Yes, it kind of does. Laughing gas is nitrous oxide, and it acts as an anaesthetic-type agent. It makes your brain feel a bit woozy in the same way that alcohol does. As a result, if you take some laughing gas, you fell a little bit drunk and a little bit cheerful. If you have enough of it, you start to feel a little bit sleepy, but it's very good at pain killing. If you're having an operation, it's sometimes used with other anaesthetics to kill pain and make you more comfortable. There is a sub-set of people in the population that have a particular form of a gene that is involved in making new blood cells. If they have this sub-set and have laughing gas, then it can affect their bone marrow in the long term. It can make your bone marrow work less well. Luckily, it's only temporary, but I don't think that I'll be inhaling lots of laughing gas.

Initially, the blood is red due to the oxygen in the haemoglobin. As it sits around, it loses its oxygen and turns a purple colour. After that, the body starts to metabolise the blood products into more red and green pigments. You can tell the approximate timing of bleeding by the combination of those pigments. Haemoglobin is made of four rings joined together, a bit like a clover leaf. When you first bleed, you get that stuff in your bleed. Very quickly after that, cells move in and start attacking that molecule and break it open into a long chain of these rings. That's a molecule called bilirubin, and another related molecule called biliverdin. Biliverdin is a green colour and bilirubin is a browny-yellow colour. Too much bilirubin is what makes your skin go yellow when you get jaundice. All these things happen just in the site of your bruise or bleed, and that's why your bruise changes colour from a red to a browny-green to yellow.

They all boil down to the same question, which is what underlies the differences between human beings between their body weight trajectories throughout life. In other words, why do some people remain thin while other people become fat. Obesity is terribly simple. There are just two sides to the equation and that's energy in, that is how much you eat, and energy out, how much you expend. So really we all know the answer, and that's that one side is greater that the other. The paradox is that it's very difficult to accurately measure energy in and energy out in any one individual throughout their life. You only need a tiny disturbance on a day-to-day basis, such as a half finger of twix too much every day for thirty years, and that can add up to 20 kilograms of weight. Our ability as scientists to measure each individual is difficult, especially when we try to take into account what people perceive as stuffing themselves. Ken's idea of stuffing himself might be nothing in comparison to my idea of stuffing myself, and I'm a big guy! Our research suggests that genetics is an underestimated factor. Body weights tend to run in families very strongly, and those genetic differences may affect the same parts of the brain that we talked about when we were saying about leptin hitting the brain. Our research is indicating quite strongly that it's variation in those parts of the brain might control both what you want to eat and in some cases, what you want to expend. If we can understand those, then perhaps we can manipulate them.

The answer to that is in fact quite difficult. It all depends on exactly how much activity that person is doing. A person doing a lot of exercise needs a lot more energy to keep them going. The advantage of exercise is that it does help to break down the fat, but I would say as a common sense notion that if you're eating more fat and having more cholesterol, it's not good for. So I would say to reduce fat.