Does a low-fat, low-calorie diet help maintain a healthy weight?
New study of almost 7,500 people across seven years shows that quality and source of fats has important implications for long-term health and weight
Q: Are low-fat, low-calorie foods best for maintaining a healthy weight?
The straight answer: No.
The facts: The standard recommendation for the prevention and treatment of obesity is a reduced-fat diet and increased physical activity, and many health organisations including the World Health Organisation and Hong Kong’s Department of Health recommend a limit of 30 per cent fat for total energy intake.
But a study published recently in The Lancet Diabetes & Endocrinology journal suggests current health guidelines that recommend a low-fat, low-calorie diet create unnecessary fear of healthy fats – in particular those present in a Mediterranean diet, which have known health benefits.
Accumulating scientific evidence suggests that total fat content is not a useful measure of harms or benefits of food, and that fats from nuts, fish and vegetable oils that are rich in phenolic acids (dietary phytochemicals that work as antioxidants) are healthier than fats from meat and processed foods.
“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,” says lead author Dr Ramon Estruch, CIBER OBN-University of Barcelona, Spain. “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.”
In a commentary that accompanied the study, Professor Dariush Mozaffarian, Friedman School of Nutrition Science & Policy at Tufts University, Boston, adds: “Dietary guidelines should be revised to lay to rest the outdated, arbitrary limits on total fat consumption. We must abandon the myth that lower-fat, lower-calorie products lead to less weight gain.
“This illusion leads to paradoxical policies that focus on total calories, rather than food quality, on restaurant menus; ban whole milk but allow sugar-sweetened fat-free milk; compel food manufacturers, retailers, and restaurants to remove healthy vegetable-derived fats from meals and products while heavily marketing fat-reduced products of dubious health value; and mislead consumers to select foods based on total fat and calorie contents rather than actual health effects.”
The study took place in 11 hospitals in Spain during 2003-10 and included 7,447 participants aged 55-80 who were randomly assigned to one of three groups – an unrestricted-calorie Mediterranean diet rich in olive oil, an unrestricted-calorie Mediterranean diet rich in nuts, or a low-fat diet where the advice was to avoid all dietary fat. Dietitians gave personalised dietary advice to all participants.
All participants were at high cardiovascular risk or had type 2 diabetes, and more than 90 per cent were overweight or obese.
After five years, total fat intake had decreased in the low-fat diet group (from 40 per cent to 37.4 per cent) and had slightly increased in both Mediterranean diet groups (40 per cent to 41.8 per cent in olive oil; 40.4 per cent to 42.2 per cent in nuts). The percentage of energy intake from protein and carbohydrate decreased in both Mediterranean diet groups. On average, participants in all three groups lost some weight, with the greatest weight loss seen in the olive oil group, which lost 0.88 kg. The low-fat diet group lost 0.60 kg and the nuts group 0.40 kg.
Waist girth increased in all three groups, with the greatest increase seen in the low-fat diet group of 1.2 cm. The olive oil group saw an 0.85 cm increase and the nuts group 0.37 cm.
Mozaffarian says just focusing on total fat to prevent heart disease is “misguided” because it overlooks the different effects of specific fatty acids. The prioritisation of total calories to prevent weight gain also ignores the diverse physiological effects of different foods.
“The fat content of foods and diets is simply not a useful metric to judge long-term harms or benefits,” he says.