For decades, those striving to lose weight have faced the dilemma of whether it is better to cut the carbs or ditch the fat.
Now scientists have declared a solution to the conundrum that is remarkably simple: it makes no difference which diet you choose - they are both just as good. Instead experts advise dieters to use their common sense and avoid junk food.
They found the key to losing weight is eating high-quality food, not the type of eating regime.
US academics were attempting to end the long-running controversy over the merits of low-fat versus low-carb diets.
Some insist that cutting out the fat in products like butter and cream is the key, while others swear by scaling back on carb-heavy foods such as pasta and bread.
Researchers at Stanford University divided 600 slimmers into two groups: half were on a low-carb regime and 300 were on a low-fat diet for a year. The results were identical as participants in both groups lost an average of 5.9kg. But there was huge variation within each diet, with some people losing more than 27kg and others putting on weight.
The academics said this was because some people are better at burning off carbs and others at burning up fat. But the key, they said, was more common sense and less processed convenience food.
Study leader Professor Christopher Gardner said fizzy drinks, for example, may be low in fat, but are not healthy. Lard is low in carbs but unlikely to help to lose weight, while a high-fat avocado is healthy and nutritious.
“We made sure to tell everybody, regardless of which diet they were on, to go to the farmers' market and not to buy processed conven- ience food,” he said.
The team sequenced the participants’ genomes in a bid to work out which would perform better on the different diets but failed to discover a link.
The study published in the JAMA medical journal closed the door on some questions, but opened the door to others, added Gardner.
He said: “I feel we owe it to people to be smarter than to just say ‘eat less’. There is an opportunity to discover some personalisation to it. Now we just need to work on tying the pieces together.”