does the body burn fat or muscle first?!
Question: Does the body burn fat or muscle first?
also, muscle is made of protein, but i've heard that the body burns protein first.. does this refer to muscle protein or food that we've just eaten that contains protein?
Is it different in different scenarios, such as starvation mode vs. running for one hour?
Depends on a lot of things. You're body will never burn your actual muscles (unless perhaps you have been starving for months and are on the brink of death?) but it does like to burn protein before it burns fat. Fat is a last resort energy reserve for your body, to be used only if you're starving. However, if you're eating constantly (6 meals a day or so) then you're body won't hesitate to burn fat as you are constantly getting energy from your food. You're body burns carbs first because they are easy to convert to energy, but interestingly enough, fat contains more energy per gram than carbs.
If you don't eat enough fuel calories (carbs or fats), then the body converts dietary protein to a very inefficient fuel source & then catabolizes it's own lean tissues for nutrition. There is no nutrition in body fat stores, only energy.
If you eat adequate fuel calories (carbs or fats) & adequate protein then the body has no need to catabolize muscles.
Carbohydrates >9g per hour triggers insulin, the storage hormone. While the body is in storage mode, it can't access body fat to burn.
Low calorie diets work by forcing the body to catabolize tissues for energy & nutrition. The body is built for survival. The body assumes it's in the middle of a famine if you can't provide adequate nutrition. Muscle tissues are a great drain of caloric needs & become expendable during times of famine.
Low carb diets work by trying to reach homeostasis (the state of being normal) & excess fat stores are not normal so it releases body fat stores but only if adequate calories & adequate protein are provided.
It takes the body a couple of days of low calories before starting to shut down the metabolism.
when you're fasting - glucose needs to be increased so you can break it down and use it for fuel. you do this by glycogenolysis or gluconeogenesis-- which occur in the liver. since you're asking only between fat and muscle, i'll ignore liver but keep in mind that is the first place your body looks toward in order to raise blood glucose levels.
so between fat and muscle, i would assume muscle would be used first. because once protein is broken down to amino acids, the amino acids can be used as carbon skeletons for gluconeogenesis to raise blood suguar.
now once you're STARVING -- beyond fasting -- The rate of gluconeogenesis decreases as the supply of amino acid carbon skeletons from muscle protein catabolism decreases. Therefore, your body now needs a new way to get fuel. You start breaking down Fatty Acids into Acetyl CoA. It does this because too much acetyl-Coa slows down TCA cycle and shunts all that Acetyl-CoA into making Ketones. Ketones is your new source of energy...
since you're asking about starvation, i would say FAT breakdown.
if you asked about fasting, i would say MUSCLE breakdown first.
My sister lost over 20 last spring using acai to help her increase her metabolism. She never felt jitterys. It might help you too.