasting than if you’re not under stressful circumstances (Lara-Padilla et al., 2015).

In other words, you can’t consider your eating habits in isolation. You need to take into account your whole lifestyle before deciding whether intermittent fasting is right for you.

So, what’s the bottom line? At this time, scientists don’t really understand the potential implications of intermittent fasting on humans — especially beyond a time-frame of 6 months (Antoni et al., 2017). As I’m sure you’ll appreciate, we are much more complicated organisms than rodents!

In-depth human research is required before we can really understand the potential long-term implications — positive or negative — of intermittent fasting.

If you’re practising intermittent fasting, or considering it, make sure you get an expert opinion on whether it’s a good fit for you. Any type of restrictive eating must be considered alongside a thorough analysis of your medical history, genetics, personal preferences, and health goals to ensure optimal safety and efficacy.


Written by Sophie Ash, BSc (Hons), DipION — Research Analyst, Functional Medicine Practitioner, and Gastrointestinal Specialist (