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Myth debunked: Neither the low-carb nor the low-fat diet is superior

Cutting either carbs or fats shaves off excess weight in about the same proportion.

Image: Shaiith via Shutterstock

NEW EVIDENCE FROM Stanford University might dismay those who have chosen sides in the low-fat versus low-carbohydrate diet debate.

The research has found that neither option is superior – cutting either carbs or fats shaves off excess weight in about the same proportion.

Furthermore, the study examined whether insulin levels or a specific genotype pattern could predict an individual’s success on either diet. The answer, in both cases, was no.

“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,” lead author Christopher Gardner said.

“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?” he said.

Past research has shown that a range of factors, including genetics, insulin levels (which helps regulate glucose in the body) and the microbiome, might tip the scales when it comes to weight loss.

The new study, published yesterday in the Jama journal, focused on genetics and insulin, in a bid to discover if these aspects would encourage an individual’s body to favour a low-carb diet or a low-fat diet.

A tale of two diets

In his journey to find out if individual biological factors dictate weight loss, Gardner recruited 699 participants between the ages of 18 and 50. About half were men and half were women. They were randomly placed into one of the two dietary groups – low-carb or low-fat.

Each group was instructed to maintain their diet for one year. By the end of that year, about 20% of participants had dropped out, due to external circumstances.

In the initial eight weeks of the study, participants were told to limit their daily carbohydrate or fat intake by just 20 grams, which is about what can be found in 1.5 slices of whole wheat bread or in a generous handful of nuts, respectively.

After the second month, the research team told the groups to make small adjustments as needed, adding back five to 15 grams of fat or carbs gradually, in a bid to reach a balance they believed they could maintain for the rest of their lives.

At the end of the 12 months, those on low-fat diets reported a daily average fat intake of 57 grams. Those on low-carb diets ingested about 132 grams of carbohydrates per day.

Gardner said he was pleased with the above statistics, given the average fat consumption for the participants before the study was around 87 grams per day, and average carbohydrate intake was about 247 grams.

What’s key, Gardner said, was emphasising that these were healthy low-fat and low-carb diets. For example, a fizzy drink may be low-fat, but it’s certainly not healthy.

“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,” he said.

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 12-month period, researchers tracked the progress of participants, logging information about weight, body composition, baseline insulin levels and how many grams of fat or carbohydrates 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.

The biggest takeaway from this study, Gardner said, is that the fundamental strategy for losing weight with either a low-fat or a low-carb approach is similar. Eat less sugar, less refined flour and as many vegetables as possible.

“On both sides, we heard from people who had lost the most weight that we had helped them change their relationship to food, and that now they were more thoughtful about how they ate,” he said.

Read: McDonald’s Ireland not impacted by US changes – the Happy Meal cheeseburger is here to stay

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