Hunger and Eating Disorders

C. George Boeree

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We usually first become aware of the fact that we are hungry when we feel "hunger pangs," which are just our stomach contractions.  For many people, this is a strong incentive to eat, but it is not, physiologically, the most significant indication of hunger.

More important is the level of glucose (blood sugar) in the blood.  Most of the food you eat gets converted to glucose, much of which is converted by the liver into fat for later use.  When the levels of glucose are low, the liver sends signals to the hypothalamus -- specifically, the lateral hypothalamus -- that levels are low.  The hypothalamus in turn triggers whatever habits you have accumulated relating to food seeking and consumption.

Another portion of the hypothalamus (the paraventricular hypothalamus) actually tells you more specifically what foods you need, and seems to be responsible for many of our "cravings."

The feeling that it is time to stop eating is called satiety.  Again, the first indicators may be the distension of the stomach and the intestines -- that full or even bloated feeling we all know from thanksgiving dinner.

There are also certain hormones that are released when food begins to move from the stomach to the intestines that signal the hypothalamus (this time, the ventromedial hypothalamus) that it's time to stop eating.

There is also a hormone released by the fat cells themselves called leptin that decreases appetite via the hypothalamus.

I'm sure you've all talked about one person having a better metabolism than another.  Some people just seem to burn calories as quick as they eat them, while others gain weight just by looking at food.  This is called the set point hypothesis.  It suggests that everyone has a certain metabolic set point, a certain weight that your body is geared towards, which is determined by your metabolism, or the rate at which you burn calories.  Different people have different set points, and it is believed that these set points can change depending on a number of factors, including eating patterns and exercise.

Hunger is not, of course, entirely a physical process.  For one thing, the cultural and even individually learned preferences and eating habits can make a difference.  For example, some of us eat regular meals and rarely snack, while others just nibble throughout the day.  Every culture has its collection of foods that are preferred and those that are avoided.  Many people like the burned flesh of large herbivores (i.e. a steak); others prefer raw squid; others still prefer to graze on a variety of vegetation....

Our culture and upbringing also provide us with various beliefs and attitudes about food and eating in general, and our personal memories can influence our eating behaviors as well.  Some of us grow up with  the idea that we should never waste food, for example, and many of us have particular attachments to what are sometimes called "comfort foods."

Eating is a social thing in human beings and can give one a sense of love and belonging.  It has been suggested that for some people, food is a "substitute" for the love they crave.  Also, some foods -- chocolate and ice cream come to mind -- seem to reduce anxiety and stress for many of us.

One of the strongest learning experiences both humans and animals have is called taste aversion:  If we get sick soon after eating something, we can develop a instant dislike for that food for the rest of our lives!  Children often say they are "allergic" to one food or another when this happens.

As is the case with anything as important as eating, human beings have developed a number of eating disorders.  One is called bulimia nervosa, and consists of a pattern of "binging" and "purging" -- periods of sometimes extreme overeating followed by periods of vomiting or the use of laxatives.

Bulimics are usually obsessed with maintaining or reducing their weight.  They tend to suffer from depression, anxiety, poor self-esteem, and poor impulse control.  They tend to come from families with a history of emotional problems such as depression, as well as families with obesity problems.

Anorexia nervosa is another eating disorder which involves dieting to the point of starvation.  The "rule of thumb" is that you are seriously underweight if you are more than 15% below your ideal weight.  Anorexics often use vomiting and laxatives, just like the bulimics.  They have an intense fear of being fat and are obsessed with being thin.  They often have a distorted body image, meaning that when they look in the mirror, they tend to see someone overweight, when others see them as walking skeletons.  Anorexics often come from very competitive, demanding families, and are often perfectionists with a strong need to control all aspects of their lives.

Physiologically, anorexia has been linked to abnormal levels of the neurotransmitter seratonin, which is involved in eating regulation.  Twin research suggests that there may be a genetic aspect to anorexia as well.

Most anorexics and bulimics are young women, including from 1 to 4% of high school and college girls.  It may be that there are physiological aspects of female adolescence contributing to the problem, but we should note that 10% of teenages with anorexia or bulimia are boys.  But a great deal of these disorders are likely social:  In our society, the standards of beauty tend to emphasize thinness, and women in particular tend to be judged on the basis of beauty, sometimes to the exclusion of all  else.  Certainly, if you look at many magazines for young women, or advertisement directed at them, you would think that looks are everything, and that fat is the kiss of death for self-worth!

It is interesting to note that, whereas the average American woman is 5 foot 4 inches and weighs 142 pounds, the average model is 5 foot 9 inches and weights 110 pounds.  If Barbie, that childhood ideal of feminine beauty, were full size, her figure would read 36-18-33!

It is interesting that cultures with standards of beauty that have more respect for a woman's personality or other traits, and cultures that appreciate heavier women, have far less trouble with bulimia or anorexia.

Obesity

For all the suffering that bulimia and anorexia are responsible for, another eating disorder causes far more:  Obesity.  The "rule of thumb" is that you are obese if you are more than 35% over your ideal weight. By that standard, about 21% of Americans are obese.  Europeans and others with "slimmer" populations shouldn't gloat too much, however:  This tendency is actually world-wide!

Physiologically, obesity is strongly associated with diseases such as diabetes, high blood pressure, heart disease, and some cancers.  In fact, obesity is associated with the same percentage of cancer deaths -- 30% -- as is smoking!  Psychologically, the toll is great as well, and obesity is associated with depres