Twins test diet theory

It’s a new year and along with it comes a lot of New Year’s resolutions concerning health and fitness. The biggest debate making its rounds is the bunting (cutting carbohydrates out of your diet) and fatty foods. British twins, Alexander and Chris Van Tulleken set out to find out which is worse.

They are both doctors, live the same kind of lifestyle and do the same exercise.

For years it was thought fat was bad for you: it made you get fat, so low-fat food was good. But the 'fat is bad' dogma is being widely challenged. Carbohydrates, including sugar, are increasingly viewed as the evil, fattening, toxic ingredient.


In a unique experiment for BBC's Horizon, Chris and Alexander set out to find the answer by going on different diets for a month. Identical twins are extremely useful in experiments because they have the same genes.

Alexander went on a no-carbohydrate diet - essentially no sugar - and Chris went on an extremely low-fat diet.


Here’s an excerpt taken from The Daily Mail, from Alexander's viewpoint:


“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. I was never hungry, and felt slow and tired. Chris on his low-fat diet didn't fare much better. He never felt full, so was constantly snacking, and found that all the pleasure had gone out of meals.


 Well-respected scientists will tell you that if you cut out carbohydrates (thus lowering your insulin levels), it's almost impossible to gain weight. 

 These scientists believe reducing our sugar intake is the only way to solve the obesity epidemic.


But, as our results show, it's a bit more complicated than this. Chris and I each lost weight on our diets - I lost the most, a remarkable 9lb in one month - but the other results were not at all what we had expected. One of the words you hear a lot when people talk about very low-carb diets is ketosis. This is where your body makes chemicals called ketones, which can act as fuel for the brain, which can't use fat. 

But they're not great brain food. While I wasn't distracted by hunger for the month, I felt thick-headed, and this was most evident in a stock trading competition with Chris. We started with £100,000 of fake money and he almost tripled what I earned over an hour.  The same was true for my physical performance. We spent a day with Nigel Mitchell, the head of nutrition at Team Sky Cycling. 


Our experiment showed that you can lose a lot of weight, as I did, on a low-carb diet, but that isn't necessarily good for you. You can lose weight on a low-fat diet, as Chris did - but over the long term unregulated consumption of sugar may also have negative health consequences.


What we discovered is that the real reason we're all getting fatter isn't fat or sugar. 


We interviewed some amazing scientists who showed us that a combination of fat and sugar (such as in milk chocolate or ice cream) has a similar effect on your brain to cocaine. Remove either and your tub of ice cream will be a lot less appetising and a lot less addictive. It'll have fewer calories, too.


What we relish is fat/sugar combinations - chocolate, ice cream, French fries.


So, what were our conclusions? If you want to lose weight it will be much easier if you avoid processed foods made with sugar and fat. 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.”