It was 2002 and Williams was in the pool at a resort in Mexico, on vacation with his girlfriend Carly, who would later become his wife. (He proposed on that trip.)
An American woman, a perfect stranger, told him she'd had gastric reduction surgery and he should consider it. Williams was flabbergasted.
"I was incredibly offended," says Williams, who is now three months away from completing his residency as a family physician. "I was very offended by the idea and just pushed it from my mind for years. But I guess she was right."
Two years ago Williams, who at one point weighed in at 350 pounds, had most of his stomach removed in a procedure known as a sleeve gastrectomy. So far he's shed 110 pounds, dropping to 210 pounds from 320 just before the surgery. He hopes to lose more. Williams has taken up skiing and running, something his joints wouldn't allow in the past.
And this week, he's climbing on a soapbox - taking to the pages of the Canadian Medical Association Journal to tell fellow doctors that for some people with weight problems, the route he has taken is the only one that will lead to real and sustainable weight loss.
In an article entitled "The formerly fat physician," Williams says that urging overweight patients to eat less and step up their exercise quotient is not a workable approach for some.
"There are some - not just physicians - people who are going to say 'You became fat by eating too much and not exercising enough. And the only way to reverse that is by eating less and exercising more,'" Williams acknowledges.
"And I think all we can say is there is a subset of patients out there, and I was one of them, for whom that's just not good enough. They're not going to be able to do it on their own. They need a little bit of help."
In his article, Williams writes that he knew that he needed to lose weight and why. He understood the risks associated with being as overweight as he was - heart disease, high blood pressure, Type 2 diabetes - and learned about them in more detail in medical school.
He made many stabs at losing weight, working diet after diet with short-term success. He'd lose 30 pounds - and gain back 40. He'd exercise. But he'd eat more.
"Although it's probably fairly arrogant to say, I am a typical Type A personality. Doctor, very well educated about the effects of obesity, very motivated in other areas of my life. And I couldn't do this on my own," he says in an interview from Nanaimo, B.C., where he lives and works.
"So to think that you know, if you just give your patients a little bit more education or you just provide them a little bit more encouragement that they will necessarily be able to lose weight on their own I don't think is true."
A couple of obesity experts agree that surgery is the best option for some people who cannot control their weight - though they disagree with each other over the approach Williams has taken in his article.
Dr. Arya Sharma, chair of obesity research and management at the University of Alberta, applauds Williams for airing the issue publicly, saying there is a lot of stigma attached to being fat - and even more to using surgery to address the problem.
Sharma says many patients who need bariatric surgery struggle with accepting it, out of a sense of shame. He tells a story about a patient who told friends she was having back surgery, because she didn't want to admit she was undergoing gastric reduction.
"The reason they are not willing to consider bariatric surgery as an option is that they would have to then admit failure to themselves, to say 'I have failed at this and now I need surgery,'" he says.
He notes that there's evidence that when people who've had the surgery admit it to others, the reaction is often: "Surgery? Oh, you took the easy way out."
But Dr. Yoni Freedhoff, an assistant professor of family medicine at the University of Ottawa and medical director of Ottawa's Bariatic Medical Institute, suggests helping people lose weight and keep it off requires more than just diet, exercise and surgery - though he does think surgery is an important and underutilized tool.
He wishes Williams had taken time during his turn on the soapbox to explore the other work that needs to be done for people to successfully shed and keep off weight, even when surgery is involved.
"It suggests that it's as simple as eat less, exercise more, except that Dr. Williams needed surgery as well to help him do that. And I'm glad that he got his help, don't get me wrong," Freedhoff says.
"But I think that somebody who's gone through real obesity and understands it well knows there's a lot more to it than having too many venti lattes and that there's reasons why people do these things.''
Freedhoff notes that Williams says in the article that he was fat because he ate too much - which is a problem that needs to be addressed, surgery or no surgery. "I guess the question of 'Why?' is a really crucial one to ask. In patient-centred care, well, that's what's important."
Williams decided to explore bariatric surgery a couple of years ago after hearing one of his medical school instructors, a surgeon, claim gastric reduction can cure Type 2 diabetes. (The evidence on that is still emerging, but study results so far are promising.)
The surgery he had involved removing most of his stomach, leaving him with one that can hold far less food. He had to slowly relearn how to eat in tiny portions.
He can eat half a sandwich or half a hamburger, Williams says, but must be careful about what he drinks and when he drinks it. Coffee before breakfast is fine, but after breakfast doesn't work "because once there's a bunch of food in my stomach, there's just nowhere for the coffee to go."
Too much food at one time will make him vomit.
He admits the psychological impact of the surgery was tough. Being unable to eat in the way he had in the past forced him come to grips with the role food played in his life.
"After the surgery I would say I was almost depressed, or I had a period of grief for awhile. I had no idea how much of my life was about food," Williams says.
Before his surgery if he was travelling between Vancouver Island and Mainland B.C., he'd take the Victoria ferry, because it offered a buffet. A buffet is no longer an option.
"I really missed eating. And for awhile, just going through the grocery store would make me sad. Because I just felt like I couldn't enjoy food," he says.
"It took me a long time to get to a point where instead of spending $25 at a buffet, I'll spend $17 on a very small portion that will be really good food and I'll feel just as satisfied. But that was hard."