Skip to main content Accessibility help
Hostname: page-component-6f6fcd54b-24xq8 Total loading time: 0.508 Render date: 2021-05-11T11:54:48.808Z Has data issue: true Feature Flags: {}

A high-fat diet containing whole walnuts (Juglans regia) reduces tumour size and growth along with plasma insulin-like growth factor 1 in the transgenic adenocarcinoma of the mouse prostate model

Published online by Cambridge University Press:  16 January 2012

Paul A. Davis
Department of Nutrition, University of California, Davis, CA 95616, USA
Vihas T. Vasu
Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, University of California, Davis, CA 95616, USA
Kishorchandra Gohil
Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, University of California, Davis, CA 95616, USA
Hyunsook Kim
Department of Nutrition, University of California, Davis, CA 95616, USA
Imran H. Khan
Department of Pathology and Laboratory Medicine, Center for Comparative Medicine, University of California, Davis, CA 95616, USA
Carroll E. Cross
Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, University of California, Davis, CA 95616, USA
Wallace Yokoyama
Processed Foods Research, US Department of Agriculture, Western Regional Research Center, Agricultural Research Service, Albany, CA 94710, USA
E-mail address:
Rights & Permissions[Opens in a new window]


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.

Full Papers
Copyright © The Authors 2012. The online version of this article is published within an Open Access environment subject to the conditions of the Creative Commons Attribution-NonCommercial-ShareAlike licence <>. The written permission of Cambridge University Press must be obtained for commercial re-use.

Prostate cancer (PCa), a leading cause of male cancer deaths(Reference Jemal, Siegel and Xu1), has been linked to fat intake(Reference Escobar, Gomes-Marcondes and Carvalho2), but the effects of both dietary fat levels and differences in unsaturated fatty acids on prostate as well as other cancers remain inconsistent and poorly characterised. Studies have suggested that n-3 fatty acids inhibit(Reference Brown, Hart and Gazi3Reference Reese, Fradet and Witte5) or have no effect(Reference Kristal, Arnold and Neuhouser6, Reference Vissapragada, Ghosh and Ringer7) on PCa, while n-6 fatty acids stimulate PCa development(Reference Szymanski, Wheeler and Mucci8). Hori et al. (Reference Hori, Butler and McLoughlin9), in a very recent review, concluded that there was little evidence to suggest that a high-fat (HF) diet is associated with increased PCa risk, but still suggested that reduced dietary fat intake in combination with a healthy diet and lifestyle may slow the progression of PCa in certain patients. Although high in fat, walnut fats are mainly polyunsaturated and the effects of consuming walnuts on PCa are unclear(Reference Spaccarotella, Kris-Etherton and Stone10). In addition, Freedland and co-workers have reported that mouse PCa xenograft tumour growth is not associated with dietary fat content(Reference Freedland and Aronson11, Reference Lloyd, Antonelli and Phillips12). Moreover, Hardman & Ion(Reference Hardman and Ion13) have shown that implanted MDA-MB 231 human breast cancer growth in nude mice was significantly less in the group consuming walnuts (human equivalent of two servings a day) compared to a control group fed maize oil and have just reported that walnuts suppress mammary gland tumorigenesis in the C(3)1 TAg mouse but the effect could not be accounted for by the n-3 content alone(Reference Hardman and Ion13, Reference Hardman, Ion and Akinsete14).

The present study evaluated the effects of whole walnuts fed as part of a moderately HF diet on tumour growth in the transgenic adenocarcinoma of the mouse prostate (TRAMP) animal cancer model(Reference Nguewa and Calvo15). The high-fat, non-walnut diet was formulated using tocopherol-stripped soyabean oil to achieve not only the same fat levels but supply substantially similar fatty acid profiles as well. The experimental and control diets' α- and γ-tocopherol levels were equalised. Importantly, the present study's experimental diet was formulated incorporating whole walnuts as a unit, i.e. as whole food. Walnuts contain multiple ingredients that have been reported to reduce cancer risk or growth rate(Reference Petrik, McEntee and Johnson16Reference Berquin, Edwards and Chen20). The use of whole walnuts in the study diets was adopted in response to the contrasting results found when specific compounds were tested alone compared with as part of a food. A recent example is the report of Hsu et al. (Reference Hsu, Bray and Helferich21) who found that an isoflavone-rich soya extract induced apoptosis in human PCa cells without inducing apoptosis in benign prostate hyperplasia cells in contrast to specific soya isoflavones at the same levels as the extract induced apoptosis in both cell types(Reference Hsu, Bray and Helferich21). An increasing number of such studies suggest that foods exert effects beyond those of any one constituent(Reference Jacobs, Gross and Tapsell22). The present work represents the first study examining the effects of whole walnut-containing diet on PCa in an animal model.

Materials and methods


C57/BL6 TRAMP × C57BL/6 male PB-Tag Line 8247 transgene mice were purchased from Jackson Laboratories. Mice (6–7 weeks old) were fed a laboratory rodent diet (no. 5001, Ralston Purina) for 1 week, then weighed and randomised by weight into three experimental dietary groups (ten to fifteen mice per group) for each of three feeding durations (9, 18 and 24 weeks of ad libitum feeding). The mice were housed four to a wire-bottomed cage with activity enhancements (e.g. toys and tunnels) in an environmentally controlled room (20–22°C, 60 % relative humidity, 12 h light–12 h dark cycle). Institutional and national guidelines for the care and use of animals were followed and all experimental procedures involving animals were approved by the Animal Care and Use Committee, USDA Western Regional Research Center, Albany, CA, USA.


