Question: How Many Miles a Week Should I Run to Lose Weight?
"I've heard that one must run approximately 15 miles a week before the "weight loss mechanism" kicks in and you'll actually start losing weight from running. My friend says that it's 20+ miles. Who's closer?"
I'd have to argue that running is a great way to lose weight
and there's really no magic number of miles per week when you start losing weight. You can lose a pound of weight if you have a calorie deficit -- achieved by exercise or cutting calories -- of about 3,500 calories. A 150-pound person will burn about 100 calories per mile of running. So, if that person runs 15 miles and is able to cut 2,000 calories over the course of a week, he can lose a pound. But the same could be said if that person ran 12 miles and cut 2,300 calories. So it's really all about eating fewer calories than your body needs to sustain its weight and exercising to burn even more calories.
What your friend may have read about is the data from the Weight Loss Control Registry, a research group that studies people who have successfully lost weight and maintained their weight loss, which points to the need to consistently burn 2,800 calories through exercise each week in order to successfully lose weight. 2,800 calories would be equivalent to about 28 miles per week, for the average runner. So, that doesn't mean that you have to run 20+ miles per week to lose weight, but you will probably be more successful if you do so (or do other exercise to supplement your running).
More: How to Run Farther
Source: Catenacci VA et. al.,"Physical activity patterns in the National Weight Control Registry" Obesity 2008 Jan;16(1):153-61.