UK twins, Alexander and Chris van Tulleken, decided to use their own bodies to figure out which foods are worse: sugars or fats? In a month-long experiment, the 35-year-old brothers challenged themselves, with one giving up sugar and the other giving up fat, to decide which of them would lose the most weight. In the end, they decided that complete elimination of either food item from their diets was probably bad for their health.

In an article for the Daily Mail, Alexander explained that the idea to simultaneously try two different diets came to him when he returned to England after gaining weight while living in the United States. Both brothers are doctors, but neither of them felt like they knew much about losing weight. “For years it was thought fat was bad for you: It made you get fat, so low-fat food was good,” Alexander wrote. “But the 'fat is bad' dogma is being widely challenged. Carbohydrates, including sugar, are increasingly viewed as the evil, fattening, toxic ingredient.”

So Chris and Alexander became dueling dieters and documented their journey on BBC’s Horizon. Alexander went on a no-carbohydrate diet, which is basically a sugar-free regimen. His brother went on an extremely low fat diet. They could eat as much as they wanted, but they had to refrain from the sugar and fat. The brothers also matched exercise routines and tried to do similar things in their day-to-day lives. Alexander said that the diets were miserable for both brothers.

“Let me tell you straight up that both of these diets were miserable. I thought I'd got the better deal: I could eat meat, fish, eggs and cheese,” wrote Alexander. “But take away carbohydrates and the joy goes out of meals. And remove all fruit and veg — they all have carbs — and you get constipated. Though I was never hungry, I felt slow and tired, and my breath was terrible.”

So which is worse —  sugar or fat?

The answer is probably “neither.” Completely eliminating anything from one’s diet — whether it be sugar, or fat, or even meat — isn’t necessarily the way to end up with a more fit physique. A balanced diet, which includes fruits, veggies, proteins, and good carbohydrates will put you on the right track better than eliminating any certain food group.

“If you want to lose weight it will be much easier if you avoid processed foods made with sugar and fat,” wrote Alexander. “These foods affect your brain in a completely different way from natural foods and it's hard for anyone to resist eating too much. And any diet that eliminates fat or sugar will be unpalatable, hard to sustain and probably be bad for your health, too.”