Semisynthetic American Institute of Nutrition (AIN)-93M(Reference Reeves, Nielsen and Fahey23)-based diets were produced using either shelled whole walnut halves (English walnuts (Juglans regia), California Walnut Commission) ground to 3 mm size (WW) or tocopherol-stripped soyabean oil (HF) as fat sources (Table 1). The WW diets incorporated 155 g of WW/kg diet, the equivalent of 80 g (approximately 3 ounces) of walnuts/d in humans, to give 20·5 % of energy from fat, while the HF diet used 100 g of tocopherol-stripped soyabean oil/kg diet supplying 20·7 % of energy from fat. A third diet, the low-fat (LF) diet, used a lower amount of stripped soyabean oil to supply 8·7 % of energy from fat. The two HF provided a closely matched fatty acid profile and the HF and WW diets were equivalent in terms of fat, protein, carbohydrate, fibre, minerals, vitamins as well as α- and γ-tocopherol levels (7·5 and 62 mg/kg of diet, α- and γ-tocopherol, respectively). Differing amounts of pure d-α- and d-γ-tocopherol (Acros Organics) were added (Table 1) to the walnut and the LF diets to adjust the α- and γ-tocopherol levels. The energy content of the LF diet was adjusted by the increased carbohydrate content. All diets were made mineral-replete by use of the Mineral mix (AIN-93M-MX). The relatively high Se content of walnuts increased the Se content of the WW to 0·7 mg/kg compared to 0·2 mg/kg in the other diets. All other nutrients were provided in all diets at concentrations that met or exceeded the minimum recommendations of the AIN(Reference Reeves, Nielsen and Fahey23).

Table 1 Diet composition (weight added/kg diet) by diet (low-fat (LF), high-fat (HF) and whole walnut (WW))

AIN, American Institute of Nutrition.

The diets were fed ad libitum with feed consumption recorded two times per week. Animals were weighed every week and then were killed by anaesthesia overdose/diaphragm puncture at the pre-planned time sampling intervals (i.e. 9, 18 and 24 weeks). Cardiac puncture was used to obtain blood; and plasma was isolated and stored as multiple aliquots at − 80°C until analysis. Prostate genitourinary intact (GUI) tract, i.e. bladder, seminal vesicles, coagulating and ampulary glands were removed and weighed. GUI weight correlates closely with other measures of prostate tumour growth(Reference Gupta, Adhami and Subbarayan24) and its use reduces time delays and minimises tissue identification ambiguities that arise during dissection as a result of the increasingly disturbed prostate tissue architecture over time in the TRAMP mouse. The GUI were bisected along the long axis of the urethra and then one portion flash-frozen in liquid N2 and the other stored in 10 % buffered formalin. Finally, whole liver was removed, flash-frozen in liquid N2 and stored at − 80°C until analysis.

Prostate pathology

For histological evaluation, prostate tissues were fixed in 10 % buffered formalin, processed and embedded in paraffin. Tissue sections (4 μm thick) were cut and stained with haematoxylin/eosin and the histology interpreted by Cardiff and colleagues(Reference Qi, Nakayama and Cardiff25).

Plasma analysis

Multiplex microbead suspension arrays (Luminex Corporation) were used to simultaneously assay several plasma analytes. Both multiple-analyte (insulin, C-reactive protein, adiponectin, leptin, tissue plasminogen activator inhibitor 1 (tPAI-1), resistin) and single-analyte microbead assays for insulin-like growth factor 1 (IGF-1) and glucagon were used according to the manufacturer's instructions (Millipore).

Plasma lipoprotein cholesterol levels were analysed using size-exclusion HPLC coupled to post-column cholesterol quantification as previously described(Reference Xu, Yokoyama and Irving26).

Liver metabolomic analysis

Liver tissue samples (n 5) at both the 9- and 18-week time points were selected at random from the HF, WW and LF diet groups and analysed using mView, a metabolomic profiling system (Metabolon, Inc.). Compounds were identified via matching with metabolomic library entries of purified standards.

Statistical analysis

Data collected were entered into Excel spreadsheets for each mouse; and statistical analysis was performed using ANOVA (JMP software v9.0 for Macintosh; SAS, Inc.) after testing for equal variances(Reference Brown and Forsythe27) and then group mean differences were tested, with P < 0·05 considered significant.

The effects of diet on whole animal weight and prostate weight time-course were estimated in a mixed-effect repeated-measures growth curve model using a square-root time scale transformation to allow for slowing of growth rates with maturity(Reference Laird and Ware28). The standard HF diet was chosen as a reference, and pre-planned comparisons were made between the LF diet and the HF diet, and between the WW and HF diets using SAS/STAT® software or R software; and all hypothesis tests were two-sided at P < 0·05. Prostate weight measures were naturally log-transformed and were with an assumed common mean size at 9 weeks before use in the mixed-effect repeated-measures growth curve model.

Metabolomics data were assessed using Welch's two-sample t test. Q values were computed, but no absolute cut-off was set in order to maximise the power to detect differentially regulated metabolites; and those ratios having a P < 0·05 were considered significant.


As anticipated, histological evaluation at the later sampling times found progressive changes in GUI histology. Assessment of the histology documented the presence of a variety of tissue derangements (e.g. engorged seminal vesicles, diffuse atypical prostate hyperplasia); and the numbers of animals with prostate tumours found are presented in Table 2. Upon statistical analysis using exact logistic regression, duration of time on the diet but not diet composition was related significantly with the number of mice with any tumour (P < 0·0001) as well as for the number of mice with only phylloides prostate tumours. Using the same analysis for the number of mice but restricting it to mice with only neuroendocrine (NE) prostate tumours, both diet composition and time on the diet approached significance (P = 0·0744 and P = 0·0765, respectively).

Table 2 Prostate tumour numbers and types by histopathology by diet group (low-fat (LF), high-fat (HF) and whole walnut (WW))

NE, neuroendocrine tumour; PHY, phylloides tumour.

