The US Food and Drug Administration publishes guidelines every five years that promote dietary lifestyle measures which can reduce the risk of disease. Consumption of about one to two tablespoons per day of oils, containing differing percentages of various fats, is mentioned as an important component of a healthy diet in the 2020 – 2025 Dietary Guidelines for Americans.1 To date, no randomized controlled trial has found significant difference in all-cause mortality or coronary heart disease mortality by reducing total dietary fat.2 However there is evidence that specific types of fat may have differing effects on disease risk. Generally, people with a diet high in saturated fats have a higher risk of heart disease than those who only consume unsaturated fats.3
Monounsaturated fat (MUFA), and olive oil in particular, was associated with a reduced cardiovascular risk in a meta-analysis of cohort studies conducted in 2014.4 The Mediterranean diet, which includes olive oil as its primary source of cooking oil, has been shown to reduce heart disease risk.5 This observation has prompted further study of the effects of olive oil on health. Estruch et al. conducted a partially randomized trial of 7,477 people over 55 years of age without cardiovascular disease at baseline for a median follow-up period of 4.8 years.6 The hazard ratio for developing a major cardiovascular event among those who consumed a Mediterranean diet supplemented with extra virgin olive oil was 0.69 (95% confidence interval [0.53 – 0.91]) compared with the control (advice to control dietary fat).
Consumption of polyunsaturated fat (PUFA) has also been linked to a reduction in the risk of coronary heart disease.7 One subtype type of PUFA called n-3 (or omega 3) fatty acid is found in oily fish and fish oil as well as walnut and flaxseed oils. This subtype of PUFA has been associated with small but statistically significant improvements in blood pressure and decreases in heart rate and arrhythmia.8 Another subtype called n-6 fatty acid found in soybean, safflower, sunflower, and corn oil lowers low-density lipoprotein cholesterol and triglycerides while increasing high-density lipoprotein cholesterol.9 Observational cohort studies have noted beneficial effects on coronary heart disease risks in individuals consuming n-6 fatty acids instead of saturated fats.7
Trans fatty acids have been found to cause cardiovascular harm, and, as a result, have been banned from use in the US since 2019.10
The relationship between fat intake and cancer is less well studied than that of heart disease. Case-control and epidemiologic studies have suggested a relationship between fat intake and the development of breast 11,12 and colon13 cancers, but these types of studies do not prove causation, and cannot offer definitive guidance on dietary recommendations. The Women’s Health Initiative randomized control trial followed 48,835 post-menopausal women for over eight years and found that reduced total dietary fat did not significantly affect the risk of colorectal 14 or breast cancer.15 To date, there is no strong evidence that total dietary fat influences cancer risk.16
References
- Dietary Guidelines for Americans, 2020-2025. 9 ed: U.S. Department of Health and Human Services and U.S. Department of Agriculture; December 2020.
- Harcombe Z, Baker JS, DiNicolantonio JJ, Grace F, Davies B. Evidence from randomised controlled trials does not support current dietary fat guidelines: a systematic review and meta-analysis. Open Heart. 2016;3(2):e000409.
- Hooper L, Martin N, Abdelhamid A, Davey Smith G. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev. 2015;(6):CD011737.
- Schwingshackl L, Hoffmann G. Monounsaturated fatty acids, olive oil and health status: a systematic review and meta-analysis of cohort studies. Lipids Health Dis. 2014;13:154. doi:10.1186/1476-511X-13-154
- The diet and all-causes death rate in the Seven Countries Study. Lancet. 1981;2(8237):58-61.
- Estruch R, Ros E, Salas-Salvadó J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet supplemented with extra-virgin olive oil or nuts. N Engl J Med. 2018;378(25):e34.
- Farvid MS, Ding M, Pan A, et al. Dietary linoleic acid and risk of coronary heart disease: a systematic review and meta-analysis of prospective cohort studies. Circulation. 2014;130(18):1568-1578.
- Mozaffarian D, Wu JHY. Omega-3 fatty acids and cardiovascular disease: effects on risk factors, molecular pathways, and clinical events. J Am Coll Cardiol. 2011;58(20):2047-2067.
- Mensink RP, Katan MB. Effect of dietary fatty acids on serum lipids and lipoproteins. A meta-analysis of 27 trials. Arterioscler Thromb. 1992;12(8):911-919.
- Food and Drug Administration. Final Determination Regarding Partially Hydrogenated Oils (Removing Trans Fat). Accessed January 4, 2020. https://www.fda.gov/food/food-additives-petitions/final-determination-regarding-partially-hydrogenated-oils-removing-trans-fat.
- Wang J, John EM, Horn-Ross PL, Ingles SA. Dietary fat, cooking fat, and breast cancer risk in a multiethnic population. Nutr Cancer. 2008;60(4):492-504.
- Howe GR, Hirohata T, Hislop TG, et al. Dietary factors and risk of breast cancer: combined analysis of 12 case-control studies. J Natl Cancer Inst. 1990;82(7):561-569.
- Potter JD. Nutrition and colorectal cancer. Cancer Causes Control. 1996;7(1):127-146.
- Beresford SAA, Johnson KC, Ritenbaugh C, et al. Low-fat dietary pattern and risk of colorectal cancer: the Women’s Health Initiative randomized controlled dietary modification trial. JAMA. 2006;295(6):643-654.
- Prentice RL, Caan B, Chlebowski RT, et al. Low-fat dietary pattern and risk of invasive breast cancer: the Women’s Health Initiative randomized controlled dietary modification trial. JAMA. 2006;295(6):629-642.
- World Cancer Research Fund International. About the Continuous Update Project. . Accessed January 5, 2020. https://www.wcrf.org/int/continuous-update-project.
