A while back, I posted a Facebook status about my 24 hour fast followed by some sprint intervals in the sun and a cold shower, and was asked why I do this. Apart from just feeling really good, there are some specific reasons I choose to intermittent fast, work out on an empty stomach, and take a cold shower every once in a while. Yeah, clearly I don't buy into the whole "eat 6 small meals a day or you will go into starvation mode, and lose all your muscle, and get fat, and unable to lose it!" I'm here to dispel some of the myths. There is lots and lots of info out there, but I'll just go through the basics...
This has a ton of health benefits for most people. It works in a similar way to calorie restriction but without the constant hunger and inevitable muscle loss that goes along with it. It is theorized our hunter gatherer ancestors went through periods of feast and famine, and this makes sense when you consider how re-enaction of this positively influences our bodies. Some of the health benefits for fasting every now and again are lower fasting insulin, greater insulin sensitivity, improved exercise recovery and improved blood lipids. Let's go through them one by one shall we??
Improved insulin sensitivity - This study showed that after two weeks of intermittent fasting (20 hours every second day), plasma adiponectin increased by 27%. Adiponectin is positively correlated with insulin sensitivity. Muscle glycogen was unchanged, while liver glycogen reduced. This makes sense in evolutionary terms as on a fast we would have needed our muscle glycogen to hunt/find food.
Workout benefits - This flies in the face of most 'conventional wisdom'. Exercising while fasted increases the insulin sensitivity benefits. It stimulates glycogen resynthesis (it was around 3 times higher in a group who exercised fasted compared to a group who exercised after a carb rich meal) Intramuscular triglycerdies were also broken down while fasted but not when carbohydtae was eaten. Muscles thus, are better able to adapt to exercise stresses when fasted, so when glycogen levels are full, your workout will be miles better as your muscles have adapoted to working on low glycogen just fine! The study also found that peak VO2 and peak power improved more when training fasted compared to training in the fed state!
Fat loss - when intermittent fasting most people tend to automatically eat less. Coupled with the increased insulin sensitivity and the fact you are giving your body a rest from the processed refined carbs that most people eat, it will be much easier to burn your fat WHILE maintainting muscle mass. It's a win win!
Longevity - It;s been widely established in many animal species that calorie restriction extends life. However, I can't imaine life being very fun if you're constantly hungry. But luckily, intermittent fasting appears to have the same benefits. Technically you're not restricting calories to a great extent, as you eat extra when you eat to make up for the food not eaten during the fast, but the intermittent nature has been shown to increase lifespan nevertheless. And MUCH easier than eating salad all day,
Brain health - Studies such as this suggest intermittent fasting and calorie restriction can improve neuronal plasticity and inhibit brain degenration
Intermittent fasting is simple yet profoundly beneficial, though I would recommend eating fairly 'primally' (that is, a lower carb diet made up of more natural, whole foods, as you can read about in my dietary philosophy) before fasting, as this way of eating primes your body to be good at burning fat as well as glucose. Thus instead of crashing when not eating, you feel full of life, as your body is efficient at burning your fat stores for energy! To find out more check out Marksdailyapple (he has many excellent, thorough and easy to read posts on the subject).