Fried Foods and Heart Disease: A new study adds a dimension to our knowledge

Jacob Schor, ND,
Fellow American Board of Naturopathic Oncology
April 5, 2012
An interesting study by Guallar-Castillón and colleagues published last January in the British Medical Journal has left me considering whether our belief that fried foods are unhealthy is correct.  Let me first tell you about their study.
This was a Prospective cohort study that followed a total of 40,757 people, aged 29-69,  for about ten years ending in 2004.  The participants were part of the Spanish cohort of the European Prospective Investigation into Cancer and Nutrition. They were recruited from five regions of Spain with the intent to maximize dietary variability.  None of the participants had coronary heart disease at the start of the study.
Trained interviewers administered intense sounding computerized dietary history questionnaires to each participant in order to assess their food consumption patterns.        Information was recorded on consumption of 662 different foods and of these foods, 212 were prepared by frying.  Information on cooking methods was obtained for foods that are prepared via a choice of cooking methods.  In addition, information was collected on non-dietary variables such as physical activity at work and home, menopausal status, weight, smoking, and other health conditions that might affect risk of cardiovascular disease.  This was a large carefully done study.
Two primary outcome measures were tracked: whether the participants developed coronary heart disease events and their vital status, that is, whether they were dead or alive.  The researchers were able to keep track of these changes by linking to various to health registers.    
So here’s where this gets interesting.  Consumption of fried foods by this Spanish population had no impact on either the occurrence of cardiovascular disease or the risk of overall mortality. It didn’t make a difference how much fried foods these people ate. 
During a median of 11 years in which cohort participants were followed, 606 coronary heart disease events and 1,135 deaths from all causes occurred. Eating large quantities of fried foods was not associated with a significant change in either disease or mortality risk.  Compared with being in the first (lowest) quarter of fried food consumption, the multivariate hazard ratio of coronary heart disease in the second quarter was 1.15 (95% confidence interval 0.91 to 1.45), in the third quarter was 1.07 (0.83 to 1.38), and in the fourth quarter was 1.08 (0.82 to 1.43; P for trend 0.74).        No association was observed between fried food consumption and all cause mortality: multivariate hazard ratio for the highest versus the lowest quarter of fried food consumption was 0.93 (95% confidence interval 0.77 to 1.14; P for trend 0.98). Repeating myself for the third or fourth time, eating  a lot of fried foods didn’t change the risk of getting heart disease or dying.[1] 
What does this mean?
There are two ways to look at these results. 
First, is that fried foods may be less detrimental to health than has been assumed; we may have been mistaken when we preached that fried foods were bad. 
The second possibility is that the benefits of a Mediterranean style diet and, in particular, olive oil, cancel out the ill effect of eating fried foods. 
Though there may be some truth in both theories, the second explanation is certainly going to be easier to swallow.
When food is fried, nutritional content changes.  Water is lost and fat is absorbed, increasing the food’s energy density.  Fried food contains more calories than if it had been baked or boiled.  The oil in which the food is cooked deteriorates during frying, especially when reused, becoming oxidized and hydrogenated, losing unsaturated fats and increasing trans fats.  Chemical constituents in the food undergo chemical reactions with the oil, producing new compounds, some of which may have impact health.  
While the assumption that eating fried foods is unhealthy is widely held, there is relatively little published scientific data supporting it.  There  is little doubt that fried food is fattening. Frying food adds calories and over time frequent consumption will cause weight gain. Numerous studies from all over the world leave little doubt that high consumption of fried foods is associated with general and central obesity.[2,3,4,5,6]                  
While central obesity is associated with cardiovascular disease risk, there appears to be little if anything published that demonstrates a direct association between fried food consumption and increased heart disease.