Fig. 1 presents the overall body weight data, while Fig. 2 presents the prostate weight data, i.e. GUI weights over time. GUI weight at the 9 and 24 weeks sampling time points did not show significant differences by diet. However, GUI prostate weights at 18 weeks did show significant differences by diet (Fig. 2) as the LF and WW diet groups' GUI prostate weights were markedly and statistically significantly lower than the HF diet group's GUI prostate weight but did not differ from each other. GUI weights are presented (Fig. 2), but both GUI weight and GUI weight/body weight gave the same results upon statistical analysis. A two-way ANOVA analysis of GUI weight data found that duration of time on the diet reached statistical significance (P < 0·05).

Fig. 1 Body weight for the different diet groups (low-fat (), high-fat () and whole walnut ()) at the different sampling times. Values are means with SEM represented by vertical bars. a,b Mean values within the same sampling time with unlike letters were significantly different (P < 0·05).

Fig. 2 Prostate weight as genitourinary tract intact (GUI) for the different diet groups (low-fat (), high-fat () and whole walnut ()) at the different sampling times. Values are means with SEM represented by vertical bars. a,b Mean values within the same sampling time with unlike letters were significantly different (P < 0·05).

The effect of diet on whole animal rate of weight gain was analysed using a mixed-effect repeated-measures growth curve model. The analysis revealed that whole body growth rate for the WW diet animals did not differ from that of the HF diet animals (4·75 v. 4·81 g/square root (weeks); P = 0·84), but that whole body growth rate of the LF diet animals was about 20 % lower (3·7 g/sqrt (weeks); P = 0·001) than that of the HF and WW diet animals. In contrast to the lack of effect on body weight, analysis of prostate weight gain using a mixed-effect growth curve model found that the WW diet animal's prostate growth (8 (sem 2·8) %/week) was reduced by 28 % (P < 0·015) relative to that of the HF diet animals (11 (sem 2·5) %/week). The prostate weight gain (8 (sem 2·8) %/week) in the LF diet animals was also reduced by 28 % (P < 0·015).

Plasma IGF-1 (Fig. 3) differed by diet group at 18 weeks. IGF-1 was lower (P < 0·05) in the LF and WW diet animals compared to the HF diet animals, but the WW and LF diet animals' IGF-1 levels did not differ from each other. Plasma resistin was lower (P < 0·05) in the 18-week WW and LF animals compared to the HF diet animals (Table 3), but the WW and LF diet animals' resistin levels did not differ from each other. Other plasma analytes, i.e. adiponectin, insulin, C-reactive protein and leptin showed a trend towards altered levels with diet group (Table 3), but all insulin failed to achieve statistical significance. LF diet insulin differed only from HF diet at 18 weeks.

Fig. 3 Plasma insulin-like growth factor 1 (IGF-1) levels are presented for the different diet groups (low-fat (), high-fat () and whole walnut ()) at 9 weeks, and 18 weeks of ad libitum feeding. Values are means with SEM represented by vertical bars. a,b Mean values within the same sampling time with unlike letters were significantly different (P < 0·05).

Table 3 Mouse plasma analyte levels (nm) either at 9 and 18 weeks or at 18 weeks-only time points by diet group (low-fat (LF), high-fat (HF) and whole walnut (WW))(Number of animals, mean values with SEM)

CRP, C-reactive protein.

a,b Mean values within a row with unlike superscript letters were significantly different (P < 0·05).

While plasma total cholesterol at 18 weeks did not differ between the HF and WW diets, at 18 weeks both WW diet group LDL-cholesterol and LDL-cholesterol:HDL-cholesterol ratios were significantly lower when compared to the HF diet but not compared to the LF diet (Table 4).

Table 4 Mouse plasma cholesterol levels (mm) in lipoprotein fractions and as total at 18-week time point by diet group (low-fat (LF), high-fat (HF) and whole walnut (WW)) (Mean values with their standard errors)

a,b Mean values within a row with unlike letters were significantly different (P < 0·05).

Metabolomic analysis of the TRAMP mouse livers found twenty and twenty-six metabolites among the 266 identified named biochemicals, showing significant (P ≤ 0·05) differences in levels between the HF and WW diet groups at 9 and 18 weeks, respectively (Table 5, see the supplementary table for metabolites identified and diet-related differences, supplementary material for this article can be found at With respect to the lipid-related metabolites identified and found to differ by diet, n-3 fatty acids along with n-3 fatty acid-containing lysolipids (i.e. linoleoyl-glycerophosphoethanolamine) were elevated in WW liver, while arachidonate, an n-6 fatty acid along with n-6 fatty acid-containing lysolipids were decreased compared to HF liver. In addition, hepatic sphingosine content was over 2-fold lower in WW mice compared to that of the HF diet group at 18 weeks and WW livers had significantly increased 9- and 13-hydroxy-octadecadienoic acids.

Table 5 Liver metabolomic results

HODE, hydroxy-octadecadienoic acid.

*Statistically significant lipid related metabolite changes (P < 0·05) are presented as the ratio of the whole walnut diet or the high fat diet abundance at 9 and 18 weeks.


High fat intake, particularly saturated fat intake, has been associated with CVD, other metabolic diseases and some forms of cancer including PCa(Reference Kris-Etherton, Hu and Ros29). Walnuts, like other nuts, are typically consumed whole, with a majority of their energy coming from fat. Although high in fat, walnut fats are mainly polyunsaturated and the effects of consuming walnuts on PCa are unclear(Reference Spaccarotella, Kris-Etherton and Stone10) and was the focus of this study. The results of the present study demonstrate that whole walnuts have a beneficial effect in an animal model of PCa. The walnut diet, irrespective of its high fat content, resulted in notable and statistically significant decreased GUI weights and rate of tumour weight gain. The present study results parallel those of Adhami and colleagues(Reference Adhami, Siddiqui and Ahmad30) who demonstrated that green tea also reduced prostate GUI weight in TRAMP mice, which they showed correlated closely with prostate tumour burden and occurrence. This congruence lends support to the conclusion that the WW diet effect is a result of walnut diet-induced decreased prostate tumour growth rate and reduced prostate tumour size.

