I would like to begin by covering what a few of the physiological factors are that can cause people to eat or not eat and then move on to specific eating disorders and some of the biopsychological views on them.
First it is important to understand the concept of hunger and fullness from physiological research and what it has shown us. Let us begin with things that have been discovered to be untrue. A common belief is that our blood glucose levels affect our hunger and satiety. However, research has shown that this is untrue; glucose levels remain fairly stable and do not fluctuate often. What does glucose have to do with hunger? The belief was that when our energy levels dropped so would our blood glucose, this would then trigger our hunger; we would then eat restoring our levels back up to a certain energy level. If this were true then people would maintain a relatively stable amount of weight because we would only eat for the amount of energy we needed. Another myth is that of the hypothalamus and its role in hunger and satiety. It was believed that it controlled satiety and feeding. Instead research has shown that the hypothalamus controls energy metabolism not eating. A very common belief is that hunger is caused by an empty stomach and satiety is caused by the feeling of a full stomach. However, it was shown that people who had their stomachs removed still experienced feelings of hunger and satiety. Research has shown instead, that the gastrointestinal tract is the source of feelings of satiety. It was also found that the stomach and gastrointestinal system released chemicals called peptides which interacted with hormones and neurotransmitters in the brain; one of the peptides responsible for increasing appetites is synthesized in the brain in the hypothalamus. The discovery of hunger and satiety peptides has re-established interest in the hypothalamus’s role as well as the role of neurons in hunger and satiety. Research has also shown that serotonin plays a role in reducing hunger, eating and weight.
That was a lot of information to digest! What it basically means is that there are several factors that affect our feelings of hunger and satiety. Messages are sent via peptides to the body from areas such as the stomach and gastrointestinal tract to tell us when we are hungry or full. So if our bodies let us know when we are full or hungry how come some of us want to eat more or very little? Let’s discuss some questions about anorexia and overeating and see if we can answer this.
Q: My parents are obese, is that why I overeat?
A: That is a very good question and often people believe that it is simply a genetic factor which makes them obese. While genetics may play a small role in the chances of being able to become obese it seems to actually be our environments that shape our eating habits. For instance if the culture we live in heavily pushes processed, fatty, and unhealthy foods that promote weight gain and it is acceptable to eat it, then we will have a higher chance of developing a weight problem. Also our families play a role in our environments, so often what we eat, the amounts we eat, and how often we eat is learned from our family environments as well. Some people consume more energy because they crave more calorie rich foods. It has also been shown that some people have a strong response to the sight or smell of food which causes them to eat more. In short it is most likely environment but it may also be linked to genes or differences in our bodies.
Q: My boyfriend and I eat together all of the time, which means that we eat the same foods and amounts, but he never gains weight like I do. Why is that?
A:One cause may be due to the difference in the amount of physical activity between the two of you. This can be from obvious sources such as going to the gym or from the amount someone sits still or not, or if one constantly fidgets and moves around. Also, our bodies are not all alike; some people tend to use excess energy more efficiently than others.
Q: My sister thinks that I’m anorexic because of the magazines and movies I watch. That I want to look like the girls in them. Maybe it’s true, but I really just don’t want to eat food. What do you think it is?
A: While there is a link between our environment and the development of eating disorders it is also possible that it could be a higher than normal insulin response which results in interest of food but feel disgusted by fatty and sweet foods. There has also been discussion in the role of positive incentives which state that the more eating declines the less there is of a positive incentive in eating it although this has not been proved.
Q: I don’t eat because every time I do I feel sick! Why?
A: As I touched on previously there could be a link between the facts that once you begin to eat less you lose incentive to eat. It has been considered that the effects on someone who is eating much less may cause adverse physiological effects. For instance people who have been deprived of food often become noxious when they try to eat. As you can see there are many possible reasons as to why one may not crave food as much as they once did. It may be that you need to try eating very small amounts of food often throughout the day and see if this helps with the feeling of being sick when trying to eat.
Pinel, J. P. J. (2007). Basics of biopsychology. Boston, MA: Allyn and Bacon.