Replacing dairy fat with rapeseed (canola) oil improves hyperlipidaemia - editorial

In this issue of the Journal, Risérus and colleagues report on their clinical trial, investigating the effect of replacing dairy fat with rapeseed (canola) oil on blood lipids, glucose metabolism and coagulation factors in hyperlipidaemic subjects [1]. In this randomized crossover study, the 3- week intervention with rapeseed oil produced rapid and clinically significant reductions in low-density lipoprotein (LDL) cholesterol (−17%), triglycerides (−20%) and the LDL : HDL cholesterol ratio (−21%), whilst the dairy fat diet did not significantly alter serum lipids. No significant differences in coagulation factors or insulin sensitivity were found between groups. However, the relative short-term intervention of 3 weeks may not have been long enough to observe a difference in glucose metabolism. While the subject numbers were relatively small (n = 20), the study design was very strong, and the intervention diets and compliance tightly controlled. All foods were provided to study participant during the intervention, and the rapeseed oil and dairy fat diets were balanced for macronutrients and energy, dietary fibre and cholesterol and differed only in their fatty acid composition. Subjects were asked to weigh and record all food and drink consumed for seven consecutive days prior to starting the clinical phase of the study to assess habitual diet. To further assess compliance, fatty acid composition of plasma cholesterol esters and phospholipids was measured. Additionally, the fatty acid composition of the test diets was analysed by nuclear magnetic resonance imaging. Such tight controls are essential for establishing the efficacy of dietary approaches for health. The study is significant for several reasons. The data highlight the importance of fat quality and the cholesterol raising effect of saturated fatty acids and demonstrate how effectively and quickly diet may be utilized in improving the blood lipid profile. Early dietary guidelines advocated reduced fat intakes to <30% of energy for Step 1 diets and <27% of energy for Step 2 diets (NCEP) [2]. More recently, dietary guidelines have relaxed the contribution of fat to total energy intake to ∼35% of calories [3]. Although the recommendation for saturated fat remains low <7% per cent of energy (E%), the level of monounsaturated has been increased from <10% to up to 20 E%. This increase in allowable level of energy from monounsaturated fat relates to positive heart health findings from studies of the Mediterranean diet, in which monounsaturated fats in the form of olive oil and nuts are key components [4–6]. While a number of studies have assessed the effect of monounsaturated fat in the form of olive oil or nuts on blood lipids, relatively few studies have assessed the effect of rapeseed oil [7]. Rapeseed oil is high in the monounsaturated fatty acid, oleic acid (18 : 1), the polyunsaturated fatty acid, linoleic acid (18 : 2), and the omega-3 fatty acid, alpha-linolenic acid (18 : 3), which constitute approximately 56%, 19% and 11%, respectively, of rapeseed oil’s composition [1]. In the current study, the habitual diet compared with the rapeseed oil diet was virtually identical in terms of total fat, 34.5 vs. 36.1 per cent of energy (E%), respectively. However, the quality of fat was much different. The rapeseed oil diet compared with the habitual diet lowered the saturated fat intake from 14.2 to 7.8 (E%) and raised the intakes of monounsaturated fat from 12.5 to 16.2 (E%), polyunsaturated fat from 5.3 to 8.7 (E%) and alpha-linolenic acid from 0.6 to 2.2 (E%). This relatively simple improvement in dietary fat quality resulted in a significant decrease in LDL cholesterol, which using the Framingham risk score for 10-year coronary heart disease risk translated into a 22% relative risk reduction in men and 13% risk reduction in women [1]. Over the past several decades, the age-specific mortality rate of cardiovascular disease has decreased by half in Western countries [8]. Whilst many factors including improvement in drug therapies and other treatments have contributed, the improvement in fat quality, the replacement of saturated fats with polyunsaturated fats and specifically the omega-3 fatty acid, alpha-linolenic acid, has correlated with the declining rates of coronary heart disease [9]. The Mediterranean diet, which is characterized by the use of healthy plant-based fats, high in monounsaturated and omega-3 fats, has been associated with reduced rates of coronary heart disease [4, 6]. The Lyon Heart Study demonstrated that a Mediterranean diet, which utilized a rapeseed oil margarine to produce a diet low in saturated fat and high in monounsaturated fat and alpha-linolenic acid, significantly reduced fatal and nonfatal cardiovascular events compared with a western diet high in saturated fat [5]. There has recently been some controversy regarding the utility of reducing intakes of saturated fats for the prevention of cardiovascular disease and that replacing saturated fat with carbohydrates may produce no benefit [10]. However, there is strong evidence that saturated fats from full-fat dairy and fatty red meats should be replaced by plant-based fats (high in polyunsaturated, monounsaturated and omega-3 fats) or low-glycaemic-index carbohydrates [11]. While dietary intervention is the first line of defence in decreasing coronary heart disease risk, it is by and large considered ineffective as the expected effect will only be modest, and individuals will not be able to adhere to the lifestyle change over a longer period of time. The study by Risérus and colleagues [1] demonstrated that large and clinically meaningful reductions in LDL cholesterol could be achieved simply by adding rapeseed oil to the diet and improving the fatty acid profile. The diets were well tolerated as evidenced by the lack of dropouts, and the improvement in blood lipids was achieved after only 3 weeks of intervention. We have observed statin-like reductions in LDL cholesterol by utilizing a low-saturated fat and dietary cholesterol diet and combining with it a portfolio of cholesterol-lowering foods or food components including vegetable proteins, viscous fibres, nuts and plant sterols [12]. In our efficacy studies, in which all foods were provided, we have observed LDL cholesterol reductions of 25–35% after 2 weeks, which were maintained over the 4-week interventions [13]. In our real-world effectiveness studies, in which subjects were only provided with dietary advice and had to purchase their own foods, the effects were less dramatic (13%). Nevertheless, those individuals that were most compliant were able to lower their LDL cholesterol levels by more than 20% for up to 1 year [14]. These studies demonstrate that there is a place for diet in cardiovascular risk reduction and that clinically meaningful and rapid changes in serum lipids can be achieved if proper dietary advice and guidance are provided. CWCK has received funding support from Loblaws, Unilever, Barilla, the Almond Board of California, the Western Pistachio Association, the International Tree Nut Council Research and Education Foundation, Pulse Canada, the Saskatchewan Pulse Growers and the Canola Council of Canada.

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