For decades, those striving to lose weight have faced a dilemma over whether it is better to cut the carbs or ditch the fat. Now scientists have declared a solution to the conundrum which is remarkably simple.
It turns out it makes no difference which diet you choose they are just as good as each other. Instead experts advise dieters to use their common sense and to avoid junk food.
They found the key to losing weight is enjoying high-quality food, not worrying about which type of eating regime to follow.
US academics were attempting to end the long-running controversy over the merits of low-fat versus low-carbohydrate diets.
Some experts insist that cutting out the fat in products like butter and cream is the key while others swear by scaling back on carbohydrate heavy foods such as pasta and bread.
The researchers at Stanford University divided 600 slimmers into two groups, half on a low-carb regime and 300 on a low-fat diet for a year.
The results were identical as participants in both groups lost an average of 13lb (5.9kg).
But there was huge variation within each diet with some people losing more than 60lb while others put on weight. The academics believe this is because some are more suited to different types of diet as their bodies are better at burning off carbs or fat. But the key, they said, is more common sense and less processed convenience food.
Study leader Professor Christopher Gardner said fizzy drinks, for example, may be low in fat but they are not healthy.
Lard may be low in carbs but it is unlikely to help you 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 don't buy processed convenience food,' he said.
Eat less sugar, less refined flour and as many vegetables as possible. Go for whole foods, whether that is a wheatberry salad or grass-fed beef.
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 they were more thoughtful about how they ate.'
The fundamental strategy for losing weight does not change whether you are pursuing a low-fat or a low-carb approach, added Professor Gardner.
We've all heard stories of a friend who went on one diet which worked great and then another friend tried the same diet and it didn't work at all,' he said. It's because we're all very different and we're just starting to understand the reasons.'
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 closes the door on some questions but opens the door to others' added the professor.
I'm hoping that we can come up with signatures of sorts. 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.' Tam Fry, of the National Obesity Forum, said: It is refreshing to see Dr Gardner's honesty. The best diet in town is not a fad but much less of what you actually fancy and stick to it.'
The research comes after a major study last week revealed that rising sales of ultra-processed' food, such as ready meals, sugary cereals and fizzy drinks, are driving up cancer rates.