Intermittent fasting seems to be the next big thing in diet circles at the moment, claiming to improve insulin sensitivity, blood pressure, cholesterol levels, reduce the risk of cancer and even prolong life and reduce weight (sounds like a miracle if you ask me). The idea of reducing your energy intake from food to lose weight is nothing new, fasting has been a part of many religions for centuries, however fasting for health and weight loss is a relatively new on-trend concept.
Intermittent fasting – What is it?
Intermittent fasting encompasses several different dietary behaviours, all of which focus on controlling the period in which food is consumed. These behaviours dictate a fasting and feeding schedule of various lengths. However, there is not a restriction placed on the types of foods consumed during feeding times.
There are a few differences between the most popular methods of intermittent fasting
- 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). To put this in context, two boiled eggs, a slice of wholemeal toast, and an apple. Fasting days can be consecutive or separated throughout the week.
- Eat-Stop-Eat: Involves fasting for 24 hours, once or twice a week.
- Time restricted eating: Daily fasting for a minimum of 12 hours. The most popular is the 16/8 Method which involves restricting your meals to an 8-hour window each day (e.g. 12pm – 8pm) and fasting for 16 hours.
Does intermittent fasting cause weight loss?
Usually the answer is yes, but before you start skipping breakfast – it is important to understand why. The reason why people who fast (or go on any diet for that matter) usually lose weight is because they are eating less kilojoules than they were before – not because of the fasting per se.
Fasting will cause weight loss – because the total amount of energy you are eating in a day is less than before. However, the research so far has not found that fasting increases metabolism or improves food choices. Scientific evidence demonstrates that people who slightly reduce their energy intake day to day by making better food choices lose the same amount of weight as those who fast.
So the question is – can you really sustain intermittent fasting for a long period of time and is it a realistic long term solution that fits with your lifestyle? 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 and is not sustainable.
Are there other health benefits of intermittent fasting?
There are currently no human studies to date that have shown that intermittent studies reduce weight in the long (LONG) term, reduce the risk of cancers, prolong life expectancy or quality of life in any way. Please speak to a qualified Dietitian before choosing an intermittent fasting diet to reduce your risk of disease.
Is fasting suitable for athletes?
We know that lower intensity exercise draws predominantly on fat as a fuel source. While higher intensities have an increased reliance on carbohydrate as a fuel. With insufficient fuel at high intensities, you slow down to allow the body to utilise more fat as a fuel. Studies have shown that in both professional and recreational athletes, VO2 max decreased by up to 12% during an intermittent fasting routine. However, regardless of type or intensity of exercise, all athletes reported feeling higher levels of fatigue.
Recovery is also significantly impacted if you are not able to refuel after a session. The ingestion of protein and carbohydrate post-exercise increases muscle synthesis and replenishes glycogen stores. If you are unable to adequately refuel post-exercise or even during the following 24 hours, this can result in muscle breakdown and inadequate energy stores to complete training on subsequent days.
With that being said, it would be difficult to incorporate intermittent fasting with a heavy training load, however, there are certain adjustments you could make to try and minimise negative effects by seeking the advice of a Sports Dietitian to develop a strategic plan.
Potential positives of intermittent fasting
- Weight loss.
- 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.
- May reduce snacking at night
Potential negatives 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.
- Constant kilojoule restriction is not practical or easy for many of us in the long term which may make this diet unsustainable for long term results.
- There is limited evidence about the long-term effectiveness or health issues related to intermittent fasting.
- You may experience headaches, fatigue, extreme hunger, mood shifts and low energy levels on fasting days. This may make it difficult to concentrate, perform at your best, (and be a supportive nice friendly human in general). Think of this like HANGRY on steroids.
- 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 may actually lead to weight gain rather than weight loss.
- Designated fasting periods may make it difficult to participate in the social sharing of a meal.
- There is no mention of exercise in studies, and many may find it difficult to exercise on fasting days.
The Bottom Line
In reality, any ‘diet’ that encourages an energy deficit – that is, means you take in fewer kilojoules than you expend through exercise and daily activities, will result in weight loss. But for lasting, long-term health benefits, it’s best to find an eating pattern that you enjoy, and can stick with.
We are all different, and there is no one-size-fits all approach when it comes to eating. While intermittent fasting may suit some people, it is not a magic bullet to improved health.
For nutrition advice specifically tailored to you, see an Accredited Practising Dietitian. They are passionate about translating the latest evidence on healthy eating into practical, everyday advice and tips, and can support you on your journey towards better health.