The TRAMP model has been much criticised as a NE-cancer model with questionable relevance to human PCa; and more recently, the C57BL/6 TRAMP mouse has been suggested to actually represent a mixed model of prostate carcinogenesis(Reference Wang, Bonorden and Li31, Reference Wang, Zhang and Zhang32). One tumour process is the phylloides tumour which is an androgen-driven glandular prostate atypical hyperplasia in the dorsolateral prostate (DLP) lobes while the other is NE-cancer in the ventral prostate (VP) lobes. This is of importance, as the TRAMP DLP lesion progression is more characteristic of human prostate epithelial adenocarcinogenesis and the majority of human PCa are adenocarcinomas. Conversely, NE-like carcinomas lack androgen receptor, express synaptophysin and belong to a distinct lineage(Reference Wang, Bonorden and Li31, Reference Wang, Zhang and Zhang32). While the present study did not find a statistically significant diet effect in terms of tumour occurrence, the tumour type showed some degree of diet dependence, as NE tumours in the walnut-fed group were nearly absent. That the walnut diet group TRAMP mice prostates are relatively free of NE-cancer while also showing reduced size may therefore reflect the walnut-related effects on phylloide tumours, as these DLP lesions account for most of TRAMP prostate weight gains(Reference Wang, Zhang and Zhang32) in combination with possible effects on prostate NE tumours. Given the nature of the genetic construct driving the TRAMP tumour model, tumour suppression by walnuts was unlikely to occur, which makes the finding of slowed growth of importance. The specificity of the walnut diet's effects with respect to tumour lineages and prostate lobes affected awaits future study.

This study's results further suggest that PCa growth does not appear to be a function of the level of dietary fat, as both the WW and HF diets had the same fat level. Freedland and co-workers have recently reported that tumour growth was not associated with dietary fat content, using a mouse PCa xenograft model(Reference Lloyd, Antonelli and Phillips12, Reference Freedland, Mavropoulos and Wang33). A similar conclusion regarding the relationship of fat content to cancer growth has been reported recently for pancreatic cancer(Reference Cheon, Strouch and Barron34). The present study's WW diet not only had the same fat content as the HF diet, but were substantially similar in their fatty acid profiles removing that as a factor for the diet-associated effects noted. In addition, the absence of similar effects despite the identical levels of α- and γ-tocopherol supplied by both the WW and the HF diets eliminates these tocopherols as a factor in the differences.

The walnut diet differs in Se (approximately 0·9 mg/kg diet in WW v. approximately 0·2 mg Se/kg diet in the HF and LF diets), as English walnuts are relatively high in Se (United States Department of Agriculture National Nutrient Database for Standard Reference, Release 24). However, the modest levels of Se for any of the study diets tested makes it difficult to ascribe the differences to Se, as much higher Se levels (3·0 mg Se/kg diet) were used in studies of Se-related effects in the TRAMP prostate model along with other rodent models(Reference Quiner, Nakken and Mason35, Reference Zhang, Wang and Li36). Added difficulty in linking Se levels to effects arises from the recent report that Se-related effects in mice depend upon composition of the basal diet consumed along with the differences linked to the form of Se tested(Reference Quiner, Nakken and Mason35, Reference Zhang, Wang and Li36).

Finally, the reduced tumour growth in the WW diet cannot be explained by differences in energy bioavailability between the diets, as there were no differences in body weights and body-weight gains between WW when compared to the HF diet-fed mice.

Diet and increased PCa have been linked via increased IGF-1(Reference Key37). The present study found that IGF-1 in WW diet mice at 18 weeks was reduced and this was associated with smaller tumour size and slower tumour growth rate. The study findings of reduced IGF-1 and smaller tumour size/growth are in agreement with other PCa studies that have either specifically modulated or monitored IGF-1 in TRAMP mice(Reference Adhami, Siddiqui and Ahmad30, Reference Wang, Bonorden and Li31, Reference Prasad, Mukhtar and Beck38). Elevated IGF-1, along with elevated insulin, has been reported to increase the risk of PCa via increased cell proliferation and cell survival(Reference Pollak39). The influence of IGF-1 levels on prostate tumour growth is highlighted by the contrast between both animal survival and prostate tumour cell growth in studies that altered IGF-1 levels. Studies with increased survival and decreased tumour cell growth were those treatments that lowered IGF-1 compared to those where IGF-1 was unaffected(Reference Lloyd, Antonelli and Phillips12, Reference Freedland, Mavropoulos and Wang33, Reference Bonorden, Rogozina and Kluczny40, Reference Thomas, Antonelli and Lloyd41). Finally, Chen et al. (Reference Chen, Fang and Sun42) have reported that enterolactone, a major metabolite of plant-based lignans inhibits PCa cell growth in vitro and does so, at least in part via inhibition of IGF-1/IGF-1R signalling.

