Why do cancer and AIDS patients lose weight so rapidly?

Chris - Actually, this is a phenomenon that's very well described. People who get malignancies very often lose dramatic amounts of weight and people who get HIV also lose enormous amounts of weight. What they both have in common is that the immune system is often driven into overdrive. It's pushed very hard. But scientists didn't really know, aside from saying, it must be some kind of production of signalling hormones in the immune system. They couldn't really tell exactly what the culprits were. But then about a year - no, a couple of years ago now almost- a paper was published in Nature Medicine. It was by Haiko Yonan et al and what they did was to find one of the factors that seems to cause this dramatic weight loss. They were using mice and they had mice in which they implanted a prostate cancer sample. And those mice went on to lose dramatic amounts of weight and when the scientists compared the levels of various chemicals in the blood of the mice with healthy mice, they found that one chemical in particular, MIC-1, Macrophage Inhibitory Cytokine -1 was at very high levels. And when they gave antibodies to that particular chemical, the mice didn't lose any weight.So it looks like it's the immune system, trying to respond to the cancer or being manipulated or thwarted by the cancer and it makes these abnormal signals that it shouldn't make. And they then cause the appetite centre in your brain's hypothalamus to go off kilter and it causes people to lose their appetite and stop taking in the right amounts of food. So, they're burning off lots of energy, but they're not replacing the calories. And as a result, they end up getting too thin and they lose all that dramatic amount of weight.The fact they've identified one of these factors is really good news because it kind of suggests that we might be able to reverse the process.