Modest Consumption of Poly-Unsaturated Fatty Acid (PUFA)
- A high intake of fat (more than 35% of the calories) generally increases the intake of saturated fat and is associated with consumption of excess calories and weight gain. Conversely a low intake of fat (less than 20% of the calories) increases the risk of inadequate intakes of essential fatty acids and vitamin E and unfavorable changes in HDL and triglyceride levels.1 Therefore, adequate intake of fat must come from polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids(MUFA).
- Linoleic acid (LA) and alpha linolenic acid (ALA) belong to the n-6 (omega-6) and n-3 (omega-3) series of PUFA, respectively. They are defined “essential” fatty acids since they are not synthesized in the human body and are mostly obtained from the diet. Food sources of ALA and LA are nuts (especially walnuts), seeds, cereals, and most vegetable oils (sunflower, corn oil, soya bean oil, safflower, sesame seed-oils).2
- As a general guide, the American Heart Association recommends up to 10% omega 6 PUFAs and up to 1.2% omega 3 PUFA.3 Therefore, it is important to know the baseline consumption of PUFA before making a recommendation to increase or decrease its consumption. Current intake of PUFA is 5-6% energy in the US, but remains unknown in India.
- A large body of evidence including the recent Science Advisory for the American Heart Association, support the health benefits of LA (the principle omega 6 fatty acid) in cardiovascular disease (CVD) prevention.3 Epidemiologically, substituting 10% of calories from saturated fat with omega 6 fats was associated with an 18mg/dL decrease in LDL cholesterol. 3
- A diet high in polyunsaturated fat including consumption of 1 pint of soybean oil a week has been shown to decrease cholesterol by 22% and reduce heart attacks by 44% (See Figure 076).4, 5
- A meta-analysis of randomized clinical trials (RCTs) which substituted saturated fats for omega 6 oils found a 24% decreased risk of CAD.3 While the Nurses Health Study found women with the highest intakes of omega 6 fats (7% of energy) had a 25% reduced risk of CAD compared to those in the lowest intakes (3% energy).3
- Polyunsaturated to saturated fatty acid ratio (P/S ratio) has been shown to be inversely related to LDL cholesterol in several studies. Most expert bodies recommend a P/S ratio less than one. 6
- In short, replacing 10% calories from saturated fat with omega 6, is associated with an 18 mg/dL decrease in LDL cholesterol and 25 % reduced risk of CAD. The argument that PUFAs are unhealthy is no longer justifiable.
Sources
1. WHO. Prevention of cardiovacular disease. World Health Organization, Genewa Switzerland2007.
2. Russo GL. Dietary n-6 and n-3 polyunsaturated fatty acids: from biochemistry to clinical implications in cardiovascular prevention. Biochem Pharmacol. Mar 15 2009;77(6):937-946.
3. Harris WS, Mozaffarian D, Rimm E, et al. Omega-6 fatty acids and risk for cardiovascular disease: a science advisory from the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation. Feb 17 2009;119(6):902-907.
4. Leren P. The Oslo diet-heart study. Eleven-year report. Circulation. Nov 1970;42(5):935-942.
5. Clarke R, Frost C, Collins R, Appleby P, Peto R. Dietary lipids and blood cholesterol: quantitative meta-analysis of metabolic ward studies. BMJ. Jan 11 1997;314(7074):112-117.
6. Guo Z, Miura K, Turin TC, et al. Relationship of the polyunsaturated to saturated fatty acid ratio to cardiovascular risk factors and metabolic syndrome in Japanese: the INTERLIPID study. J Atheroscler Thromb. Aug 31 2010;17(8):777-784.