The Not So Fast food truckers fix fare that our hunter-gatherer ancestors would have liked.

That song “Up on the Roof” keeps ringing through my head. Because that’s where we are — up on the roof of the Whole Foods at Seventh and University in Hillcrest, 7:00 at night.

Me and shadowy figures and three food trucks parked in an L-shape.

I’ve come for the first one. It’s the same color as the Coaster, that light bluey-green. Called “Not So Fast!” They tweeted they’d be here tonight, serving up food that’s got me curious. Food that our ancestors ate for two-and-a-half million years. The paleo diet — we’re talkin’ cavemen.

At least, that’s the promise. A notice stuck to a window on the side of the truck reads:

“Not So Fast! is a unique mobile kitchen that specializes in fresh, wholesome, nutritious meals on the go. Utilizing local farms and sustainable sources…we offer truly healthy fare…”

Uh-huh. Here, I’m starting to tune out, because isn’t every restaurant in town telling us the same thing? Local, sustainable, nutritious…

But now it gets more interesting. I get in line and continue reading.

“…that is gluten-free, soy-free, sugar-free, grain-free, legume-free, with no preservatives…All our sandwiches are served on lettuce wraps, unless otherwise specified. We do not encourage the use of grains or gluten.”

I first discovered these guys at a Third Friday food-truck gathering at 57 Degrees, the wine shop in Middletown. I had an “El Pavo Diablo,” a turkey burger, with “grilled jalapeños, roasted red peppers, and spicy garlic aioli, $8.”

Lots of other things were up on the marker-board menu, like bison burger ($11) and beef, pork, and mushroom burgers ($8–$10), plus wild-cod tacos ($9). (It’s hard to imagine our caveman granddaddies recognizing any of these foods in this form, but the “now” and the “then” have to meet somewhere.) The turkey was meaty, spicy, and, with the bacon and avocado, tasty. I asked for it in a bun, too, which you could see they didn’t want to do.

So: meat, good; bun, bad. What’s going on? We’re not talking vegan, or even vegetarian, here.

That’s why I’m back tonight: I want to know why we’d return to eating what our distant ancestors chowed down on.

Plus, last time, I saw two dishes that I wanted to try — the bison burger ($11) and the “Bomb-Bomb Hash” ($5), “sweet-potato hash loaded with avocado and house-cured bacon.”

Now I’m at the front of the line. I do one more check of the board, see a sweet-and-sour spicy pork. “Julian, California, pastured pork sloppy joe with pineapple, scallions, house-cured bacon, and primal sweet-and-sour pepper reduction,” $10.

Sounds delish, but I stick with plan A, the bison burger, “with red wine, caramelized onions,” and, wow, “Kerrygold grass-fed cheese.” (Grass-fed cheese? Imagining cheeses happily munching out in a field…) I also get the Bomb-Bomb Hash. Not cheap, but we’re talking organic prices. The bison’s $12 — extra dollar’s for avocado — and it’s $5 for the hash. Seventeen buckeroos. But if it reintroduces me to grandpa and to the right way to eat, it’ll be worth it. (Only 400 generations separate us from our pre-agricultural, Stone Age ancestors — I looked it up.)

June takes my order. She and her partner Bob run this truck, and they reckon they’re the only Paleolithic food truck on the West Coast.

Co-owner June reckons she runs the only paleolithic food truck on the west coast.

“When we humans started farming 10,000 years ago,” June says, “we went off the rails. My partner Bob, the chef here, was getting sick on all the glutens and excess sugars and salts of the normal diet. Then we heard about the paleo diet, eating what our stomachs had evolved over millions of years to handle — meats, plants — and not what we’ve thrown at them over just the last 10,000. Grains, sugars, salts, glutens, dairy, processed food. So we switched to eating paleo. And Bob’s condition cleared up.”

“The gut is our number-one organ,” says Bob, as he brings over my two paper plates of food. “You’ve got to look after it. A month after I switched to this diet, my allergy problems with glutens cleared up. It makes sense.”

Whatever. This food makes it easy to adapt. The hash is sweet, interesting with the bacon and avo adds. The lettuce-wrapped “burger” takes getting used to, but the taste is there, and the “house-cured” bacon is thick and flavorful. And, hey, at the bottom they’ve put some plantain chips, little dried banana-type slices to chew on.

Tony and Tess shared a “true cod” fish taco with jalapeños and avocados.

Couple sharing a fish taco (“Grilled true cod, with jalapeños, avocado, and primal Sriracha”…not sure about “true,” but “primal” means no preservatives or stuff like xanthan gum and sodium bisulphate), Tony and Tess, believe this helps keep them healthy. “I’m a pescatarian,” says Tony. “Only eat fish.”

Meaning, I guess, that fish is the only “meat” he eats, but not the only food.

The group of gals next to them have a dish called “Wich Came First?” It’s “free-range pulled chicken with fried egg, bacon, pico de gallo.”

“I’ve got an auto-immune problem,” says Rianne. “I started eating paleo last September. It’s working. I’d always have painful rashes. Now I feel less bloated, the rashes have gone down from eight on the pain scale to a three, and I sleep. And how beautiful that is. Every time I bust out and eat gluten, soy, or dairy, I get stomach aches.”

Suddenly, it’s 7:30. Cinderella time. Vehicles have to be out and off the roof. June lowers the sides of the truck and locks them.

It’s a little strange, here in the half-light, a clump of food-truck fanatics up on the roof of a market, chowing and chatting away.

But, kinda wonderful, you have to feel. And maybe these guys are onto something, calling the food industry out on a massive agricultural experiment gone wrong, saying they’re not willing to be the lab rats anymore.

Hey, maybe grandma (times 400) did know best.

The Place: Not So Fast food truck, 619-924-9244

Prices: El Pavo Diablo turkey burger, $8; bison burger, $11; Beefeater beef burger, $8.50; sweet-and-sour spicy pork, $10; Shroomie mushroom burger, $8; wild-caught cod tacos, $9; Bomb-Bomb Hash (sweet-potato hash), $5

Hours: For day and evening locations and times, check with website (notsofastfoodtruck.com), Facebook, Twitter