Monday, April 4, 2011
The Lifestyle of a Spud
On page 187, Shubin talks about how humans were built for an active lifestyle, not a couch potato lifestyle. Why were humans and other earlier creatures built this way? (include "boom/bust") Why is it detrimental to our health to eat too much fat? Include the effects of obesity on everyday functions like metabolism on a molecular level.
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Humans were built for an active lifestyle because natural selection favored such adaptations, like, most notably, the ability to store energy as fat. As anthropologist James Neel suggested, “our human ancestors were adapted for a boom-bust existence… as hunter-gatherers” because they would have “boom” periods with large quantities of available food resources and “bust” periods with a lack of available food resources (Shubin 187).
ReplyDeleteThe ability to store energy in this way is somewhat similar to the manner in which the pancreas regulates blood sugar concentration levels – when the blood sugar concentration is too high, the pancreas secretes insulin, which causes cells to take up glucose and store it as glycogen for later use (Campbell 982). Although this serves primarily to regulate the concentration of sugar in the blood stream, this process shares a theme with the evolution in humans of an active lifestyle in that they both store energy from one form to another for later use. When the body’s blood stream needs an increase in glucose, the pancreas releases glucagon, which causes the cells to break apart their stored glycogen into glucose to release into the blood stream – when a human body needs energy to ultimately turn into ATP, it breaks down its stored fat.
The body does this by breaking down triglycerides into glycerol and fatty acids, then to acetyl CoA, and finally to ATP through the Krebs Cycle and the electron transport chain (http://www.free-online-health.com/how-fat-is-burned-article.htm). The majority of the generated ATP comes from the electron transport chain, though, as only substrate-level phosphorylation generates ATP in the Krebs Cycle, which is relatively insignificant compared to the amount of ATP created through the electron transport chain (Campbell 166).
Humans’ need for a large energy reserve in the form of fat comes largely from our high energy demands (our high metabolic rate), owing to features like being omnivorous and being endothermic, actively engaging with other animals in predator-prey relationships and regulating our own body heat (Campbell 863).
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ReplyDeleteAlthough the ability and inclination to consume and store extra energy as fat developed as an evolutionary advantage, with higher survival and reproduction in human ancestors that were more efficient at fat storage than others, such features now can cause adverse effects in couch potatoes.
Two examples of such negative effects are atherosclerosis and arteriosclerosis, the buildup of soft plaque in arteries from low-density lipoproteins and the hardening of arteries from plaque with calcium deposits, respectively (Campbell 914). If the blood supply to part of the heart, for instance, becomes too blocked with plaque to provide blood flow to that part of the heart, a heart attack results, and if that part of the heart does not receive blood for more than a few minutes, its tissue might die. Cholesterol, the primary cause of these conditions, comes from fats; saturated and trans-fats have more low-density lipoproteins than monounsaturated and polyunsaturated fats, meaning that saturated and trans-fats are the actual main causes of these diseases (http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/fats-and-cholesterol/). The reason that saturated fats are “worse” in causing these conditions is that saturated fat molecules are packed much more closely together at room temperature than those of unsaturated fats, because unsaturated fats have a cis double bond that causes bending and structural kinkiness (Campbell 75).
Furthermore, obesity, the storage of excessive fat, has its own intrinsic problems. The heart needs to pump blood to more capillaries throughout the body in an obese person, meaning that the heart has increased cardiac output and the body has higher blood pressure, which eventually weakens the cardiovascular system (http://www.blood-pressure-hypertension.com/special-cases/high-blood-pressure-obesity.shtml).
Even without obesity, a sedentary lifestyle can have negative effects on human health. Movement in leg muscles enables “our blood to climb from feet to chest,” which “works superbly in an active animal, which uses its legs to walk, run and jump,” but it does not “work well in a more sedentary creature” because blood can pool in the leg veins and cease to circulate throughout the body (Shubin 188). Such pooling of blood can cause the veins to swell and possibly even form hemorrhoids.
Activities like reading textbooks and blogging may also contribute to a sedentary lifestyle.
- Vincent Fiorentini
(vincent@panatechcomputer.com)
Just as Vincent had stated, humans and earlier creatures were built for an active lifestyle for the simple reason that it was a selective advantage for this to be so. The more inactive or unhealthy a person is the more prone he/she is to sickness or death. Shubin explains that the four leading causes of death like “heart disease, obesity, and stroke” because we live in “an environment where rich foods are available 24/7” (Shubin, 187). In contrast, the more active a person is, the body functions at a higher rate and more efficiently. Our ancestors began as hunter-gatherers and survived through cycles of “booms” and “busts” (Shubin, 187). The boom period was when there was an abundance of prey, and the bust period was a period of famine. The adaptation of the bodies to adjust to this sort of lifestyle eventually created an efficient fat storage system over time as these humans evolved. Fat storage was essential to the survival of hunter-gatherers because a portion of the fat was used, as energy for the activities being done and rest was stored for later (Shubin, 187). Campbell explains that joining three fatty acid molecules to a glycerol by an ester linkage makes fats, creating a triacylglycerol (Campbell, 75). Triacylglycerols are used as energy sources in a human’s metabolism and aids in stomach digestion (“Triacylglycerol Metabolism in the Intestines, Liver, and Mammary Gland”, LipidLibrary). However, there are saturated fats and unsaturated fats, and too much of one can lead to health problems such as high or low cholesterol. Saturated fats, as Vincent had explained, are known to be less healthy because they are less “kinky” or without cis double bonds. Unsaturated fats that have cis double bonds prevent them from packing too close together that they would solidify at high room temperatures, which is a risk for a high concentration of saturated fats.
ReplyDeleteObesity refers to having an excessive amount of body fat. The important thing to understand is that it is different from being “overweight”- where a person has extra body weight from muscle, bone, fat, and/or water (“What are overweight and obesity”, National Heart Lung and Blood Institute). Because of this increased fat, there is increased cardiac output as Vincent had explained, but this occurs in a shorter time. Therefore, their heart almost “reverse-conditions” and slows metabolic functions. Furthermore, an increase in trans fats or saturated fats means less cis bonds and more closely packed molecules, which could lead to solidification and other conditions outside of obesity including atherosclerosis or high cholesterol. Because obesity slows the functioning of the body, it is likely to lead to other diseases or illnesses such as heart disease or stroke. Because we are so exposed to foods containing high amounts of saturated or trans fats, obesity has,unfortunately, become more common to our society because we've lost the need to maintain or fat content levels because of our increasingly inactive lifestyle.
Sonia Doshi (soniadoshi7@gmail.com)