European Journal of Clinical Nutrition (2001) 55, 88±96 ß 2001 Nature Publishing Group All rights reserved 0954±3007/01 $15.00 www.nature.com/ejcn A stearic acid-rich diet improves thrombogenic and atherogenic risk factor pro®les in healthy males FD Kelly1, AJ Sinclair1*, NJ Mann1, AH Turner2, L Abedin1 and D Li1 1Department of Food Science, RMIT University, Melbourne, Australia; and 2Medical Laboratory Science, RMIT University, Melbourne, Australia Objective: To determine whether healthy males who consumed increased amounts of dietary stearic acid compared with increased dietary palmitic acid exhibited any changes in their platelet aggregability, platelet fatty acid pro®les, platelet morphology, or haemostatic factors. Design: A randomized cross-over dietary intervention. Subjects and interventions: Thirteen free-living healthy males consumed two experimental diets for 4 weeks with a 7 week washout between the two dietary periods. The diets consisted of 30% of energy as fat (66% of which was the treatment fat) providing 6.6% of energy as stearic acid (diet S) or 7.8% of energy as palmitic acid (diet P). On days 0 and 28 of each dietary period, blood samples were collected and anthropometric and physiological measurements were recorded. Results: Stearic acid was increased signi®cantly in platelet phospholipids on diet S (by 22%), while on diet P palmitic acid levels in platelet phospholipids also increased signi®cantly (8%). Mean platelet volume, coagulation factor FVII activity and plasma lipid concentrations were signi®cantly decreased on diet S, while platelet aggregation was signi®cantly increased on diet P. Conclusion: Results from this study indicate that stearic acid (19 g=day) in the diet has bene®cial effects on thrombogenic and atherogenic risk factors in males. The food industry might wish to consider the enrichment of foods with stearic acid in place of palmitic acid and trans fatty acids. Sponsorship: Grant from Meat Research Corporation, Australia and margarines donated by Meadow Lea Foods Ltd, Australia. Descriptors: stearic acid; palmitic acid; platelets; fatty acids; haemostatic factors; lipoproteins; platelet aggrega- tion; mean platelet volume European Journal of Clinical Nutrition (2001) 55, 88±96 Introduction (Hegsted et al, 1965; Keys et al, 1965). This was attributed to the stearic acid in the cocoa butter. Since then, various The relationship between dietary fatty acids and blood predictive equations incorporating individual saturated fatty cholesterol levels was reported in the late 1950s when acid contributions to plasma cholesterol changes show Keys et al (1957) found that saturated fatty acids (SFA) stearic acid as neutral (Kris-Etherton & Mustad, 1994). from 12 to 18 carbon atoms were potent cholesterol-raising The risk of coronary events however is not solely agents. Subsequently, it was found that the predictive dependent on plasma cholesterol levels. Carefully con- equations for dietary fatty acids on plasma cholesterol ducted autopsy studies have demonstrated that thrombotic levels were inadequate when cocoa butter was used obstruction of the coronary artery is involved in most cases of sudden cardiac death (Davies & Thomas, 1984). Arterial *Correspondence: AJ Sinclair, Department of Food Science, RMIT thrombosis involves clot formation based around existing University, GPO Box 2476V, Melbourne, Victoria 3001, Australia. plaque and arterial lesions with the ®rst step involving E-mail: [email protected] Guarantor: AJ Sinclair. platelet aggregation, followed by ®brin formation through Contributors: FDK, AJS, NJM and AHT initiated the study. FDK prepared activation of the coagulation pathways. Any factor leading the drafts of the paper, did dietary analysis, collected data, helped in to increased platelet activity or up-regulation of the coagu- laboratory assays and did the statistical analysis. AJS selected the study site, lation cascade will thus increase the risk of thrombotic supervised the project and secured the funding. LA and DL helped in events. laboratory assays. All authors contributed to the drafts of the paper. Received 13 June 2000; revised 6 October 2000; Early studies suggested that stearic acid was prothrom- accepted 9 October 2000 botic based on three levels of evidence. Firstly, Connor Stearic acid-rich diet FD Kelly et al 89 (1962) reported that stearic acid was particularly effective at Subjects were counselled prior to commencement of the shortening thrombus formation time during in vitro studies ®rst intervention period on which foods were to be excluded using citrated blood and sodium salts of fatty acids. Sec- from the diet (included in a detailed information booklet). ondly, Renaud and Gautherton (1975) reported that diets Advice was provided on suitable low-fat alternatives to rich in stearic acid were associated with increased coagula- substitute for foods normally eaten, such as regular fat tion in New Zealand rabbits. This change was speculated to dairy products, pastries and cakes etc. Subjects were given result from an enhanced activity of platelet factor 