Forget counting calories because new research has found that sticking to a Mediterranean may be a more effective way to lose weight.
A study by scientists in Spain found that people who stuck to a Mediterranean diet rich in olive oil, without calorie restrictions, lost more weight than people on a diet that generally avoided all kinds of fat.
The researchers said this contributes to a growing body of evidence that suggests eating foods traditionally considered to be "low fat" may not be the best way to maintain a healthy weight.
During the study, a group of more than 7,000 participants followed one of three diet plans.
The first group were assigned an unrestricted Mediterranean diet especially rich in olive oil, the second group stuck to a similar diet with a focus on nuts, while the third group were told to avoid all kinds of fat.
At the start of the study, 90% of the participants were overweight or obese and all had Type 2 diabetes or were considered at high risk of heart disease.
After five years, all three groups were found to have lost a small amount of weight, but people on the olive oil-rich Mediterranean diet lost the most - an average of 0.88 kg (1.9 pounds).
People who'd been on the low-fat diet lost 0.60 kg (1.3 pounds) while those on the nut-rich diet lost 0.40 kg (0.88 pounds).
Cutting out fat consumption was found to be the least effective way to trim “spare tyres”.
Waist circumference increased by 1.2cm in the low-fat group compared with 0.85cm in the olive oil group and 0.37cm in the nuts group.
Lead researcher Dr Ramon Estruch, from the University of Barcelona in Spain, told PA: "More than 40 years of nutritional policy has advocated for a low-fat diet but we’re seeing little impact on rising levels of obesity.
“Our study shows that a Mediterranean diet rich in vegetable fats such as olive oil and nuts had little effect on bodyweight or waist circumference compared to people on a low-fat diet.
“The Mediterranean diet has well-known health benefits and includes healthy fats such as vegetable oils, fish and nuts. Our findings certainly do not imply that unrestricted diets with high levels of unhealthy fats such as butter, processed meat, sweetened beverages, deserts or fast-foods are beneficial."
Commenting on the findings, nutrition expert Professor Dariush Mozaffarian, from Tufts University in Boston, said it's time to reevaluate “outdated” guidelines on fat consumption.
“Calorie-obsessed caveats and warnings about healthier, higher-fat choices such as nuts, phenolic-rich vegetable oils, yoghurt, and even perhaps cheese, should also be dropped," he said.
“We must abandon the myth that lower-fat, lower-calorie products lead to less weight gain.”
He added: "The fat content of foods and diets is simply not a useful metric to judge long-term harms or benefits. Energy density and total caloric contents can be similarly misleading.
"Rather, modern scientific evidence supports an emphasis on eating more calories from fruits, nuts, vegetables, beans, fish, yoghurt, phenolic-rich vegetable oils, and minimally processed whole grains; and fewer calories from highly processed foods rich in starch, sugar, salt, or trans-fat."
But leading British expert Susan Jebb said the study is inconclusive.
"It is impossible from this study to draw any conclusion about the impact of the low fat diets on body weight since each group consumed more than the UK average (35% fat) and way more than the World Health Organisation recommendation (30% fat)," she said.
Dr Alison Tedstone, chief nutritionist at Public Health England, added: “Diets high in fruit and vegetables, containing some meat, fish and unsaturated fats, such as olive oil, often described as a Mediterranean diet, tend to be associated with health benefits - particularly heart health.
"This is similar to UK Government advice to follow a diet consistent with the Eatwell Guide, where up to 35% of your calories can come from fats of which no more than 11% should be from saturated fats."
The results are published in the journal The Lancet Diabetes & Endocrinology.