Junk food is cheap at a store featured in the HBO series “The Weight of the Nation.”

If you plan to snack while watching HBO’s new documentary series “The Weight of the Nation,” better grab some fruit. And better yet, grab it from a farmers market.

The first half of the four-part program debuted Monday night; the program concludes tonight with two more episodes dedicated to our ballooning waistlines. “Weight” hammers home the message that humans evolved to store calories, and in a society that has industrialized food production and engineered out activity, that’s making us sick. But it’s not all bad news. Several folks featured in the series are working to change habits, including Preston Maring, a physician with Kaiser Permanente (one of the partners in the HBO project), who recognized how badly some of his patients were eating.

His solution: hospital farmers markets. Employees get fresh lunch options, patients can pick up produce after appointments and neighbors have a regular reminder to eat their veggies. After Maring got one off the ground in Oakland, Calif., in 2003, that seed of an idea grew into something much bigger.

Now there are more than 40 KP-sponsored markets and farm stands (with a single vendor), including five locations in the Mid-Atlantic region. The newest one, a farm stand in Gaithersburg (655 Watkins Mill Rd.), opened Monday.

One hurdle to shopping at farmers markets is the price, but as the program notes, the real cost of unhealthy foods is much higher. You’ll have to shell out for junk later in health care costs, and taxes keep the prices of processed foods artificially low due to government subsidies for corn and soy.

Maring believes the bigger problem is the ubiquity of fattening foods. “When you get down to the reality check, what we choose to eat is because it’s right in front of us,” says Maring, who thinks that putting produce everywhere can change that. “We need to make the right thing the easy thing to do.”

Watch Out

See it free at Theweightofthenation.hbo.com or attend a screening at 6 p.m. today at Prince George’s County Community College (301 Largo Road, Largo, Md.) in the Rennie Forum.