Recent clinical studies targeting the IGF-1R receptor alone or in combination with chemotherapy have shown potent PCa growth inhibition(Reference Gualberto and Pollak43). However, the theoretical constructs linking prostate tumour growth and IGF-1 signalling axis have proven difficult to rationalise as the effects of genetically modifying IGF-1 levels or IGF-1 signalling pathways on PCa in TRAMP mice have given mixed results(Reference Majeed, Blouin and Kaplan-Lefko44Reference Sutherland, Knoblaugh and Kaplan-Lefko46). The accelerated lesion progression and more aggressive phenotype upon knockout of prostate epithelial cell IGF-1R in the TRAMP model has suggested that there are different thresholds for prostate IGF-1 signalling and that complete IGF-1R knockout cannot recapitulate diminished but intact IGF-1/IGF-1R signalling(Reference Sutherland, Knoblaugh and Kaplan-Lefko46). Interestingly, Wang et al. (Reference Wang, Bonorden and Li31) suggested that Se inhibition of PCa tumour growth might be via effects on both IGF-1 ligand and receptor. Again, the present study's WW and HF diets' identical α- and γ-tocopherol, fat content and substantially similar fatty acid profiles removes these as factors for the IGF-1 effects noted in this study. The extent to which changes seen in the present study are from direct effects on the prostate IGF-1 axis, as reported in the case of green tea(Reference Adhami, Siddiqui and Ahmad30) and silibinin(Reference Raina, Blouin and Singh47), remains to be further explored.

Although earlier reports have suggested that altered resistin levels are not associated with PCa(Reference Housa, Vernerova and Heracek48), recent results from Kim and colleagues have suggested that they are elevated in PCa(Reference Chung, Kim and Chang49) and stimulate PCa growth(Reference Kim, Lee and Won50). The present study revealed that mice on the WW diet had reduced levels of resistin compared to the HF diet group animals, a similar pattern to that found for IGF-1 levels. Other plasma analytes showed a trend towards altered levels with diet, but none of these achieved statistical significance. For example, low levels of adiponectin have been linked to PCa(Reference Housa, Vernerova and Heracek51, Reference Grosman, Fabre and Mesch52) and WW diet mice at 18 weeks had tended to have increased adiponectin levels (P = 0·051) compared to the HF diet. Aronis et al. (Reference Aronis, Vamvini and Chamberland53) have very recently reported that walnut consumption acutely increases plasma adiponectin in obese patients. The connection between changes in PCa growth and the effects of altered resistin and, potentially, adiponectin remains to be further clarified.

Mice in the WW group exhibited significant changes in plasma cholesterol metabolism, specifically decreased LDL-cholesterol and altered LDL-C:HDL-C ratios relative to those in the HF diet. Circulating cholesterol has been reported to promote prostate tumour growth(Reference Solomon, Pelton and Boucher54, Reference Llaverias, Danilo and Wang55). LNCaP PCa cells when cultured in vitro with decreased endogenous cholesterol availability increase their LDL receptor activity, presumably in order to acquire cholesterol required to support their growth(Reference Krycer, Kristiana and Brown56). Recently, using the same TRAMP mouse model, a high-fat (60 % of energy as fat) in combination with 0·2 % cholesterol diet (i.e. a ‘Western’ diet) was shown to elevate plasma cholesterol, alter LDL-C:HDL-C ratios and accelerate prostate tumour onset and progression(Reference Llaverias, Danilo and Wang55). Specific lipoprotein classes such as LDL and HDL are associated with delivery or removal of cell cholesterol(Reference Krauss57) and have been linked to PCa(Reference Kok, van Roermund and Aben58). The changes noted with diet in the plasma markers studied are echoed in the liver metabolomics results. Interestingly, despite the similarities in fats between the two diets, the WW diet group liver metabolome showed elevations of n-3 fatty acid-related lipids while n-6 fatty acid-related lipids decreased compared to the HF diet group livers. These changes are probably of significance as n-3 fatty acid metabolism and their effects in PCa have been of high interest(Reference Brown, Hart and Gazi3Reference Vissapragada, Ghosh and Ringer7). In addition, the diet-driven changes noted in the metabolites in the liver are noteworthy, given the liver's central role in both IGF-1 and in plasma lipid and lipoprotein metabolism(Reference Ohlsson, Mohan and Sjogren59). However, the linkage of PCa and other cancers with specific fatty acids is proving to be very complex. The n-3 fatty acid, DHA, has been recently reported as positively associated with high-grade PCa, contrary to what the study authors had hypothesised(Reference Brasky, Till and White60). In addition, Hardman and colleagues(Reference Hardman, Ion and Akinsete14) have just reported that while consumption of walnuts significantly reduced the incidence, multiplicity and size of mammary tumours, a cancer that shares multiple characteristics with PCa(Reference Risbridger, Davis and Birrell61), the n-3 content alone did not account for the extent of tumour suppression due to the walnut diet.

In summary, the present study found that whole walnuts fed as part of a HF diet (i.e. the WW diet) reduce TRAMP mouse PCa tumour growth and size. The walnut diet-consuming animals also showed declines in plasma IGF-1, resistin as well as LDL, elevations of which have all been linked to tumour growth. The study results further suggest that the walnut effects are not due to their specific fatty acid or tocopherol content. The differences found between the effects of the whole walnut and the control HF diet when coupled with the disappointing α-tocopherol chemopreventative clinical trials emphasises that whole foods and complete diets probably exert effects beyond those of an individual constituent(Reference Kristal, Arnold and Neuhouser6, Reference Jacobs, Gross and Tapsell22, Reference Hoffmann62). Moreover, the disparate diet effects observed at the same elevated dietary fat intake suggest that total dietary fat intake is not strongly linked to PCa tumour biology. The study results show that excluding walnuts based on their fat content is unjustified and that consumption of walnuts, already linked to reduced CVD risk(Reference Kris-Etherton, Hu and Ros29), will probably reduce the risk of PCa in humans. Finally, these findings point to the need for studies using whole foods such as walnuts to truly assess their effects on PCa and to identify effective, food-based chemoprevention diets for PCa as well as other cancers.


