Obese and in Denial
It is well established that people under-estimate the amount they eat daily and not just those who are overweight. Normal weight people can under-estimate their daily caloric intake by as much as 16%. This under-estimation increases dramatically in overweight populations and it can’t be totally explained by reporting bias. In other words, there is a significant conscious and subconscious denial mechanism at work in overweight and obese people.
This denial is best exemplified in people who have been unable to lose weight via caloric restriction diets because they have “slow metabolism”. One study looked at a group of obese patients who reported an inability to lose weight despite increased activity and caloric intake (as low as a reported 1,200 calories per day) and compared them with a similar group who were able to lose weight with caloric restriction. The “diet resistant” group was more likely to blame “genetics” or “slow metabolism” for their inability to lose weight and were more likely to take thyroid medication. The study authors found that while both groups had very similar physical activity levels and resting metabolic rates, the “diet resistant” group under-reported their actual food intake by 46% and over-estimated their amount of physical activity by 50%!
What leads to this denial? It turns out that it is normally very difficult to accurately estimate that amount of food intake that one eats per day without knowing and painstakingly recording the exact caloric makeup of everything you put into your mouth. Unfortunately, very few obese people tend to be obsessive-compulsive dietitians with a fetish for caloric minutiae. Simply “eye-balling” your food portions is not enough nor is it accurate, especially in many restaurants where portion sizes tend to be larger and where Americans get 50% of their meals from. Even experts like dietitians tend to under-estimate the caloric make up of restaurant portions. Obese people also tend to ignore or discount food intake that does not coincide with a full meal such as snacks and middle of the night meals as well as other caloric sources like non-diet sodas and alcohol.
Risk factors for under estimating daily food intake are low-income and low-literacy populations and eating large meals and/or meals in social situations. These factors correlate highly with eating at chain restaurants or fast food establishments. To make matters worse, a recent study found that restaurant portions may have up to 18% MORE calories than what is listed on the menu. It’s not clear what the cause is but ever increasing restaurant portions may be outpacing their most recent caloric data. In any case, this only helps the obese to validate their under estimations of their dietary intake.
But metabolism is always a two sided coin with caloric intake on one side and physical activity on the other. As the study above found, it is just as easy for obese people to over-estimate their amount of daily physical activity as it is for them to under-estimate their daily caloric intake. Once again, this is due to the fact that people tend to discount activity that is not specifically set aside for exercise such as “working out” or “taking a walk”. Even though 15-30 mins of daily cardiovascular exercise does burn through a lot of calories, the majority of our daily activity and hence the majority of our calorie burning occurs when we are NOT exercising. Therefore it is possible for someone who exercises daily for 15-30 mins but who otherwise is very inactive at all other times (deskjob, watches TV), to burn less calories during the day than someone who does not exercise but who is more active throughout the day (walking, yard work, standing; this source has an excellent example of how this happens).
This apparent paradox is validated by a 2004 study which found that thinner people tend to “fidget” more than obese people. Even this seemingly inconsequential activity (likely combined with more standing and walking than obese people) leads to more daily calorie burning. Every doc has seen examples of this when observing their obese patients in the waiting or exam rooms. These patients sit perfectly quiet and still without any significant movement of any kind. The over-estimation of activity comes from the fact that usually sedate people place too much emphasis on their few mins of exercise a day while discounting the rest of the time when they are nearly motionless.
Though this is not to say that regular exercise is over rated (maybe only a little). Most people who exercise regularly tend to be more active during the day and though there is no data on this as of yet, I suspect that regular cardiovascular exercise may increase the amount of “fidgeting” as well as other activity throughout the day. The problem comes when couch potatoes think that 15 mins of running on the treadmill will make up for hour upon hour of motionless desk work or TV watching. The same applies to dieters who think that a cob salad at lunch will make up for their 3 bag Funyun orgy in the afternoon.
The bottom line is that there is no such thing as “slow metabolism” as a cause of obesity that is refractory to diet and exercise and the best way to estimate your actual daily caloric intake and physical activity level is by your weight gain or loss over several weeks. If your weight is not going in the direction you wanted or expected then you are not doing it right! Eat less and/or get more physical activity. Don’t make it complicated. And lay off the thyroid meds. And the Funyuns.