Sugar Vs. Fat: What We Can Learn from One Weight Loss Challenge

Perhaps you've seen the article about the British identical twins -- both doctors -- who decided to donate their bodies, and their identical genetics, to science for a month to figure out which was the better way to lose weight: a no-carb diet or a low-fat diet. The twins, Alexander and Chris van Tulleken, are 35 years old and both, as Alexander describes them, "gluttons." As they approached middle age, they realized they needed to pay better attention to their diets if they were going to maintain a healthy weight. However, despite their medical training, neither of them knew much about eating well. And because both fat and sugar have been demonized as the reason we're collectively getting so fat, the twins decided to test out which of the two was actually worse.

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For a month Alexander cut out carbohydrates -- pasta and bread, yes, but also fruits and vegetables, which are high in carbs via their natural sugars. And Chris cut out almost all fat. (He didn't do a no-fat diet because everyone needs a little bit of fat for their bodies to operate properly.) Other than that, they could eat as much as they wanted, though the two also exercised the same amount, so any weight they lost would be controlled on that front.

At the end of the month, Alexander had lost 9 pounds, and Chris had also lost weight (though the amount is unspecified). But they both claim that their respective diets were miserable. Alexander -- the no-carb twin -- thought that his diet would have the edge on being better for you. Carbs, he thought, would help keep his blood sugar steadier and prevent his body from storing fat. However, he found that the diet had a host of other "side effects" -- things like bad breath, feeling sluggish and tired, and constipation. Though he was never hungry, he says, the joy had gone out of eating. And his twin, though he was always hungry and snacked throughout the day, felt the same way: there is no joy in pasta without olive oil.

The twins also participated in a series of "sugar vs. fat" challenges during the month to see how their diets were affecting them physically and mentally. Chris, the low-fat twin, beat his brother soundly at the cycling challenge as well as the stock-trading competition meant to check out their mental states.

I find this "experiment" to be pretty fascinating, but not for the obvious reasons. It is interesting to note, of course, that you could possibly lose a lot of weight on a no-carb diet -- more than on a low-fat diet. And some people might take that as evidence that cutting carbs really is the way to better health. But that is not the case at all. After all, Alexander said it was clear that his no-carb diet made it difficult for him to function at his normal capacity: "Though I wasn't distracted by hunger, I felt thick-headed," he writes. The carbs he was denying his body were actually where his brain got its fuel as well, and without them, he couldn't think as clearly or quickly. Even more revealing are the tests that showed that without carbs, his body may have essentially been fueling itself by breaking down his muscles.

I think this is pretty compelling evidence that we need to re-think the mentality that any diet that helps you lose weight is a good diet. Taking the number on the scale as the signal for success or failure is extremely dangerous. Our food and our activity level influences much more than how much we weigh -- they are fundamental to how our bodies and minds function on a day-to-day basis. The more we fuel our bodies with high-quality, unprocessed, whole foods, the better we will feel and the easier it will be to function at a high level in all aspects of our lives.

So let's toss these low-carb/no-carb, low-fat diet fads out the window and opt for healthful, sustainable meals that nourish body and mind -- and don't leave us suffering from constipation or halitosis.

Photo Source: Lizzie Heiselt

- By Lizzie Heiselt

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