If all works out as planned, we could have unambiguous evidence about the biological cause of obesity in the next half a dozen years. The Hormone Hypothesis To understand what makes the hormone hypothesis of obesity so intriguing, it helps to grasp where the energy-balance hypothesis falls short. The idea that obesity is caused by consuming more calories than we expend supposedly stems from the first law of thermodynamics, which merely states that energy can neither be created nor destroyed.
As applied to biology, it means that energy consumed by an organism has to be either converted to a useful form metabolized , excreted or stored.
Thus, if we take in more calories than we expend or excrete, the excess has to be stored, which means that we get fatter and heavier. So far, so obvious. But this law tells us nothing about why we take in more calories than we expend, nor does it tell us why the excess gets stored as fat. Specifically, why do fat cells accumulate fat molecules to excess? This is a biological question, not a physics one. Why are those fat molecules not metabolized instead to generate energy or heat?
And why do fat cells take up excessive fat in some areas of the body but not others? Saying that they do so because excess calories are consumed is not a meaningful answer. Answering these questions leads to consideration of the role that hormones—insulin, in particular—play in stimulating fat accumulation in different cells.
Insulin is secreted in response to a type of carbohydrate called glucose. When the amount of glucose rises in the blood—as happens after eating a carbohydrate-rich meal—the pancreas secretes more insulin, which works to keep the blood glucose level from getting dangerously high. Insulin tells muscle, organ and even fat cells to take up the glucose and use it for fuel. It also tells fat cells to store fat—including fat from the meal—for later use. As long as insulin levels remain high, fat cells retain fat, and the other cells preferentially burn glucose and not fat for energy.
The main dietary sources of glucose are starches, grains and sugars. In the absence of carbohydrates, the liver will synthesize glucose from protein. The more easily digestible the carbohydrates, the greater and quicker the rise in blood glucose. Fiber and fat in foods slow the process. Thus, a diet rich in refined grains and starches will prompt greater insulin secretion than a diet that is not.
Sugars—such as sucrose and high-fructose corn syrup—may play a key role because they also contain significant amounts of a carbohydrate called fructose, which is metabolized mostly by liver cells.
The result, according to the hormone hypothesis, is an ever greater proportion of the day that insulin in the blood is elevated, causing fat to accumulate in fat cells rather than being used to fuel the body. As little as 10 or 20 calories stored as excess fat each day can lead over decades to obesity. The hormone hypothesis suggests that the only way to prevent this downward spiral from happening, and to reverse it when it does, is to avoid the sugars and carbohydrates that work to raise insulin levels.
Then the body will naturally tap its store of fat to burn for fuel. The switch from carbohydrate burning to fat burning, so the logic goes, might occur even if the total number of calories consumed remains unchanged. Cells burn the fat because hormones are effectively telling them to do so; the body's energy expenditure increases as a result. To lose excess body fat, according to this view, carbohydrates must be restricted and replaced, ideally with fat, which does not stimulate insulin secretion.
This alternative hypothesis of obesity implies that the ongoing worldwide epidemics of obesity and type 2 diabetes which stems to great extent from insulin resistance are largely driven by the grains and sugars in our diets. It also implies that the first step in solving these crises is to avoid sugars and limit consumption of starchy vegetables and grains, not worrying about how much we are eating and exercising.
Forgotten History Conventional wisdom did not always favor the energy-imbalance hypothesis that prevails today. Until World War II, the leading authorities on obesity and most medical disciplines worked in Europe and had concluded that obesity was, like any other growth disorder, caused by a hormonal and regulatory defect. Something was amiss, they believed, with the hormones and enzymes that influence the storage of fat in fat cells. Gustav von Bergmann, a German internist, developed the original hypothesis more than a century ago.
Breathing problems related to weight can make it harder to keep up with friends, play sports, or just walk from class to class. Sleep apnea. This condition where a person temporarily stops breathing during sleep is a serious problem for many overweight kids and adults. Sleep apnea can leave people feeling tired and affect their ability to concentrate and learn. It also may lead to heart problems. High blood pressure.
When blood pressure is high, the heart has to work harder. If the problem continues for a long time, high blood pressure can damage the heart and arteries. High cholesterol. Abnormal blood lipid levels, including high cholesterol, low HDL "good" cholesterol, and high triglyceride levels, increase the chances of having a heart attack or stroke when a person gets older. A buildup of bile that hardens in the gallbladder forms gallstones.
These can be painful and require surgery. Fatty liver. If fat builds up in the liver, it can cause inflammation , scarring, and permanent liver damage. Joint and muscle pain. Wear and tear on the joints from carrying extra weight may lead to arthritis in adulthood.
Slipped capital femoral epiphyses SCFE. SCFE is a painful hip problem that requires immediate attention and surgery to prevent further damage to the joint. Pseudotumor cerebri. This is a rare cause of severe headaches in obese teens and adults. There is no tumor, but pressure builds in the brain. Besides headaches, symptoms may include vomiting, double vision, and other vision problems. Polycystic ovary syndrome PCOS. Although it's normal for girls to have some testosterone the male hormone , girls with PCOS have higher testosterone levels in the blood.
They also may have irregular periods , too much hair growth, and bad acne. There may be places in your area that support physical activities from parks, trails, and sidewalks to recreation and fitness centers. Even malls provide opportunities for fitness walking. Understanding environmental opportunities and barriers that we face in our pursuit for a healthy lifestyle may provide some of the knowledge necessary to promote healthy living.
This information may also provide ideas for advocacy and civic participation. For more information on how you can support a positive environment for physical activity in your community, visit: Community Physical Activity Strategies. Therefore, the large increase in. Childhood obesity: future directions and research priorities. How do genes affect obesity? Science shows that genetics plays a role in obesity. Genes can directly cause obesity in specific disorders such as Bardet-Biedl syndrome and Prader-Willi syndrome.
However genes do not always predict future health. Genes and behavior may both be needed for a person to be overweight.
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