Ash Thomas - Dietitian, Nutritionist & Triathlete
There are way too many diet trends. Why? Because everyone eats, everyone has an opinion and we still don’t know everything about the human body and frankly I don’t think we ever will. If you look at most of the current diet fads; Paleo, 5:2 diet, fasting, ketogenic, there is a common trend in all of these. Caloric restriction!
There are pros and cons to every eating regimen, but l will focus now on Intermittent Fasting, as there is much talk about it.
What is Intermittent Fasting - IF?
IF hit popularity over the last few years due to its proposed benefits of reducing fat mass, insulin sensitivity, cholesterol levels and decreased inflammation. Fasting is defined as choosing to abstain from all foods and calorie containing drinks for a set period of time. The most popular fasting diet is the 5:2 diet, where you consume 500-600 calories for two days of the week, then there is a five day period of flexible eating where there is not often a caloric target to hit. There is also the 16:8 diet, where you fast for 16 hours a day and eat within an 8 hour window.
Does intermittent fasting assist weight loss and enhance metabolic health?
There are a number of studies that conclude that fasting may; boost the body’s defenses against blood pressure, assist control of insulin levels, assist gut health, reduce inflammation and YES weight loss (mostly in obese population). However the reason why we get these health benefits is due to the reduced caloric intake. The question is could you stick to these periods of fasting for months on end? I certainly couldn’t! Most of the research done on intermittent fasting to date has been based on animal studies, obese populations and some on athletic males. While animal studies can be a good indication on a topic, a rat’s body does not work the same as a human’s body. This is the same for obese population metabolism to athletic population and males to females, hence clear conclusions are hard to be made.
Pros to intermittent fasting
- Potential weight loss (mostly in obese population)
- May curb cravings
- May reduce inflammation (mostly in obese population)
- May assist insulin sensitivity (mostly in obese population)
- May improve cholesterol (mostly in obese population)
- May assist gut health
- Training fasted may assist mitochondria adaptations in muscle cells in males
Cons to intermittent fasting
- No consideration for quality of diet
- Training fasted can easily put an athlete into relative energy deficiency (REDs), impede recovery and reduce training performance
- When women fast their cortisol (our stress hormone) levels spike, which may encourage central fat storage
- When you come out of a fast your body is likely to respond by storing energy away to prepare for the next fast
- Your metabolism may down-regulate (slow down)
- Impedes on social activities
- May experience headaches, fatigue, extreme hunger and low energy levels on fasting days
Ash’s verdict on intermittent fasting
If you choose to add in intermittent fasting do it while you sleep! There Is a 10-12 hour window overnight where fasting is natural, your metabolism is already low and therefore you don’t get into a compromised position of low energy availability. If you are looking for mitochondrial adaptations to training only fast before really easy sessions e.g. easy swim, easy bike. For females fasting before training may counter adaptations to training by increased cortisol levels so eat something small (150-200cal) before you workout, especially in the morning!