3 (PF3) training in recording their food intakes and completed a 7 due to an increase in stearic acid in the platelet phospholi- day weighed food record of their habitual diet prior to the pids. Thirdly, Renaud et al (1978) found that saturated fat study. Seven day weighed food records were also obtained and especially stearic acid were signi®cantly correlated with during each intervention period and washout phase. Dietary clotting activity and platelet aggregation in several popula- composition was determined using Diet 1 (Version 4, tion comparisons in man. These data alerted researchers to NUTTAB 95, Xyris Software Pty Ltd, Queensland, Austra- potentially negative effects of stearic acid on thrombotic lia) based on Composition of Foods, Australia (National factors and resulted in several short-term studies being Food Authority, 1995). The database was modi®ed by the conducted in humans (Tholstrup et al, 1994, 1996; Schoene inclusion of fatty acid data, for a wider variety of foods, for et al, 1992; Mutanen & Aro, 1997; Dougherty et al, 1995). C12:0 to C18:0 (lauric, myristic, palmitic and stearic acids), However, few of these have examined more than one palmitoleic acid (C16:ln-7) and oleic acid (C18:ln-9), lino- measure of thrombosis tendency. Because there are often leic acid (18:2n-6) and alpha linolenic acid (18:3n-3) interactions involving more than one component of the obtained from Dr M James, University of Adelaide. haemostatic system, there is no single screening test During the two intervention stages, the percentage which can be used to identify a thrombotic tendency. energy derived from fat, carbohydrate and protein was Therefore a range of screening tests should be adopted to kept constant for each individual, based on habitual food detect markers known to be associated with cardiovascular records. The high stearic and high palmitic acid test fats risk (Giddings & Yamamoto, 1995). were supplied by Meadow Lea Foods (Sydney, Australia). The aim of this study was to compare the thrombosis Test fats were supplied to subjects in the form of baking and potential of diets rich in stearic acid with palmitic acid-rich spreading margarines and incorporated into biscuits, cakes diets by measuring platelet aggregation, platelet volume and and muf®ns given as snacks and in salad rolls supplied for other key components of the haemostatic pathways. weekday lunches. Breakfasts, dinners and weekend lunches were left to the subjects' discretion following dietary modi®cation advice. The remaining fat intake was obtained Methods from commercially available foods low in fat. Subjects Test fats Thirteen free-living healthy males were recruited following The stearic acid-enriched baking margarine was produced advertisement of the study throughout RMIT University. by an interesteri®ed blend of 35% hardened canola (100% Subjects were aged 35 Æ 12 y (mean Æ s.d.), of normal body hydrogenated) and 65% Sunola1 (a high oleic acid variety weight (body mass index (BMI) 26.0 Æ 3.3 kg=m2. Sub- of sun¯ower seed oil), and the stearic acid-enriched spread- jects had no known metabolic, endocrine or haematological ing margarine was a blend of 30% hardened canola and 70% diseases, were non-smokers, not on any form of medication Sunola1. The palmitic acid-enriched baking margarine was and had a moderate activity level. Subjects were advised not produced by interesterifying a blend of 55% palm stearin, to take any form of non-steroidal anti-in¯ammatory drugs 20% palm olein and 25% Sunola1. The palmitic acid- 14 days prior to commencement and during the study. enriched spreading margarine was produced as a mixture Subjects were counselled to maintain their usual intake of of interesteri®ed palm stearine (50%) and Sunola1 (50%). alcohol and to abstain from consuming alcohol 24 h prior to Both stearic acid and palmitic acid levels in their respective blood sampling. All subjects were required to give written margarines were maximized within the limits of physical consent to participate and were free to withdraw at any time. property characteristics conducive to normal use. The oleic The study protocol was approved by the Human Research acid content in the stearic acid-rich fats and biscuits was Ethics Committee of RMIT University (approval number higher than for the palmitic acid-rich fats and biscuits in 17=96). order for stearic acid products to be spreadable at room temperature. The fatty acid pro®le of the margarines used is Experimental design shown in Table 1. The dietary intervention consisted of subjects consuming both a high stearic (diet S) and a high palmitic acid diet (diet Physiological measurements P) for 4 weeks in a random crossover design, with a 7 week Subjects had their weight, height and body mass index wash-out (habitual diet) period between the two phases. (BMI, kg=m2) determined, and percentage body fat mea- Subjects consumed the equivalent of approximately two- sured using a bioimpedence fat analyser=scale (TBF-501 thirds of their habitual fat intake, as the test fats, during the Tanita Corporation, Illinois, USA).