Welcome to Wendy’s, how may I help you?” If you replied, “Make mine the Triple Baconator Combo Meal with small fries and a small Coke,” you’ve just agreed to pack on 1,850 calories, 106 grams of fat (43 of them saturated) and 2,780 milligrams of sodium.

And we wonder why Americans are so fat. That calorie count was from a new book, "10 Worst Fast Food Meals in America," and you’d do no better with the Large Triple Whopper with Cheese Value Meal (with fries!) from Burger King (1,790 calories). It’s no wonder that, according to the Centers for Disease Control and Prevention, the average American male between 20 and 74 has a 39-inch waist and weighs 194.7 pounds (up 28.4 since 1960). The news isn’t much better for women: They weigh in at 164.7 now (with a 37-inch waist).

As Automotive News (subscription required) recently noted, there’s a car angle to this. Automakers are bending over backwards to reduce the weight of their cars, using lightweight steel and carbon fiber whenever possible. It’s the quickest way to improve fuel economy. Ford cut 30 pounds from the automatic transmission in the Focus. The Chevy Cruze and the Hyundai Elantra have even done away with the spare tire. “But while engineers are removing one spare tire, their customers and passengers have each been adding one of their own,” writes columnist Larry Vellequette.

It’s simple math: If the car loses 30 pounds, but the driver gains the same amount, we’re left with a wash in terms of fuel economy. With two big and talls in the car, you’re losing ground.

The auto industry’s focus on losing weight is a welcome change. According to Christopher Knittel of MIT, formerly of the Institute of Transportation Studies at the University of California, Davis, “From 1980 to 2004, the average fuel economy of the U.S. new passenger automobile increased by less than 6.5 percent. During this time, the average horsepower of new passenger cars increased by 80 percent, while the average curb weight increased by 12 percent.” That’s awful. And, he adds, “[I]f weight, horsepower and torque were held at their 1980 levels, fuel economy for both passenger cars and light trucks could have increased by nearly 50 percent from 1980 to 2006; this is in stark contrast to the 15 percent by which fuel economy actually increased.”

OK, so now we have the cars losing weight and people gaining. Well, they were gaining back then, too, but all that extra poundage is cumulative. Now, here’s where the cars and calories thing comes together. As the Los Angeles Times reports, “A new study finds that living in an area populated by fast-food restaurants and not having a car may make your weight climb.” This is sociology writ large: poverty equals pounds.

Talk about a vicious circle. In this case, fast-food proximity erases the undeniable benefit of walking. The heavyweights making the springs sag down will actually melt some of the fat away through the very act of owning a car.

The report, based on data from 2,156 adults in the Los Angeles Family and Neighborhood Study database and first reported in the Journal of Urban Health, reveals that car owners on average weighed 8.5 pounds more than pedestrians. But when those same non-car-owners lived in “lower middle socioeconomic status areas,” i.e., poor, neighborhoods, they weighed 12 pounds more than people living there with cars. Why is that? Because without a car you can’t drive to the affordable grocery stores that are usually located elsewhere, but you can walk to conveniently located Denny’s, Burger King and McDonalds.

This is kind of obvious, but the study’s authors write, “Car ownership may reduce the local effect of fast-food outlets in the neighborhood, while lack of car access tends to exacerbate it.”

The solution to all of this is either healthy fast food (fat chance of that!) or cheap green cars, so the urban poor can buy rides to take them food shopping. That would also help extend hybrid and electric vehicle ownership beyond the affluent early adopters to a broad — and I do mean broad — cross-section of all Americans.

Here's Natalie to give you the skinny on some popular fast-food choices. She's a bit preachy, but she gets the job done:

Jim Motavalli ( @jmotavalli ) writes about cars, technology and the environmental world to anyone curious enough to ask.

Fuel economy and our obesity problem: A weighty connection?
A new study shows Americans have packed on almost 30 pounds since 1960, and that's erasing all the gains automakers have made by putting their cars on a diet.