It could be less than you think—but it could actually be more. Food politics writer Marion Nestle wrote a few weeks ago about the origins of the 2,000-calorie-per-day diet business, and notes that when the FDA set out to determine that number (in 1941), it found women typically reported consuming 1,600 to 2,200 calories per day, men 2,000 to 3,000 and children 1,800 to 2,500. But the FDA wanted one standard of daily caloric intake. It originally picked 2,350, except everyone said this was too high (“Nutrition educators worried that it would encourage overconsumption, be irrelevant to women who consume fewer calories, and permit overstatement of acceptable levels of ‘eat less’ nutrients such as saturated fat and sodium,” writes Nestle). So the FDA went with 2,000 calories instead, more or less because it sounded nice and was somewhat within the range of calorie-consumption totals people reported—not really based on the research.
The whole formula is a bit more complicated than a one-size-fits-all number anyway, or even just a breakdown between men and women. To really get a good estimate of how many calories you should consume to maintain or lose weight, you need to factor in your age and activity level, too. And clearly type of calorie matters as well—you can eat more calories from vegetables and good fats than from junk food or fatty foods and stay fit. As part of a special obesity series, British journal The Lancet has launched a tool that allows you to enter your age, weight, height and activity level, and it will calculate how many calories you should be eating daily for weight loss or maintenance. [Yes, calorie estimators like these are a dime a dozen, but this one is developed by scientists.]
According to the most recent report from the USDA (from 2002), a 2,000 calorie-per-day diet is appropriate for a sedentary (defined as ‘less than 30 minutes a day of moderate physical activity in addition to daily activities’) female between 19-25. For sedentary 26-50 year olds, this number drops to 1,800 calories, and to 1,600 after that. Active adult women (those who get 60 or more minutes a day of moderate physical activity in addition to daily activities) between the ages of 19-25 should consume 2,400 calories daily, dropping to 2,200 calories between ages 26-60, and 2,000 after that. Moderately active 19-25 year olds need about 2,200 calories, which drops to 2,000 in moderately-active 26-50 year olds and 1,800 in moderately-active 50+ women.