Estimating intake: everyone’s bad at it
When it comes to the whole calories in/calories out model, by far the more ‘controversial’ half of the equation is intake. Most people I come across have no problem believing that they’re not that great at estimating how much energy they’re using in a day. At the gym, it has become holy writ that the estimates on treadmills and ellipticals is not to be trusted. People I work with cheerfully admit to having no clue to how many calories they might use doing their job.
Now most people I think have a tendency to way underestimate how much energy they use doing day-to-day stuff while overestimating calories burned during purposeful exercise or sports.
Here’s the thing though, telling someone who’s 30 years old, has an active job and goes running several times a week that there’s pretty much no way, short of a diagnosable condition, that they’re only burning 1200 calories/day* won’t get any argument.
However, telling that same person that there’s no way they’re only eating 1200 calories/day if they’re weight-stable will very quickly escalate. Am I calling them a liar? Am I saying that they don’t know what they’re eating and they’re just stuffing their face all the time? WHO THE HELL DO I THINK I AM???
People hate to think that they don’t really know how much they’re eating. It makes sense. Our society is filled to the brim with puritanical judgement about the consumption and enjoyment of food. That you even grab a mint oreo cookie on your way through the kitchen is bad enough, but that you might not realize you’re doing it five times a day is even worse.
But, no one is great at estimating their intake. One of my favorite studies on this is this one comparing the estimated intake and actual intake of dietitians and non-dietitians. Now, the conclusions of the study, which I don’t disagree with, were that dietitians were better than average people at estimating intake. However, they still underestimated by an average of 223 calories/day. And this wasn’t just a food recall survey, the participants were told that they needed to be as accurate as possible and were trained on how to do this.
Importantly, however, the rates of underreporting were similar between tertiles of adiposity. Most (68%), but not all, underreporters were found in the lowest tertile for reported EI. CONCLUSIONS: A low reported EI and greater BMI may help identify energy underreporters. However, whilst underreporters may more frequently be ‘bigger’ (by BMI), they are not necessarily fatter (using direct measures of body fat). As underreporting was present among all tertiles of BMI and adiposity, these results emphasise the importance of following past recommendations to identify and exclude energy underreporters in nutritional studies
Basically, yes, fat people in general underestimate their intake, but so does everyone else.
More interesting to me is why this is so. I suspect it’s a cultural phenomenon born of the fact that 1)Food is completely demonized and 2) People are fairly ignorant of what a ‘normal’ energy expenditure is with many women especially believing that they only burn 1500 calories/day.
In at least one study I found, there was a small correlation between a history of dieting and fear of “negative evaluation” and underreporting of energy intake. Again, in a culture saturated with dieting and fear of being seen as ‘fat’ (where ‘fat’ is anyone not apologizing for enjoying food, honestly) the fact that nobody wants to say “yeah, I eat 3,000 calories every day!” is not surprising.
*This is hypothetical. I do not go around arguing with people about how much they eat or how much energy they use. That would be weird.