"There is no evidence that there is any health issue with any of the products on the market. And there is nothing particular to the technology itself that makes it dangerous," said Kent Bradford, director of the Seed Biotechnology Center at UC Davis, which uses genetic engineering to develop agricultural seeds.

He dismisses the idea that there is not enough testing of genetically engineered food, saying the voluntary testing by companies that modify crops has created a pile of credible evidence.

But such tests are biased by commercial interest and too short to show the long-term impacts of eating engineered food, says anti-GMO activist Jeffrey Smith, who has written two books and made a film criticizing the technology.

Smith lives in Iowa but has been touring California promoting his work and Proposition 37. His film, "Genetic Roulette," features about a dozen doctors describing health problems – including allergies, diabetes, gastrointestinal distress and autism – they associate with eating GMOs.

"I decided strategically – because I think it's a greater motivation – to focus on the health dangers," said Smith, whose background is in marketing not science.

One solution, he said, is labeling engineered food so people know what they're eating.

Proposition 37 is more about ideology than science, said Bob Goldberg, a UCLA biologist who teaches a class on genetic engineering.

"I'm against this proposition because I'm a scientist and I'm a person who has done genetic engineering my entire career," Goldberg said. "In many respects, I don't view this as a political campaign, I view this as an anti-science campaign."

Goldberg, a member of the prestigious National Academy of Sciences, said the organization believes it's wrong to lump all genetically engineered foods into the same category because they use the same laboratory technique. Instead, he said, the safety of crops and food products – whether the result of genetic engineering or other scientific processes – should be judged on a case-by-case basis.

A National Academy of Sciences spokeswoman said the group has not evaluated whether it's safe to eat genetically engineered food.

Goldberg points to a statement this month by the American Association for the Advancement of Science that says, "The science is quite clear: crop improvement by the modern molecular techniques of biotechnology is safe."

Doctor suggests diet change

Dr. Kelly Sutton isn't convinced. She is a board-certified internist in Fair Oaks who describes her approach to medicine as "holistic," incorporating both science and spirituality.

"I've practiced for 40 years so I've come through a long stretch of seeing changes in health," Sutton said, including huge increases in allergies, skin problems and cancer.

"We are living longer but living sicker," she said.

When people come to her with such problems, Sutton said one of the first things she suggests is a change of diet, including a move toward organic and non-GMO foods. She said her patients' health usually improves.

"I am only speculating from experience," Sutton said. "There is no serious study that says genetically modified food does this but not that."

Lang, the Fair Oaks mother, said the anecdotal evidence she's seen in her son is enough for her to keep GMOs out of her kitchen by eating organic and avoiding most packaged foods.

A day after organizing a Proposition 37 rally with organic farmers last week, Lang made her family a soup of carrots, Swiss chard, broccoli and homemade chicken stock. Potatoes baked in the oven while she whipped up her own dressing for a salad and chopped mango to top fish cakes.

"Since the answers aren't there," Lang said, "I choose to proceed on a precautionary principle."