How Many Calories Make a Pound of Fat?
In politics, a lie repeated often enough becomes the truth. In obesity, a false assumption too often becomes the basis for policy and innumerable publications. So it is with the false assumption that 3500 calories make a pound of fat.
A recent publication in Biological Psychiatry used that assumption to conclude that the metabolic effects of daily stresses can account for a weight gain of up to 11 pounds per year. That assumption drew a response from Michelle Bohan Brown and colleagues at the University of Alabama at Birmingham, pointing out that the real number, based on current knowledge, would be much much lower.
So what’s the big deal? At the end of the day, calories still matter. As Yoni Freedhoff points out, there’s hardly “a more painful discussion in nutrition and obesity these days.”
But it matters because it’s false. Even reputable sources like the Mayo Clinic continue to repeat this lie. The relationship between calories and weight is anything but simple and linear. It matters because this false assumption becomes the basis for perpetuating the notion that the cause and cure for obesity boils down to a simple math problem, that obesity is the inevitable result of sloth and gluttony.
The truth is that obesity is the result of a complex adaptive system gone awry. Metabolic rates adapt to changes in weight and circumstances of life. The adaptation makes weight easy to gain and hard to lose under present conditions. Simple answers to obesity translate into simplistic policies that simply don’t work.
Arya Sharma is on the mark when he says, “This is physiology, not physics.”
Click here for the consensus statement on this subject from the American Society for Nutrition and the International Life Sciences Institute. Click here for the study that used the obsolete rule of thumb and here for the commentary from Brown et al. Finally, if you want a good model for the relationship between calories and pounds, go here.
Lipid Necklace, photograph © m.kocun / flickr
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December 15, 2014 at 11:59 am, Emily Dhurandhar said:
We recently published an new model that provides even more realistic predictions for weight change that can be expected from interventions in free-living settings (the types of settings public health interventions usually apply to), in case it is interesting to some…
It’s described here: http://www.soph.uab.edu/news/norc-researchers-find-behavioral-response-health-interventions
The publication is here: http://www.nature.com/ijo/journal/vaop/naam/abs/ijo2014184a.html
And the calculator website is here: http://www.soph.uab.edu/e-balance/
December 15, 2014 at 2:27 pm, Ted said:
Excellent, Emily. Thank you. I had this study open on my desktop. Shame on me for not incorporating it into the references and thank you for helping me out!
December 15, 2014 at 5:57 pm, Emily Dhurandhar said:
the full text/final version is only JUST out. glad it’s helpful! happy to discuss anytime.
December 20, 2014 at 4:53 pm, Trudy Williams said:
The interesting title got me reading but I think the title is misleading.
Your article does not directly challenge the energy density of fat but rather it correctly challenges the tired myth that a deficit of 3500 kcals results in a 1 lb weight loss.
The weight loss predictor calculator (linked in one of your reference article and from Pennington Biomedical Research Center) shows (and uses) an energy density of fat energy mass as 9500 kcal’s per kg (about 4300 kcals per lb).
But weight loss is not just loss of fat mass is it and some fat free mass is lost during the process so that’s the start of complications.
Weight loss rates are neither linear not predictable but weight loss does require an energy deficit to continue. The too many variables that impact on our input and output influence rates of weight loss, and these are what make the rule of ‘3500 kcals results in 1 lb loss” obsolete and a myth.
When it comes to the bottom line though, what number do you suggest is used to represent the actual energy density/content of body fat? How much energy is stored in body fat? I am curious as to your thoughts.
December 21, 2014 at 5:00 am, Ted said:
Thanks, Trudy, for your thoughtful comments. Though you ask me for my thoughts, I’m not sure I can add a lot to what you’ve written. I agree with virtually all of it. You are correct that a pound of fat has a known energy content, but the energy deficit to lose it or surplus to gain it is highly variable. This is physiology, not physics.