a1 Department of Nutrition, University of California, Davis, CA 95616, USA
a2 Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, University of California, Davis, CA 95616, USA
a3 Department of Pathology and Laboratory Medicine, Center for Comparative Medicine, University of California, Davis, CA 95616, USA
a4 Processed Foods Research, US Department of Agriculture, Western Regional Research Center, Agricultural Research Service, Albany, CA 94710, USA
Prostate cancer (PCa) has been linked to fat intake, but the effects of both different dietary fat levels and types remain inconsistent and incompletely characterised. The effects on PCa in the transgenic adenocarcinoma of the mouse prostate (TRAMP) cancer model of an elevated fat (20 % of energy as fat) diet containing 155 g of whole walnuts were compared to those of an elevated fat (20 % of energy as soyabean oil) diet with matched macronutrients, tocopherols as well as a low-fat (8 % of energy as soyabean oil) diet. Mice, starting at 8 weeks of age, consumed one of the three different diets ad libitum; and prostates, livers and blood were obtained after 9, 18 or 24 weeks of feeding. No differences were observed in whole animal growth rates in either high-fat (HF) diet group, but prostate tumour weight and growth rate were reduced in the walnut diet group. Walnut diet group prostate weight, plasma insulin-like growth factor 1, resistin and LDL were lower at 18 weeks, while no statistically significant prostate weight differences by diet were seen at 9 or 24 weeks. Multiple metabolites in the livers differed by diet at 9 and 18 weeks. The walnut diet's beneficial effects probably represent the effects of whole walnuts' multiple constituents and not via a specific fatty acid or tocopherols. Moreover, as the two HF diets had dissimilar effects on prostate tumour growth rate and size, and yet had the same total fat and tocopherol composition and content, this suggests that these are not strongly linked to PCa growth.
(Received October 10 2011)
(Revised December 06 2011)
(Accepted December 06 2011)
(Online publication January 16 2012)
p1 Present address: Department of Medicine, Division of Oncology, National Jewish Health, Denver, CO 80 206, USA.
Abbreviations: GUI, genitourinary intact; HF, high-fat diet; IGF-1, insulin-like growth factor 1; LF, low-fat diet; NE, neuroendocrine; PCa, prostate cancer; TRAMP, transgenic adenocarcinoma of the mouse prostate; WW, whole walnut diet