Walnuts Slow Cancer‐Associated Weight Loss But Not the Growth of a Transplantable Tumor

Abstract

Walnuts are a unique food, rich in both omega‐3 fatty acids and antioxidants. Several studies have shown that walnuts can slow or prevent breast and prostate tumor growth in genetically‐programmed mice or nude mice. We tested the following hypothesis using a rat transplantable tumor line: walnuts slow tumor growth and cancer‐associated weight loss. A diet containing walnuts (W) was compared to a diet that replaced the walnuts with corn oil and additional protein and fiber (R). Male Fisher 344 rats were randomly assigned to either diet. The diet was consumed for 20 days and on day 21 the Ward colon carcinoma was implanted subcutaneously on the left hind flank in half the animals (TB) while the other half were sham operated and received no tumor (NTB). Body weight, food intake, and tumor growth were monitored daily. Tumor growth was divided into two periods: 1) latent when the tumor was not palpable and 2) observable when the tumor was palpable. After 47 days, the animals were sacrificed. Addition of walnuts to the diet significantly enriched liver fatty acids with omega‐3 fatty acids of both NTB and TB animals (R NTB: 11.7:1, R TB: 8.5:1 n‐6:n‐3; W NTB: 7:3:1, W TB: 6.3:1 n‐6:n‐3) but not the tumor (R TB: 15:1 n‐6:n‐3; W TB: 15:1 n‐6:n‐3). During latent tumor growth, the rate of host weight gain was significantly greater (p<0.03) for the W TB animals (0.7 ± 0.4 g/day) compared the R TB animals (0.3 ± 0.4 g/day). By the end of the latent period, the W TB animals weighed on average 6 g more. This extra body mass persisted throughout the observable tumor growth period. At the time of sacrifice, the W TB animals weighed more, yet caloric intake was not significantly greater than the R TB. At sacrifice, there was no significant difference in tumor weight between the two diet groups (R TB: 25.3 + 13.3 g; W TB: 25.1 + 14.5 g). Plasma IGF‐1 was significantly lower in TB animals compared to NTB animals and there was no significant difference between the W and R groups (R NTB: 931 ± 63 pg/mL, R TB: 563 ± 71 pg/mL p<0.01; W NTB 751 ± 45 pg/mL, W TB 542 ± 53 pg/mL p< 0.03, pg/mL) suggesting these changes are not mediated through IGF‐1. Plasma insulin was lower in the TB animals compared to NTB but not significantly. Despite enriching cell membranes with omega‐3 fatty acids, tumor growth continued unabated. However, the addition of walnuts to the diet did promote greater weight gain during the latent phase of tumor growth which helped conserve the tumor‐bearing host's body weight during the observable phase of tumor growth. The mechanism is unknown and warrants further investigation. Thus, walnuts may be a beneficial food for slowing the cancer‐associated weight loss without adversely affecting tumor growth.Support or Funding InformationFunded by the American Institute for Cancer Research and the California Walnut Commission