We all know them--people in our lives who are so sure that calories in vs calories out is all there is to weight loss. If you use up more energy than you take in, you'll lose weight.

Bull puckey.

Can you eat unlimited amounts of calories and not gain weight? No. But it's not just a numbers game. There's the old mystery wheel of metabolism at play.

In the latest issue of New Scientist (sorry, to read the whole story you have to subscribe but I'll do a full review here), is a story about the results from a study by scientists at Sweden's Linkvping University. They set out to replicate author Morgan Spurlock's death-by-McDonald's results in his documentary drama-queenization, "Supersize Me."

Can you tell I wasn't a fan of the Spurlock piece and, in fact, thought he was a serious drama queen with a questionable method?

Anyway, scientist Fredrik Nystrvm put 18 volunteers through a supersize regime, feeding them an estimated 6,600 calories a day on energy-dense fast foods and keeping exercise at a minimum.

If you recall, when Spurlock did a similar McDonald's regimen after a month he had a "sagging libido and soaring cholesterol" to go with his 13% gain in body weight and, he claimed, pending liver damage.

In the Swedish re-enactment, the results were surprisingly different. The volunteers' body changes were all over the map.

The article used nursing student Adde Karimi as one example of the surprising results. At the end of the binge, Karimi did gain about 10 pounds, half of which was muscle. Rather than soaring, his cholesterol was a little bit lower. The maximum amount of weight the volunteers were allowed to gain was 15 percent of their body weight. Some of the volunteers never reached that despite their diet; others gained that much in two weeks, starting from the same beginning weight and eating the same number of calories.

"We're used to being told that if we're overweight, the problem is simply too much food and too little exercise, but Nystrvm has been forced to conclude that it isn't so straightforward," the article says. "Some people are just more susceptible to obesity than others."

Quoting again: "If you're lucky, your body can adapt to cope with an extra cream doughnut or even a blow-out dinner by burning off the excess energy in the form of heat. He suspects many of his volunteers fall into this category because they were all slim on their normal diet and because they often commented on feeling warm all the time while overeating. If Nystrvm is correct, this is what makes his study so unusual and potentially valuable. Most research into obesity is done on people who are already overweight; in other words, those least resistant to calories."

The researchers point out that the ability to store excess energy as fat was an advantage to our ancestors who had to deal with feast or famine.

Nystrvm hopes that by studying the data from this experiment he will be able to identify new approaches to tackling the obesity epidemic. "Because we have such a huge amount of data we should be able to start teasing apart some of the influences that make some people more susceptible to obesity than others," he said.

Now, what does all this mean?

It should give those who are unconvinced yet another reason to look again at the "metabolic advantage" of the low carb or carb-conscious way of eating, for one thing. Probably not much else, realistically.

For me, the "calories in, calories out" mantra is preached to me by people who've never had more than five or 10 pounds to lose. Anyone with an obesity-prone metabolism knows it just isn't that simple.