High-fat Mediterranean diet does not lead to weight gain: study
Low-fat diets have been extolled by dieticians and doctors for decades, but obesity rates keep climbing. New research shows healthy fat should shed its stigma – hopefully soon. Belinda Smith reports.
Are the days of calorie counting numbered? They should be, according to a new study published in The Lancet Diabetes and Endocrinology – eating a Mediterranean diet high in vegetable fats doesn't lead to significant weight gain in older people compared to a low-fat diet.
The Mediterranean diet, which is rich in "good fats" such as those found in vegetables, fish and nuts, has known health benefits. Yet many countries' health guidelines recommend low-fat diets without differentiating between the good fats and "bad fats", such as those found in red meat and butter.
So researchers in Spain randomly placed 7,447 men and women aged more than 55 years on one of three diets: a Mediterranean diet supplemented with olive oil, a Mediterranean diet with added nuts, and a low-fat diet.
The subjects were at "high risk" of cardiovascular disease, meaning they either had type-2 diabetes or at least three of the following: current smoking, high blood pressure, high "bad" cholesterol, low "good" cholesterol, had a family history of heart disease or were overweight or obese.
More than 90% of participants were overweight or obese.
The groups following the supplemented Mediterranean diets were given personalised plans and instructed to either consume 50 millilitres of extra-virgin olive oil per day or 30 grams of mixed nuts (15 grams of walnuts and 7.5 grams each of almonds and hazelnuts). These products were donated by olive oil and nut companies.
Dieticians regularly met each subject throughout the study's duration. Those in the Mediterranean diet groups were randomly urine-tested for biomarkers associated with extra-virgin olive oil or walnuts to make sure they stuck to their diet.
After five years, daily fat intake in the low-fat group dropped from 40% to 37.4%, while it rose in the olive oil group from 40% to 41.8%, and in the nut group from 40.4% to 42.2%. And all groups, overall, lost a little weight.
This is in contrast to the Spanish population as a whole which, according to an Organisation for Economic Co-operation and Development 2014 report, saw rising obesity levels between 2003 and 2010 when the study ran.
But as people age, they tend to gradually put on weight, then drop it as they lose lean muscle mass. Waist circumference, the researchers write, is a better indicator of body fat in older people than weight alone.
Each of the three groups saw a slight increase in waist measurements, which isn't surprising for older people, but the low-fat group ended up with the biggest increase – 1.2 centimetres – compared to 0.85 centimetres for the olive oil group and 0.37 centimetres for the nut group. There were no differences in gender, age or diabetes status.
So given a little extra-virgin olive oil and nuts each day aren't making obese people stack on loads of weight, should we start frying everything in olive oil and downing nuts by the handful?
No, says Clare Collins, a nutritionist at the University of New South Wales in Sydney, Australia. How nuts and oil were used by the participants was important: "Olive oil isn't a frying oil. It's used in dressings or dipping bread, instead of margarine." And 30 grams of nuts isn't a huge amount – only a very small handful.
"The good news is these foods in moderation don't necessarily mean weight gain. Now's the time to focus on fat quality and ditch our usual poor habits."
Dariush Mozaffarian from Boston's Tufts University agrees, writing in a Comment piece: "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.
"We ignore this evidence [...] at our own peril."