Thursday, January 31, 2013
Yesterday, the New England Journal of Medicine published a paper that addresses common myths, presumptions, and facts about obesity.
As the authors note in their introduction,
“Passionate interests, the human tendency to seek explanations for observed phenomena, and everyday experience appear to contribute to strong convictions about obesity, despite the absence of supporting data. When the public, mass media, government agencies, and even academic scientists espouse unsupported beliefs, the result may be ineffective policy, unhelpful or unsafe clinical and public health recommendations, and an unproductive allocation of resources.”
In this paper, the authors address seven myths, six presumptions and nine facts, which I hope to address individually in upcoming posts.
The first myth addressed in the paper is the common misconception that a continuous daily excess of a few calories per day will result in continuous weight gain.
This myth (also referred to as the 3,500 Calorie Rule) is often presented in a way that numerically adds up the number of excess calories you may be eating per day (say 100) and translates this into weight gain by simply equating 3,500 extra calories to one pound weight gain.
Thus, even academic publications often suggest that a 100 extra calories per day over a year (say about 350 days) would result in 35,000 extra calories or a ten pound weight gain.
You will also often find the converse, where simply burning an extra 100 calories a day is equated to losing 10 lbs.
This, as explained in the paper is a myth because such simplistic calculations do not take into account the physiological mechanisms that result in compensatory energy conservation or expenditure, thereby limiting changes in body weight.
Thus, although a pound of body fat may well represent about 3,500 calories (which it roughly does), an extra pound of body fat is not simply the numerical result of ingesting an extra 100 calories per day for 35 days.
Nor does a daily caloric deficit of 500 calories result in a weight loss of one pound a week, week after week after week, till you finally disappear.
As I have previously explained, significant and ongoing weight gain or weight loss actually requires a substantially greater level of daily caloric excess or restriction that may have to incrementally increase over time to sustain continued gain or loss.
It is therefore safe to ignore statements that are commonly found both in academic publications and in popular media presenting simplistic statements like, “an extra potato chip a day over 20 years can lead to a 50 lb weight gain or an extra can of pop a day can lead to a 20 lb weight gain in one year”.
In reality, ingesting 3,500 extra calories does not simply translate into an extra pound of body fat – nor does burning 3.500 extra calories result in a pound of weight loss.
Or, as I say in my talks, “This is not physics, this is physiology!”
For a detailed discussion of how many calories it actually takes to lose or gain weight click here.