The big fat question: How do we actually lose weight?

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January’s store shelves are groaning with new diet books, all promising to finally reveal the universal formula for weight loss.

That promise, however, is as empty as the calories in a Timbit. It’s not going to happen.

“People want to hear that there are ‘good’ and ‘bad’ foods, and that you simply need to avoid the bad foods and only eat the good foods and you’ll be fine,” says Yoni Freedhoff, the founder of Ottawa’s Bariatric Medical Clinic and one of Canada’s foremost obesity clinicians.

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InteractiveSuccesses and struggles: Meet our weight loss warriorsPollHave you ever tried to shed pounds? Did it work? Yes - and I've kept it off Yes - but I've gained a little backYes - but I put it all back on (and then some)I've never tried to lose weight

Results & past polls

25%1587 votesYes - and I've kept it off 31%1978 votesYes - but I've gained a little back27%1760 votesYes - but I put it all back on (and then some)17%1127 votesI've never tried to lose weightMore polls globe.poll.display({'id':'1873147','context':'sidebar'});VideoEngage your core - and inner thighs - with these crunches

Over the past few decades, we’ve tried cutting carbs, eliminating fat – or meticulously optimizing the ratio between them; we’ve eliminated meat and subsisted on liquids; we’ve even eaten according to our blood type. The result? When Statistics Canada went out and actually measured thousands of Canadians (instead of trusting them to tell the truth about their weight) between 2007 and 2009, they found that 61 per cent of us were overweight.

As we begin a new decade, obesity researchers are turning away from this search for “good” foods – a quest that has led us down a nutritional rabbit hole, in which the rich complexities of the human diet are reduced to didactic edicts that change every few years.

Instead, they’re focusing more on the physiology and psychology of why people eat what they do, how societal forces influence their choices, and what they can do to change. The code hasn’t been cracked yet, but here’s what we do know about weight loss.

For starters, it’s clear that losing weight isn’t just about eating certain foods. Last fall, Mark Haub, a nutrition professor at Kansas State University, subsisted for 10 weeks on 1,800 calories a day – about 800 fewer than usual – of Twinkies, Doritos, brownies and other convenience-store staples. In the process, he lost 27 pounds and improved health markers such as cholesterol levels.

While Dr. Haub’s experience runs counter to the advice in anti-carb polemics like Gary Taubes’ new book, Why We Get Fat, his slim result was no surprise to obesity researchers.

“Of course you can lose weight by eating pizza and junk food,” says Jean-Philippe Chaput, a scientist in the Healthy Active Living and Obesity Research unit at the Children’s Hospital of Eastern Ontario Research Institute in Ottawa. “And you can gain weight by eating apples, if you eat more apples than you eat pizza.”

There are many compelling nutritional reasons to choose apples over pizza and Twinkies. But if you’re primarily concerned about weight, researchers have found that people can successfully shed pounds on pretty much any diet, as long as it involves a reduction in calories.

A 2005 study published in the Journal of the American Medical Association, for example, followed 160 overweight volunteers assigned to the Atkins, Ornish, Weight Watchers or Zone diet. After a year, the average weight loss was about six pounds, but there was no statistically significant difference among any of the diets.

Instead, the results showed the best predictor of weight loss was how closely the subjects had managed to stick with their prescribed diet. The true mark of a successful diet, after all, isn’t losing weight, it’s keeping it off – and that’s where the Twinkie diet, and any other diet that you’re not prepared to maintain for the rest of your life, fails.

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The most famous equation in nutrition is “calories in = calories out.” But the right-hand side of the equation is more complicated than most people realize.

If you add one 60-calorie cookie to your daily diet, simple math suggests you’ll gain weight for the rest of your life at a rate corresponding to about a pound of fat for each 3,500 calories. But, in fact, as you gain weight, your body has to spend more energy maintaining the new tissue, using up some of the excess calories. A paper published last year in JAMA calculated that the weight gain would level off at six pounds after a few years.