|MadSci Network: General Biology|
Hello, Lindsey. Just to clarify, calories do not transform food into fat, nor are they stored. When food is oxidized, (burned), it provides the body with energy. The amount of energy a particular food source provides is measured in calories. Therefore, calories are simply a unit of measure. The body's first priority is to produce energy. After one's energy requirements have been met, other nutrients are used to build and repair tissue, and carry out functions that essentially keeps us alive and healthy. Any calories obtained from food in excess of what we really need, is converted into fat and stored. Eating fat, does not make one fat. The conversion to fat can just as well come from sugars, protein, or alcohol, as long as more is being consumed than is actually required. For every 9 kilocalories of food eaten in excess of the body's requirements, 1 gram of fat is stored. The transformation of food into fat involves the breakdown of food into simpler components, a task handled by enzymes. Depending on the length of the fat molecules, they may have to be rebuilt prior to leaving the small intestine. Nutrients are not really "in" the body, until they get absorbed into the circulatory system. Once there, they usually head to the liver for furthur processing, where they leave wrapped in special protein coats, destined for some of the 12 to 18 trillion fat cells in an average adult body. It is impractical to give you a precise timeline for the conversion of food into fat, because there are too many variables. Are you referring to the formation of fat while still in the small intestine, or only when the fat gets stored into fat cells? The latter occurs at a later time. Rates of digestion are very variable, ranging from 6 to 14 hours, in the stomach and small intestine alone! A faster metabolism will convert excess calories into fat more readily than a slower one. Muscular people likewise have higher metabolic rates. The type of meal or food one is eating is important, because in the race to be digested, carbohydrates advance faster than proteins, while fats are the slowest. Age is another factor, as older people have slower biochemical processes than younger people. Hormones count too, - higher insulin levels cause fats to be formed more quickly than lower insulin levels. Neither is the presence of fat in the bloodstream gauged to your latest meal. Rather, there is a constant dynamic exchange between the fat stored in tissues and the bloodstream. An equilibrium is maintained throughout the day. If we must come up with an estimation of a timeline for fat formation from excess calories, we would need to disregard the previously mentioned variables, and focus solely on average digestion times, prior to its absorption into the bloodstream. With this in mind, fat can be formed at approximately 5 to 8 hours, on average, from the start of a meal. However, in my opinion, our focus should not be diverted by how fast fat is being formed, but rather, on how quickly we're getting fat. As the comedian Buddy Hackett once said, "I was reading one of those weight-and-height charts the other day, and I discovered something: I'm not too fat, I'm just too short." Hope that helps. Peter Bosani. For furthur reading on food and digestion, log on to www.madsci.org and key in my answer to - How long does the entire digestive procees take? References: www.howstuffworks Wholesome Diet - TimeLife Books Human Body - Life Science Library
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