The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 11 No. 4 • July 2008


Reducing Risk of Breast Cancer Recurrence by Lowering Insulin Levels

A recent news report1 in the Journal of the National Cancer Institute discussed the work of doctors attempting to increase the effectiveness of breast cancer chemotherapy and to reduce the risk of recurrence by including concurrent treatments to reduce insulin levels. One doctor-researcher, Pamela Goodwin, M.D., said, “If you look at the effect of insulin, the women in the highest quartile levels in the studies that have been done all yield the same result. They have a triple risk of death. If we could lower those insulin levels by 25%, we might see a 5%–6% absolute improvement in outcome, and that’s huge.” Goodwin and coworkers published a prospective study in 2002 looking at the outcomes for 512 nondiabetic women with early-stage breast cancer. They reported that the “women with the highest fasting insulin levels had three times the risk of recurrence and death compared with women with the lowest insulin levels.”

In a new paper,2 unrelated researchers did a meta-analysis of 39 studies that reported cancer risk estimates for glycemic index (GI, glucose released from carbohydrate-containing foods compared to pure glucose) and glycemic load (GL, the glucose derived from all carbohydrate-containing foods consumed per day). Overall, both GI and GL were significantly associated with a greater risk of colorectal or endometrial cancer but not (after correcting for publication bias) for breast cancer.

Other studies were reported in Ref 1 to support the hypothesis that higher insulin is associated with increased risk of breast cancer. The NCI-sponsored Health, Eating, Activity, and Lifestyle (HEAL) study found that “higher body mass index and lower physical activity levels are associated with higher insulin levels in breast cancer survivors and that women with invasive disease and the highest insulin levels have three times the risk of death of women with the lowest insulin levels.” These data were reported by Melinda Irwin, Ph.D., an epidemiologist at the Yale School of Public Health in New Haven, Connecticut, at the American Association for Cancer Research’s prevention meeting last year. Michael Pollak, M.D., professor of oncology at McGill University in Montreal, was quoted in the report: “The high-insulin effect is large. The adverse effect of high insulin on outcome of postmenopausal breast cancer is in the same order of magnitude as the beneficial effect of adjuvant chemotherapy. This is nothing subtle.”

The rest of the article reported on attempts of doctors to follow up on this by using metformin as an adjuvant treatment because of its insulin-lowering effects. Metformin is a drug approved for use in the treatment of diabetes. Goodwin was reported to have recently completed a prospective phase II clinical trial of 32 nondiabetic breast cancer patients that found that metformin treatment produced an insulin reduction of 22%.

There are a number of ways to reduce insulin levels, however, which do not involve the use of xenobiotic drugs. One way is to reduce the amount of high-glycemic-index carbohydrates in your diet and increase fiber and resistant starch.3-7 In fact, we developed our Glycemic Control line of low-glycemic-index, high-fiber (beta-glucan) barley products (flour, nuggets, and quick flakes, and cookie, pudding, and cake mixes) and Durk & Sandy’s resistant starch and erythritol for the explicit purpose of reducing blood glucose and insulin for better health and longer life.

Another effective method is exercise. The JNCI article1 reported on a recent study by Melinda Irwin in which 75 overweight, sedentary, postmenopausal breast cancer survivors performed an aerobic exercise regimen for 6 months and had a 6% reduction in their insulin levels, as compared to a 36% increase in insulin levels in the control (not exercised) group.

Incidentally, breast cancer risk is a definite health issue for Sandy. Although she does not have it, her sister did (quite a few years ago), and the risk of breast cancer is increased two-fold for a woman whose sister (or other first-degree relative) has had this cancer.

Insulin Signals Plentiful Nutrient Supplies, which Stimulates Cell Growth and Proliferation

One reason that high insulin levels are a risk factor for cancer is that insulin stimulates a signaling pathway (PI3K-PTEN-Akt-TOR) that promotes cell growth and proliferation.8,9 In fact, numerous tumor suppressors act on this pathway, “suggesting that it must be important in cancer since it is kept under such tight negative regulation. . . . Persistent activation [of this pathway] by excess nutrients can lead to insulin resistance and diabetes.”7 Inflammation is also associated with insulin resistance.10 Caloric restriction reduces insulin levels, among its many longevity-inducing effects.

References

  1. Hede. Doctors seek to prevent breast cancer recurrence by lowering insulin levels. J Natl Cancer Inst 100(8):530-2 (2008).
  2. Gnagnarella et al. Glycemic index, glycemic load, and cancer risk: a meta-analysis. Amer J Clin Nutr 87:1793-801 (2008).
  3. Dumesnil et al. Effect of a low-glycaemic index–low fat-high protein diet on the atherogenic metabolic risk profile of abdominally obese men. Br J Nutr 86:557-68 (2001).
  4. Achour et al. Metabolic effects of digestible and partially indigestible cornstarch: a study in the absorptive and postabsorptive periods in healthy humans. Amer J Clin Nutr 66:1151-9 (1997).
  5. Yamada et al. Effect of bread containing resistant starch on postprandial blood glucose levels in humans. Biosci Biotechnol Biochem 69(3):559-66 (2005).
  6. Robertson et al. Insulin-sensitizing effects of dietary resistant starch and effects on skeletal muscle and adipose tissue metabolism. Amer J Clin Nutr 82:559-67 (2005).
  7. Behall et al. Consumption of both resistant starch and beta-glucan improves postprandial plasma glucose and insulin in women. Diabetes Care 29:976-81 (2006).
  8. Zandonella. Life’s throttle: the PI3K-PTEN-Akt-TOR pathway in cell growth and survival. The New York Academy of Sciences eBriefing, posted Sept. 28, 2007.
  9. Luo et al. Targeting the PI3K-Akt pathway in human cancer: rationale and promise. Cancer Cell 4:257-62 (2003).
  10. Shoelson et al. Inflammation and insulin resistance. J Clin Invest 116(7): 1793 (2006).

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