Recently as part of a nutritional science module I was given several options of essay subjects, and one of them really jumped out at me.
A diet high in SF reduces esterification of cholesterol and leads to higher concentrations of non-esterified cholesterol. In response to this, hepatic concentration of LDL receptor mRNA is reduced, consequently LDL receptor activity is reduced leading to raised plasma LDL. In the development of CVD LDL particles are oxidized within the arterial matrix. Oxidised LDL leaks into, and accumulates in the sub endothelial space. Macrophages preferentially take up the oxidised LDL forming foam cells. Foam cells deposit accumulated oxidised lipids between the endothelium and the arterial smooth muscle, causing stenosis. This can lead to both ischemic heart disease and cerebrovascular accident. Imagine LDL particles as drunk drivers there is a greater risk these guys are going to crash into the side of the arteries and cause a massive tail back. HDL essentially acts as the police or the AA cleaning up after these inconsiderate atherogenic little buggers.
When evaluating the recommendations to lower SF intake, it is important to consider the nutrients that replace them. Current guidelines are to replace SF with MUFA and PUFA.
To investigate the implications of these dietary changes, eleven cohorts were pooled encompassing 344,696 participants with follow ups varying between four and 10 years. Five percent total energy from SF was replaced by PUFA, MUFA or carbohydrate. PUFA was associated with significant reductions in cardiac death and coronary events, RR 0.74 and 0.87 respectively. Replacement with carbohydrate was associated with a significant increase in coronary events and a non-significant reduction in coronary deaths RR 1.07 and 0.96 respectively. MUFA replacement was no associated with any change in CVD.
Is it Important to Differentiate between Saturated Fatty Acid Types and Sources?
Foods Containing High Levels of each Saturated Fat subtype
Lauric Acid - Pal kernel oil, coconut oil, coconut flesh and butter.
Myristic Acid - Coconut oil, palm kernel oil, coconut flesh, unsalted butter and cream
Palmitic Acid - Palm kernel oil, shortening unsalted butter, lard and beef tallow.
Stearic Acid - Beef tallow, lard, pork fat, chocolate
More food based studies would translate effectively to public health and the general public. These would also fully encompass the whole nutrient profile of a food group. This method could be used to assess the effect of MUFA from vegetable and fruit sources, as seen in the Mediterranean diet, on CVD. If the evidence base does become strong enough to warrant a change in guidelines, the French guidelines would still require reduction in average SF intakes (12.6% to 12%) and would also draw attention to foods high in the more hypercholesterolemic SF. Food based recommendations would convey a more simplistic message that is more likely to be adopted by the public.
Many other factors need to be considered when evaluating the evidence on a single nutrients contribution to CVD risk. CVD is a multifactorial condition with many contributing factors. Furthermore better treatments and changes in associated risk factors will have also played a role in CVD trends. CVD is a leading cause of premature mortality and morbidity in the UK, so diet advice should aim to reduce this burden however, other prominent issues must be considered in these guidelines e.g osteoporosis, obesity and diabetes.
MOZAFFARIAN, D., MICHA, R. AND WALLACE, S., 2010. Effects on Coronary Heart Disease of Increasing Polyunsaturated Fat in Place of Saturated Fat: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. PLoS Med. March, vol. 7, no. 3, p.e1000252.