Best-selling author Mark Bittman prepares a lunch inspired by fresh ingredients in Washington, D.C. Bittman’s new book, "VB6," advocates a vegan diet before 6 p.m. (Nikki Kahn/THE WASHINGTON POST)

It’s the first day of the season at the 14th and U Farmers Market in the District, and I'm looking at asparagus, turnips, herbs, kale, arugula, strawberries and more with Mark Bittman. We’re doing what so many shoppers do at markets like this one across the country, week in and week out: comparing one farmer’s produce with another’s, and trying to decide what would make a good lunch and maybe an even better dinner.

When I tell Bittman I have carrots and kale at home, he proposes a stir-fry. “Is your kale nicer than this guy’s kale, or not as nice, or about as nice?” he asks. I try to envision the crisper drawer of my refrigerator back in my apartment, where we’re headed next, and feel comfortable in choosing Option 3. Even though it’s several days old, it’s just about as nice, I figure.

He asks because he knows that for any cooking, but especially the kind of off-the-cuff dishes that helped make him famous, the key is to start with excellent ingredients — a strategy that bears repeating for those of us who take it for granted. And for the kind of lunch we’re going to make, one without any animal products, the tactic might be even more important. The stir-fry won’t have, say, the smoky fat of bacon to hide any blandness in those vegetables. If the turnips he wants to mash don’t have enough flavor, cream and butter won’t be able to rescue them.

But he’s not worried. Bittman, 63, describes himself as a cross between Larry David and Julia Child, but his mood at the market is decidedly Julia-esque, not cranky in the least. At the beginning of a busy book tour that mostly involves talking, and signing, and appearing on TV and radio shows, he’s grateful for a change of pace. “A train ride followed by a walk on a nice day, and then shopping and cooking? That’s fine with me,” he says. “Other times it’ll get a little grueling.”

In case you haven’t noticed (although how could you have missed it?), Bittman, the bestselling author of “How to Cook Everything” among many others, has a new book out. The subtitle of “VB6” explains the concept: “Eat Vegan Before 6:00 to Lose Weight and Restore Your Health . . . for Good.” The idea stems from his doctor’s suggestion six years ago that in order to reverse a course headed toward diabetes and heart disease, Bittman should go vegan. The patient — perhaps in a Larry David mood this time — balked. “I asked, ‘Can’t I compromise?’ Sid looked at me and said, ‘You’re a smart guy. Figure something out.’ ”

That something was the idea to forgo all animal products and “hyper-processed” foods for breakfast and lunch and snacks, and to let himself eat whatever he wanted for dinner and beyond. It’s a strategy based on the knowledge that deprivation often backfires, that calorie-counting is too laborious to keep up for long, but that something had to change. After 30 days, he was down 15 pounds; after four months, he had lost 35 — and he has kept them off (and returned his cholesterol and blood-sugar levels to normal). “VB6” is a diet book, no doubt, but Bittman also sees it as a way to get people to move away from what’s been called SAD, or the Standard American Diet of processed foods and more meat than our bodies need. As an opinion and Dining columnist for the New York Times who writes about sustainable food issues, Bittman hopes the book might make an environmental impact, too.

What may come across as gimmicky, with the acronym and the time stamp and all, becomes less so once you read or listen. For one thing, that 6 o’clock reference is just a device to mark off part of the day from the rest, to give eaters structure without asking them to obsess. Want cream with your morning coffee? Going out to lunch one day and don’t want to seek out a vegan entree? Want to eat bacon at breakfast and a vegetarian dinner? Don’t sweat the details. “The point is to eat less meat and other animal products,” he says when we’re back in my Dupont Circle kitchen. “VB6 is a way to do that, but it’s certainly not the only way.”

Bittman has dinner plans, and because it’s well before 6, we won't be crumbling any feta into that mash. What would be the point of that? I’d rather see his tips and techniques for making a plant-based (or as “Engine 2” author Rip Esselyn likes to call it, “plant-strong”) meal. It all boils down to one tip, really, which he reiterates from earlier: “Start with good stuff, and go from there.”

First, he combines the turnips, their greens and some baby bok choy with water and sets it to a low boil. “I’ve been really into mashes lately. Sort of an Eastern European thing, I guess,” he says, although I immediately think of colcannon, the Irish dish of mashed potatoes and cabbage or kale. He cooks the vegetables with more water than I would have imagined, for longer than I would have thought and with more olive oil than I would have been inclined to use. “When you’re not using meat or dairy, you don’t have to worry about the amount of oil, really,” he says.

While the turnip mixture is cooking, he heats up my wok, swirls in canola oil then throws in thick carrot coins along with garlic and onion. He lets the carrots sear until nicely browned before tossing in the asparagus — everything but the tender stems, which he saves for later in the process. He tips water (from his drinking bottle) into the wok a time or two, creating clouds of steam and keeping the mixture lubricated. I find roasted poblano pepper strips in my refrigerator for him to toss in, in the interest of making something spicy, “but next time I think I’d just use red pepper flakes,” he says. Into both dishes he folds large handfuls of herbs: mint to offset the poblano in the stir-fry, parsley to add a fresh grassiness to the mash. Smart cooks learn from good cooks, and after tasting that mash — which is barely mashed, actually — I mentally add it to my repertoire of easy vegetable dishes. That olive oil — not so much, now that I think of it — has given the combination just enough silky richness.

“Do you want to make an arugula salad?” he asks. I do. We have super-peppery greens from Mountain View Farm, one of my favorite vendors at 14th and U, and I dress them simply, first in high-quality extra-virgin olive oil to keep them from wilting, and then with a handcrafted white wine vinegar from Virginia Vinegar Works, plus flaky sea salt.

As we sit down to eat, he takes a bite of each dish and then points at the salad. “This is the best thing on the table,” he says. “People tend to put arugula in lettuce mixes, but it’s really spectacular by itself. I could eat arugula all day long.”

All day, sure, but what about all night? After he talks to a crowd at the Sixth and I Historic Synagogue, Bittman is hitting Fiola for dinner. I’m sure he wouldn't refuse a nice arugula salad as part of the spread, but he also might like a veal chop. It will be after 6, so he has no plans for restraint.