Fried Foods and Heart Disease

Guallar-Castillón P, Rodríguez-Artalejo F, Lopez-Garcia E, 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. 

Prospective cohort study

A total of 40,757 people aged 29 to 69, who were part of the Spanish cohort of the European Prospective Investigation into Cancer and Nutrition, were followed from baseline in 1992 to 1996 until 2004. Study participants were recruited from 5 regions of Spain with the intent to maximize dietary variability. Participants were free of coronary heart disease at the start of the study.

Computerized dietary history questionnaires administered by trained interviewers were used to assess participant 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 nondietary variables such as physical activity at work and home, menopausal status, weight, smoking, and other health conditions that might affect risk of cardiovascular disease.

Two primary outcome measures were tracked: coronary heart disease events and vital status. Changes in either were identified through linkage to health registers.  

Consumption of fried foods by this Spanish population had no impact on either the occurrence of cardiovascular disease or risk of overall mortality. During a median of 11 years in which cohort participants were followed, 606 coronary heart disease events and 1135 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 (HR) of coronary heart disease in the second quarter was 1.15 (95% confidence interval [CI]: 0.91-1.45); in the third quarter was 1.07 (95% CI: 0.83-1.38); and in the fourth quarter was 1.08 (95% CI: 0.82-1.43; P for trend=0.74). No association was observed between fried food consumption and all-cause mortality: multivariate HR for the highest vs the lowest quarter of fried food consumption was 0.93 (95% CI:0.77-1.14; P for trend=0.98). 

There are 2 ways to look at these results. 

 

The first interpretation is that fried foods are less detrimental to health than has been assumed, and 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 olive oil in particular cancel out the ill effect of eating fried foods. 

 

Though there may be some truth in both theories, the second explanation is certainly easier to swallow. 

 

When food is fried, its 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 it is reused, and becomes oxidized and hydrogenated, losing unsaturated fats and increasing trans fats. Chemical constituents in the food undergo chemical reactions with the oil to produce new compounds, some of which may have impact health. Frying food certainly adds calories, and over time, this 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.^1-5

Yet, while central obesity is certainly 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.

 

A 2011 study by Belin et al that examined fish consumption and congestive heart disease risk reported a surprising conclusion regarding fried fish consumption. While eating 5 or more servings of baked or broiled fish per week lowered the risk of having heart failure by 30%, eating fried fish 1 or more times a week was associated with a 48% increase in risk for heart failure. This study did not report finding an association with total fried food intake and heart failure.⁶

 

In a case control study from Costa Rica, Kabagambe et al found no association between fried food consumption and risk of nonfatal acute myocardial infarction. The researchers 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 to 2 servings per day compared to 0 servings tripled the risk.⁷

 

Interheart, a large international case control study that compared various dietary patterns does suggest a positive association between fried foods and acute myocardial infarction, in as much as large amounts of fried foods are considered a component of a western diet.⁸ It does not appear that the researchers in this case examined the contribution of fried foods directly but only in context of the western diet, which was characterized as high in fried foods, salty snacks, eggs, and meat.

 

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. 

 

Keep in mind that 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.”⁹ 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.¹⁰ As part of the Mediterranean diet, olive oil 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.^11,12 Olive oil—in particular the extra virgin grades—has been shown to act as antioxidants in heart disease patients, and practitioners have recommended that these patients supplement their diet with these oils.¹³

 

One study that clearly associated fried food consumption with cardiovascular risk factors was a 2003 report by Soriguer et al. This research team demonstrated 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.¹⁴

 

Interestingly, 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 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 oils developed and released volatile compounds, the profile varied with type of fat.¹⁶ 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 and preserved more vitamin C than stir-frying with soy, peanut, or safflower oils.¹⁷

 

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.¹⁸

 

Focusing on 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 insert an addendum to this and say that food fried in olive oil is not necessarily bad for the heart. That food is 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 365º F and 400º F. Suggested temperatures for frying food are below this. The cost of using high quality olive oil may be enough to dissuade people from overconsumption.