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Estimating intake: everyone’s bad at it

June 19, 2009

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.

Now there have been some studies suggesting fat people tend to underreport their intake by a larger margin, but other studies have found little difference:

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.

12 Comments leave one →
  1. June 19, 2009 12:45 pm

    I love this kind of stuff, because I am a giant nerd. But yes, I agree that most people don’t have much clue about their actual caloric intake. It’s just that my opinion is — it kind of doesn’t matter, assuming you’re able to pay attention to hunger/satiety and all that stuff (by which I mean, just general indicators that you’re getting enough to eat — I dislike the notion that anyone need sit down and do a 24 hour recall each day and then calculate how many calories they ate.)

    So, as part of my job, I have done an OBSCENE amount of calorie counts — meaning, I do all the math on those 3-day food records or 24-hour recalls that people fill in when they see a dietitian. I have spent entire months of my life doing nothing but that — GOOD TIMES.

    And, short of doing a record or recall on myself, I really have no idea how much I eat on any given day. I know that it varies. In school, I’ve been required to do a few self records, and I’ve done some at work too, out of idle curiosity. And I do think that I probably eat somewhere between 2200 – 3000 kcals on any given day. It’s how much I appear to be hungry for, and my weight has remained pretty stable. (Thankfully, since I don’t have quite as many hang-ups about food being bad or calories being bad as a lot of people, I think I’ve been able to be pretty honest and objective about what I ate when doing those assessments.)

    The thing I find interesting is that there sometimes seems to be a couple days of “lag time” between a day when I’ve expended more or less energy, and the time when I actually eat more or less to make up for that.

    Okay, enough geeking out. But I am interested enough in this that I’d love to get my hands on that little monitor thingy you were using recently. I’d love to know what’s actually going on in my body, and how that relates to my sensations of hunger, etc.

    My god I talk too much.

    • June 19, 2009 5:09 pm

      I love love love that you geek out about this stuff!

      I agree that for most people, how much they’re eating isn’t that important. My main concern is how many women I talk to/read about who are trying to eat absolutely tiny amounts of food. Because they’ve read some stupid general guidelines that say women should only eat 1200 calories on a diet or, more commonly these days, because they honestly believe that they’re only eating around 2000 each day. I think it’s such a bad idea for so many reasons not the least of which is the kind of shame spiral people go through when they are unable to maintain these insane kind of deficits. Honestly, there is just so much shame around appetite period and it makes me sad. There’s nothing wrong with food, ffs!

      I have the lag time effect too. I find some odd kind of comfort in those awesome kind of homeostatic mechanisms.

      The bodybugg is really such a fascinating look into the relationship between movement and hunger. The friend who is borrowing it now was convinced that she must be using it wrong because she found that she was least hungry on days when she moved the most, but I told her that I often found the same thing and we just talked about leptin-sensitivity and delayed hunger and blah blah geek blah.

    • June 19, 2009 9:05 pm

      I also meant to add that I kinda feel oddly strong about this because there is such an anti-food feeling in our culture. And the strong feelings people have about eating “too much” and equating any eating a non-thin person does with ‘overeating’ …… the belief that a ‘normal’ person only needs this small amount of food per day ties into that. And even people who I think are very body-positive, who celebrate their bodies and don’t constantly harp on them will instantly get very defensive at the idea that they could be eating more than that 2000kc/day number.

      And of course, part of that is that fat people’s eating habits are treated as automatically disordered even if they’re eating in response to hunger or maintaining their weight.

      But I’m a big believer that demystifying things like metabolism and actual food intake can be a big help in letting people see that each time they eat some chocolate is not a binge nor is it ‘gluttony’ if they eat more than 500kc at a meal. Whenever diet talk happens at work or around friends, I like to bring up how much I eat. Not to shock or anything, but the idea that someone could be losing weight on 2600+ calories/day is unbelievable to most people.

      I’m kind of babbling here, but I hope I’m being clear.

