Note: this post follows on my posts “Are Processed Food and Environmental Contaminants the Main Cause of the Rise of Obesity? and “Livestock Antibiotics, Lithium and PFAS as Leading Suspects for Environmental Causes of Obesity.”

Many drugs have “paradoxical effects”: for a minority of people they will have the opposite of the usual effect. Also, for a minority of people drugs can cause the opposite of a usual side effect. To suss out evidence of environmental contaminants messing with our weight, this means we should look for increases in both obesity and anorexia. One may affect more people, but both should be going up if there is an environmental contaminant. They are. Since 1980, both obesity and anorexia have increased a lot.

It may seem strange that a chemical could have both an effect and—on a smaller fraction of people—the opposite of that effect. But look at the scatterplot across countries between obesity and eating disorders at the top of this post, between the two images of slimemoldtimemold posts. There is a strong relationship between rates of obesity and rates of anorexia. Basically, a given chemical messes with something in the body and sometimes immediate effect of the chemical and the body’s further reaction can go the opposite of the usual direction. (For more on this, see the Wikipedia article “Paradoxical reaction.”)

Not only are the two extremes of fatness and thinness increasing in humans, the prevalence of those extremes is increasing in animals as well, as the “Anorexia in Animals” post shown above argues.

These effects can differ by gender. In humans, the extremes of high and low weight seem to have been burgeoning especially for females. For those who have daughters at home, the following speculation about per- and polyfluoroalkyl substances (PFAS) contamination from the “Paradoxical Reactions” blog post shown above is worth paying attention to:

It’s notable that anorexia most often occurs in teenagers and young adults, especially young women. Are young women being exposed to large doses all of a sudden, just as they start going through puberty? Where would these huge doses come from? It may not be that much of a stretch — PFAS are included in many cosmetics.

In addition to arguing for environmental contaminants contributing to the rise in obesity—and anorexia—the “A Chemical Hunger” series of blog posts is also important in making the case for the powerful influence of a “lipostat.” A lipostat is a fat-regulating mechanism in your body that pulls us strongly toward a particular weight—a weight that can get pushed around by chemicals. Our lipostats invalidate the naive version of “calories in/calories out” that treats calories in and calories out as if they were entirely under our conscious control. One of the reasons this is wrong is fidgeting. Here is the relevant passage from the “Paradoxical Reactions” blog post:

… avoiding food and collecting cookbooks isn’t the lipostat’s only method for controlling body weight. It has a number of other tricks up its sleeve.

Many people burn off extra calories through a behavior called “non-exercise activity thermogenesis” (NEAT). This is basically a fancy term for fidgeting. When a person has consumed more calories than they need, their lipostat can boost calorie expenditure by making them fidget, make small movements, and change posture frequently. It’s largely involuntary, and most people aren’t aware that they’re burning off extra calories in this way. Even so, NEAT can burn off nearly 700 calories per day.

… people with anorexia fidget like crazy. A classic symptom of anorexia is excessive physical activity, even in the most severe stages of the illness. When one group measured fidgeting with a highly accurate shoe-based accelerometer, they found that anorexics fidget almost twice as much as healthy controls.

This kind of fidgeting is the classic response in people whose bodies are fatter than they want to be. In studies where people were overfed until they were 10% heavier than their baseline, NEAT increased dramatically. All of this is strong evidence that people with anorexia have lipostats that mistakenly think they desperately need to lose weight.

Don’t despair. Ultimately, we may collectively figure out how our lipostats work and be able get them back on track. In the meantime, fasting works for those who tend toward overweight. (Fasting is a very bad idea for those who are underweight!) If you have a disregulated lipostat tending toward making you overweight, it might take a lot of fasting sprinkled into each year to get to and stay at a healthy weight, but it can be done. I assess that to be my own situation: personally, in order to stay even at a healthy weight, I seem to need to do an extended fast that adds up to about as many days as the number of weeks since I last did an extended fast. (“Increasing Returns to Duration in Fasting” explains why I do extended fasts.)

For organized links to other posts on diet and health, see:

• Miles Kimball on Diet and Health: A Reader's Guide