Mireille Guiliano knows the best diet trick ever. Simply eat half of what's on your plate, then ask yourself if you really want the rest. Eat half of what's left, and so on. "It's so basic," says Guiliano of her tactics in general. "I'm amazed how many people don't know about this common sense, or have forgotten it." Talking about her hugely successful French Women Don't Get Fat, she emphasizes that "what the book is about, in one word, is pleasure. It's the ultimate nondiet book." Recently in Vancouver to launch her second manifesto on how to live well and lose weight, French Women for All Seasons: A Year of Secrets, Recipes and Pleasures (Random House Canada, $32.95), Guiliano is chic in black pants and a turquoise jacket. She's slim, not wind-tunnel gaunt, but with the kind of trim, well-toned shape that suggests hours on the treadmill. But that's not her. "Gyms are fine if you like that sort of thing (they are somewhat social and give pleasure and activity)," she writes in her latest book, but walking, she says, is just as efficient, and you can do it in your street clothes. "In addition to what it does to your body from the waist down, it's what [walking] does to your head," she adds. Too true. On a morning like this, sunlight streaming into the lounge at Bacchus in the Wedgewood Hotel, the concept of a brisk stroll around town far outweighs the idea of being indoors with a bunch of spandexed gym bunnies.

Guiliano's own weight started to climb in her late teens when she left France for school in the U.S. She piled 10 kilograms on to her petite 1.6-metre frame, then, back in Paris, added five more. Quelle horreur, said her parents. They called in the family doctor, who, she says, "reacquainted me with the way I grew up". She now weighs about 50 kilos, "not skinny, just normal".

It's time to order breakfast. Guiliano requests multigrain toast with a poached egg. "Just one?" asks the server. Just one. Portion size is key, she says. To North Americans, the idea of a 120-gram serving of salmon is unusual, and a 120-gram steak? Any Texan would fall down laughing. At one Vancouver steakhouse, Morton's, steak doesn't come any smaller than 240 grams. The steak you get with your frites in a French bistro is normally 120 grams. Do the math.

Guiliano's new book isn't just about losing weight–it's about learning to live the good life, right down to those enviable French scarf-tying tricks. It's especially about taking time to relish the culinary joys that each season offers. A week's menu suggestions reads more like a Parisian table d'hôte, with a springtime lunch offering a salad of hardboiled egg, tuna, and haricots verts, plus a slice of bread, a pear, and a square of chocolate, and a dinner composed of salmon with sorrel, tagliatelle with lemon, two slices of baguette, a coffee petit pot, and a glass of red wine. Guiliano stresses the importance of eating three meals a day–no mid-morning muffin, no Oreos while you watch Desperate Housewives, but still, hardly deprivation. (What recipes aren't in the book are on her Web site, www.mireilleguiliano.com/.)

Guiliano wrote her first book for her American friends, she says, citing a number of cultural differences. "A lot of American women don't love to cook. For a French woman, it is an act of love. The table is more than where you sit. It's all about talking and laughing. You eat slowly, you eat less, you don't get fat." The way she explains it in person, and in her book, this way of eating is so entirely logical and pleasurable, you can't imagine why you would ever look at a Big Mac again. The 21st-century trap, she says, is that there's food everywhere. In her book, and in person, she talks of being in an airport at 10 a.m. with "hundreds of people eating. I looked around; I couldn't find pleasure."

Thing is, her ideas work. Especially that 50 percent trick, and particularly if you kick off your new eating resolutions with her famed weekend leek-a-thon. "For a French person, leek is the most famous vegetable. It flushes your toxins. It's good for the skin." Calling her approach "my little French quiet revolution", Mireille Guiliano finishes her one-egg breakfast, slides into an amethyst-coloured coat, dons her sunglasses, and sets off to her next appointment.