Satiety
by
Tom McCullough MEd.

When someone attempts to lose weight a negative energy balance must be created. The first choice to obtain this negative energy balance is to cut the caloric intake. Most of the time when calories are cut controlling hunger then becomes a big problem. Hunger is best described as the primary physiological drive to find and eat food. This state is driven by several different internal forces that all work together to extinguish the need for food and put the body in a state of satiety, meaning the desire to eat ceases. These internal forces that drive us to eat may be responsible for over-eating and obesity. So what exactly are these internal forces?

The hypothalamus

This is a part of the brain that play a particular important role in feeding behaviors, Why? Because it actually regulates satiety. In many studies where specific nerve cells in the hypothalamus were destroyed, satiety either increased or decreased causing either obesity or weight lose. It is thought that various brain cells can be destroyed by specific chemicals, surgery, and certain forms of cancer.

Nutrients in the blood

This is perhaps one of the biggest contributors to the control of satiety. After we eat and digest a meal , the amino acids, glucose, and fatty acids are all absorbed into the blood stream. This absorption causes a state of satiety and hunger is decreases. Within a few hours after we eat, the concentration of these nutrients falls as they are used for fuel. As the available nutrient concentration in the blood falls, the satiety level decreases and hunger signals begin to start once again.

Neurotransmitter production

It is also though that neurotransmitter production of histamine and serotonin may also control hunger. Studies have shown that when subjects were deprived of calories or sufficient protein, histamine production increased causing an increase in the synthesis of the amino acid histidine, thus a significant decrease in hunger and food intake is experienced.

Changes in serotonin production have also been linked to satiety controls. Various nutrients, especially carbohydrates, increase serotonin production. High levels of this neurotransmitter cause increased synthesis of the amino acid tryptophan which appears to clam oneÕs mood, induce sleepiness, and decrease the desire to eat more carbohydrates.

Hormonal regulation of feeding

Many different hormones, drugs and hormone like compounds have been shown to influence feeding patterns. For instance, after a meal, blood concentrations of cholecystokinin, secretin, gastrin, glucagon and a few other hormones increase. These hormonal increase have been shown to increase satiety.

Endorphins, cortisol, and insulin all lead to decreased satiety or increased hunger. The significant presence of cortisol in those genetically prone to obesity may be a big problem. Insulin however, is a double edge sword. High insulin levels increase liver metabolism of nutrients. In this case it promotes satiety. However, as insulin does its job by ridding the blood of nutrients, it then causes hunger to return.

Gastrointestinal distention

Distention is nothing more than the expansion of the walls of the stomach or intestines due to pressure caused by the presence of gases, food, liquids, or other factors. This added pressure appears to quell hunger causing satiety.

Adipose cell size

Adipose or fat cells, are have different sizes depending on the concentration of body fat. As the body stores excess nutrients in these adipose cells, the cells produce an enzyme called adipsine. This enzyme acts as a communication link between the adipose cell and the brain. As the fat cell fills, adipsine production increases, thus shutting off hunger. In contrast, if the fat is released from the adipose cell, the production of adipsine is stopped and sensations of hunger resume until there is an increase in food production causing these cells to be once again filled.

As the adipose cells become increasing larger, they tend to become resistant to insulin. As we know, insulin stimulates the uptake of fat when we have an excess of calories. Once these cells become resistant to the actions of insulin, fat storage decreases, thus protecting the adipose cell from becoming too large.

Level of physical activity

It appears that the level of body fat may directly influence whether or not the exercising individual will be hungry or not after exercise. Lean individuals compensate for increased energy expenditures and adjust the food intake upward to maintain their body compensation. On the other hand, obese individuals donÕt seem to have increased hunger and food intake after exercise.

External forces

Psychological factors like emotional states and personal beliefs can affect the way we eat. Eating disorders have been shown to increase of decrease the amount of food we consume in spite of the physiological controls.

Environmental factors, such as availability of food, time of day, social obligations, food characteristics, temperature, and humidity all have affects on ho much we eat.

Social customs, peers, and authority figures may also affect our eating habits. Taste, texture, color, previous experience are contributors to satiety.

So how do we control these extermal factors and control satiety while we diet? It is highly unlikely that we can easily control hypothalamus cell damage problems, but nutrient blood levels can easily be controled by eating 4 to 5 several smaller meals instead if 2 to 3 big meals. By spreading out the intake of your daily caloire over the day, you will keep the nutrient level a little more constant. Thus, satiety will be easier to control.

Limiting the intake of sugars will also control large increases and drops in insulin levels. When the insulin levels drop low, hunger is increased.

The level of physical activity seems to be especially important in obese individuals to control the level of hunger. Exercise not only stablizes insulin production, but it also increases glucagon production. Low intensity exercise also limits cortisol production. Because obese individuals have plenty of stored fat in the adipose, exercise does not seem to cause and increase in humger as it does in leaner individuals.

It is also very important to address any of the many external forces that may control hunger. Psychological, environmental, and social problems have all been linked to over-eating and obesity.