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By Laura Petersen, E&E reporter
Backpacking, hunting, skiing and other recreational activities people engage in while visiting national forests burn an estimated 289 billion calories per year, according to a new study from the Forest Service.
That's the equivalent of 83 million pounds of body fat, or enough French fries placed end to end to reach the moon and back, twice. Put another way, it's enough activity to fulfill the Centers for Disease Control and Prevention's recommended amount of aerobic exercise for 7.1 million adults and children for a year.
"It's a lot of exercise going on in national forests," said Jeff Kline, a research forester for the Pacific Northwest Research Station and lead author of the study published in the Journal of Forestry.
Kline admitted the results of the study are by no means earth-shaking. "It's saying what we already knew -- hiking is good for you -- but how many calories is that? We were curious, was it a big number [or] a small number?"
The agency collects large amounts of data about visitor use and experience during 173 million annual visits made to to the nation's forests and grasslands. Kline and colleagues converted data on visitors' statements about their "primary activities" from 2004 to 2009 into calories burned to determine the average annual total, the most intense activities and regional differences.
Overall, downhill skiing, hunting, hiking and walking, developed camping, fishing and backpacking accounted for 76 percent of the total energy expended annually. Backpacking burns the most calories by far, but is not as common as other activities. In contrast, some popular activities like driving through forests did not result in high energy expenditures.
Total visits and calories burned were highest in the West, where there are significantly more national forests. However, forest and grasslands in the Northeast and Southeast yielded proportionally greater net energy expenditures.
This may be partly due to closer proximity to major population centers in the East. About half of all visits were made by "locals," people who live within 60 miles of forest boundaries, indicating people living closer to forests may use them for routine exercise activities, Kline said.
Regional differences may also be explained by the types of activities visitors engaged in. Hunting, a relatively high-energy activity, is much more popular in the East, accounting for 16 percent of visits in the Northeast and 15 percent in Southeast, versus only 6 percent in the West.
The authors caution their study is "somewhat of a back-of-the-envelope analysis," but also point out their calculations are very conservative. They used the lowest figure in the range of "relative metabolic equivalents" for various activities used to determine calories burned. And they only calculated energy expenditures for primary activities; so if a family went camping, it's likely they also did some walking or hiking, which is not included in the grand total of expended energy.
"This is not an exact number," Kline said. "It gives us a rough idea how big a number it is."
By quantifying the physical health benefits -- not to mention the mental health benefits of spending time outdoors -- the study helps highlight the significant role national forests can play in national initiatives promoting outdoor recreation and combating childhood obesity, the authors said.
"Since cutting back dramatically on timber harvest in the 1990s, the Forest Service has been struggling to figure out what their mission is," Kline said, adding public health might be part of the answer and help justify investment in national forests.
The agency can use this data to help garner support for investments and programs with public health benefits, such as developed camping, which leads to longer visits and greater energy expenditures.