The Paleo Diet - Loren Cordain [43]
Other Diseases Related to Insulin Resistance
It’s only recently that scientists have begun expanding the scope of insulin resistance. In research worldwide, this condition is being linked to many other chronic diseases and health problems. Scientists are exploring the role of insulin resistance in certain types of cancer, nearsightedness, polycystic ovary syndrome, and even acne—although in all of these, as in heart disease, many causative factors are believed to be involved. It is premature to establish a direct cause-and-effect relationship. But if these diseases ultimately do turn out to have insulin resistance as their underlying cause, you’ll be protected—because the Paleo Diet contains all of the dietary elements known to stop insulin resistance.
Breast, Prostate, and Colon Cancers and Insulin Resistance
Over the last five years, scientists have discovered through a chain reaction of metabolic events that elevated levels of insulin in the bloodstream increase blood levels of a hormone called “insulinlike growth factor one” (IGF-1) and decrease another hormone called “insulinlike growth factor binding protein three” (IGFBP-3). The decrease in IGFBP-3 causes tissues to be less sensitive to one of the body’s natural chemical signals (retinoic acid) that normally limits tissue growth. In addition, IGF-1, a potent hormone in all tissues, is a major regulator of growth: Increased levels of IGF-1 encourage growth, and reduced levels slow growth. Children who are below normal height have low levels of IGF-1. When IGF-1 is injected into these children, they immediately start to grow taller. As you might expect, tall children have higher levels of IGF-1. Studies of growing children by Dr. William Wong and colleagues at the Children’s Nutrition Research Center in Houston found that girls who were taller and heavier and who matured earlier had higher blood levels of both insulin and IGF-1 and lower levels of IGFBP-3. Diets that cause insulin resistance—particularly, high-glycemic-carbohydrate diets—increase IGF-1 levels, lower IGFBP-3 levels, and decrease tissue sensitivity to retinoic acid. These hormonal changes, in turn, accelerate growth in developing children.
What does this have to do with adult health? It’s been found that IGF-1 is a powerful stimulator of cell division—growth—in all cells during all phases of life. In fact, scientists suspect that IGF-1 may be one of the primary promoters of all unregulated and tissue growth in the body. But IGFBP-3 prevents unregulated cell growth by causing cancer cells to die naturally through a process called “apoptosis.” Over the last decade, numerous scientific papers have shown a strong association between elevated levels of IGF-1, lowered levels of IGFBP-3, and breast cancer in premenopausal women, prostate cancer in men, and colorectal cancer in all adults. In animal models of many types of cancer, scientists can promote cancer by adding a key ingredient—IGF-1; conversely, adding IGFBP-3 slows cancer. Synthetic derivatives of the body’s natural retinoic acid powerfully inhibit the cancer process in cell cultures. So, the whole chain of hormonal events initiated by elevated blood levels of insulin tends to promote the cancer process.
Two risk factors for breast cancer are early onset of puberty and above-average height. It is entirely possible that the same high insulin levels that elevate IGF-1 and lower IGFBP-3 (in other words, the levels that make children taller and make puberty happen sooner during childhood) also increase susceptibility to cancer during adulthood.