Could consumption of olive oil help protect against obesity?

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I’m currently in Portugal, and practically all of my main meals have come in the form of meat or fish plus salad. The salads have come dressed with olive oil, and I’ve noticed here this is used quite sparingly. Part of the reason for that is that there is a common perception here that olive oil is fattening. On the other hand, the fat conscious Portuguese (well the ones I spend time with, anyway) will happily eat mounds of starchy carb. For instance, bread accompanies every meal, irrespective if that meal is loaded with rice or potatoes.

These same people think it’s odd that when I prepare a salad, I use very generous amounts of olive oil to dress it. What they also think is odd, from what I can gather, is how I can eat salads swimming in oil twice a day and not be overweight.

I thought about this when I came across a recent Spanish study that looked at the relationship between oil consumption and risk of obesity [1]. Basically, this study found that the consumption of olive oil (rich in monounsaturated fat) or a mixture of oils (including olive oil) were at significantly reduced risk of becoming obese over time compared to those consuming predominantly sunflower oil (rich in omega-6 polyunsaturated fats). Even though this study controlled for so-called confounding factors such as caloric intake and age, an epidemiological study of this nature cannot tell us whether or not olive oil somehow helps protect against obesity and/or if omega-6 fats somehow help cause it.

To answer this question, we would require long terms studies in which individuals are fed these different fats in controlled conditions for relatively long periods of time. I’m not aware that such studies have been done. However, there is an interesting study in monkeys. In this study, two groups of monkeys were fed different diets for 6 years. One group of monkeys was fed a diet which contained 8 per cent of calories in the form of trans fat (usually industrially produced fats). The other group of monkeys ate a diet enriched with monounsaturated fat. In both diets, 35 per cent of calories came from fat. Both groups were fed the same number of calories too.

At the end of the study, monkeys fed trans fat gained more than 7 per cent in body weight, compared to less than 2 per cent of the monkeys fed monounsaturated fat. Also, the trans fat-fed monkeys tended to accumulate their weight in an around the abdomen ” precisely the form of excess weight most strongly linked with conditions such as heart disease and diabetes.

This study provides at least some evidence that consuming olive oil might help afford some protection from obesity. It also provides good evidence that when it comes to weight and obesity, a calorie is not a calorie.


1. Soriguer F, et al. Incidence of obesity is lower in persons who consume olive oil. Eur J Clin Nutr 2009 Jul 22. [Epub ahead of print]

2. Kavanagh K, et al. Trans fat diet induces abdominal obesity and changes in insulin sensitivity in monkeys. Obesity 2007;15(7):1675-84.

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