Why did he do it? His financier wife, Joanna Wang, was posted back to her home city, and he followed. Once there, Saint Cyr, 44, saw a chance to combine his profession with his self-confessed geeky passion for computers and the internet.
The result is the expat-oriented website myhealthbeijing.com which has become the go-to source for all matters relating to well-being, whether it is coping with pollution, avoiding tainted baby formula, seeking reassurance that Japan nuclear-plant radiation will not affect the city, or checking where children can get their vaccine jabs.
Unsurprisingly, pollution is by far the hottest topic, especially in recent months, when the air in Beijing reached suffocating levels. The US embassy's website uses an air quality index that says more than 500 is hazardous; some accounts had the January index at a dangerously high 900.
"Where I was working in Sonoma, California, it usually registered as five," says Saint Cyr. "When it reached 900 in Beijing, it was extraordinarily dangerous, a public health emergency. I was telling people not to go outside.
"That is where social media can be very useful. Originally, I started the website and blog aimed at expatriates coming here; everyone is always nervous as to whether the air is as bad as they have heard."
Saint Cyr's day job is with United Family Hospital group, where he is a marketing executive and practising physician. Until recently, his musings were followed almost exclusively by expatriates, but since he started on the social networking site Weibo, Chinese have also shown interest.
"Food safety is always on people's minds," he says. "It's a tough issue; the standards here are not what you would be used to if you came from Europe or America. But in general, it is easier to have healthy food here than in America. The availability of vegetables is much greater.
"Having said that, Chinese have adopted the Western diet more and more, and the rates of stroke and heart disease are approaching, or even higher than, those in the West. As for the whole recycled cooking-oil scandal, that is pretty bad, too. There is cancer-causing stuff in there. Unfortunately, you do have to pay attention when you are buying food."
Saint Cyr has been surprised by some questions from the local community. One woman asked if it was advisable to try for a child after having a simple X-ray, as friends had told her to wait a month or even six months.
"I told her there was no delay - it is completely safe - and asked her who was telling her these crazy things. There's a lot of misinformation. I've been trying to promote the idea that people should use a car seat for babies. If you look around, you see a mother or grandmother holding the baby in the front seat. Most Chinese people think it is safe, but it is incredibly dangerous; in an accident, the baby will fly out of your hands and hit the windscreen."
One blog entry highlighted the vices that some expat men find hard to resist. "That's the type that smokes and drinks and sleeps around far more than they would ever consider doing back at home," he says. "I'm mostly concerned about the businessman mentality here, where it's culturally accepted, if not indirectly coerced, to binge-drink and smoke at business dinners - not to mention the implication that success allows you to have mistresses.
"I see a lot of broken marriages as well as alcoholism and chronic bronchitis in these types of expats, and I wonder if their often phenomenal business success was worth the trade-off in their physical and family health."