Coded gray.

Wednesday 28 December 2005

Screenshot anime Narue no Sekai

Pic of the day: Leptin also plays an important role in determining the onset of puberty, particularly in females. I suppose this is why Japanese girls develop more slowly, since they grow up on seafood and physical exercise. (The youngsters in this picture are supposedly 14.) On the other hand, Japanese boys who are Born to be Fat can become sumo wrestlers instead of bullying victims. A more refined form of entertainment than ours, don't you think?

How is our leptin today?

It is definitely winter, even though there is nearly no snow. A small sprinkling of powder came down for some minutes, but the wind soon took most of it away. It has been blowing, blowing, blowing day and night. The wind magnifies the already below-freezing temperature to a truly arctic level. While I can carry stuff from one apartment to the next, a distance of 20 minutes, I have to walk briskly to keep my body temperature up, even with the stuff I am carrying. On a mere two trips yesterday I burned around 1000 kcal.

(Over and above a casual walk, doubling your speed will increase your oxygenation eightfold. Since you only use half the time, you only use four time as much energy, but that's still pretty drastic. So it doesn't just matter how far you go, but also how fast. I am not sure how long this particular "cube law" stretches, but it probably doesn't matter since there are limits on how fast you can run and for how long. You may now have an idea on WHY superspeed is not a very feasible superpower in real life, and why athletes have to train for years to squeeze out an extra tenth of a second.)

You may already remember this, but the average office man burns 2500 kcal in 24 hours. Women mysteriously manage to squeeze it down to 2000, despite having at least as high body temperature and a faster heart rate. I guess they are better insulated... the thin layer of fat just under the skin is very efficient, and women tend to have more of this even when they are not fat otherwise. Also men have a larger muscle mass, on average, and this mass burns more calories even when in standby mode. We are genetically predisposed to be ready for action at any time. Intelligent Design? You be the judge... (Judges seem to take a particular interest in that topic lately. Heh.)

***

Back on the topic of calories, I read an article in Scientific American from 1997 before I threw it away. (Yes, still throwing away stuff ... will it never end?) It didn't really tell me much that I didn't already know, but there were some details that passed me by back when the magazine was new and I was less interested in these matters than today.

That was the year after the hormone leptin was discovered, the signal molecule made by the body's fat storage (adipose tissues) which informs the brain and the rest of the body how much fat there is in store. To the dismay of the researchers, no obese humans had the mutation that they had found in mice. Also they had found 4 more mutations that produced spherical mice, so it dawned on the scientific community that this would not be such an easy matter to fix after all. More research was needed into how (and why?) the human body handled fat.

What they found was that humans have ... not quite a set point, but a slowly sliding point. Eat less, and the body starts to save energy, and disproportionally so. (Like 20-30% less energy used by muscles when you have lost 10-15% body mass.) Eat more than you need, and the body starts to burn calories just for fun. However, it does so mainly with carbs. Eat lots of carbs, and your body will start pointless burning within hours at most. But eat fat, and the body's fat metabolism hardly budges. It has other, long-term consequences, like regulating appetite, but no rapid response feedback.

This is where I am today, thanks to my problems with digesting fat. I have lost nearly 15% of my body weight, my leptin levels are almost certainly quite low (although there is still enough fat left for a few weeks of life). As a result, I am "eager for my meals" as the scientists so nicely puts it when they observe test animals. Presumably my muscles are operating way more efficiently, and my body is more reluctant to use my precious energy reserves just for heating, so I notice the winter cold more than before. But when push comes to shove, as it does when I confront the arctic winter, it is better to burn off half a day's energy ration than freeze to death. The human body is nothing if not pragmatic.

One interesting point that came up in the article was our glycogen management. I have already mentioned my theory that my family is burning fat at a glycogen level where most humans would burn sugar. As a result, we don't put on fat easily, but this is not as cool as it sounds: We will get insulin tolerance at a lower body weight than those who save all the fat as long as they have sugar. The article went far in saying that there are differences in various bloodlines as to how they manage the glycogen reserves, which are normally enough for roughly one day's use. As diplomatic as feasible, they pointed out that some ethnic groups put on weight much faster than others.

Oh, and sadly the controlled experiments on human volunteers gutted the old "knowledge" that yo-yoing your weight will make you fat. It won't make you any slimmer either. What happens is that people gradually gain weight after 20. When you diet, you fall behind your predisposed weight curve. But when the bubble bursts – and it virtually always does – you go right back to the weight you should have had, which is more than you used to have. You will still not be seriously obese unless you are genetically predisposed for it. And even then, you need to actually eat all that fat and not work it off. As a Norwegian fitness expert somewhat cynically said on another occasion, he had watched movies of the prisoners coming out of Hitler's concentration camps and none of them were fat, no matter their genetic disposition. The Sci-Am article was way more diplomatic about saying the same thing. They drew comparisons between native Americans of the same stock living in the Mexican mountains and in US plains and found a drastic difference.

Oh, and there was a direct correlation between gas (petrol) use in Britain and the body mass of the British. This and not the food consumption seemed to explain why they were putting on weight. This makes perfect sense to me. No matter how fat you are, you will lose weight if you move around on your two legs. Because if you carry 200 pounds extra, you are doing a lot of hard work just fetching your mail. Imagine walking for an hour with that much luggage. You'd probably burn thousands of calories... if you survived. (I think I'd start a bit smaller in that case.)

***

The article did not with a word touch on the connection between temperature and metabolism. I'll do, however. It is a well known fact that people who have lost much weight don't tolerate cold as well as we do. Whether as a result of chemotherapy, eating disorders or controlled caloric restriction for a longer life, they all start feeling cold before the rest of us. In part this is because of the insulating fat under the skin, as I mentioned above. But also the human body automatically burns with a hotter flame when the weather is cold. If you spend time outdoors or don't heat fully indoors, the winter season will gradually tune up your metabolism. If it can, that is.

People who naturally live in areas with cold winters used to have "brown fat cells" throughout their lives, not just in childhood as most of us have. These cells burn fat just for the heat of it, without using the energy for any meaningful work. Because of modern insulated homes, few adults have these cells anymore. They are lost when no longer needed. There are still some who have them in large quantities, but most of us don't. And if you grew up in Florida, forget growing brown fat if you move to Alaska to work there. Like the white fat cells, the brown don't multiply in adults, though they can become more efficient if they already exist.

Oh, and one more thing. Animal tests have shown that a balanced diet with only 70% calorie intake will substantially increase the maximum lifespan of an animal, as well as the time it stays young and healthy. Some humans are trying this now to live longer. In an unrelated experiment, human volunteers lost 15% of their body weight and were then given injections of leptin, As reported in The Economist, their appetite returned to the level they had while well fed, as did the energy usage of their muscles. The magazine thought this might be a way to keep your weight after losing those extra pounds, although it doesn't help to lose them in the first place.

But unless I am sorely mistaken, leptin will probably also negate the life-prolonging effect. I also notice that people who live low-calorie lives also lose their sex drive. (Evidently this takes somewhat more radical measures than I have been through, though...) I suspect that this is another "intelligent design" to let the organism survive through the lean years after some natural disaster, so they can bounce back and breed when the good times come back. Once you have passed on your genes (or had the chance but not used it), the natural order of things is that you die. (In humans, passing on the genes also includes raising your children and grandchildren, which is why we live such unusually long lives.) Give people leptin, and this energy-saving mode is likely to never kick in. Tinkering with nature is a tricky business.


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Six years ago: Shambhala spoiler
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