Sunday 29 May 2005

Pic of the day: "The plan is... I want to make every woman on the planet fat except me" says this girl in the anime Sensei no Ojikan. It seems to be working, although the men are still fatter. But how exactly does it work? Can you really gain weight from sweets alone?

Sugar & Fat

I think I am gradually starting to understand more about body chemistry, particularly how we handle our energy reserves. It is a lot more interested when you can do hands-on experiments with your own body, and the experiments are a lot more interesting when you know what happens inside. Here's how I see it so far:

Insulin is your friend. This middle manager among hormones acts quickly rather than over time like the "brain hormones" that execute the body's master plans. Within its domain, it is pretty powerful. It reacts narrowly to blood sugar, which means you can kind of fool it, but it is not the only king on the hill. Here's what happens: When blood sugar goes up (as a result of eating), the islets in the pancreas make insulin. (There is no logical reason why these tiny organs should be in the pancreas. They have nothing to do with its digestive function at all. Probably the Creator just wanted them out of the way in a safe spot.) The insulin is basically an order for anyone who wants sugar to go get it. The two main customers are glycogen stores and fat stores.

The muscles store their own glycogen, like private businesses. The liver is the main reserve, 10% or so of the liver is glycogen storage. This is enough for a couple days of quiet fasting, or a couple hours of desperate fighting. (Which is why it is pointless to have your soldiers fight long battles unless you let them eat honey, as prince Jonathan pointed out.) The liver will do its best to keep the blood sugar level constant, and it is pretty good at it. Kidneys and intestines also store some glycogen and are willing to share if needed. The muscles don't even share with each other. The egoists.

Fat cells (in adipose tissue, or "fat weave" as we call it in Norway) also get the message from the insulin. For the duration, they will sensibly refrain from putting fat back into the bloodstream, since there is more than enough energy to go around already. They may be able to convert some sugar to fat, but humans are not very good at it. We need some building blocks of the fat from our food (or from storage) and can at best expand on it a little. The main reason why sugar fattens us is that we stop burning fat, which we would have done if not flooded with sugar. If you ate nothing but sugar cubes and water, you would not grow fatter in the long run. You would however get sick, it is very hard for the body to regulate the wild spikes of blood sugar that comes from eating pure candy. The blood sugar goes up and down like crazy as insulin forces the sugar out and then you get hungry and munch again, creating a new spike. Fun but not healthy.

Fat has its own secrets. The fat cells secrete tiny amounts each of another hormone, leptin. Less famous and less dramatic, it is simply a message to whoever wants to listen: There is now so and so much fat in stock. The brain uses this info to regulate appetite over time (insulin may influence it on a shorter timescale, but leptin triggers effects that last for days). The liver probably also takes this into consideration, as it does quite a bit of the body's fat processing, most famously cholesterol. If there is lots of fat in the food and the storage is not full, the surplus is sent via the liver to the fat cells. If you don't eat fat but have it in stock, the flow is reversed. If you eat almost no fat (less than 10% of daily calorie need) the body will even start dissolving the fatty plaques inside your arteries.

(This observation has earned a certain Dean Ornish, MD, a lot of fame, but only a few thousand people have been able to stand the pain of not eating fat. You think guys are suffering when they get "lonely"? Try setting them on fat-free diet for a week and they'll change their tune. It is a very real withdrawal, although it can be alleviated by various supportive techniques. Sounds to me like a pretty good alternative to dying young, but evidently most people prefer a lifetime on pills or the occasional surgery. I guess that says something about the power fat has over the human mind. Ornish still thinks it is a good idea, since it not only solves the artery thing but also prevents diabetes, erectile dysfunction and bad breath.)

In related news, complex starches (from fruit, veggies, oatmeal etc) give off sugar to the blood slowly over time. This is widely considered a good thing, since you don't get the roller-coaster of sugar and insulin spikes. But in truth, most people handle this sugar yo-yo quite fine, unless they are also fat. Why? That proved hard to find out, because the most quoted nutritionists – despite their internal rivalry – are united in an almost fundamentalist hate toward refined sugar. I think I have an idea, though.

As I mentioned at the start, insulin has two basic functions: Convert sugar to "animal starch", and store fat. If the stores are full, there is not much you can do. In an emergency you can rid yourself of sugar through the kidneys, but by then you probably already have diabetes ... it is one of the most notable symptoms. If you are lean, however, it is easy for the body to stove away all the fat for the duration of the sugar spike, and also to spend some of the glycogen during off hours. The less fat on the body (and less leptin in the blood) the more likely the body is to use of the sugar reserves and let some of the fat stay. After all, fat has many uses in the body. It is a component in hormones, it is used to shield the nerves (much of the brain is fat) and it is used in the walls of the cell to give them the right consistency. Fat is indispensable, so the body will spend less and less of it the less there is left. (Women will also often retain a cache to help them through one pregnancy and some months of breastfeeding. Only outright hunger can make them use this reserve for other purposes. Sounds about right to me.)

So, the less fat you have on your body, the less likely your carb storage is also full. Thus, when you get a sugar spike, the alarm sounds and the cells all rush out in the street, grab the sugar and haul it in. In an amazingly short time, it is all out of sight, and life goes on. If you are fat, the sugar stores are almost full as well, and nobody can be bothered to do anything about the sugar. At least that's the theory that makes sense to me. Further experimentation is in order.