H Veeder <[email protected]> wrote: > > I wonder if it can also explain why some people can eat relatively little > and not wither away. >
This is always caused by effective digestion. There are large differences in how much food some people can digest than others. People who eat a lot but remain thin are excreting a great deal of undigested food. This is not healthy. In some cases it is because they lack the genes to digest one particular food group, such as milk. There are no differences in metabolic efficiency. That is, 1 g of fat always converts to 16.8 J heat and energy. There are minor differences in basal metabolic rate (BMR) for different people. It depends on your size and weight, but even people of the same size and weight may vary by ~5% or 10%. This was established during WWII when hundreds of volunteers in the U.S. were subjected to starvation under medical supervision. Some obese people have the notion that they have "slow metabolism" (which can only mean a low BMR as far as I know). They think this causes obesity. They are wrong. The widest range in metabolism for a given body weight and size amounts to about 50 kcal per day. One piece of bread will make up for it. See: http://dietuni.com/diet/the-myth-of-slow-metabolism This shows a short segment of a BBC documentary in which they measure a woman's BMR but putting a large face mask over her. They also use "double labeled water" to track the amount of food she eats, by analyzing her urine. This is water with unnatural isotopic ratios in both the oxygen and hydrogen. One dose is enough to let them track for about a week, I think. http://www.ucsdeparc.org/index.php?option=com_content&view=article&id=100&Itemid=82 - Jed
