Leaving the Calories In/Calories Out Myth Far Behind
It’s day 4 of launch week for the Weight and Healthcare newsletter and today I’m discussing a classic myth. If you like what you are reading, please consider subscribing and/or sharing!
The idea that the body works on a simple calories in/calories out (ci/co) model that can be used to effectively manipulate body size is one of the most pervasive myths that I hear, and it’s particularly harmful to fat* people.
Content note: This piece discusses calories and caloric restriction and may be triggering, especially for those dealing with disordered eating/eating disorders.
The myth goes like this:
If you just eat less and/or exercise more and create a caloric deficit (which is to say - give your body less fuel than it requires to function,) your body will consume itself to survive, you will lose weight, and by losing weight you will become more healthy. If you fail to lose weight, it just means that you lack the willpower to create a caloric deficit over a long enough period of time.
I talked about the mistake of conflating weight and health here, so today let’s just talk calories in/calories out.
It sounds logical, until you apply it to how the human body actually works.
First, it turns out that accurately calculating the “calories out” side of the equation is, at best, an awfully indirect science producing questionable results.
The Basal Metabolic Rate (BMR) formula is one of the most popular used to determine how many calories we utilize at rest. But the formula doesn’t account for muscle mass, which utilizes more calories than other body tissue at rest. Except that there is controversy about just how many calories a pound of muscle utilizes – some reputable scientists say 35, some say 10. (And it’s actually more complicated than that, since we also have to look at the difference between the caloric needs of fast and slow twitch muscle etc.) Also, most methods used to measure muscle mass are fairly imprecise, or really expensive, so very few people have access to a correct measurement even if we could use that number to get an accurate BMR, which we can’t.
Besides which, a BMR-type calculation would be only be reasonable if we were, say, a lawnmower. We can calculate the fuel needs of a lawnmower and then have a clear expectation of how much grass it can mow based on the fuel we give it, and what will happen when the fuel runs out.
Well, in today’s flash of the obvious, our bodies are not lawnmowers. The way we utilize fuel (calories) and what happens when we run out is vastly different and extremely individualized and impacted by all kinds of things including:
Genetics
Sleep
Smoking/Alcohol consumption
Medications
Stress
Illness
Menopause
Other health conditions
Past Caloric Restriction (dieting) history which can actually change the body to predispose it to gain and maintain weight
What concerns me even more is that semi-starvation is advocated based on the idea (really, the desperate guess against all evidence and reason) that a starved body will simply burn excess fat for fuel and become smaller with no negative repercussions. That’s not the case. The human body is excellent at surviving. It is not so good at fitting into a cultural stereotype of beauty.
The body doesn’t think of calories as evil things that take it farther from an arbitrary standard of beauty, it thinks of calories as fuel to do its many jobs. When you give your body fewer calories than it needs to perform its basic functions, it does not think “Wow, good job ignoring all of my signals and underfeeding me.” It thinks “Oh no, I’m starving. I have to do something!”
Let’s go back to the lawnmower example:
If I give my lawnmower half of the gas it needs to cut my lawn, it will simply stop working half-way through. If next week I only give it half the gas it needs, only half my lawn will get cut. My lawnmower will never adapt to use less fuel, it will simply stop working when the fuel runs out - call it the fuel in/fuel out equation.
If I give my body half the fuel that it needs just to lay in bed all day, and proceed to run on a treadmill, it doesn’t stop (at least not right away,) it adapts. My body can’t imagine a scenario in which it needs food, there is food, but I’m intentionally not feeling it, so it interprets this situation as “I’m starving, there is no food, and I have to run away from stuff.”
If I continue to underfeed my body while making physical demands on it, it will likely drop a little weight at first while adapting to function on fewer calories, even if that means performing its functions (you know the ones - thinking, moving etc.) sub-optimally.
If I continue underfeeding it the long-term, I will experience additional negative impacts (see below). If I stop underfeeding my body there is a good chance that my body will maintain its adapted lower level, at least for a while, while possibly also resetting my natural set point to a higher weight permanently while storing anything it can as fat.
My body is trying to help me out – what it has learned (what I have taught it through my actions) is that I live in an environment where sometimes there is not enough food, at the same time that massive physical labor is required. So it’s storing up fuel for the next low food/high physical activity period. If I continue to do this over time (as in the case of repeated weight loss attempts), then the damage to my metabolic rate and my body’s functions can increase.
And that doesn’t even touch the psychological toll that underfeeding our bodies takes on us. In the Minnesota Starvation Study participants who were restricted to 1,560 calories per day (hundreds more than many current weight loss plans recommend) for just 12 weeks (far less time than many current weight loss plans are meant to be followed) experienced depression, up to and including self-harm, hysteria, marked food preoccupation, disordered eating patterns, guilt about eating, decline in physiological processes, concentration, comprehension and judgment, and a 40% drop in BMR. For many the disordered eating continued for months after the study was concluded.
So while semi-starvation seems like a reasonable weight loss technique if you believe in a ci/co equation, we have to judge it on three standards:
Validity of Methodology
Fail. The fact that we can’t accurately calculate how many calories a body will expend or predict how a body will respond to prolonged restriction makes this methodology invalid.
Probability of Success
Fail. The use of caloric deficit has a success rate of less than 5% over 5 years – that’s within the margin of error for most studies, and we have solid data on that for literally decades.
Risk/Benefit Analysis
Fail. When we recommend ci/co weight loss attempts, we risk people’s physical and psychological health for a miniscule chance at a smaller body. Especially considering research shows that weight-neutral options can provide more health benefits with less risk, ci/co simply falls short of being an ethical, evidence-based intervention.
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More Research
For a full bank of research on this, check out https://haeshealthsheets.com/resources/
*Note on language: I use “fat” as a neutral descriptor as used by the fat activist community, I use “ob*se” and “overw*ight” to acknowledge that these are terms that were created to medicalize and pathologize fat bodies, with roots in racism and specifically anti-Blackness. Please read Sabrina Strings: Fearing the Black Body – the Racial Origins of Fat Phobia and Da’Shaun Harrisons Belly of the Beast: The Politics of Anti-Fatness as Anti-Blackness for more on this.