Posted by fachad on December 12, 2004, at 22:26:08
In reply to Mechanism for weight gain on ADs?, posted by Racer on December 12, 2004, at 14:32:13
There are multiple mechanisms for drug induced weight gain. Sometimes just one factor comes into play; in other cases multiple factors lead to weight gain. A partial list of the mechanisms of drug induced weight gain:
1. reduced resting metabolic rate / reduced energy expenditure.
In some cases, the drug appears to lower the rate of calorie burning across the board. In this instance, if a person were to eat exactly the same amount of food and perform the same exercise, they could still gain weight. Likewise, they could even eat less food and exercise more and still gain weight.
2. Increased appetite / H1 and or 5HT2 blockade.
Rat brain studies show that if you block histamine or 5HT2 receptors, feeding increases, sometimes dramatically.
3. Reduced saity / blunting of natural saity hormones.
People do not feel full. They eat more because of increased appetite, and they keep eating because of decreased saity.
4. Changes in glucose handling / impaired glucose tolerance.
Some drugs raise blood sugar, which causes the body to secrete insulin, which causes the blood sugar to be stored as fat. When cells are insulin resistant, more insulin is secreted, which results in more fat storage, and the resulting decreased blood sugar results in increased appetite. The ultimate end of this process is type II diabetes, but one does not have to develop type II D to experience weight gain from this mechanism.
5. slowed GI transit time / increased nutrient absorption.
Some drugs slow the passage of food through the GI tract, allowing more calories to be absorbed before the food passes. Thus eating the same amount, and exercising the same amount, and maintaining baseline glucose handling, one could still gain weight as a result of the increased calories that are absorbed.
6. sedation / increased sleep time / time spent at resting metabolic rate.
Some drugs cause sedation and increase the amount of time a person spends asleep, which is when fewest calories are burned. Daytime sedation tends to cause less overall spontaneous movement, which means less calories burned, which means more calories stored as fat.
7. systemic shift of weight regulation mechanisms.
The body has complex systems of weight regulation. This is how most people's weight can remain relatively stable over time, even with variations in calorie intake and activity levels.
People do not gain exactly 1 pound of body fat for every 3,500 excess calories they ingest. Some people can ingest excess calories every day without gaining weight. Likewise, people do not lose 1 pound of body fat for every given amount of exercize.
This is because the body has mechanisms that regulate how food is absorbed, how blood sugar is regulated, how much energy is spent on maintaining body temperature, etc.
The body uses it's systems to maintain a constant weight, burning off extra calories and slowing down metabolism when less food is eaten. That way weight stays relatively stable for most people.
Some drugs seem to disturb this balance and kick off mechanisms that tell the body to increase the amount of stored fat. All of the other mechanism can happen as isolated side effects (someone gets increased appetite, but none of the others) or they can happen in combination OR they can happen because the body's regulatory mechanisms are trying to store more fat.
If your body wants to store more fat, it increases your appetite, does not saite, lowers your metabolism, makes you sleep more (think hibernation), slows transit to allow for greater nutrient absorption, and secretes insulin to make sure that what food you do eat gets converted to fat and stored in fat cells.
So that's my best picture at this time of how drugs cause weight gain. In regards to the mechanisms, it is multiple choice, plus 'all of the above'.
Drug companies really try to downplay drug induced weight gain, and many pdocs buy their propaganda. Hence people do not expect the sometimes very substantial, sometimes very persistent amount of weight that is gained on psych drug regimens.
poster:fachad
thread:428335
URL: http://www.dr-bob.org/babble/20041211/msgs/428632.html