Twin Brothers Put Diet Crazes to Ultimate Test

If you follow diet trends closely, you could get whiplash. One year fat is seen as the enemy; the next, sugar is poison. Recently, twin brothers Chris and Alexander "Xand" van Tulleken set out on a month-long radical experiment to try to put the debate to rest over which is worse.

Chris adopted a super-low-fat diet, allocating only 2 percent of his total daily intake of fat, the minimum required to maintain his health. Xand opted for a high-protein diet that ditched all forms of carbohydrates, from table sugar to flour to fruit. The brothers, who both work as physicians, shared similar daily routines and stuck to the exact same fitness regimen. Furthermore, because they claim to share identical DNA, they surmised that any changes they experienced would be attributable to diet, not genetics. A film crew followed their nutritional journey, and it's airing as a documentary on BBC2 on Wednesday.

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Xand was motivated because he was at his highest weight ever—245 pounds. He told the Daily Mail he looked like the "fat version of his twin" and was a living, breathing "cautionary tale." He realized that while he and Chris were both doctors, they really didn't know a great deal about nutrition and diet. "These topics fall between the cracks at medical school. Yes, we understood biochemistry and food metabolism and knew a lot about the consequences of being overweight," he said. "But which diets work, why we eat too much and why losing weight is so hard don't sit within any medical specialty."

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The diets were easy to follow because the rules were so specific. Although there was no limit on how much the twins could eat, Xand says both plans were, ultimately, "miserable." Initially, he thought he had the better deal, devouring piles of meat, eggs, and fat — but eliminating sugars had some nasty side effects. His breath stank and he felt constipated. Moreover, he was sluggish and tired, and his brain was in a fog. When he and Chris raced each other uphill on bikes, he realized that his endurance was shot. Chris flew up the hill while Xand's heart rate surged. "He just keeps getting further away and I cannot make my legs go any faster," Xand huffed to the camera crew.

Xand was the weight loss winner, dropping a total of 9 pounds, but he says his high-protein, low-carb diet caused his body to go into ketosis — a state in which the body burns fat but doesn't effectively provide the brain with the glucose (sugar) it needs for energy. Nutrition expert Angela Lemond explained to Yahoo Shine that high-protein diets produce chemicals called ketones, which promote weight loss but can lead to kidney failure. "We recommend staying above 100 grams of carbohydrates per day to avoid going into ketosis," she said, adding, "We know people cannot sustain this way of eating and therefore, they regain the weight."

Meanwhile, Chris wasn't faring much better than his twin. He had lost a little weight, but without the added fat, even supposedly decadent foods, such as pasta, tasted like cardboard. Lemond explained that fat increases the feeling of satisfaction, and indeed, Chris experienced a constant gnawing hunger.

At the end of the month, neither brother felt like his diet was superior. Speaking with scientists working in cutting-edge nutrition, they decided that the real health problem was the combination of sugar and fat found in many processed foods. "We should not vilify a single nutrient," Chris told the Sunday Express. "It is too easy to demonize fat or sugar but that enables you to let yourself off the hook in other ways. The enemy is right in front of us in the shape of processed foods."

The brothers concluded that searching for "one toxic ingredient" was fruitless and we should instead be watching calories and portion size and eating whole foods whenever possible. It's an unsexy approach that won't spark any diet crazes or launch a best-seller, but could actually work.

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