Fried-food intake is linked to a heightened risk of major heart disease and stroke, finds a pooled analysis of the available research data, published online in the journal Heart.
And the risk rises with each additional 114 g weekly serving, the analysis indicates.
It’s clear that the Western diet doesn’t promote good cardiovascular health, but it’s not clear exactly what contribution fried food might make to the risks of serious heart disease and stroke, say the researchers.
To shed some light on this, they trawled research databases, looking for relevant studies published up to April 2020, and found 19.
They pooled the data from 17, involving 562,445 participants and 36,727 major cardiovascular ‘events’, such as a heart attack or stroke, to assess cardiovascular disease risk.
And they pooled the data from six, involving 754,873 participants and 85,906 deaths over an average monitoring period of 9.5 years, to assess the potential link between fried food consumption and deaths from cardiovascular disease and from any cause.
Their analysis showed that compared with the lowest category of weekly fried food consumption, the highest was associated with a 28% heightened risk of major cardiovascular events; a 22% heightened risk of coronary heart disease; and a 37% heightened risk of heart failure.
These associations held true when stratified by various study and participant characteristics. What’s more, a linear association emerged between fried food consumption and major cardiovascular events, coronary heart disease, and heart failure.
These risks substantially increased by 3%, 2%, and 12%, respectively, in tandem with each additional 114 g weekly serving.
Several studies included only one type of fried food, such as fried fish, potatoes, or snacks, rather than total fried food intake, which may have underestimated the associations found, suggest the researchers.
No associations were found for deaths from cardiovascular disease or from any cause, but this might be because of the relatively small numbers involved, say the researchers.
The design of the included studies varied considerably, added to which, they all relied on memory—factors that should be taken into consideration when interpreting the results, caution the researchers.
And how exactly fried foods might influence the development of cardiovascular disease isn’t entirely clear, they point out, but suggesting several possible explanations.
Fried foods boost energy intake because of their fat content and they generate harmful trans fatty acids from the hydrogenated vegetable oils often used to cook them.
Frying also boosts the production of chemical by-products involved in the body’s inflammatory response, while foods, such as fried chicken and French fries, are usually high in added salt, and often accompanied by sugar-sweetened drinks, particularly when served in fast food restaurants, they say.
Consumption of fried foods and risk of coronary heart disease: Spanish cohort of the European Prospective Investigation into Cancer and Nutrition study
Frying is one of the most commonly used methods for cooking in Western countries. When food is fried its nutritional content changes—the food loses water and takes up fat, increasing its energy density.1 2
Frying modifies both the foods and the frying medium because oils deteriorate during frying, especially when reused, through the processes of oxidation and hydrogenation, leading to a loss of unsaturated fats and an increase in trans fats.1 Thus fried food absorbs degradation products of the frying oil.3
At the same time, frying may also improve palatability by making food crunchy.4 5
Fried foods have been associated with various cardiovascular risk factors in cross sectional studies. In Spain, the Pizarra study of 1226 adults showed that consumption of food fried with reused oils was associated with a higher prevalence of arterial hypertension.6
Furthermore, a cross sectional analysis of the Spanish cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC) study concluded that consumption of fried foods was positively associated with general and central obesity.7
Similarly, in the SUN (Seguimiento University of Navarra) cohort in Spain, more frequent consumption of fried foods at baseline was associated with a higher risk of becoming overweight or obese during a six year follow-up.8 Lastly, in another cross sectional study in 2090 Italian adults, consumption of fried food was associated with lower high density lipoprotein cholesterol levels and a larger waist circumference.9
Only a few studies have evaluated the effect of fried foods on risk of cardiovascular disease. A case-control study in Costa Rica found no association between consumption of fried foods and risk of non-fatal acute myocardial infarction.10
Another case-control study, INTERHEART, observed a positive association between fried foods and acute myocardial infarction.11
Therefore, although interest in the associations of dietary patterns and specific cooking techniques with risk of disease is increasing,12 little is known about the health effects of fried foods. We evaluated prospectively the association between consumption of fried foods and the risk of coronary heart disease in the EPIC-Spain cohort.
An average 138 g of fried food was consumed daily, including 14 g of oil used for frying. About 7% of the total amount of food consumed was fried. Fried food consumption ranged from 0-817 g/day for men and 0-657 g/day for women. Sixty two per cent of participants used olive oil for frying and the rest used sunflower oil or other vegetable oils.
Participants with a higher fried food intake were younger, of a higher level of education, more often smokers, and less often sedentary at work (table 1⇓). Moreover, they had a lower prevalence of diabetes mellitus and hyperlipidaemia, a higher energy and ethanol intake, and a lower consumption of non-fried vegetables, fruit, dried fruit and nuts, milk products, and
non-fried fish (table 2⇓). They also had a lower frequency of diagnosed hypertension. Among women, the frequency of menopausal status decreased with the consumption of fried food (table 2).
During a median follow-up of 11 years, 606 definite coronary heart disease events occurred (466 myocardial infarctions and 140 anginas requiring revascularisation). There were also 712 definite, possible, or probable coronary heart disease events and 1135 deaths from all causes.
