Appetite

Old systems in our brain regulate appetite, eating behaviors, and manage body weight. We call this brain device the Appetite Control System (ACS). The ACS integrates information about body weight, temperature, activity level, season, reproductive cycle (in women), food availability, and expected energy needs to decide how much food is needed today. 

If you are in the weight management business you have the deepest respect for ACS. You can compare ACS programs to the programs built into computers as read-only memory (ROM). When you turn the computer on, programs are read from ROM to initiate basic computer operations. You are never of aware of ROM contents, but you experience the results. ACS programs operate spontaneously and establish your basic eating behaviors and responses to food. ACS deals in the basic patterns of life, and has a vocabulary of states such as hunger, thirst, sleep, wakefulness, flight, fight, fear, and anger to let you know why you are doing what you are doing. You cannot access ACS through your conscious mind, but ACS can access you! The way it seems to work is that you get regular messages from ACS in the form of urges, needs, desires, wants, appetites, and sometimes discomforts - "Your bladder is full now. Rush to the toilet." "You are hungry, now go and eat food." You cannot override these old programs with conscious control.

ACS establishes a weight and temperature "set-point" and tries to maintain these values even when the food supply varies a great deal. This is a complex system that is based on the oldest of life-programs. You are born with these programs in read-only-memory.

ACS works at three levels:

1. Changes eating behavior
2. Changes metabolism
3. Changes physical activity

When ACS wants you to do something, you feel hungry and are driven to find food. ACS fools consciousness most of the time to think that you have some decision-making ability, but really most of your behavior is preprogrammed and run on auto pilot. When this system says go, you are running to the refrigerator to get ice cream. You may think as your feet move you towards the goal, it would be better to have celery, but you do eat the ice cream. If ASC says "Stop!", there is no delicious morsel on earth that would tempt you enough to eat.

The appetite system is based on programs in the old reptilian brain. This system is designed to establish the most efficient path to reliably available food, then to lock in the behavior and repeat it without further modification. Our appetite system tends to run automatically at this primitive level and defies conscious attempts to alter the program. Any insightful person will be able to track the importance of food searches in their own behavior. If you watch the people around you, you will readily confirm the primacy of feeding behaviors in human social existence.

It is possible to construct a rather elaborate model of brain function in terms of the brain's attempt to regulate the molecular flow of food materials. Feeding behaviors are highly automated and seem to be designed around recursive loops, already discussed under addictive behavior. If we think of our brains as chemical processors whose first job is to steer us through a chemical soup so that we get the right stuff to function normally, a lot of human behavior makes sense or is more understandable nonsense.

If you assume the task of inventing a simple brain that self-regulates by controlling eating behavior, you might get some insight into how we and other animals operate. You would have to assume that the basic system built into old brain ROM is not very smart and could not read this book for clues as to how to modify its own behavior. You would have to start with chemical sensors (tongue and nose) and simple programs that direct food searching, eating, stopping-eating, and switching to other programs which do something else when you have had enough to eat, and so on.

<more sweet is better than less; go back for more>

<when in trouble, eat more sugar>

< more food now is better than less food later>

<if inside temperature drops, eat more sweet less salt>

<if inside temperature rises, eat less sweet more salt>

<when you are ready to reproduce, eat more sugar>

<when average daily light gets less, eat more fat>

These routines would all have survival value in the wild, but when they persist in human beings in modern affluent societies, the programs may produce the wrong results. Obviously, there are overlaying layers of food selection programs, including the high level intelligence manifest in this book.

Old appetite control programs get input from chemical sensors in the nose and tongue -smell and taste. Immune sensors in the nose, mouth, and along the digestive tract also play a regulatory role, adding to the information derived from chemical sensors. The smell system is the old brain or limbic system that regulates moods, emotional life, sexual behavior and at the same time feeds essential information into the neural computers that regulate appetite and eating behaviors.

The hypothalamus is a key brain region that integrates body-status information to determine the four-F behaviors. The hypothalamus receives chemical data from the blood and messages from various regulatory tissues in the body including insulin, sex hormones, and peptides secreted by GIT as it processes food. This appetite computer must integrate information about body weight, temperature, activity level, season, and reproductive cycle (in women) to decide how much food is needed. It is convenient to think that the system works by establishing a set point for body weight and then tries to maintain this value even when the food supply varies a great deal. A malfunctioning appetite computer might allow the setpoint to slide up or down causing overeating and obesity on the one hand or anorexia and progressive weight loss on the other.

This system shows a variety of two state transitions. The most basic feeding two states are stop and go. The hypothalamus can be divided into two zones, a middle (medial) zone that tends to stop eating and inhibits aggression and a lateral zone which tends to turn eating on and excite (predatory) aggression. In animal studies, damage to the medial hypothalamus produces animals who are irritable, eat too much, and become obese. Damage to the lateral go-system results in animals who eat little and tend to starve. The hypothalamus is also the brain link to the body's hormonal network, regulating the pituitary gland, which in turn regulates the endocrine glands. Hormones are the blood-born molecules that regulate our metabolic and reproductive functions. The ingestion, digestion, and metabolism of food is one the chief concerns of the endocrine system. There are numerous opportunities for this regulatory system to fail. Often appetite and weight regulation is unstable for short periods of weeks but produces dramatic, lasting changes in size and shape.

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Eating and Weight Management

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