Fact-checking – “French fries cooked in olive oil are healthier than boiled potatoes”

1. Facts under analysis?

A recent news report, published in some media outlets such as SIC Notícias , claims that potatoes fried in olive oil are healthier than boiled potatoes. This news is based on a study published in 2015 in the journal Food Chemistry by a team of researchers from the University of Granada, Spain. What conclusions are drawn from the study that allow us to infer such a claim?

2. Analysis of the fact(s) based on scientific evidence

The study compares the polyphenolic content of several foods (potato, eggplant, tomato, and pumpkin) depending on whether they are subjected to different cooking processes, namely frying in extra virgin olive oil, sautéing, or boiling in water or a water/oil mixture. The total antioxidant capacity of each food/cooking process combination was also determined using three different methods.
This quite exhaustive set of data (18 different phenolic compounds were analyzed individually) showed, in summary, that foods fried in extra virgin olive oil exhibit a higher quantity of some polyphenolic compounds, with the final content also depending on the base product subjected to the respective method.
While there is reasonable evidence regarding some mechanisms that relate the polyphenol content in the diet and health (see, for example, here ), it has been more difficult to prove this association in some specific diseases, such as hypertension , breast cancer , or colorectal cancer , to name just a few.
On the other hand, although the Mediterranean diet constitutes a dietary model that provides a certain level of these and other compounds whose effects are already relatively well established, it is no less true that the evidence regarding the effects of this diet, which prioritizes vegetables, fruits and olive oil, still lacks absolutely conclusive proof of its benefit on markers such as cardiovascular disease or others .
Therefore, it is not even unequivocal, in light of the best science currently available, that a higher level of this type of polyphenol is synonymous with better health.

For these and other reasons, the article makes no conclusion about frying being more or less healthy than other cooking methods, only mentioning its higher polyphenol content and antioxidant capacity.

3. Final verdict of “Thinking Nutrition”

The conclusion that french fries are healthier than boiled potatoes is, therefore, a gross and incorrect extrapolation of the honest conclusions of the article, and we consider this title to be "FALSE" .

As an additional note, it should be mentioned that news of this type, favoring frying as a cooking method, constitutes, in our view, the wrong signal in terms of public health, for several reasons. Firstly, the increase in the energy density of the food is associated with an increase in the prevalence of obesity, which is surely one of the most important public health problems we face at the moment. Secondly, because many families and restaurants do not fry with extra virgin olive oil, it is very unlikely that the polyphenol content is equally high in these fried foods, adding to the problem that the resistance of cooking oils to high temperatures is sometimes lower than that of olive oil. Finally, it is important to mention that the Mediterranean diet is a complex dietary model, which includes other facets of lifestyle that go beyond the foods themselves, and therefore it becomes quite reductive to try to explain it based on a few chemical compounds, without this disregarding the essential value of this type of research.

Written by

Nuno Borges

Nutritionist, Associate Professor at the Faculty of Nutrition and Food Sciences, University of Porto  |  Website