Unfortunately, there is no accurate way to predict how fast you’ll gain weight or how many pounds you’ll put on if you eat more calories than your body needs to maintain its current mass. The media has preached for decades that a pound of fat is 3,500 calories, so eating 3,500 calories more than usual should result in a one-pound weight gain.
But that is a busted myth. “Weight gain is affected by many things,” says sports dietitian, Marni Sumbal. Your age and genetics can affect your metabolism, or how your body processes food, for example. And as Dutch researchers pointed out in a paper published in the Journal of the American Medical Association, so can weight gain.
As you gain weight, your body’s energy requirements increase as well. To keep gaining weight, you’ll have to consume more and more extra calories. “A person who consumes an extra cookie every day,” the researchers wrote, “will initially experience weight gain, but over time an increasing proportion of the cookie’s calories will go into repairing, replacing, and carrying the extra body tissue. After a few years of daily cookie eating, weight gain will level out at approximately 2.7 kg (6 lb).”
Therefore, the rate at which you’ll gain weight when eating extra calories is variable and dependant on much more than those calories alone, including your metabolism and activity level. “Other factors that many increase body composition are lack of sleep (or interrupted sleep), stress, and medications,” Sumbal says. “We can't assume that eating a specific amount of calories above your resting metabolic rate will instantly add pounds to your frame.”
The bottom line: Don’t go dropping $155.40 plus tax on 20 Steak’n’Shake 7x7s just to see what happens; inhaling 20-pounds of cow in one day won’t necessarily make you 20 pounds heavier the next.
Should you do it, however, and wake up to find yourself significantly heavier the next morning, your instant bloat most likely would come from water retention, not new fat or muscle mass.
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