We get asked about this approach all the time because a lot of people have been told or have read on social media that this approach is better for fat loss than other diets because of the fasting element. So we wanted to give you the facts so you can decide whether this method is for you, based on the current evidence!
WHAT IS INTERMITTENT FASTING?
Many people think that this approach is much more complex than it actually is. Intermittent fasting is essentially an eating pattern where you cycle between periods of eating and fasting. It is (like all other diets) a method of calorie restriction, with the only real difference between IF and “normal” caloric restriction being that the fasting periods are longer in duration and further apart from each other. If you think about it, we actually all do some form of IF every single day when we sleep!
There are some different types of intermittent fasting which include the following:
- Alternate day fasting (ADF): this involves a 24-hour fasting or very low calorie (~25% of daily energy requirements) period, alternated with a 24-hour eating period.
- Whole day fasting (WDF): this usually involves 1-2 days of fasting or very low calorie (~25% of daily energy requirements) periods per week, with the remaining days of the week eating at maintenance (which is essentially what the 5:2 diet is).
- Time-restricted feeding (TRF): this involves a fasting period of 16–20 hours and an eating period of 4–8 hours daily. The most popular approach is the 16:8 (16-hour fasting period, 8-hour eating period).
WHAT ARE THE CLAIMS?
The claimed health benefits of intermittent fasting range from improved weight loss, to prevention of diabetes and cardiovascular disease, to preventing or even treating cancer. However, most (if not all) of these claims are not supported by convincing evidence. Furthermore, the evidence we do have is usually from animal models. These are 4 of the most common claims that are made about the benefits of IF in terms of body composition:
- Improved fat loss
- Higher Resting Metabolic Rate (RMR)
- Increased muscle retention/building
- Increased insulin sensitivity
WHAT DOES THE EVIDENCE SAY?
A large systematic review of intermittent fasting conducted by scientists from The University of Sydney, which analysed 40 studies on intermittent fasting (with 12 comparing it directly to normal calorie restriction dieting), found no significant benefits related to body composition, fat loss, insulin sensitivity, or hormones. Here are some of the takeaways:
- IF and normal calorie restriction results in identical weight and fat loss when calorie and protein intakes are the same.
- IF and normal calorie restriction results in no significant difference in muscle loss when calorie and protein intakes are the same. Under normal circumstances, no serious muscle loss can occur until you’ve fasted for 12 to 16+ hours.
- IF does not result in better muscle growth than a normal calorie-restricted diet.
- In most studies, the reduction in metabolic rate is similar with IF and with normal caloric restriction, when total calorie intake was the same and when measured on feeding days.
- Studies that compared IF to normal calorie restriction reported variable results with regard to improvements in insulin sensitivity when total calorie intake was the same.
- Both IF and normal calorie restriction results in comparable reductions in leptin, free androgen index, high sensitivity C-reactive protein (inflammatory marker), total and LDL cholesterol, triglycerides and blood pressure.
So what’s the bottom line? IF provides similar benefits to normal calorie restriction when it comes to weight loss and metabolic effects.
WHEN WE WOULD RECOMMEND IF
Now that we’ve discussed the science stuff, let’s talk about what you really want to know – should you consider intermittent fasting? Here are some reasons why you might:
- It works. We know that in order to lose weight we must be in a calorie deficit (eating fewer calories than we are burning). By fasting, you are making it easier to restrict your total caloric intake over the week, which can lead to consistent weight loss.
- It can improve your compliance. By reducing your eating period each day, IF allows you to enjoy bigger meals, which can help you to feel fuller for longer. This alone can help you stick to your diet for longer, which will provide better results.
- It simplifies your day. Having to prepare, pack, eat, and time your meals every 2-3 hours can be extremely time-consuming. By reducing your eating period, you can save A LOT of time as you only need to worry about preparing and eating 1-3 meals. It can also save you money on your grocery bill!
- It can remove food obsession. From our experience (both personally and through working with our clients), a lot of people can get obsessive over when their next meal will be. Because you are eating less often with IF, it can help you to stop constantly thinking about food.
WHEN WE WOULDN’T RECOMMEND IF
For some people, fasting can be harmful to their health depending on their current health status. Keep in mind that IF is not for everyone. People with impaired glycaemic control (diabetics) should avoid fasting as it causes poorer glucose response. Also, if you’re pregnant, underweight, younger than 18, or have a history of disordered eating, IF is probably not for you. It’s always best to speak to your health practitioner before starting any new health or diet regime.
TAKE HOME MESSAGE
Intermittent fasting isn’t for everyone. Some people love it and some people don’t! At the end of the day, IF is just one of many different (and effective) approaches for improving your health, performance, and body composition.
As always: Do what works for YOU and remember that the best diet is the one you can stick to!