Why are so many Americans so fat?

That's pretty easy. We're fat because we eat too much and we move too little. Why are we so inactive and so indulgent? That's easy, too. Because we can be.

People, like every other creature on earth, respond to their environment. The American environment, especially the environment created in the last 50 years, overwhelmingly encourages us to sit on our backsides and stuff ourselves.

Eighty-five percent of the horrible blight we know as "sprawl" has occurred in the last fifty years. Suburb after suburb, big box stores, strip malls and acre upon acre of asphalt.

These are development and land use decisions based on the hallowed automobile and the ingeniously engineered "need" of it, not genuine human needs of activity, aesthetics, interaction, clean air, clean water and safety. Joni Mitchell had it right. We've paved paradise and put up a parking lot. What's worse is that it is accepted as "normal."

We drive everywhere, robbing us of the opportunity for normal bi-pedal activity, i.e. walking. We rarely stop to consider the ludicrousness of driving three blocks. We have also changed from a greatly active agrarian society to a fairly active industrial society to an information society that is hardly active at all. Even contemporary leisure activities are sedentary.

Like our use of cars, our food intake is gluttonous. We consume almost twice our daily calorie need. Why?

Because it's there, because we can, because we've come to believe enormous portions are normal. Not so, of course. Portion sizes have steadily increased over the last 20 years.

Even dishes have gotten bigger. Dinner plates used to be closer in size to a salad plate than to a platter. A 20-ounce ice cream bowl is obscene, and, unless you're feeding a family of four, don't consider "grande" anything.

All of this wouldn't amount to anything, except that it's killing too many of us, wreaking havoc on our health, making a sizable dent in our productivity and causing other significant ripples in the quality-of-life pond.

While we are like other creatures on the planet who respond to their environment, we differ significantly.

Unlike our inhabitants, we can choose the quality of our surroundings. We can use our opposable thumbs and our brains and create the environment we deserve, and not settle for one foisted upon us.

Brenda Berstler is the founder of the Walking Example Group (WE-GO) a non-profit organization encouraging walking and walkable communities. Visit their website at www.we-go.org.