Intermittent fasting seems to be all the rage at the moment – mostly for its perceived weight-loss benefits. You may have heard claims that intermittent diets can improve insulin sensitivity, blood pressure, cholesterol levels, reduce the risk of cancer and even prolong life (wow that’s a long list!). One of the reasons this pattern of eating gets so much attention is because of the hope it offers for people caught in the yo-yo diet cycle. It is a topic we have been asked about a lot at our recent corporate talks, so we thought we’d delve into it a bit further. As always, our job is to pull apart the science and see if this is all nutibollocks or legitimate science.
What is intermittent fasting?
Intermittent fasting (of some sort) has been around for hundreds of years as part of different cultures and religions – or maybe just because food sources were scarce. The basic premise of intermittent fasting is an eating pattern that cycles between periods of fasting (not eating) and eating. It does not specify which foods you should and shouldn’t eat, but rather when you should eat them. In this sense, it is more like a pattern of eating rather than a ‘diet’.
What are the various types of intermittent fasting?
All fasting diets require you to restrict your usual energy intake and go for extended periods without foods, but there are differences amongst the popular approaches that you need to know about:
- 5:2 Diet: one of the most popular intermittent fasting diets which involves a ‘normal’ healthy eating days for 5 days a week and ‘fasting’ for 2 days a week. On these ‘fasting’ days you eat one-quarter of your usual meals, which is around 2100 – 2500 kJ (or 500-600 calories). Fasting days can be consecutive or separated throughout the week.
- 16/8 Method: involves restricting your meals to an 8-hour window each day (e.g. 12pm – 8pm) and fasting for 16 hours.
- Eat-Stop-Eat: involves fasting for 24 hours, once or twice a week.
Does intermittent fasting cause weight loss?
Yes (usually). Before you jump to conclusions and join the intermittent fasting bandwagon – it’s important to understand why.
The reason people who fast intermittently will usually lose weight is because they are eating less kilojoules than they were before – not because of the fasting per se. In fact, this is why most ‘diets’ (regardless of the rules/restrictions) will cause weight loss – because the total amount you are eating is less than before. The research so far has not found that fasting increases metabolism or improves food choices – so the question is – can you really sustain yourself for a long period of time on this diet (we couldn’t!). Therefore, while it may cause short-term weight loss, as with most diets, in the long term it is unlikely to be an effective weight loss strategy.
Does intermittent fasting have other health benefits?
Most of the research done on intermittent fasting to date has been based on animal studies. While animal studies can shed light on a topic, a rat’s body and a human’s body don’t work the same way and hence we can’t make clear cut conclusions. The small amount of research that has been down (on rodents) has shown some initial benefits of fasting such as improvements in gut health and cholesterol levels. One of the theories behind the benefits of fasting is that the body’s cells adapt to the mild stress of fasting periods and this is thought to enhance resistance to disease. Think of it like exercise – where your muscles are under stress. As long as your body has time to recover, it will grow stronger. There is a similarity between how cells respond to the stress of exercise and intermittent fasting. It’s still unclear whether any of these health benefits are due to the act of fasting or just the overall reduction in kilojoules.
So far no human studies have shown that intermittent studies reduce weight in the long term, reduce the risk of cancers or prolong life expectancy, so please don’t use these reasons to jump on the bandwagon.
Potential benefits of intermittent fasting
- Weight loss.
- Contrary to what you may expect, early research shows that people do not over-consume kilojoules on non-fasting days.
- May curb food cravings.
- May help you tune into your hunger signals.
- May reduce inflammation.
- May improve cholesterol levels.
Potential downsides of intermittent fasting
- The quality of your diet may not improve, since you are not educated around what types of foods to eat or not eat (we want to encourage people to choose healthier foods).
- Constant kilojoule restriction isn’t easy nor practical for many of us in the long term, so you may not sustain the diet long enough to see results.
- There is limited evidence about the long-term effectiveness or health issues related to intermittent fasting.
- You may experience headaches, fatigue, extreme hunger and low energy levels on fasting days. This may make it difficult to concentrate, perform at your best.
- A smaller total number of meals means there is less opportunity to get essential nutrients in if you do not plan carefully.
- May slow your metabolism – some fasting diets appear to slow metabolism in an effort to conserve energy. This might mean you gain even more weight when you finish.
- Designated fasting periods may make it difficult to participate in the social sharing of a meal.
- There is no mention of exercise, and many may find it difficult to exercise on fasting days.
The Biting Truth’s verdict
While intermittent may help you to lose weight in the short term – the long term effectiveness and health benefits are yet to be understood. Personally, we do not like the idea of starving the body. It is important to understand that all diets essentially result in weight loss by ensuring that you eat less kilojoules than you spend – they’re just different means of doing so.
The main thing you need to consider is whether the diet is sustainable in the long term for YOU. Our approach is to adopt healthy eating habits that you can sustain for life and which nourish you rather than restrict you to certain foods. To figure out whether intermittent fasting is your match, see an Accredited Practising Dietitian.