11/19/2013 10:44 am ET Updated Jan 23, 2014

Are Sugar and Sloth the Causes of Obesity -- Or Just Convenient Whipping Boys?

San Francisco's proposed tax on sugar-sweetened beverages, generating funds to support fitness activities, is a good idea. Sugar isn't health food, and exercise has many advantages. But don't expect the measure to have any effect on childhood obesity. When it comes to weight problems, sugar and exercise are red herrings, for the most part.

The real causes of the obesity epidemic have become clear in figures from the U.S. Department of Agriculture. Over the past century, the most notable changes are huge increases in meat eating -- rising from 124 pounds of meat per person per year in 1909 to over 200 pounds in 2004 -- and in cheese intake -- rising from less than 4 pounds in 1909 to 34 pounds today. That means Americans are shoveling in 75 pounds more meat and 30 pounds more cheese -- every person every year -- compared with a century ago. Ice cream and cooking oils -- that is, fryer grease -- have risen, too.

It's not your imagination. Too many Americans put meat at the center of the meals. Collectively, Americans now eat more than one million animals every hour. And those wide flat boxes everyone seems to be carrying home in the evening are nothing but vehicles for cheese -- which turns out to be about 70 percent fat. And every last fat gram packs nine calories -- more than double the calories found in sugar.

The fact is, sugar is a convenient whipping boy. It is easy to blame sodas when we have not come to terms with our collective addiction to the meat and cheese that are making us and our kids fat -- or when we lack the courage to confront the industries that sell them.

Don't get me wrong. Taxing sugary drinks is a good idea. Nobody needs sugar-sweetened beverages. And the tax should apply to all sugary drinks, including milk. After all, the main nutrient in skim milk is lactose sugar, which is why it has about the same number of calories as soda. Whole milk is actually far higher in calories. No child needs milk's load of fat and sugar.

As for exercise, well, lacing up your sneakers is healthful. But researchers have shown that the changes in physical activity over recent decades are far too small to account for the obesity epidemic. Don't believe it? Go to the nearest gym, hop on a treadmill, and run flat out for a mile. As you wipe your sweaty brow, push the little button that tells you how many calories you've burned. It turns out to be about 100 -- that's about half the calories in a small order of fries -- and less than half the calories in a bottle of soda, for that matter. Exercise is good for many things, but it is a tough way to slim down.

So enough whipping boys, already. Blaming childhood obesity on sodas and inactivity diverts attention from the real causes.

The good news is that Americans are finally cutting back on meat. Since 2004, meat eating has slid by about six percent in the U.S. But we still have a long ways to go. The more we set aside the meat and cheese and embrace simple vegetables, fruits, whole grains and beans, the healthier we will be.

For more by Neal Barnard, M.D., click here.

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