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Biology 202, Spring 2005
Second Web Papers
On Serendip

Hunger and Obesity: Are We Really Hungry?

Shu-Zhen Kuang

My mother always said that being overweight is a blessing because only the rich can afford to be fat. Having lived most of her life in a rural countryside in China, my mother never thought there could be other reasons why people are overweight. America is the richest country in the world, and obesity has become a major health concern. A person is considered obese if their body weight is 20% over the normal weight (1). With obesity on the rise, the health problems that come along with being overweight are major concern in most American households. Being obese carries with it the predisposition to get diabetes, heart disease, and many other serious illnesses (2). Our bodies have biological mechanisms that tell us when we are hungry and when we are full. Do obese people have a defect in their biological mechanisms that control their weight or are other issues, such as lifestyle and psychology, affecting their weight?

From a biological prospective, our body must have a way of telling us when we need to eat to ensure survival. People are usually aware of their hunger when their stomach starts making noises. These noises are stomach contractions, but this sign is not the most important indication of hunger (2). The feeling of hunger comes from the hypothalamus, which is responsible for maintaining our body weight by telling us to consume more or less calories in order to have a properly functioning body (4). The mechanism starts when blood glucose levels are low. Then the liver, which changes food into glucose, sends a signal to the lateral hypothalamus. In order to increase the blood glucose levels, the lateral hypothalamus activates the behavior that each individual has for finding and consuming food (2). Low levels of leptin, a hormone released by fat cells, when detected by the hypothalamus, have also been showed to generate the feeling of hunger (4).

The hypothalamus controls the sensation of hunger, but it also plays a role in the amount of food consumed. Satiety is when we feel full, and as a result, we stop eating. When food begins to move from the stomach to the intestines, certain hormones are released from the stomach that signals the ventromedial hypothalamus to stop consumption (1), (5). Leptin is also released from fat cells in response to increased levels in caloric storage (4).

Each individual has a similar mechanism that controls his or her body weight, but some people are predisposed to be obese. Forty to 70% of body mass can be associated with genetics (2). An example of genetic predisposition is indicated in studies that show adopted children's weight being similar to their biological parents' weight instead of their adoptive parents (5). A case where genetics severely affects hunger is in the rare genetic disorder called Prader-Willi Syndrome. Because the hypothalamus functions abnormally, people with this syndrome are constantly hungry and can never be satisfied no matter how much is consumed. Unless parents set up a controlled diet early on in the child's life, obesity will be one of the results of this syndrome (6).

Another biological aspect that relates to hunger is the set point hypothesis. This is the idea that the weight of every individual is determined and maintained by their hypothalamus. As a result, when a person tries to lose weight, the hypothalamus resists these changes. When people are on a diet, their leptin levels decrease and in turn cause the hypothalamus to trigger the feeling of being hungry. In other words, this continual cycle is the downfall of many people who attempt dieting. In addition, the set point for obese people may be higher than for healthy individuals. Studies have found that satiety point, which is determined by the hypothalamus, is higher in obese individuals compared to average weight individuals (5). Therefore, the biological mechanisms that maintain a certain weight may be different for obese individuals compared to healthy individuals.

Although genetics plays an important role in regulating our weight, a large portion of our body mass is determined by the daily choices we make. The time, amount and type of food we consume are selected by us. For some people, it is the lack of willpower that leads to the path of obesity. Although the extra snack eaten every day may not seem to contribute to the overall weight gain, the extra calories from this snack gets converted to fat and build up overtime (3).

Since most people who tried dieting have failed, many physicians have resorted to treating the side effects of obesity such as diabetes instead of a cause of the diabetes which is obesity (2). Because not enough emphasis has been placed on diet and exercise, there is an increasing trend toward obesity. One national study states that 65% of American adults are overweight compared to 56% in 1994 (3). This study shows that genetics is not to blame for all cases of obesity. Part of the increase can be associated with our inability stay with the regimen of diet and exercise. The way our culture chooses to deal with this problem is not working since the continuation of fad diets still persists along with obesity.

For others, unhealthy eating habits are developed from upbringing and culture. In America, advertisers spend a great deal money promoting unhealthy foods to children and adults. This temptation is hard to resist for many who have grown accustomed to eating these foods. However, other parts of the world are also experiencing the same obesity trend as America (2). Perhaps, the spreading of Western culture is influencing the diets of other cultures as well.

There is more than just the biological explanation of hunger. Physical hunger and psychological hunger are very different things. Some people have developed the habit of eating during a certain time of the day ever since they were children. The time of day can be a component that triggers the feeling of hunger for many people. For others, the smell of certain foods could instantaneously make the person feel hungry even though they may have just consumed a meal not long ago. As most people have experienced, these sudden urges are not satisfied until the certain type of food is consumed. Many people also use food as a way to suppress an emotional problem in order to avoid dealing with the actual problem (5). These people find that by eating food, their emotional problems become temporarily solved. High fat and sweet foods have been found to give off a pleasurable sensation through the brain after consumption (7). These external stimuli provide other ways to signal the hypothalamus to make us feel hungry even though the signals are not physiological.

There has been much debate about whether biology or other aspects play a greater role in obesity. Genetics is only one of the many factors that are involved in determining a person weight. Subconsciously, most people know that living a healthy lifestyle through diet and exercise is the best way to avoid obesity whether you are genetically predisposed or not. However, our culture is providing conflicting messages about weight control. The food and snack industry continually promotes fattening foods while it promotes diet foods at the same time (2). Among scientists, there is still a difference of opinion on whether genetics or self-control affects a person's weight more (3). Because none of these viewpoints can provide a definitive answer to the current obesity trend, it is possible that the combination of genetics and self-control determines a person's weight. Regardless of these issues, the dramatic increase of obesity among populations is a warning sign that we are leading unhealthy lives. A more comprehensive understanding of all the issues surrounding obesity will hopefully lead to healthier lives.


1)Weight Loss: What is obesity?, an article on WedMD

2)Hunger and Eating Disorders, provides the biological and psychological side of hunger

3)The Great Weight Debate, an article on WedMD

4)Hypothalamic Neuropeptides: Responding to Caloric Challenges

5)Hunger and Eating, provides info about hunger and obesity

6)Prader-Willi Syndrome

7)Why do we eat what we eat: biology of food choice

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