The only definitie evidence was Belin et al’s 2011 study on fish consumption and congestive heart disease risk.  They reported a surprising conclusion regarding fried fish consumption.  While eating five or more servings of baked or broiled fish per week lowered the risk of having heart failure by 30%, eating fried fish one or more times a week was associated with a 48% increase in risk for heart failure. They did not report finding an association with total fried food intake and heart failure.[7]  
In a case control study in Costa Rica, Kabagambe et al found no association between fried food consumption and risk of non-fatal acute myocardial infarction. They did report significant increases in risk with consumption of particular short chain fatty acids.  The most striking increase in risk they found from particular foods was from cheese, 1-2 servings per day compared to none, tripled risk. [8]
Interheart, a large international case control study that compared various dietary patterns (Western Oriental, Prudent) does suggest, in as much as high amounts of fried foods are considered a component of a Western Diet, a positive association between fried foods and acute myocardial infarction. [9]        It does not appear that they examined our question of fried foods directly but only in context of a pattern described as a Western Diet that was defined as high in fried foods, salty snacks, eggs, and meat.        Thus it could any part of the Western Diet that was to blame.  Or simply that we watch more television than anyone else.
It comes as a surprise to this writer, that, given how certain we all have been that fried food is unhealthy, that there are no definitive studies that fried food causes heart disease or impacts mortality.
But this is actually more complicated.        The participants in the current Guallar-Castillón study all lived in Spain, a country where olive oil is the most common oil used for frying.        High consumption of olive oil is often cited as an explanation for the Mediterranean Paradox, where there is a “… high prevalence of cardiovascular risk factors with low incidence of myocardial infarction in the population….” [10]            In contrast, consumption of hydrogenated or even partially hydrogenated vegetable oils is associated with increased risk factors for heart disease in particular dyslipidemia and hypertension. [11]   Olive oil, as part of a Mediterranean diet, is associated with a decreased risk of heart disease.  The phenols in olive oil trigger changes in low-density lipoproteins reducing their tendency toward oxidation while increasing high-density lipoprotein levels.[12,13]          Olive oil, in particular the extra virgin grades have been shown to act as antioxidants in heart
disease patients and it has been suggested that these patients should supplement their diet with these oils.[14]
The effect of the olive oil polyphenols does not appear to be lost when the oil is used for frying. For example, food fried in extra-virgin olive oil improves postprandial insulin response in obese, insulin-resistant women.[15]       
One study that clearly associated fried food consumption with cardiovascular risk factors was Soriguer et al’s 2003 report.  They showed that the oil breakdown products created during frying led to elevated blood pressure in people who frequently ate fried foods.  They also reported that consuming monounsaturated fatty acids, in particular those found in olive oil, reduced risk of hypertension. [16] 
Foods change chemically during frying and the type of oil determines some of these reactions. Ramierez reported in 2004 that when pork loin was fried in different types of oils, different chemical reactions occur.  While all developed and released volatile compounds, the profile varied with type of fat.[17]        Morena et al reported in 2007 that stir-frying broccoli using olive or sunflower oil had less detrimental effect on the food’s antioxidant content, preserving more vitamin C, than if using soy, peanut or safflower oils. [18]
Napolitano measured acrylamide formation when potatoes were fried in extra virgin olive oil.  Cooking did not change the polyphneol content of the oil.  The higher the polyphenol content of the oil that was used to fry the potatoes, the less acrylamide formed during cooking. [19] 
Coming back to the current study, the easiest explanation for these results is that the benefits of the olive oil commonly used to fry foods with in Spain are enough to cancel out the possible negative impact that frying may have had on cardiovascular disease risk.  Frying foods in hydrogenated or even partially hydrogenated oils, a common practice in the United States may still have detrimental effects.  Thus our common assumption that fried foods are bad for the heart may still be true but we need to put an addendum to this and say, foods fried in olive oil are not bad for the heart.  They are still fattening though.
Olive oil actually works well for frying. The smoke point varies with quality, higher quality oils have higher smoke points.  A good extra virgin olive oil will start to smoke somewhere between 365ºF and 400ºF.  Suggested temperatures for frying food are below this. The cost of using high quality olive oil may be enough to dissuade people from overconsumption.
1. Guallar-Castillón P, Rodríguez-Artalejo F, Lopez-Garcia E, León-Muñoz LM, Amiano P, Ardanaz E, Arriola L, 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 Jan 23;344:e363.
2. Guallar-Castillón P, Rodríguez-Artalejo F, Fornés NS, Banegas JR, Etxezarreta PA, Ardanaz E, et al. Intake of fried foods is associated with obesity in the cohort of Spanish adults from the European Prospective Investigation into Cancer and Nutrition. Am J Clin Nutr. 2007 Jul;86(1):198-205.
