Evolution and Anorexia Nervosa

There was a bit of a dust-up in the paleo and low carb blogosphere about some comments Gary Taubes apparently made about anorexia and insulin in an interview.  He noted that insulin was used as a therapy for anorexia, thus suggesting that (perhaps) anorexia, like obesity, is a disorder of fat metabolism. My suspicion is that Gary was using those studies as an example of how insulin could cause weight gain.   On the other hand, one doesn't need exogenous insulin to refeed anorexics  - the time-tested method is to keep those far gone enough to have medically dangerous symptoms (unstable blood pressure, dropping electrolytes, or super slow heart rate) under lock and key and get calories in whatever way possible (including via a tube inserted into the stomach.)

One of my attendings in at Children's Hospital characterized anorexia as "a desperate disease."  Often purging and starvation are combined (though this combination would be more correctly called "eating disorder not otherwise specified" or "anorexia nervosa, bingeing-purging subtype" than strict anorexia nervosa), and there were many cases of young teenagers hiding vomit and stool in places in their rooms to conceal purging and to get laxatives (not surprisingly, constipation is a symptom of anorexia).

Cowboy Junkies - Bea's Song (one of the better songs ever written - right click to open in new tab)

My evolutionary psychiatry interest has always been in how psychiatric disorders have changed over the past 100 years of rapidly changing lifestyle and diet.  Anorexia nervosa is one of those illnesses that was exceedingly rare until 50 years ago, then escalated rapidly, then leveled off so far as prevalence, though those who are affected encompass more children and more men now than ever before.  My educated guess is that only a small percentage of us are capable of starving ourselves outright without being under lock and key, and that vulnerable population shows symptoms earlier and earlier in life as societal pressures and the obesogenic environment increases.

A quote from my previous blog post linked above (the medical literature references can be found there):

All eating disorders remain relatively rare [though in total they are more common than schizophrenia and bipolar I disorder]. Anorexia afflicts about 0.5% of women and 0.1% of men. Bulimia around 1-3% of women (also 0.1% of men), and binge eating disorder 3.3% of women and 0.8% of men. Anorexia nervosa remains the most deadly of all psychiatric disorders, with a 5-10% death rate within 10 years of developing the symptoms, and an 18-20% death rate within 20 years. Anorexia is endemic in the fashion industry, to the point where models are now being airbrushed to add curves. Another model, Isabelle Caro, died at age 28 of anorexia, and Ana Reston of Brazil died at age 20, still modeling with a BMI of less than 14.

Photo of Isabelle Caro from Wikipedia

The current state of the art treatment of anorexia begins with refeeding, mostly because we know that semi-starvation itself causes obsessions, depression, and fixation on food.   In the hospital, patients work closely with dietitians, trying to learn how to eat a healthy amount and to establish a better relationship with food.  While medicines that promote weight gain are prescribed, antidepressants and other agents are fairly useless in a starvation situation.

You can imagine the typical well-meaning dietician designed diets for these sick young people.  It's the food pyramid with way too many grains, too little fat, and a focus on "healthy" rather than good old fashioned farm fresh food.  And while I don't really have any objections a food pyramid Mediterranean-style whole foods diet (autoimmune issues with grains notwithstanding), I know that what happens in real life is not skipping breakfast, a light lunch, and a late supper of mussels, olive oil, roasted peppers, tapenade and homemade sourdough bread, but rather three meals and two snacks a day, a version of Weight Watchers™ with Skinny Cow ice cream sandwiches, whole grain Rice o Roni, cans of beans, omega-6 laden commercial salad dressing, boneless skinless chicken breasts,  and "lite" yogurt.

The problem with so many meals a day is that one has to think about food constantly.  I don't think that is the best way to recover from an eating disorder, though one would have to be careful with fasting as well.  I believe intermittent fasting is a valuable practice, a way to lower food reward and to ultimately establish a good relationship with food - I don't have to have it right now, but later would probably be fine too - however, fasting can trigger binges in those who are vulnerable.  It is not verboten in those of normal or excess weight, but should be undertaken with care and support.  In my mind, the healthiest diet is one that you don't have to think about all that much - poached eggs, a beef stew with some liver chunks you cook once and eat all week long.  Cold potatoes and butter.  Forgetting to eat every now and again.