For definite coronary heart disease events, no association with fried food consumption was observed in analyses adjusting for energy intake, age, sex, and centre (table 3⇓, model 1). The hazard ratio of coronary heart disease for the highest versus the lowest quarter of fried food consumption was 0.94 (95% confidence interval 0.72 to 1.23; P for trend 0.52). Similar results were obtained after additional adjustment for the main confounders (table 3, model 2): 1.11 (0.84 to 1.46; P for trend 0.60).
Finally, no association was observed between fried food and incident coronary heart disease after adjusting for possible mediators such as body mass index, waist circumference, and hypertension (table 3, model 3). Compared with the first (lowest) quarter of fried food consumption, the multivariate hazard ratios of coronary heart disease were 1.15 (0.91 to 1.45) in the second quarter, 1.07 (0.83 to 1.38) in the third quarter, and 1.08 (0.82 to 1.43) in the fourth quarter (P for trend 0.74). Lastly, after full adjustment, a 100 g increase in the consumption of fried food did not show an association with risk of coronary heart disease (hazard ratio 1.00, 0.90 to 1.11).
The results were similar after censoring the first two years of follow-up and after excluding those who reported a change in their diet during the previous year. The results did not vary between those who used olive oil for frying and those who used sunflower oil or other vegetable oils (P for interaction 0.22), or between the sexes (P for interaction 0.19).
Similar results were also obtained in the combined analysis of definite, possible, and probable coronary heart disease events. Compared with the first (lowest) quarter of fried food consumption, the multivariate hazard ratio of coronary heart disease in the fully adjusted model (model 3) was 1.08 (0.88 to 1.34) for the second quarter, 1.06 (0.84 to 1.33) for the third quarter, and 1.04 (0.81 to 1.34) for the fourth quarter (P for trend 0.83).
Fried food consumption also failed to be associated with all cause mortality. Compared with the lowest quarter of fried food consumption, those in the highest quarter had a hazard ratio of 0.93 (0.77 to 1.14; P for trend 0.98). Moreover, no association was observed between a 100 g increase in intake of fried food and total mortality (1.00, 0.92 to 1.08; table 3, model 3).
Of the total amount of fried food consumed, 24% (34 g/day) was fish, 22% (31 g/day) meat, 21% (30 g/day) potatoes, and 11% (15 g/day) eggs. No association was observed between each of these fried food groups and incident coronary heart disease (table 4⇓).
Comparing the highest and lowest quarters, the multivariate hazard ratio for the fully adjusted model was
1.13 (0.89 to 1.44; P for trend 0.26) for fried fish, 1.09 (0.82 to 1.43; P for trend 0.32) for fried meat, 0.90 (0.70 to 1.15; P for trend 0.45) for fried potatoes, and 0.87 (0.68 to 1.13; P for trend 0.30) for fried eggs. These fried foods also failed to show an association with all cause mortality (table 4).
Our results are directly applicable only to Mediterranean countries with frying methods similar to those in Spain. Firstly, oil (mainly olive and sunflower) rather than solid fat is used for frying in Spain. It is well established that olive oil is less prone to oxidation than other edible oils or fats.40 41 Secondly, consumption of fried foods in Spain is not a proxy for fast food
intake. Fast foods are generally prepared by deep frying with oils used several times, and are consumed mostly away from home. In Spain, fried foods are consumed both at and away from home, and both deep frying and pan frying are used.
Moreover, we can assume that oil is not reused many times for foods consumed at home; however, the cardiovascular effects of food fried with overly reused oils merit further research.
Finally, consumption of fried snacks high in salt is fairly low in Spain, whereas in other countries such as the United States they provide an important percentage of energy intake.42
Contributors: CM-I is coordinator of the European Prospective Investigation of Cancer and Nutrition (EPIC)-HEART-Spain. CAG is coordinator of the EPIC-Spain. CM-I and CAG contributed equally to the study. PG-C and FR-A conceived the study and drafted the manuscript. They are the guarantors. PG-C, FR-A, EL-G and LML-M analysed the data. PA, EA, LA, AB, GB, M-DC, MD, J-MH, NL, PM, CM, EM, CN, JRQ, LR, and MJS provided the original data and information on the respective populations and helped design and analyse the study. AB, MD, CN, JRQ, MJS, and CAG were the principal investigators for EPIC. All authors interpreted the results and contributed to writing the manuscript and take responsibility for the integrity of the data and the accuracy of the data analysis.
Funding: This study was funded by research grants from FIS (PI04-0257, PI06-0366, PI04-2342, PI04-1822, PI04-1821, PI04-2188, and PI08-0166); RETIC (RD06/0020) of the Instituto de Salud Carlos III; and funds from the Spanish regional governments of Andalusia, Asturias, Basque Country, Murcia, and Navarra, and the Catalan Institute of Oncology. EL-G has a Ramón y Cajal contract from the Ministry of Education. Authors of this report, and not the funding agencies, are responsible for its content. The funder did not have any role in the study design; collection, analysis, and interpretation of the data; the writing of the report; and the decision to submit the article for publication.
Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work.
Ethical approval: This study was approved by the ethics committees of the International Agency for Research on Cancer (Lyon, France) and Bellvitge Hospital (Barcelona, Spain).
Data sharing: No additional data available.
REFERENCE LINK : DOI: 10.1093/jn/nxaa272
More information: Fried-food consumption and risk of cardiovascular disease and all-cause mortality: a meta-analysis of observational studies , Heart (2021). DOI: 10.1136/heartjnl-2020-317883