3. Wu J, Mo J, Huang CW, Peng LW, Xu L, Yang XC, Yu X. [Obesity and its influencing factors in primary school students from Kaifu District of Changsha City]. Zhongguo Dang Dai Er Ke Za Zhi. 2008 Apr;10(2):231-5.
4. Al-Rethaiaa AS, Fahmy AE, Al-Shwaiyat NM. Obesity and eating habits among college students in Saudi Arabia: a cross sectional study. Nutr J. 2010 Sep 19;9:39.
5. Krachler B, Eliasson M, Stenlund H, Johansson I, Hallmans G, Lindahl B. Reported food intake and distribution of body fat: a repeated cross-sectional study. Nutr J. 2006 Dec 22;5:34.
6. Ghosh A, Bose K, Das Chaudhuri AB. Association of food patterns, central obesity measures and metabolic risk factors for coronary heart disease (CHD) in middle aged Bengalee Hindu men, Calcutta, India. Asia Pac J Clin Nutr. 2003;12(2):166-71.
7. Belin RJ, Greenland P, Martin L, Oberman A, Tinker L, Robinson J, et al. Fish Intake and the Risk of Incident Heart Failure: The Women's Health Initiative. Circ Heart Fail. 2011 May 24.
8. Kabagambe EK, Baylin A, Siles X, Campos H. Individual saturated fatty acids and nonfatal acute myocardial infarction in Costa Rica.        Eur J Clin Nutr. 2003 Nov;57(11):1447-57.
9. Iqbal R, Anand S, Ounpuu S, Islam S, Zhang X, Rangarajan S, et al. Dietary patterns and the risk of acute myocardial infarction in 52 countries: results of the INTERHEART study. Circulation. 2008 Nov 4;118(19):1929-37.
10. Covas MI, Fitó M, Marrugat J, Miró E, Farré M, de la Torre R, et al. [Coronary disease protective factors: antioxidant effect of olive oil]. Therapie. 2001 Sep-Oct;56(5):607-11.
11. Esmaillzadeh A, Azadbakht L. Different kinds of vegetable oils in relation to individual cardiovascular risk factors among Iranian women. Br J Nutr. 2011 Mar;105(6):919-27.
12. Gimeno E, de la Torre-Carbot K, Lamuela-Raventós RM, Castellote AI, Fitó M, de la Torre R, et al. Changes in the phenolic content of low density lipoprotein after olive oil consumption in men. A randomized crossover controlled trial. Br J Nutr. 2007 Dec;98(6):1243-50.
13. Weinbrenner T, Fitó M, de la Torre R, Saez GT, Rijken P, Tormos C, et al. Olive oils high in phenolic compounds modulate oxidative/antioxidative status in men.
J Nutr. 2004 Sep;134(9):2314-21.
14. Fitó M, Cladellas M, de la Torre R, Martí J, Alcántara M, Pujadas-Bastardes M, Marrugat J, et al. Antioxidant effect of virgin olive oil in patients with stable coronary heart disease: a randomized, crossover, controlled, clinical trial. Atherosclerosis. 2005 Jul;181(1):149-58.
15. Farnetti S, Malandrino N, Luciani D, Gasbarrini G, Capristo E. Food fried in extra-virgin olive oil improves postprandial insulin response in obese, insulin-resistant women. J Med Food. 2011 Mar;14(3):316-21.
16. Soriguer F, Rojo-Martínez G, Dobarganes MC, García Almeida JM, Esteva I, Beltrán M, et al. Hypertension is related to the degradation of dietary frying oils.  Am J Clin Nutr. 2003 Dec;78(6):1092-7.
17.  Ramírez MR, Estévez M, Morcuende D, Cava R. Effect of the type of frying culinary fat on volatile compounds isolated in fried pork loin chops by using SPME-GC-MS. J Agric Food Chem. 2004 Dec 15;52(25):7637-43.
18. Moreno DA, López-Berenguer C, García-Viguera C. Effects of stir-fry cooking with different edible oils on the phytochemical composition of broccoli. J Food Sci. 2007 Jan;72(1):S064-8.
19.  Napolitano A, Morales F, Sacchi R, Fogliano V. Relationship between virgin olive oil phenolic compounds and acrylamide formation in fried crisps. J Agric Food Chem. 2008 Mar 26;56(6):2034-40. Epub 2008 Feb 22.