All authors participated in the design of the present study. Diets were produced and animal husbandry supervised by W. Y. Tissue and plasma samples were obtained by P. A. D., K. G., W. Y. and H. K. Plasma analytes were determined by I. H. K. and W. Y. Data analysis was performed by P. A. D., except as noted herein. The initial manuscript draft was written by P. A. D., critically revised by C. E. C., W. Y., H. K., I. H. K., V. T. V. and K. G. The final version was assembled by P. A. D. and all authors read and approved the final manuscript. This study was supported by a research grant to the University of California, Davis from the California Walnut Board. Statistical analysis support was provided by grant number UL1 RR024146 from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH), and NIH Roadmap for Medical Research. The manuscript's contents are solely the responsibility of the authors and do not necessarily represent the official view of the NCRR or NIH. The authors have no conflicts of interest to declare.


1Jemal, A, Siegel, R, Xu, J, et al. (2010) Cancer statistics. CA Cancer J Clin 60, 277300.CrossRefGoogle ScholarPubMed
2Escobar, EL, Gomes-Marcondes, MC & Carvalho, HF (2009) Dietary fatty acid quality affects AR and PPARgamma levels and prostate growth. Prostate 69, 548558.CrossRefGoogle ScholarPubMed
3Brown, MD, Hart, C, Gazi, E, et al. (2010) Influence of omega-6 PUFA arachidonic acid and bone marrow adipocytes on metastatic spread from prostate cancer. Br J Cancer 102, 403413.CrossRefGoogle ScholarPubMed
4Berquin, IM, Min, Y, Wu, R, et al. (2007) Modulation of prostate cancer genetic risk by omega-3 and omega-6 fatty acids. J Clin Invest 117, 18661875.CrossRefGoogle ScholarPubMed
5Reese, AC, Fradet, V & Witte, JS (2009) Omega-3 fatty acids, genetic variants in COX-2 and prostate cancer. J Nutrigenet Nutrigenomics 2, 149158.CrossRefGoogle ScholarPubMed
6Kristal, AR, Arnold, KB, Neuhouser, ML, et al. (2010) Diet, supplement use, and prostate cancer risk: results from the prostate cancer prevention trial. Am J Epidemiol 172, 566577.CrossRefGoogle ScholarPubMed
7Vissapragada, S, Ghosh, A, Ringer, L, et al. (2010) Dietary n-3 polyunsaturated fatty acids fail to reduce prostate tumorigenesis in the PB-ErbB-2x Pten(+/ − ) preclinical mouse model. Cell Cycle 9, 18241829.CrossRefGoogle ScholarPubMed
8Szymanski, KM, Wheeler, DC & Mucci, LA (2010) Fish consumption and prostate cancer risk: a review and meta-analysis. Am J Clin Nutr 92, 12231233.CrossRefGoogle ScholarPubMed
9Hori, S, Butler, E & McLoughlin, J (2011) Prostate cancer and diet: food for thought? BJU Int 107, 13481359.CrossRefGoogle ScholarPubMed
10Spaccarotella, KJ, Kris-Etherton, PM, Stone, WL, et al. (2008) The effect of walnut intake on factors related to prostate and vascular health in older men. Nutr J 7, 13.CrossRefGoogle ScholarPubMed
11Freedland, SJ & Aronson, WJ (2009) Dietary intervention strategies to modulate prostate cancer risk and prognosis. Curr Opin Urol 19, 263267.CrossRefGoogle ScholarPubMed
12Lloyd, JC, Antonelli, JA, Phillips, TE, et al. (2010) Effect of isocaloric low fat diet on prostate cancer xenograft progression in a hormone deprivation model. J Urol 183, 16191624.CrossRefGoogle Scholar
13Hardman, WE & Ion, G (2008) Suppression of implanted MDA-MB 231 human breast cancer growth in nude mice by dietary walnut. Nutr Cancer 60, 666674.CrossRefGoogle ScholarPubMed
14Hardman, WE, Ion, G, Akinsete, JA, et al. (2011) Dietary walnut suppressed mammary gland tumorigenesis in the C(3)1 TAg mouse. Nutr Cancer 63, 960970.CrossRefGoogle Scholar
15Nguewa, PA & Calvo, A (2010) Use of transgenic mice as models for prostate cancer chemoprevention. Curr Mol Med 10, 705718.CrossRefGoogle ScholarPubMed
16Petrik, MB, McEntee, MF, Johnson, BT, et al. (2000) Highly unsaturated (n-3) fatty acids, but not alpha-linolenic, conjugated linoleic or gamma-linolenic acids, reduce tumorigenesis in Apc(Min/+) mice. J Nutr 130, 24342443.CrossRefGoogle ScholarPubMed
17Ju, YH, Clausen, LM, Allred, KF, et al. (2004) β-Sitosterol, β-sitosterol glucoside, and a mixture of β-sitosterol and β-sitosterol glucoside modulate the growth of estrogen-responsive breast cancer cells in vitro and in ovariectomized athymic mice. J Nutr 134, 11451151.CrossRefGoogle Scholar
18Maguire, LS, O'Sullivan, SM, Galvin, K, et al. (2004) Fatty acid profile, tocopherol, squalene and phytosterol content of walnuts, almonds, peanuts, hazelnuts and the macadamia nut. Int J Food Sci Nutr 55, 171178.CrossRefGoogle ScholarPubMed
19Han, DH, Lee, MJ & Kim, JH (2006) Antioxidant and apoptosis-inducing activities of ellagic acid. Anticancer Res 26, 36013606.Google ScholarPubMed
20Berquin, IM, Edwards, IJ & Chen, YQ (2008) Multi-targeted therapy of cancer by omega-3 fatty acids. Cancer Lett 269, 363377.CrossRefGoogle ScholarPubMed
