What do a svelte marathon veteran and a 400-pound sumo wrestler have in common? Both completed the Los Angeles Marathon recently, and both ran as strong testaments against the recycled rhetoric of today's anti-obesity activists.

Exhibit A: Joe D'Amico, a long-time distance runner who ate only fast food for the month leading up to the race. He finished 29th out of 23,542 competitors and set a personal best time of just over two and a half hours.

Exhibit B: Kelly Gneiting, a sumo-wrestling veteran who shot for a world record as the heaviest man to finish the 26.2 mile race. He succeeded, albeit in slightly under 10 hours.

Both men violated two of the so-called "rules" of food and obesity. The first is that eating fast food is a recipe for weight gain and an unhealthy lifestyle. The second is that simply being obese is a huge health threat. Both deserve a skeptical second look.

Firstly, there's no such thing as "bad" food. All food has calories; some foods provide more than others. But everybody needs a certain number of calories every day to live. Weight gain is caused by the number of calories from food exceeding the number of calories burned through activity.

The key is moderation. Fast food every day might not be the paragon of a healthy diet unless you too are training for a marathon and can burn off excess calories. (Although, there are plenty of healthy options at fast-food restaurants.)

Rule number two is not as intuitive. Can an overweight person be healthy? The answer is yes (though it's much harder to be, and I wouldn't recommend it). Gneiting stays physically active and, despite his largeness, says his blood pressure is normal and his resting heart rate is 60 beats per minute. (That's on the healthy end of the American Heart Association's scale.)

His case highlights the growing scientific evidence finding that it's how fit we are, not how fat we are, that ultimately has the strongest implications for our health.

A 2009 commentary in the British Medical Journal reported that "obese men who were moderately/highly fit had less than half the risk of dying [from cardiovascular disease] than the normal-weight men who were unfit."

Similarly, an article in the New England Journal of Medicine reported that the most physically fit had just one-fourth the risk of dying as the least fit. And a 2007 study in the Journal of the American Medical Association (JAMA) determined that low physical activity levels, regardless of weight, determine the likelihood of dying prematurely.

Therein lies the problem in the national Battle of the Bulge: Some people oversimplify the issue, often to serve a larger agenda. There are trial lawyers who need to demonize "junk" food so that they can sue restaurants. And then there are nanny-state puppet masters who think that targeting certain foods under the tax code will put us on a national diet.

These are by no means the only popularly held conceptions about obesity that are flawed. Consider another: The shrill claim by some public health activists that our children could be the first generation to not live as long as their parents.

Here's a reality check: According to the U.S. government's life expectancy estimates, children born today can expect to live to about 80 years — longer than any previous generation, including their parents'.

And then there's the idea that "cheap food" is always unhealthy, and that healthier options are too expensive for lower-income Americans.

The U.S. Department of Agriculture's Economic Research Service tosses cold water on this claim. Researchers there analyzed the prices for over 150 common fruits and vegetables and found that the average prices ranged between 20 cents and $2.

There's a lot we don't know about obesity. And though I'm not excusing being obese, those two marathon runners offer context to the debate over government's role in what we eat. Both men chose to take control and stay fit. For most Americans, that's probably the healthiest advice they can have.