You are a little off on the nutritional value of these aliens. Our bodies can process amino acids of a different chirality. You still might die of malnutrition though because our bodies only have pathways to build non-essential amino acids from scratch. You might also die from Kidney or liver failure as breaking down amino acids in the liver releases toxic ammonia, which the liver must turn into urea and then excrete through the kidneys. Normally more than less than 10% percent of proteins are broken down further than their constituent amino acids but imagine that number going to 100%. That would put one hell of a strain on your organs.

So organ failure or death from malnutrition...one of them will eventually get you on this sinister alien planet.