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Eggs May Promote Colon Cancer

glucose meterEggs have been a controversial topic in nutrition for many years. Starting in the 1970s, a heavy focus was placed on reducing dietary cholesterol, and eggs were considered dangerous, since eggs are the most concentrated source of cholesterol in the American diet. Over time, the association between dietary cholesterol and heart disease was questioned, and the research suggested that for healthy people, eggs were only harmful in large quantities. Findings from the Physicians’ Health Study published in 2008 found a 23% increase in risk of death (from any cause) in those who ate more than one egg/day, and additional studies reported similar results. These risks were magnified in diabetics, whose risk started to climb at a smaller quantity, about 5 eggs per week.1-3 A more recent study linked higher egg consumption to increased atherosclerotic plaque area, and suggested that eggs could be harmful in smaller quantities than originally thought. Subjects eating more than 3 eggs per week had significantly more plaque area in their carotid arteries than those eating less than 2 eggs per week.4

Other studies linked similar amounts of eggs to prostate cancer risk. An 81 percent increase in the risk of lethal prostate cancer was found for men eating 2.5 or more eggs per week compared to those eating less than half an egg per week.5,6 Now, a new analysis of data from forty-four studies focused on gastrointestinal cancers (esophagus, stomach, colon, and rectal cancers), and found that eggs are strongly linked to these cancers as well.

The collective analysis of forty-four studies, separated over 400,000 participants into groups who consumed less than 3, 3-5, or greater than 5 eggs per week. As egg consumption increased, so did the risk of gastrointestinal cancers. Compared to no egg consumption, there were 13, 14 and 19 percent increases in risk for the less than 3, 3-5 and more than 5 eggs per week groups. When looking at the specific cancer sites, the authors noted that the strongest correlation was present for colon cancer. For colon cancer specifically, the less than 3 and 3-5 eggs per week groups had similar increases in risk—about 15 percent—and the group eating more than 5 eggs per week had a 42 percent increase in risk.7

Why might eggs contribute to cancer?
Eggs are very rich in cholesterol and choline, each of which may have cancer-promoting properties. Higher blood cholesterol and choline are both linked to increased risk of prostate cancer.8-10 Cholesterol is enriched in tumor cells and cholesterol influences cell proliferation and migration, processes that are vital to cancer development.11-13 Choline is also enriched in tumor cells and has been implicated in colorectal cancers. Similar to carnitine from red meat, choline from eggs is metabolized by gut bacteria into a pro-inflammatory compound that may contribute to chronic diseases, cancer included.14-16 Plus, egg whites are a highly concentrated source of animal protein, which carries its own risks by elevating circulating insulin-like growth factor 1 (IGF-1), a hormone associated with cancer promotion.

How many eggs can we eat safely?
Those with diabetes, cardiovascular disease or cancer (or who are at risk of these conditions) should not eat eggs. This new research has identified a risk associated with only 1-2 eggs per week; demonstrating that eggs are more harmful than we previously thought. Therefore, even for healthy people, eggs, like other animal products, should be limited.


References:

1. Djousse L, Gaziano JM: Egg consumption in relation to cardiovascular disease and mortality: the Physicians' Health Study. Am J Clin Nutr 2008, 87:964-969.
2. Qureshi AI, Suri FK, Ahmed S, et al: Regular egg consumption does not increase the risk of stroke and cardiovascular diseases. Med Sci Monit 2007, 13:CR1-8.
3. Hu FB, Stampfer MJ, Rimm EB, et al: A prospective study of egg consumption and risk of cardiovascular disease in men and women. JAMA 1999, 281:1387-1394.
4. Spence JD, Jenkins DJ, Davignon J: Egg yolk consumption and carotid plaque. Atherosclerosis 2012, 224:469-473.
5. Snowdon DA, Phillips RL, Choi W: Diet, obesity, and risk of fatal prostate cancer. Am J Epidemiol 1984, 120:244-250.
6. Richman EL, Kenfield SA, Stampfer MJ, et al: Egg, red meat, and poultry intake and risk of lethal prostate cancer in the prostate-specific antigen-era: incidence and survival. Cancer Prev Res (Phila) 2011, 4:2110-2121.
7. Tse G, Eslick GD: Egg consumption and risk of GI neoplasms: dose-response meta-analysis and systematic review. Eur J Nutr 2014.
8. Johansson M, Van Guelpen B, Vollset SE, et al: One-carbon metabolism and prostate cancer risk: prospective investigation of seven circulating B vitamins and metabolites. Cancer Epidemiol Biomarkers Prev 2009, 18:1538-1543.
9. Platz EA, Clinton SK, Giovannucci E: Association between plasma cholesterol and prostate cancer in the PSA era. Int J Cancer 2008, 123:1693-1698.
10. Pelton K, Freeman MR, Solomon KR: Cholesterol and prostate cancer. Curr Opin Pharmacol 2012, 12:751-759.
11. Cruz PM, Mo H, McConathy WJ, et al: The role of cholesterol metabolism and cholesterol transport in carcinogenesis: a review of scientific findings, relevant to future cancer therapeutics. Front Pharmacol 2013, 4:119.
12. Steinmetz KA, Potter JD: Egg consumption and cancer of the colon and rectum. Eur J Cancer Prev 1994, 3:237-245.
13. Cruse P, Lewin M, Clark CG: Dietary cholesterol is co-carcinogenic for human colon cancer. Lancet 1979, 1:752-755.
14. Tang WH, Wang Z, Levison BS, et al: Intestinal microbial metabolism of phosphatidylcholine and cardiovascular risk. N Engl J Med 2013, 368:1575-1584.
15. Wang Z, Klipfell E, Bennett BJ, et al: Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease. Nature 2011, 472:57-63.
16. Richman EL, Kenfield SA, Stampfer MJ, et al: Choline intake and risk of lethal prostate cancer: incidence and survival. Am J Clin Nutr 2012, 96:855-863.

 

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