21Hsu, A, Bray, TM, Helferich, WG, et al. (2010) Differential effects of whole soy extract and soy isoflavones on apoptosis in prostate cancer cells. Exp Biol Med (Maywood) 235, 9097.CrossRefGoogle ScholarPubMed
22Jacobs, DR Jr, Gross, MD & Tapsell, LC (2009) Food synergy: an operational concept for understanding nutrition. Am J Clin Nutr 89, 1543S1548S.CrossRefGoogle ScholarPubMed
23Reeves, PG, Nielsen, FH & Fahey, GC Jr (1993) AIN-93 purified diets for laboratory rodents: final report of the American Institute of Nutrition ad hoc writing committee on the reformulation of the AIN-76A rodent diet. J Nutr 123, 19391951.CrossRefGoogle ScholarPubMed
24Gupta, S, Adhami, VM, Subbarayan, M, et al. (2004) Suppression of prostate carcinogenesis by dietary supplementation of celecoxib in transgenic adenocarcinoma of the mouse prostate model. Cancer Res 64, 33343343.CrossRefGoogle ScholarPubMed
25Qi, J, Nakayama, K, Cardiff, RD, et al. (2010) Siah2-dependent concerted activity of HIF and FoxA2 regulates formation of neuroendocrine phenotype and neuroendocrine prostate tumors. Cancer Cell 18, 2338.CrossRefGoogle ScholarPubMed
26Xu, R, Yokoyama, WH, Irving, D, et al. (1998) Effect of dietary catechin and vitamin E on aortic fatty streak accumulation in hypercholesterolemic hamsters. Atherosclerosis 137, 2936.CrossRefGoogle ScholarPubMed
27Brown, MB & Forsythe, AB (1974) Robust tests for equality of variances. J Amer Statist Assoc 69, 364367.CrossRefGoogle Scholar
28Laird, NM & Ware, JH (1982) Random-effects models for longitudinal data. Biometrics 38, 963974.CrossRefGoogle ScholarPubMed
29Kris-Etherton, PM, Hu, FB, Ros, E, et al. (2008) The role of tree nuts and peanuts in the prevention of coronary heart disease: multiple potential mechanisms. J Nutr 138, 1746S1751S.CrossRefGoogle ScholarPubMed
30Adhami, VM, Siddiqui, IA, Ahmad, N, et al. (2004) Oral consumption of green tea polyphenols inhibits insulin-like growth factor-I-induced signaling in an autochthonous mouse model of prostate cancer. Cancer Res 64, 87158722.CrossRefGoogle Scholar
31Wang, L, Bonorden, MJ, Li, GX, et al. (2009) Methyl-selenium compounds inhibit prostate carcinogenesis in the transgenic adenocarcinoma of mouse prostate model with survival benefit. Cancer Prev Res (Phila Pa) 2, 484495.CrossRefGoogle ScholarPubMed
32Wang, L, Zhang, J, Zhang, Y, et al. (2011) Lobe-specific lineages of carcinogenesis in the transgenic adenocarcinoma of mouse prostate and their responses to chemopreventive selenium. Prostate 71, 14291440.CrossRefGoogle ScholarPubMed
33Freedland, SJ, Mavropoulos, J, Wang, A, et al. (2008) Carbohydrate restriction, prostate cancer growth, and the insulin-like growth factor axis. Prostate 68, 1119.CrossRefGoogle ScholarPubMed
34Cheon, EC, Strouch, MJ, Barron, MR, et al. (2011) Alteration of strain background and a high omega-6 fat diet induces earlier onset of pancreatic neoplasia in EL-Kras transgenic mice. Int J Cancer 128, 27832792.CrossRefGoogle Scholar
35Quiner, TE, Nakken, HL, Mason, BA, et al. (2011) Soy content of basal diets determines the effects of supplemental selenium in male mice. J Nutr 141, 21592165.CrossRefGoogle ScholarPubMed
36Zhang, J, Wang, L, Li, G, et al. (2011) Mouse prostate proteomes are differentially altered by supranutritional intake of four selenium compounds. Nutr Cancer 63, 778789.CrossRefGoogle ScholarPubMed
37Key, TJ (2011) Diet, insulin-like growth factor-1 and cancer risk. Proc Nutr Soc (epublication ahead of print version 3 May 2011).CrossRefGoogle ScholarPubMed
38Prasad, AS, Mukhtar, H, Beck, FW, et al. (2010) Dietary zinc and prostate cancer in the TRAMP mouse model. J Med Food 13, 7076.CrossRefGoogle ScholarPubMed
39Pollak, M (2008) Insulin and insulin-like growth factor signalling in neoplasia. Nat Rev Cancer 8, 915928.CrossRefGoogle ScholarPubMed
40Bonorden, MJ, Rogozina, OP, Kluczny, CM, et al. (2009) Intermittent calorie restriction delays prostate tumor detection and increases survival time in TRAMP mice. Nutr Cancer 61, 265275.CrossRefGoogle ScholarPubMed
41Thomas, JA 2nd, Antonelli, JA, Lloyd, JC, et al. (2010) Effect of intermittent fasting on prostate cancer tumor growth in a mouse model. Prostate Cancer Prostatic Dis 13, 350355.CrossRefGoogle ScholarPubMed
42Chen, LH, Fang, J, Sun, Z, et al. (2009) Enterolactone inhibits insulin-like growth factor-1 receptor signaling in human prostatic carcinoma PC-3 cells. J Nutr 139, 653659.CrossRefGoogle ScholarPubMed
43Gualberto, A & Pollak, M (2009) Clinical development of inhibitors of the insulin-like growth factor receptor in oncology. Curr Drug Targets 10, 923936.CrossRefGoogle Scholar
44Majeed, N, Blouin, MJ, Kaplan-Lefko, PJ, et al. (2005) A germ line mutation that delays prostate cancer progression and prolongs survival in a murine prostate cancer model. Oncogene 24, 47364740.CrossRefGoogle Scholar
