For decades, two diets have ruled the roost when it comes to weight loss. If you’ve ever dieted, chances are you’ll have followed either a low-carb (Atkins) or low-fat plan. You might also know of someone who had weight loss success on one of these diets and another who didn’t lose a single pound.
The variation in weight loss results has baffled researchers for a number of years. A team from Stanford University School of Medicine set out to discover which is better - low-fat or low-carb - and discovered that, actually, neither is. In fact it’s not the diet that you should be mindful of, but your body.
“We’ve all heard stories of a friend who went on one diet - it worked great - and then another friend tried the same diet, and it didn’t work at all,” said lead author and professor of medicine Christopher Gardner. “It’s because we’re all very different, and we’re just starting to understand the reasons for this diversity. Maybe we shouldn’t be asking what’s the best diet, but what’s the best diet for whom?”
Past research has shown that a range of factors including genetics, insulin levels and microorganisms found in the body can impact weight loss. The new study sought to discover if these factors would encourage an individual’s body to favour a low-carbohydrate diet or a low-fat diet.
Researchers recruited 609 participants, split evenly between men and women, aged 18-50. They were put on either a low-carbohydrate or low-fat diet for a year.
For the first eight weeks of the study, participants were told to limit their carbohydrate or fat intake to just 20 grams a day - roughly 1.5 slices of whole wheat bread or a generous handful of nuts.
After the second month, they were instructed to make incremental adjustments as needed, adding back 5-15 grams of fat or carbs gradually and aiming to reach a balance they believed could be maintained for the rest of their lives.
At the end of the year, people on a low-fat diet reported a daily average fat intake of 57 grams while those on low-carb diets consumed about 132 grams of carbs per day. It’s worth noting that average fat consumption for the participants before the study started was around 87 grams a day, and average carbohydrate intake was about 247 grams.
Gardener said: “We made sure to tell everybody, regardless of which diet they were on, to go to the farmer’s market, and don’t buy processed convenience food crap.
“Also, we advised them to diet in a way that didn’t make them feel hungry or deprived - otherwise it’s hard to maintain the diet in the long run. We wanted them to choose a low-fat or low-carb diet plan that they could potentially follow forever, rather than a diet that they’d drop when the study ended.”
Over the course of a year, researchers monitored participant progress, logging information about weight, body composition, baseline insulin levels and how many grams of fat or carbohydrate they consumed daily.
By the end of the study, individuals in the two groups had lost, on average, 13 pounds. There was still, however, immense weight loss variability among them. Some dropped upward of 60 pounds, while others gained close to 15 or 20. Contrary to what they suspected, there were no associations between the genotype pattern or insulin levels and weight loss.
The biggest takeaway from the study is that the strategy for losing weight - whether you’re following a low-fat or a low-carb approach - is very similar. As such, Gardener advises people to eat less sugar, less refined flour and as many vegetables as possible. He’s also keen for people to eat more ‘whole foods’ too, whether that’s a wheat berry salad or grass-fed beef.
Moving forward, he and his team will continue to analyse the data collected to uncover what is behind individual weight loss. “I’m hoping that we can come up with signatures of sorts,” he said. “I still think there is an opportunity to discover some personalisation to it [dieting] - now we just need to work on tying the pieces together.”