Effects of Dietary Fats on Blood Cholesterol and Other Measures Related to Chd Risk in Male and Female Laboratory Mice

Juvenile and adult male and female Swiss mice were fed one of four specially-formulated, pelleted diets containing respectively 8 percent saturated vegetable fat, 8 percent soya oil, 8 percent olive oil and 2 percent soya oil (with identities hidden from the experimenter) or a local commercial rodent food. It was intended to assess their impact on some blood indices linked to risk of coronary heart disease (CHD). Subjects were individually housed and their blood concentrations of cholesterol, high-density lipoprotein cholesterol (HDLC) and triglycerides were assessed. Clearly, these non-isocaloric diets differed in palatability, producing complex effects on growth as well as physiological measures. Many indices were influenced by age, sex, and the duration of dietary exposure. Interactions between factors were common but it appeared that males showed the greater increase in risk factors in response to some diets. Introduction Dietary fatty acids can be classified as saturated, monounsaturated, and (n-3) polyunsaturated and (n-6) polyunsaturated compounds. Grundy and Denke (1990), suggested that the different classes of fatty acids have varied effects on lipid metabolism and the fatty acid portion of the lipid molecule is responsible for its characteristics. Fatty acids occurring in food stuffs e.g. lauric or dodecanoic acid contain even numbers of carbon atoms in unbranched chains. Unsaturated fatty acids have one, two or sometimes up to six double bonds. A fatty acid with one double bond is referred to as a monounsaturated fatty acid (e.g., olive oil), whereas a fatty acid containing two or more double bonds is considered a polyunsaturated fatty acid (e.g., soybean oil). N-3 and n-6 fatty acids are widespread in food sources. They are considered essential fatty acids (EFAs) because they must be supplied in the diet (the body cannot synthesize them in significant amounts) to humans (Bjerve, 1989) as well as rodents (Burr and Burr, 1929). Cholesterol is an important component of all animal tissues and plays essential roles in the body. However, high levels of cholesterol in the blood are associated in many countries with an increased risk of CHD (Benton, 1996). Conversely, Muldoon et al. (1990, 1992, 1993), shown that cholesterol reduction is associated with a lower mortality rate from CHD but with a higher mortality rate from other causes (including suicide and violence). This applied whether the lipid lowering was achieved by dietary regulation or pharmacological treatment. It suggests that lowered cholesterol values may be associated with behavioural changes that predispose the individual towards risk-taking. Engelberg (1992) has suggested that the increased rate of suicide and other violent death observed in cholesterol-lowering trials may be explained by alteration in mood or behaviour arising from a reduced expression of serotonin receptors on cell membranes. This whole area is still contentious (several authors challenge the view that a low cholesterol-high risk association exists). The area is substantially reviewed by LaRosa (1997) and the current evidence seems to substantially favour the view that low cholesterol carries a risk. The type of dietary fat is a crucial determinant of plasma cholesterol concentration. Pioneering studies clearly pointed out the importance of fatty acids. More recent information (Bonanome and Grundy, 1988; Grundy, 1986; Hayes et al., 1991; Khosla and Hayes, 1991) suggests, however, that saturated fatty acids cannot be regarded as a single factor. In deed, the various saturated fatty acids have variable influences on plasma cholesterol concentrations. Kris-Etherton et al. (1993) found that linoleic acid (a component of soya oil diet) has a more potent hypocholesterolemic effect than oleic acid (a component of olive oil). Bourre et al. (1993) showed that soya oil contains n-3 fatty acids and it was suggested that these substances reduce the plasma cholesterol level in rats by increasing the transfer of cholesterol into bile. Bonanome and Grundy (1988), Hegsted et al. (1965), Keys et al. (1965) and Thomasson et al. (1967) essentially concluded that 16:0 fatty acids elevate total cholesterol and low-density lipoprotein cholesterol in men and women who are hospitalized or otherwise institutionalized. This may lead one to conclude that diets with a low percentage of polyunsaturated fatty acids decrease the level of blood cholesterol. Grundy (1987) showed that olive oil diet lowered the risk of heart disease by suppressing blood cholesterol level. More recently, workers have stressed the importance of fish oils in controlling cholesterol values (largely stemming from the observation that humans with a diet rich in fish have a low incidence of CHD). For example, Yaquoob et al. (1995) showed that serum cholesterol concentrations in rats were higher after ten weeks of feeding 20 percent by weight of olive oil, safflower oil, or Evening primrose oil diets than in counterparts given a 20 percent Menhaden (fish) oil or a low fat diet. The present study analyzed whether diets differing in their type and/or amount of fat produced systematic changes in a range of blood incidences linked to clinical CHD risk in a mouse model. The effects of different durations of exposure were assessed in mice of different sex. Materials and Methods Animal Husbandry: Swiss albino mice, bred and housed in the Animal Facility of the King Fahad Research Medical Centre (Jeddah, Kingdom of Saudi Arabia) were used in this study. The subjects were kept with white lights on from