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This might seem like an obvious question, but I'm currently exercising a lot and losing a lot of weight (through diet), and I'm afraid that shedding this much weight that I'm putting myself in a catabolic state (i.e., shedding muscle as well).

My question is will you counter the catabolic effect if you're ingesting under 1200 calories (for example) but taking a lot of protein?

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If you take a look at my answer to a question on the max amount of protein the body can absorb, and use the ballpark number there, you will have sufficient protein to prevent your muscles from being catabolized.

I'm assuming the diet is very low carb or ketogenic? Essentially, when your dietary carbohydrate intake is lower than what the brain demands for food (roughly 125g/day), your body releases a few hormones to compensate. One of them is glucagon, which releases stored fat for energy as well as any stored glycogen in your muscles. After the glycogen stores are depleted (roughly 3 days) the body goes into ketosis, where the liver converts fat into ketone bodies--while at the same time starting gluconeogenisis which converts protein into energy. This is the catabolic state to be wary of.

The good news is that the gluconeogenisis is happy to convert dietary protein into energy, which saves your muscles and organs. This is also precisely why all ketogenic diets are medium to high protein intake.

Do be aware that intense exercise including heavy lifting, sprinting, or anything that gets your heart rate up high will increase your body's demand for energy. It can easily get to the point where gluconeogenisis will outpace a moderate protein intake. If you are intent on performing exercise like this, it is highly recommended to periodically do a carb refeed. Periodically is either once a week, or directly after your training. The purpose is to replenish your glycogen stores and help your muscles recover from the effort.

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