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Weight and Genetics

Generally whenever I mention the statistic from Gina Kolata’s Rethinking Thin that 50-70% of our body weight is inherited, I receive such dirty looks that I often add that there have been challenges a plenty to this conclusion. Now, however, The New England Journal of Medicine has weighed in on the subject by publishing the conclusions of a twin-study on eating and weight, and it looks as if Kolata was right on the mark.

The NEJM study had male identical twins consuming 1,000 extra calories per day for 84 out of 100 days. Theoretically, each volunteer should have put on 24 pounds but, lo and behold, although each twin in a set gained about the same amount as his brother, there was a striking difference in weight gained between twin sets, within a range of 9.5 and 29 pounds. The researchers’ explanation was that “40% of our weight may be determined by the genetic cards we’re dealt.”

The first factor cited in establishing weight was brown fat cells. Brown fat, which we’re all born with, burns calories more quickly than white fat and enables the human body to generate heat in the very early stages of development. As we learn other ways to stay warm, brown fat cells disappear in the majority of people. When they remain, however, they continue to help burn more energy, which means burning off more calories. The second factor mentioned is how efficiently cells burn fat. Apparently, there’ a wide range of efficiency. The more efficient cells are at burning fat, the more calories they burn and the less weight is gained. The third factor is how much muscle people have, because muscle burns more calories than fat, even when you’re doing absolutely nothing. So if you have a muscular build, you’ll probably have less trouble slimming down (and staying slim) than if you lack muscular bulk.

I blog about genetic and metabolic differences when it comes to weight because of the job the once-size-fits-all diet mentality has done on our self-esteem. We look at people who’ve lost weight and kept it off and believe we’re failures if we’re still struggling. I’ll keep on saying it—everyone starts off at a different place with weight and no two bodies are alike. The eating and weight game are not played on an even field. You may live a lifetime ignorant of whether you have brown fat or if you possess cells which burn fat rapidly. You don’t need to know these things. What’s important is that you recognize that your body and metabolism are unique. Instead of comparing yourself to others, challenge yourself to do the best you can to eat “normally,” exercise, and live a healthy lifestyle. You’re stuck with your genes, but you can change your thoughts and behavior.