On a cleanse/starvation diet your brain is deprived of glucose (from food) and will become fatigued, headaches, etc……true. When you deprive your body of sustenance it uses your fat (first) and muscle (days later) for nutrients. The highest “energy source” “stored” in your body is found in adipose tissue (fat). When you don’t eat or starve/cleanse your body goes through a process called ketosis (fat (triacylglycerol) is cleaved into 3 fatty acids and 1 glycerol (carb)) which allows the brain to feed off “glucose” to function. Bodybuilders use this technique in there profession on a daily basis and can track ketosis through ketone strips that they urine on (you can purchase them at Walmart). If you starve yourself to lose weight, you will find rapid weight loss. You’ll lose the weight right off, and you’ll look great. However your body is smart. It knows that you starved it, so as soon as you start eating again, it stores anything and everything it can from the food you are eating, just in case you starve yourself again so that it has something to live off of. You can use a cleanse technique for 24hrs to shed off toxins/pestisides/herbisides/etc found in the body…fat surrounds these toxins in order to protect the body from harm (lots of speculation), whatever the case, the body breaks down fat (FOR ENERGY). I recommend cleansing once or twice/month, allowing the body to break down adipose tissue without dramatically affecting ones metabolic rate.