M83  Midnight City (right click to open in new tab)

I believe Jamie sent me this recent paper, Role of the evolutionarily conserved starvation response in anorexia nervosa.  It is a fascinating piece, with an in-depth consideration of biology, evolution, and insulin.

The authors speculate that "AN [anorexia nervosa] may be caused by defects in the evolutionarily conserved response to food and nutrient shortage associated with reduced calorie intake."

Some more facts about eating disorders - in 10-20% of patients, the disorder is short-lived.  In 20-30% it is chronic and unremitting.  The most seriously affected are at greatest risk for hypothyroidism, loss of bone density, electrolyte disturbances, low blood cell counts, amenorrhea, suicide, and death.

In anorexia, the physiology of starvation is paramount.  Both brain and peripheral metabolism responses come into play, orchestrated by the brain and the endocrine system (I don't think obesity is far different - I see no reason that obesity would be regulated by fat tissue or the liver when the brain and endocrine system are doing their thing).

The goal of the starvation response is to conserve energy, delay growth, preserve ATP (by increasing efficiency of energy metabolism) and to minimize oxidative damage.  In starvation, changes in the hypothalamus of the brainstem result in a fall in blood insulin levels and a suppression of other anorexogenic factors.  Once ketosis occurs with the depletion of glycogen stores, there is an increase in output from the sympathetic nervous system and stimulation of food-seeking behaviors.  These multiple pathways explain why fasting can be healthy, but also stressful.

One of the major biochemical pathways activated is the IGF-1/FOXO response (an insulin growth factor 1 pathway).  So the authors of this paper postulate something a bit similar to Gary Taubes - anorexia arises when there is defective regulation in the starvation pathway, similar to how insulin deficiency (due to insulin resistance) is a factor in diabetes.  Meaning there is a lot going on with respect to home life, environment, stress, and temperament in eating disorders, but only a select few have the genetic capability to deliberately starve themselves is response to the environment, and those few may have differences in the IGF-1/FOXO pathway.  The researchers were able to find some yeast, fruit flies, worms, and mice with defects in that pathway who tend to restrict food and develop more slowly (or, alternatively, eat more and spontaneously gain weight), and who have genetic differences in the IGF-1/FOXO pathway.

Evidence for genetic vulnerability to anorexia includes the fact that eating disorders are highly heritable. (Uruguayan model Luisel Ramos and her sister both died from anorexia in recent years).   When doing genome-wide linkage analysis of families with eating disorders, many components of the starvation response pathway are located in highly suspect genetic areas.  In practical terms, the increased impetus on thinness and subsequent dieting brings out the reinforcing starvation response as a result of the genetic vulnerability.  A single episode of excessive caloric restriction seems to bring out long-term changes in the neurotransmitter production mediated by FOXO.

Thus caloric restriction and weight loss predispose to additional episodes of dieting, especially in susceptible individuals wih defective regulation of their starvation response, or with perseverative bias in behavior, reflected in obsessive thoughts and compulsivity.

How do these general ideas affect treatment?  Family therapy, distress tolerance, and cognitive behavioral therapy around distorted body image is a cornerstone of therapy for eating disorders, along with the refeeding.

Should we use insulin to treat anorexia?  Well, the reactive hypoglycemia and other risks are problematic.  A more sophisticated approach is to use IGF-1 itself - it can increase appetite and reverse bone loss seen in anorexia.  Long term treatment tends to result in hyperplasia of the lymphatic tissue, tumor promotion, and excess accumulation of body fat.  

Better that we never begin dieting in the first place.  Skipping the processed foods and ensuring there are plenty of healthy fat and nutrients for the brain and muscles seems like the optimal and common sensical approach in that regard.  I'm not sure what to do about the fashion industry...