  2. ciocia permalink
    June 19, 2009 3:56 pm

    Nobody has any idea how much they eat, and they tend to estimate wrong, largely because we are human. Fat and thin people are human alike. I remember reading about the difference in obesity findings between in-person interviews and telephone interviews. Many more people were found to be obese in person. For women, it was because they underestimated their weight, and for men, it was because they overestimated their height. 🙂

    I am a WW lifer, so I write down all my stuff in a diary. If not, I would not remember half of what I ate, or would over/under estimate it. Doing a diary keeps me from thinking I didn’t eat when I did, or that I was eating off the chart when I didn’t eat all that much. I’ve gone both ways. Memory is a mother, and not always a nice one.

    • June 21, 2009 8:05 am

      for men, it was because they overestimated their height.

      That’s hilarious.

      I’m keeping close track of what I eat now in order to track protein intake (I’m trying to eat more of it) and yeah, the difference between what I write down when I track as I go vs trying to remember later is generally pretty significant. I figure my brain has more important things to do than recall each and every thing I eat.

  3. brahnamin permalink
    June 19, 2009 6:20 pm

    This is why IF was my godsend this time around.

    I so know I suck at guestimating what I’m eating. Dropping 3-4 meals a week makes it easy to create a calorie deficit without driving myself nuts over it.

    • June 21, 2009 8:10 am

      I find IF so interesting, but I’m not sure if I could do it now. I think when the semester starts back up and I’m not working so much it would be a neat thing to try.

      • brahnamin permalink
        June 22, 2009 5:04 pm

        Yeah, the whole fasting thing can be intimidating, but it’s been well worth it – and I found once I started doing it I was fine with it.

        The key for me is I never take it past 24 hours and I always start the night before, right after dinner, so I can end my fast with dinner the next day and not go to bed hungry either day.

  4. June 21, 2009 6:41 pm

    I’m starting to be aware of how off I am. I used to figure that I ate about 2000, now I figure it’s probably more like 2500, and maybe i burn 3000/daily. I have no basis for even this estimation, but occasionally I’ll eat a meal I can calculate, and a 600 calorie lunch, shared 1/4 with dog, will leave me hungry in less than 3 hours, if I’m doing anything other than sitting on couch. One of these days I may eat all processed, just so I have calorie counts better than my estimation.

    As I approach what is considered “normal weight”, I’m becoming less and less afraid of food, with less tolerance for much of that craziness. I had more than enough food/weight morality growing up, I’m so burnt on it. Considering all that I eat, and that I still slowly lose weight, I’m learning to trust my appetite. I don’t need calorie counts on every bloody thing I eat, I can tell if it’s heavy by how it tastes and feels in my tummy. Maybe I’m lucky to be someone who got fat because of disordered eating alone, and now that I’m not, it’s all coming off, and I won’t have to think of it anymore. Maybe I’ll someday be one of those people who have no food/weight obsession, and I can fix the rest of my life.

  5. cicadasinmay permalink
    June 25, 2009 9:07 am

    I have no idea how you’re supposed to try and count your calories if you don’t subsist entirely on processed, nutrition-label-having foods. I can try and make a rough guess based on that one day I ate an entire frozen pizza and knowing how many calories are in a Luna bar, but there is no way I can find out how many calories are in things I actually eat, especially since a lot of them are veganized versions of things, and even if I look up the meat-version I find lots of different numbers, because hey, they are not all the same and they come in lots of sizes! Plus, I don’t have a science lab of mass and volume measuring devices in my kitchen! And if I were off 100 calories on 3 meals, that would be 300 calories, which seems like a lot when it makes the difference between 2000 (which has the image of “OMG women should not eat that much ever I don’t care how tall you are”) and 2300 (which I imagine most people would describe as “you stupid fatty fatty glutton stop destroying the planet”).

  6. June 26, 2009 7:09 pm

    I love discovering that dieticians can’t count calories accurately either!

    I used to weigh and measure and count calories and write everything down… and it worked! I don’t know how accurate I was in terms of actual calories, but I got really good at knowing how much I could eat to either gain, lose or maintain weight. But sheesh, what a pain in the ass it all was!

  7. June 11, 2010 1:57 am

    I wrote a similar blog regarding this subject but your is better.

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