A recent study offered some alarming news for bodybuilders and others who regularly follow a high-protein diet: High protein was linked to cancer. While obesity has been associated with an increased risk of several types of cancer, the study used lean subjects eating various amounts of protein. Three groups of 21 people each were divided into the following:
1) A low-protein, low-calorie, raw-food vegetarian-diet group.
2) A typical Western diet group—more protein and calories than group 1; and subjects engaged in running an average of 48 miles per week.
3) A sedentary group that did no exercise but ate a standard Western diet consisting of higher sugar, refined grains and animal products.
The subjects were matched for age, sex and demographic factors. None smoked or had diabetes, cancer, cardiovascular disease, lung disease or any other chronic illness.
Those in the low-protein group ate an average of 0.73 grams of protein per kilogram of bodyweight. Thus, a 200-pound man got only 65.7 grams of protein daily, less than in one average bodybuilding protein drink. The runners got a daily protein intake averaging 1.6 grams per kilogram of bodyweight, while the sedentary group averaged 1.23 grams per kilogram of bodyweight. In contrast, the suggested daily intake of protein for a nonathlete is 0.8 grams per kilogram of bodyweight.
Those in the low-protein group had the lowest levels of a hormone called insulinlike growth factor 1. Some scientists believe that IGF-1 is linked to various types of cancer, such as breast, colorectal and prostate cancers. That’s based on the observation that those particular cancer patients have higher blood levels of IGF-1. In addition, IGF-1 is known to promote cell division, and cancer is marked by out-of-control cell division. Other studies involving animals, such as rats and mice, link lower levels of IGF-1 to increased longevity.
Scientists have long known that the amount of IGF-1 in the body is directly related to diet. A high protein intake makes for IGF synthesis in the body, while lowering both calories and protein decreases IGF-1. This study suggests that a high-protein diet increases cancer risk because it increases IGF-1.
IGF-1 is familiar to many bodybuilders. Under the influence of growth hormone, IGF-1 is synthesized in the liver, then released into the blood for systemic use. It’s considered the active anabolic component of growth hormone; that is, the anabolic effects of GH result from IGF-1, rather than GH itself. IGF-1 is also produced locally in muscle, where two variants of it play a major role in muscular repair after exercise and muscular growth. The effect is so potent that many athletes directly inject IGF-1 drugs.
Like other hormones, IGF-1 is associated with various protein carriers that extend its time in the body before it’s degraded in the liver. The primary carrier is known as insulinlike growth factor-binding protein-3. If IGF-1 is attached to IGFPB-3, it isn’t active but lasts as a reserve in the blood for more than 12 hours. GH itself degrades after about an hour. For that reason, GH activity is measured by how much IGF-1 is in the blood.
Before you consider abandoning a high-protein diet because of cancer fears, consider a few other facts about IGF-1. First, there’s still no direct evidence that IGF-1 promotes cancer. The rate of cancer incidence reaches a peak in older people—who usually have the lowest levels of IGF-1. If IGF-1 directly promoted cancer, teenagers, who have the highest levels of it, should also have the highest rates of cancer, and that just ain’t so. While some studies have demonstrated an indirect relationship between IGF-1 and cancer, others have not. The picture is hardly definitive.
A few researchers suggest that it’s a case of the chicken or the egg in the sense that tumors or cancer cells may themselves produce IGF-1 as a means of generating tumor replication and spread. Other scientists (mistakenly) believe that IGF-1 partly causes the initial tumor; the vast majority of IGF-1 is tightly bound to its carrier protein in the blood, which makes it incapable of promoting anything, much less cancer. Several studies have shown that IGF-1 is absolutely vital to maintaining the health of brain and heart cells. Without sufficient IGF-1, brain cells rapidly die. Many brain diseases, such as Alzheimer’s, are characterized by low IGF-1. Without sufficient IGF-1, the heart cells also die, resulting in heart failure. IGF-1 is now being considered as a medication to treat heart failure. Lowered IGF-1 is thought to be related to muscle loss that occurs with aging, a.k.a. sarcopenia. One proposed treatment is gene therapy to restore IGF-1 synthesis in aged, atrophied muscles. Older animals treated that way show muscle size and strength equivalent to teenagers.
The authors suggest that people should eat more vegetables and fruits to ward off cancer, which is good advice. They also suggest that the best diet would be vegetarian and low in protein—anathema to anyone interested in any degree of muscularity.
On the other hand, the same issue of the journal that carried the low-protein/cancer prevention study also reported a study involving 1,542 women. In it, women who took in the highest amounts of citrus fruits and vitamin C also showed the highest levels of IGF-1 coupled with the lowest levels of IGFPB-3—the same metabolic profile shown in the previous study to promote cancer. Numerous studies show that, if anything, citrus fruits and vitamin C help prevent cancer. The study also showed a lesser relationship between consumption of cruciferous vegetables, such as broccoli, brussels sprouts and cabbage, with higher IGF-1 levels. That’s significant because those particular vegetables have by far the greatest anticancer properties.
It turns out that promoting cancer requires more than just IGF-1. You also need an active IGF-1 cell receptor, and antioxidants such as vitamin C are known to interfere with the locking of IGF-1 to its cellular receptor. Studies show that one form of vitamin C prevented the proliferation of a type of brain tumor and the most deadly cancer—pancreatic—by downregulating the number of IGF-1 cell receptors. Other elements found in various fruits and vegetables interfere with cell signaling induced by IGF-1, nullifying tumor mischief from IGF-1.
ALLSo if you’re concerned about a high-protein diet in relation to cancer, make your day include at least five—with nine to 11 being ideal—servings of fruits and vegetables, particularly cruciferous vegetables. IM
Fontina, L., et al. (2006). Long-term low protein, low-calorie diet and endurance exercise modulate metabolic factors associated with cancer risk. Amer J Clin Nutr. 84:1456-62.
Tran, C.D., et al. (2006). Relation of insulinlike growth factor (IGF-1) and IGF-1-binding protein-3 concentrations with intakes of fruit, vegetables and antioxidants. Amer J Clin Nutr. 84:1518-26.