There are four types of nuclear radiation: alpha, beta, gamma and neutron radiation. The first three are the ones most commonly talked about but if asked which is the most damaging most would reply with gamma rays, probably thinking of the Hulk before all else. Their answer is sort of true. If you wanted to be stuck in a room with an emitter of radiation you would probably ask for an alpha emitter. But if you has to ingest the radioactive substance instead your answer should switch to the gamma ray emitter. This is because damage caused by ionising is inversely proportional to the distance these radiation can travel. The more ionising the more likely to ionise the air and be stopped. Gamma is the least ionising but will pass through anything that isn’t a metre of concrete. Alpha is the most ionising but won’t even get through a piece of paper let alone your skin. These effect of these three types of radiation on the body are well understood but what isn’t known is the effect of space radiation.
The radiation in space is of a different breed. Proton and neutron radiation is common along with fast moving heavy ions all together known as high energy particle radiation. Carbon-12, oxygen-16, silicon-28 and iron-56 all cause severe ionisation when passing though the body, even worse then alpha particles (helium-4) due to their much grater mass and charge. A study was performed by exposing mice to the worst offender, iron-56, and seeing what came as a result. It was consistently shown that apart from expected results, like cancer, the mice all seemed to gain weight over the twelve months after receiving the doses. It is believed that the mice have had their leptin producers damaged. Leptin tells the body when it needs to finish eating by inhibiting hunger once consumption begins. It should be noted that the radiation exposure was ten times the expected amount a human would sustain travelling to Mars. So the chances of astronauts gaining considerable weight is unlikely. But we should still be wary of radiation affecting the hormones and other possible illnesses that could result.