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Frequently eating food fried in olive oil wasn't any more risky than the occasional indulgence among more than 40,000 Spaniards followed for 12 years in a study by Pilar Guallar-Castillón, MD, MPH, PhD, of the Autonomous University of Madrid, and colleagues.
The hazard ratio for coronary heart disease was a nonsignificant 1.08 for the highest intake versus the lowest, they reported online in BMJ.
All-cause mortality likewise showed no impact from even the highest intake of fried foods in the study (adjusted HR 0.93, P=0.98 for trend).
"This result may seem surprising because frying is generally considered an unhealthy way of preparing food," an accompanying editorial acknowledged.
But that's an assumption that has largely gone unchallenged, with only sparse and inconsistent data on hard outcomes, explained Michael F. Leitzmann, MD, DrPH, of the University of Regensburg, Germany and Tobias Kurth, MD, ScD, of Université Bordeaux Segalen in Bordeaux, France.
"However, this does not mean that frequent meals of fish and chips will have no health consequences," they warned.
Frying foods boosts calorie content, and eating them has been linked to obesity, high cholesterol, and high blood pressure.
Instead of a blanket conclusion on fried food, the type of oil used, whether it's used to deep fry or pan fry, and how many times it is reused may be relevant, Leitzmann and Kurth concluded.
The study dug into one aspect -- type of oil -- using the Spanish cohort of the ERIC study (European Prospective Investigation into Cancer and Nutrition).
Detailed dietary interviews analyzed for 40,757 adults, ages 29 to 69, without baseline coronary heart disease indicated that about 7% of food eaten was fried for a total of roughly 5 oz each day (the equivalent of a medium serving of french fries).
Consumption was higher among younger, more educated individuals who smoked more and didn't sit as much at work.
After adjusting for energy intake, body mass index, hypertension, and other factors, the risk of incident coronary heart disease during 12 years of follow-up was not elevated significantly at any level of fried food intake.
The hazard ratio was 1.15 for the second quartile averaging 106 g (3.7 oz) of fried food each day, compared with the lowest intake at an average 47 g (1.6 oz) per day (95% CI 0.91 to 1.45). Other hazard ratios were:
- 1.07 for the third quartile averaging 158 g (5.6 oz) compared with the lowest intake group (95% CI 0.83 to 1.38)
- 1.08 for the top consumers averaging 250 g (8.8 oz) versus the bottom quartile (95% CI 0.82 to 1.43)
The results were the same for the 62% of people who used olive oil to fry food as for the rest who used sunflower or other vegetable oil (P=0.22 for interaction).
Nor was there any difference across genders (P=0.19 for interaction).
None of the most commonly fried foods -- fish, meat, potatoes, and eggs -- were linked individually to either heart disease or all-cause mortality.
The researchers cautioned that their findings came from a population that followed the traditional Mediterranean diet with greater use of olive oil, which is less prone to degradation during frying.
"Frying with other types of fats may still be harmful," they warned.
While large amounts of fried foods are eaten both at and away from home in Spain, fried foods aren't a proxy for fast food or for high salt content there, unlike in the U.S., the group pointed out.
Limitations of the study included dietary assessment only at baseline, which didn't account for changes over time, and inability to separate out the effect of the method of cooking from that of the food cooked.
From the American Heart Association:
The study was funded by research grants from FIS and the Instituto de Salud Carlos III and by funds from the Spanish regional governments of Andalusia, Asturias, Basque Country, Murcia, and Navarra, and the Catalan Institute of Oncology.
The researchers and editorialists reported having no conflicts of interest to disclose.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
BMJSource Reference: Guallar-Castillón P, et al "Consumption of fried foods and risk of coronary heart disease: Spanish cohort of the European Prospective Investigation into Cancer and Nutrition study" BMJ 2012; 344: e363.
BMJSource Reference: Leitzmann MF, Kurth T "Fried foods and the risk of coronary heart disease" BMJ 2012; DOI: 10.1136/bmj.d8274.