BMI and Eating Disorders: It’s All About Undereating

Imagine you are definitely body mass index (BMI) 30++. You have had an active eating disorder for years. You restrict your food intake every. single. day. You have a host of mounting health problems and the number on the scale tells you and everyone else that you are “obese” and your health problems are all about your weight and nothing but your weight.

You stumble onto this website. You realize that there’s a very strong likelihood that the source of all your health problems is the fact that you under eat severely. You are shocked. You e-mail me as this site’s owner (and everyone who thinks that they aren't “thin” enough to have an eating disorder does this) to confirm that the re-feeding guidelines apply to you. You confer with trusted in-person family and friends and maybe if you’re very, very lucky, a decent doctor. You decide to support your energy requirements and begin the recovery process.

It’s a big deal when someone can overcome their own fattism directed at themselves. We all absorb the fattist culture around us and it’s an accomplishment to become self-aware enough to identify that cultural norms are not automatically good, right and true.

Eating disorders happen right across the BMI spectrum and this site and its forums try to be a particularly safe space for the two-thirds of those with active eating disorders who have never been (and will never be) “clinically” underweight and yet suffer the same misery and damage from an active eating disorder as those who get the anorexia nervosa diagnosis.

Many gain weight while actively restricting food intake relative to their energy requirements. They are starving and increasing in mass. I explain how this happens in the blog post Gaining Weight Despite Calorie Restriction.

Everyone is equipped with two ways of surviving an energy deficit in the body for a short time: one way is the body will catabolize cells (losing mass and destroying organs) and the other is that it will suppress metabolic function (slow or stop entire biological systems, such as reproductive functions). However, both these ways happen in different proportions in each individual (and the amount of catabolism vs. metabolic suppression may change over time too).

That’s why some individuals can gain mass on 1200 kcal/day and others cannot maintain mass with 2500 kcal/day—it’s all about how much metabolic suppression the body applies. A highly efficient metabolic clamp, and you gain despite calorie restriction of 1200 kcal/day; a very inefficient metabolic clamp, and the body depends entirely upon catabolism to handle the energy deficit and you are losing weight on 2500 kcal/day.

But the difference in metabolic efficiency does not reflect “less damage”—both catabolism and metabolic suppression are damaging to the body long term. Catabolism and metabolic suppression are only short term mechanisms to try to keep you alive until you can replenish the energy deficit that’s mounting in the body.

When attending the 4th Annual Weight Stigma Conference here in Vancouver last week, I crossed paths with an attendee who made the repeated assertion that body mass is correlated to food intake levels, although she allowed for the possibility that the correlation might be weak. I was taken aback as I had spent an entire lunch where I and many other attendees were all quoting the same critical literature at each other (ask Carmen Cool for the exact number for lowered mortality from Katherine Flegal’s NHANES studies—she has it memorized).

There are no systematic reviews and meta-analyses that actually reveal any correlation between food intake level and BMI. Many reviews of national nutritional surveys actually confirm there is no correlation between food intake level and BMI. Of course, we need to keep in mind that self-reports are as good as useless when it comes to accuracy. If you want to review the scientific material on this topic, consider the blog posts on Weight Gain Correlates: Part I and Part II where you can source the references at the end of those posts.

But upon reflection I realize that, were we not living in a fattist society, food intake levels would indeed correlate closely with body mass. While there are variations in energy requirements from one person to the next and even within the same person over time, the larger you are then the more energy you expend. It’s not a linear progression as there are presumably formulaic metabolic efficiencies associated with increased mass (Kleiber’s law), but we have so many of us not meeting energy needs with adequate energy intake that we have created a strange artifact in scientific research thanks to making permanent dieting a way of life in our populations.  

The close tie that should exist between the energy our body requires to function optimally and the food we consume is completely unhitched. It’s more accurate to say that body mass correlates with catabolic and metabolic compensations in response to progressive energy depletion.

Maybe, when we finally grind down the pervasive fattism within the research, medical and practitioner communities, we’ll experience yet another “science goes wrong” déjà-vu.

In the 1920s, when scientists were trying to identify the origins of sudden infant death syndrome (SIDS) they discovered, in post-mortems, that the thymus gland of children who had presumably died of SIDS was enlarged. It was theorized that the enlarged thymus was pressing down on the trachea thereby causing SIDS. From there, preventative treatment ensued:

all experts in major pediatric circles advised that parents irradiate their children’s thymus glands to limit thymus swelling and growth. You were considered an irresponsible parent if your children did not undergo the procedure, so thousands of concerned parents urgently scheduled doctors’ appointments.” 1

The thymus glands of these children were not enlarged. They were of normal size. The catastrophic mistake that had been made was assuming that thymus gland size that had been seen repeatedly non-SIDS children and adult post-mortems reflected “normal.” However, the thymus gland size from those post-mortems reflected a shrunken size, the result of the body’s exposure to either prolonged illness and, more commonly, malnutrition.

I know, we’re pretty sure that we are the smartest people to ever walk the earth and therefore we couldn’t possibly make such tragic mistakes in medicine today as they did in the 1920s. Well except for the fact that we urge those with enlarged fat organs to undergo stomach mutilation—it’s the responsible thing to do right?

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