Intermittent fasting or IF has gained momentum over the past decade or so for it's claims of effective fat loss and health benefits.
But is it any different from a normal calorie deficit fat loss plan, and what about muscle loss ?
Firstly lets take a look at the different methods for IF
A daily fast- This is known as restricted feeding and involves an eating window of anything from 2-8 hours and a fasting period from 22-16 hours (including sleep time)
For example you could start your first meal at 12pm and finish eating by 8pm acheiving an 8 hour eating window and leaving a 16 hour fasting window until 12pm the next day.
This is the most popular method within the fitness industry.
Alternate day fasting- This involves fasting for 24-36 hour and usually once a week but could be more or less. This approach is regularly used in research and is highly effective at creating a calorie deficit. Eating slightly above your TDEE (total daily energy expenditure) is common during non-fasting days.
Extended fasting-This envolves fasting for more than 36 hours at a time and is usually done once a week or less. This is much less common and one that most individuals would find hard to stick to.
Pseudo-fasting- This method is very commonly used in research due to increased adherence in users. This involves two days a week on a very low calorie day usually 400-600 kcals and eating normally on the other five days (the 5:2 diet). A good approach would be to eat 25% of your maintenance calories twice a week and maintenance calories for the remaining five days.
Researchers concluded that IF energy restriction can be effective, however merely noted that IF appears to be comparable to continuos energy restriction ( a traditional diet)
with no difference between groups in terms of improving glucose tolerance and insulin sensitivity providing weight loss occured.
It was also noted that weight loss and waist cirumference reduction as well as blood triglycerides and pressure improved both in the fasting group and traditional dieting group.
A further study looked at muscle breakdown when comparing the two groups of a 16 hour fast and traditional diet, both at maintenance calories with adequate protein.
Some small differences where seen with the fasting group losing some body fat while maintaining muscle mass. ( both groups maintained muscle, only the fasting group lost a small amount of fat) The fasting group also saw in an increase in adiponectin, a protein used in fatty acid breakdown. However this was paired with a reduction in testosterone and thyroid hormone input so should be interpreted with caution.
What this shows us is fasting is no more than a form of calorie restriction.
However as a method this can really work for some individuals and adherence has shown to be high probably due to the strict eating and non-eating timeframes put in place.
It's also a good tool to experience true hunger as many of us have actually forgotten or never experienced it and some studies show that ghrelin ( the hunger hormone) can become blunted during the fasting period.
A note on fasted training- If training fasted nutritional intervention containing protein and carbs immediately afterwards is important as muscle protein breakdown rapidly increases after training.
If not training fasted, immediate post-workout nutrition is not needed though regular protein every 3-5 hours (depending on protein portion) is paramount for muscle protein synthesis.
Overall IF can be a great tool for fat loss if it works for you and your lifestyle. It can have individually varying benefits by reducing hunger, increasing dietary flexibilty and reducing cognitive effort. If you choose to give this method a go just make sure to tune in to your bodies response both physically and mentally.