45Anzo, M, Cobb, LJ, Hwang, DL, et al. (2008) Targeted deletion of hepatic Igf1 in TRAMP mice leads to dramatic alterations in the circulating insulin-like growth factor axis but does not reduce tumor progression. Cancer Res 68, 33423349.CrossRefGoogle Scholar
46Sutherland, BW, Knoblaugh, SE, Kaplan-Lefko, PJ, et al. (2008) Conditional deletion of insulin-like growth factor-I receptor in prostate epithelium. Cancer Res 68, 34953504.CrossRefGoogle ScholarPubMed
47Raina, K, Blouin, MJ, Singh, RP, et al. (2007) Dietary feeding of silibinin inhibits prostate tumor growth and progression in transgenic adenocarcinoma of the mouse prostate model. Cancer Res 67, 1108311091.CrossRefGoogle ScholarPubMed
48Housa, D, Vernerova, Z, Heracek, J, et al. (2008) Serum resistin levels in benign prostate hyperplasia and non-metastatic prostate cancer: possible role in cancer progression. Neoplasma 55, 442446.Google ScholarPubMed
49Chung, WH, Kim, TH, Chang, IH, et al. (2009) Relation of resistin to prostate cancer differentiation and aggressiveness. Korean J Urol 50, 540546.CrossRefGoogle Scholar
50Kim, HJ, Lee, YS, Won, EH, et al. (2010) Expression of resistin in the prostate and its stimulatory effect on prostate cancer cell proliferation. BJU Int 108, E77E83.CrossRefGoogle ScholarPubMed
51Housa, D, Vernerova, Z, Heracek, J, et al. (2008) Adiponectin as a potential marker of prostate cancer progression: studies in organ-confined and locally advanced prostate cancer. Physiol Res 57, 451458.Google ScholarPubMed
52Grosman, H, Fabre, B, Mesch, V, et al. (2010) Lipoproteins, sex hormones and inflammatory markers in association with prostate cancer. Aging Male 13, 8792.CrossRefGoogle ScholarPubMed
53Aronis, KN, Vamvini, MT, Chamberland, JP, et al. (2011) Short-term walnut consumption increases circulating total adiponectin and apolipoprotein A concentrations, but does not affect markers of inflammation or vascular injury in obese humans with the metabolic syndrome: data from a double-blinded, randomized, placebo-controlled study. Metabolism (epublication ahead of print version 9 November 2011).Google ScholarPubMed
54Solomon, KR, Pelton, K, Boucher, K, et al. (2009) Ezetimibe is an inhibitor of tumor angiogenesis. Am J Pathol 174, 10171026.CrossRefGoogle ScholarPubMed
55Llaverias, G, Danilo, C, Wang, Y, et al. (2010) A Western-type diet accelerates tumor progression in an autochthonous mouse model of prostate cancer. Am J Pathol 177, 31803191.CrossRefGoogle Scholar
56Krycer, JR, Kristiana, I & Brown, AJ (2009) Cholesterol homeostasis in two commonly used human prostate cancer cell-lines, LNCaP and PC-3. PLoS ONE 4, e8496.CrossRefGoogle ScholarPubMed
57Krauss, RM (2010) Lipoprotein subfractions and cardiovascular disease risk. Curr Opin Lipidol 21, 305311.CrossRefGoogle ScholarPubMed
58Kok, DE, van Roermund, JG, Aben, KK, et al. (2011) Blood lipid levels and prostate cancer risk; a cohort study. Prostate Cancer Prostatic Dis 14, 340345.CrossRefGoogle Scholar
59Ohlsson, C, Mohan, S, Sjogren, K, et al. (2009) The role of liver-derived insulin-like growth factor-I. Endocr Rev 30, 494535.CrossRefGoogle ScholarPubMed
60Brasky, TM, Till, C, White, E, et al. (2011) Serum phospholipid fatty acids and prostate cancer risk: results from the prostate cancer prevention trial. Am J Epidemiol 173, 14291439.CrossRefGoogle ScholarPubMed
61Risbridger, GP, Davis, ID, Birrell, SN, et al. (2010) Breast and prostate cancer: more similar than different. Nat Rev Cancer 10, 205212.CrossRefGoogle ScholarPubMed
62Hoffmann, I (2003) Transcending reductionism in nutrition research. Am J Clin Nutr 78, 514S516S.CrossRefGoogle ScholarPubMed
Supplementary material: PDF

Davis Supplementary Material

Davis Supplementary Material

Download Davis Supplementary Material(PDF)
You have Access
Open access

Send article to Kindle

To send this article to your Kindle, first ensure is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

Note you can select to send to either the or variations. ‘’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

A high-fat diet containing whole walnuts (Juglans regia) reduces tumour size and growth along with plasma insulin-like growth factor 1 in the transgenic adenocarcinoma of the mouse prostate model
Available formats

Send article to Dropbox

To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

A high-fat diet containing whole walnuts (Juglans regia) reduces tumour size and growth along with plasma insulin-like growth factor 1 in the transgenic adenocarcinoma of the mouse prostate model
Available formats

Send article to Google Drive

To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

A high-fat diet containing whole walnuts (Juglans regia) reduces tumour size and growth along with plasma insulin-like growth factor 1 in the transgenic adenocarcinoma of the mouse prostate model
Available formats

Reply to: Submit a response

Your details

Conflicting interests

Do you have any conflicting interests? *