Topical Area: Diet and Cancer
Carbohydrates are the main source of energy in older adults in the US. Moreover, they increase insulin and insulin-like growth factor-1 (IGF1), which are implicated in tumor growth by increasing cell survival. Previously, we found low carbohydrate (LC) diets slow prostate cancer (PC) growth and increase survival vs. a Western diet (WD) in mice. However, long-term adherence to a LC diet can be difficult for cancer patients. Thus, we aimed to determine whether modifying carbohydrate quality without changing quantity could result in the same outcome as when quantity is reduced. Carbohydrate quality was based on a glycemic index (GI), which indicates how carbohydrates affect blood glucose levels. Low GI carbohydrates are absorbed more slowly and result in a lower and slower increase in glucose levels and insulin demand than high GI carbohydrates. We hypothesized that high carbohydrate intake but with a low GI would slow PC growth, by reducing insulin levels.
A xenograft mice study compared the effect on PC growth of 3 diets: HiGI WD (48% carbohydrate: sucrose), HiGI LC (20% carbohydrate: sucrose), and LoGI WD (48% carbohydrate: amylose, amylopectin, maltodextrin). Male SCID mice were fed an ad lib HiGI WD. At day 14, they were injected with 5x105 LAPC-4 cells. When tumors reached ~200 mm^3, mice were single-housed and randomized to their diets (n=33/group). Mice were pair-fed to ensure all had the same weight throughout the study. Tumor volume and body weight were measured 2X per week. Body composition was determined by Echo-MRI. The outcomes of the study were tumor volume, survival, glucose, insulin, IGF-1 and IGFBP-3 levels, and tumor tissue analysis.
LoGI WD mice had lower tumor volumes, insulin, IGF1, and IGF1:IGFBP3 ratio, and higher IGF-BP3 levels, than the other two groups. Blood glucose was similar across arms. Even though body weight was similar across arms, LoGI WD mice had lower body fat. In a meal tolerance test, glucose was higher in HiGI WD mice with comparable results between the other two diets.
Feeding mice a low GI diet delayed PC growth and decreased serum insulin, IGF1 and IGF1:IGFBP3 ratios vs. a high GI diet. These data suggest carbohydrate quality is important for PC growth. Whether a low-carbohydrate and low GI diet would have additive benefits remains to be tested.
Funding Sources : American Institute for Cancer Research