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Grain-based Chow Diets
In the past, Western-type diets have been made by adding high levels of fat and cholesterol to grain-based chow diets. The addition of ingredients to chows can dilute other nutrients (i.e. vitamins, minerals, protein, etc) and non-nutrients (i.e. phytoestrogens), so their use in research has been criticized (1).
Purified Diets
In order to avoid this issue, purified ingredient diet formulas which are open to the public (i.e. AIN-76A) can be easily revised to intentionally alter the phenotype by adding in fat calories (i.e. dairy butter, hydrogenated coconut oil) in place of purified carbohydrate calories only (i.e. sucrose, corn starch). This method of modification maintains nutrient to calorie ratios, which is important as animals typically eat for calories, not weight of food. Furthermore, casein-based purified diets contain no phytoestrogens (or other phytochemicals) unlike typical grain-based chows which can have highly variable levels (2). Since the presence of phytoestrogen containing sources (i.e. soy protein and isolated isoflavones) has been found to influence atherosclerosis and lipoprotein metabolism in various rodent models (3-9), the use of purified Western-type diets provides a clean ‘reagent’ for inducing this disease. That being said, not all rodent models respond the same to a given Western-type purified diet due to genetic differences.
1. Cybulsky,MI, Lichtman,AH, Haijra,L, Iiyama,K. Leukocyte adhesion molecules in atherogenesis: Clinica Chimica Acta 286:207-218, 1999
2. Thigpen,JE, Setchell,KD, Ahlmark,KB, Locklear,J, Spahr,T, Caviness,GF, Goelz,MF, Haseman,JK, Newbold,RR, Forsythe,DB: Phytoestrogen content of purified, open- and closed-formula laboratory animal diets. Lab Anim Sci. 49:530-536, 1999
3. Brown,NM, Setchell,KD: Animal models impacted by phytoestrogens in commercial chow: implications for pathways influenced by hormones. Lab Invest 81:735-747, 2001
4. Mezei,O, Banz,WJ, Steger,RW, Peluso,MR, Winters,TA, Shay,N: Soy isoflavones exert antidiabetic and hypolipidemic effects through the PPAR pathways in obese Zucker rats and murine RAW 264.7 cells. J Nutr. 133:1238-1243, 2003
5. Kirk E, Sutherland P, Wang S, Chait A, LeBoeuf R: Dietary isoflavones reduce plasma cholesterol and atherosclerosis in C57BL/6 mice but not LDL receptor-deficient mice. J Nutr 128:954-959, 1998
6.Torvar-Palacio C, Potter SM, Hafermann JC, Shay NF: Intake of soy protein and soy protein extracts influences lipid metabolism and hepatic gene expression in gerbils. J Nutr 128:839-42, 1998
7.Blair,RM, Appt,SE, Bennetau-Pelissero,C, Clarkson,TB, Anthony,MS, Lamothe,V, Potter,SM: Dietary soy and soy isoflavones have gender-specific effects on plasma lipids in Golden Syrian F1B Hybrid Hamsters. J Nutr 1323585-3591, 2002
8.Ascencio,C, Torres,N, Isoard-Acosta, F, Gomez-Perez,FJ, Hernandez-Pando,R, Tovar,AR: Soy protein affects serum insulin and hepatic SREBP-1 mRNA and reduces fatty liver in rats. J Nutr 134:522-529, 2004
9. Adams,MR, Golden,DL, Anthony,MS, Register,RC, and Koudy Williams,J: The inhibibory effect of soy protein isolate on atherosclerosis in mice does not require the presence of LDL receptors or alteration of plasma lipoproteins. J Nutr 132:43-49, 2002
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