Theoretically, to gain 1 pound (0.45 kg) of body weight per week, you'd need to consume an additional 500 calories per day above your typical intake. Some people are hard gainers and require more calories than other people do to add weight. In one landmark research study (Sims 1976), 200 prisoners with no family history of obesity volunteered to be gluttons. The goal was to gain 20 to 25 percent above their normal weights (about 30 to 40 pounds [14 to 18 kg]) by deliberately overeating. For more than half a year, the prisoners ate extravagantly and exercised minimally. Yet only 20 of the 200 prisoners managed to gain the weight. Of those, only 2 (who had an undetected family history of obesity or diabetes) gained the weight easily. One prisoner tried for 30 weeks to add 12 pounds (5 kg) to his 132-pound (60 kg) frame, but he couldn't get any fatter.
A varied response was also seen in another study of identical twins who were overfed by 1,000 calories for 100 days. Some twins gained only 9.5 pounds (4.3 kg), whereas others gained 29 pounds (13.2 kg). Each twin pair gained a similar amount of weight, suggesting strong genetic control (Bouchard 1990).
This discrepancy mystifies researchers. What happened to the excess calories that didn't turn into fat? Some say the body adjusts its metabolism to help maintain a predetermined genetic weight (Leibel, Rosenbaum, and Hirsch 1995). Others look at increases in fidgeting and greater activity in daily life (Levine, Eberhardt, and Jensen 1999).
If you are a hard gainer, take a good look at your genetic endowment. If other family members are thin, you probably have inherited a genetic predisposition to thinness. You can alter your physique to a certain extent with diet, weight training, and maturing, but you shouldn't expect miracles. Marathoner Bill Rodgers will never look like bodybuilder Charles Atlas, no matter how much eating and weightlifting he does.
Among my clients, I've observed that hard gainers are good fidgeters. They twiddle their fingers, swing their legs back and forth while sitting, and seem unable to sit still. All this involuntary movement burns calories. In comparison, the people who complain about their inability to lose weight generally sit calmly. I tell the fidgeters to mellow out. Chronic fidgeting can burn an extra 300 to 700 calories per day.
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