Myth: People who are overweight have slower metabolic rates.
Truth: With rare exceptions, people who are overweight have metabolic rates similar to or higher than lean people.
Studies comparing the resting energy expenditure of overweight people and lean people show little difference in basal metabolic rates. The ones that do show a difference show overweight people have higher metabolic rates.
Thielecke, J. Möseneder, A. Kroke, K. Klipstein-Grobusch, H. Boeing and R. Noack. Determination of total energy expenditure, resting metabolic rate and physical activity in lean and overweight people. Zeitschrift für Ernährungswissenschaft Vol. 36, No. 4, December 1997 P310-312
Summary: A new2H/1H and18O/16O equilibration device was tested, standardized and employed for the determination of total energy expenditure. It was shown that overweight men and women have increased resting metabolic rate as well as increased total energy expenditure when compared to their lean counterparts. The physical activity level (PAL)index was slightly decreased which possibly suggests a decreased physical activity in obese people.
I have measured the resting energy expenditure of a large number of overweight people using the Korr ReeVue, and almost all of them were shocked when told their metabolic rate was average or above. Almost all were convinced they had slow metabolisms and claimed they ate very little. Once they started accurately weighing, measuring and recording their daily calorie intake, it became obvious the real problem was excessive calorie intake. They grossly underestimated the amount of calories they consumed daily. Studies using double-labelled water have also shown many overweight people underestimate their calorie intake, or in some cases are simply under-reporting it to researchers.
By contrast, many people who claim to have difficulty gaining muscle often overestimate the amount of calories they consume, and fail to gain simply because they are not consuming enough quality food to support muscle growth.
The solution for both is to accurately weigh or measure and record calorie intake. Everything that goes in your mouth, food and drink, gets weighed or measured and written down along with the amount of calories. If you are not doing this or have not done this consistently for a long period of time then you can not make any claims with regards to how much you are or are not eating because you do not know.
While some people do have slower metabolic rates due to hypothyroidism or other conditions, this is rare, and while some people may have genes that predispose them to gain fat more easily than others, these genes do not cause the fat gain. Read that last sentence again. Some people may have genes that make it easier for them to gain fat than others, but these genes do not cause the fat gain. The fat gain is caused by a person’s behavior – mostly their eating habits but also their activity level. As a species, we have not changed much over the past quarter million years, much less the past hundred, so genetics is not an excuse. What has changed? The availability of inexpensive, high-calorie food and drinks and and increase in labor-saving devices has made it incredibly easy to consume far more calories while expending far fewer. However, this doesn’t mean we have to eat more calories or be less active, nobody is forcing people to overeat or be lazy. It just means we have to be more conscientious about the choices we make about what we put in our mouthes and what we do with our time.