New research in human nutrition evaluated the differential effects of fatty acids on important predictors of cardiovascular health in postmenopausal women.
The first evidence for the role of fatty acids in cardiometabolic health was shown in the early 1950s. Since then, scientists have established the significance of a low saturated fatty acid intake to reduce cardiovascular risk. However, the number of direct human studies is still limited in this area and the independent effect of different fatty acids on various cardiovascular outcomes is yet to be firmly established.
High risk of cardiovascular disease in postmenopausal women
The risk of cardiovascular disease in postmenopausal women is significantly high making it a leading cause of death in women. A decline in the levels of estrogen, among other factors associated with menopause, appears to be a strong reason for an increased cardiovascular disease (CVD) risk in women after menopause. Estrogen receptors are found in the endothelium, myocardium, and coronary arteries. A lack of estrogen impacts circulation through a direct effect on the vessel wall physiology and endothelial dysfunction leading to an imbalance between the molecules produced by the endothelium and causing impaired vasodilation.
Endothelial dysfunction is an early marker of CVD. There are many methods available for assessment of endothelial function. Flow-mediated dilatation (FMD) is the most commonly used method that uses high-resolution ultrasound to measure blood vessel health. Other methods include measuring blood plasma markers such as nitric oxide (NO) which is a vasodilator produced by the vascular endothelium.
The availability of endogenous NO can be measured by estimating plasma nitrite and nitrate. Another method of assessing endothelial dysfunction is a measurement of circulating adhesion molecules such as VCAM-1, ICAM-1, and E-selectin, that play an important role in vascular function and are expressed on the surface of damaged endothelial cells and. Increased levels of these molecules have been linked to a higher risk of cardiovascular disease.
Dietary improvements greatly reduce the prevalence of cardiovascular disease
The prevalence of CVD is greatly reduced by dietary improvements. It is well known that saturated fatty acids (SFA) increase the levels of low-density lipoprotein (LDL) cholesterol which is a strong risk factor for CVD. Past studies have shown that reducing saturated fatty acid intake to less than 7% of total energy intake and substituting it with monounsaturated fatty acids (MUFA) and omega-3 and omega-6 polyunsaturated fatty acids (n-3, n-6 PUFA) is beneficial in reducing the risk of CVD. However, not many studies have evaluated the differential impact of fatty acids on CVD risk markers.
Investigating the roles of different fatty acids
For an effective nutritional approach to reduce CVD risk, it is important to understand the differential effects of fatty acids on vascular health. A recent study published in the Journal of Nutrition determined the effects of sequential meals rich in MUFAs and n-6 PUFAs on post-meal measures of vascular function and other CVD risk biomarkers compared with SFA-rich meals in postmenopausal women. The acute randomized, double-blinded, crossover study conducted at the University of Reading, UK, recruited 36 nonsmoking postmenopausal women aged 65 years or younger.
The researchers used a sequential meal protocol that resembled the habitual dietary pattern of the participants. The test meal was composed of breakfast containing 50 g of total fat, of which 33-36 g were SFAs, MUFAs, or n-6 PUFAs and lunch containing 30 g total fat, of which 19-20 g were SFAs, MUFAs, or n-6 PUFAs, respectively. After the screening and familiarization visits, the participants were assessed at three post-meal visits. The researchers measured several biomarkers of cardiovascular health including flow-mediated dilatation, systolic and diastolic blood pressure, and several other molecular markers for inflammation and health.
Varying types of fatty acids affect the risk of cardiovascular disease differently
The consumption of different test fats did not initiate a significantly different flow-mediated dilatation response in the participants. The results did show a significant impact of MUFA consumption on the reduction of postprandial diastolic blood pressure compared with the saturated fats-rich meal. In addition, plasma nitrite response was significantly impacted by the test fat, with a greater reduction seen after the consumption of saturated fats-rich meals compared with MUFA-rich meals. Furthermore, the researchers observed a beneficial effect of n-6 PUFA-rich meals on markers of endothelial activation compared with after MUFA- and SFA-rich meals. Postprandial lipid, glucose, and insulin response did not vary significantly in association with the fatty acid composition of meals.
The results of this study suggest how different types of fatty acids affect cardiovascular disease risk in postmenopausal women. Although the results showed no effect of meal fatty acid composition on vascular reactivity or flow-mediated dilatation, the researchers found beneficial effects of MUFA and PUFA-rich meals on blood pressure, plasma nitrite response, and circulating adhesion molecules.
The main strength of this study is the use of a meal protocol that closely resembled the habitual dietary pattern of the participants. The main limitation is the inclusion of only postmenopausal women in the study which means that the results may not reflect the general population.
Study findings support meals rich in monounsaturated fatty acids for lowering blood pressure
This study provides evidence to support the favourable effects of MUFA-rich meals on lowering post-meal diastolic blood pressure and maintaining a higher plasma nitrite response compared with saturated fats-rich meals thus suggesting a positive effect of MUFA on endothelial function. In addition, compared to SFA-rich meals, n-6 PUFA-rich meals reduced the postprandial levels of cell adhesion molecule sICAM-1 that is a marker of endothelial abnormalities.
Future studies should examine the effects of replacing saturated fatty acids
Overall, the findings reinforce the association between unsaturated fatty acid intake and cardiovascular health. However, the study was not able to show an advantageous effect of unsaturated fatty acids with respect to flow-mediated dilatation. The authors suggest that future studies may benefit from using these findings to further examine the effects of replacing saturated fatty acids on cardiovascular disease risk in postmenopausal women.
Written by Preeti Paul, MS Biochemistry
Reference: Kumari M Rathnayake et al. Meal Fatty Acids Have Differential Effects on Postprandial Blood Pressure and Biomarkers of Endothelial Function but Not Vascular Reactivity in Postmenopausal Women in the randomized Controlled Dietary Intervention and VAScular function (DIVAS)-2 Study. The Journal of Nutrition, Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions. March, 2018; doi: https://doi.org/10.1093/jn/nxx042
