If I had a nickel for every time someone talking about weight loss said to me “It’s just calories in/calories out, right? Just eat less and move more!” I’d be able to retire on a beach in Hawaii with a big fat Mai Tai always at my fingertips. Alas, no one has paid me anything to listen this sort of horse manure so now it’s my turn to disabuse everyone of this ridiculous notion.
In case you have been spared this silly platitude, I’ll give a little background. It all starts with the idea that 1 pound of fat = 3500 kilocalories (or what we know as just “calories”). This estimate was derived by researcher Max Wishnofsky, MD, in 1958, for who knows what reason. The derivation of the math is pretty straightforward (skip this if math puts you in a coma):
- 1 pound = 454 grams (fact!)
- 1 gram of fat is estimated to equal 9 calories
- Human adipose tissue is estimated to contain around 87% lipids.
So then… 454 g adipose tissue x 87% x 9 calories = 3,555 calories/pound of fat (rounded up from 3,554.82)
Then it was rounded down to 3,500 calories because, hey, it’s just easier to remember so why the hell not? The idea is that if you reduce your caloric intake by 3,500 calories a week, then you will lose a pound of fat a week. There’s a ton of rounding and estimating going on here, and yet people cling to this calculation like it came down written in stone from Mount Sinai as the 11th Commandment.
But let’s pretend for one moment that this calculation works. So you reduce your caloric intake weekly by 3,500 calories a week (500 calories a day) and that takes care of the Calories In part. Now you just need to rev up your Calories Out half of the equation in the form of ramping up your exercise. If you’re managing the 500-calories-a- day-less deal and exercising too, then you can definitely lose even more than 1 pound a week, right?
Oh…except we forgot something. There’s another part of the equation… it actually looks like this:
Exercise AND Metabolism.
Oopsy, we forgot that tiny little factor – our metabolism (specifically something we call Resting Metabolic Rate, or RMR, the calories you burn while at rest, which accounts for 60-70% of our total energy expenditure). And it turns out that our metabolism is not something of which we are completely in control. This is borne out in science time and again; in fact, I recently had the pleasure of supervising the research project of a dietetic intern whose research consistently showed that RMR decreased with intentional weight loss. You can check out this particular research here and here and here and here and here and here. Sometimes the RMR remained low throughout the entire study, occasionally it eventually returned to normal, but in most of these studies the weight lost also began to return within the study period.
What happens when you start to eat less? Your body doesn’t know you’re just trying to lose weight for the sake of vanity or a misguided belief that it will make you healthier. No – after a few pounds are lost, your body eventually senses that you are in a place of food insecurity, and so to save your life it slooooows down its engine, the metabolism. Now you are eating less but also burning less in the way of your RMR – this is essentially your body’s way of maintaining homeostasis – stable internal conditions. Because that’s what the body wants more than anything – to remain at homeostasis. You might think you can compensate for this decrease in metabolism by exercising more – except that your metabolism will continue to compensate in the downward direction still as it continues to perceive this energy imbalance. This alone does not explain why most weight loss attempts end in lost weight being regained, but it’s a good start (I can think of some other reasons: unpalatable, unsustainable diets and hunger. Lots of hunger.).
Many health professionals have given up on this equation because they know it just doesn’t work all that well. Some researchers are working on new mathematical equations that will better predict how much a person should eat to lose weight and maintain the loss. Because – and this is dripping in sarcasm – we should definitely be eating according to a mathematical equation.
For me it all goes back to the idea of homeostasis. Our bodies want to remain in happy equilibrium, and they have amazing mechanisms to help us do so. Two of these mechanisms are a sense of hunger and a sense of fullness, which is why it is so important for us to use those internal mechanisms to guide our eating. Yep, back to the ol’ Intuitive Eating we go!
I think we’ve done a lot of damage with dieting over the years by ignoring those internal cues and trying to eat-by-the-numbers. Let’s forget this bad science and start paying attention to what our bodies tell us.