"Soy is known to have a number of health benefits, including the suppression of cancer. Based on our results, some of this benefit may be due to a group of molecules known as sphingolipids," said Merrill.
Soy GlcCer is just one of the many types of sphingolipids found in plants and animals. Merrill and colleagues have already shown that milk sphingolipids can suppress tumor formation. But this is the first study, he said, that has established that the sphingolipids of plants - which are structurally different - can also inhibit colon cancer. Other foods rich in sphingolipids are eggs, cheese and wheat flour.
The study is the latest in a series of findings showing the medical benefits of the soybean. Earlier this year, researchers from Cincinnati Children's Hospital, Colorado State University and Brigham Young University found that eating soy can help reduce the risk of prostate cancer.
In Merrill's latest study, he found soy GlcCer was able to reduce the number of tumors in both mice with an inherited defect that leads to GI cancer and in mice exposed to a chemical that causes colon cancer.
One feature that makes Merrill's results especially promising is that it didn't take massive doses of soy GlcCer to show an anti-cancer effect. The amounts used in the study were similar to those naturally found in soybeans.
Another result was that unlike many substances that are digested, soy GlcCer survives the journey through the stomach and intestine with enough power to affect cancerous cells in the colon. Ensuring that cancer-fighting substances reach the cells is always a hurdle in any kind of cancer research.
Cancer is most often found in cells that experience rapid division, such as gastrointestinal, skin, lung and breast cells, explained Merrill. As the cells divide, mutations can occur that alter the function and chemistry of the cells. Each mutation a cell experiences leaves it more vulnerable to others. Cancer results when cells have accumulated a series of genetic mutations accompanied by unregulated growth.
It is not known exactly how sphingolipids suppress cancer; there are probably many mechanisms involved, said Merrill. But targeting beta-catenin, a protein involved in cell growth, seems to be one method. Too much of this protein, and the cells grow unchecked. Soy GlcCer reduces the amount of beta-catenin in the cells, helping the body regain control. "In essence, sphingolipids are bypassing the genetic defect," said Merrill.
With funding from the National Cancer Institute, Merrill and colleagues are developing new compounds based on sphingolipids that might be useful as anti-cancer drugs. "We are looking for even more potent forms of these molecules that might be effective for cancer treatment," he said.
He hopes to begin studies to see if sphingolipids have similar effects on humans as they have for mice. "If naturally occurring sphingolipids like soy GlcCer suppress cancer in humans, this has the potential to allow the public to select their diets in a more rational way," he said.
But because sphingolipids haven't been classified as a nutrient, they don't appear in food composition tables, so epidemiologists cannot evaluate their importance to public health.
"Foods contain many substances that are beneficial to health that haven't yet been categorized as nutrients. The new challenge for the field of diet and health is to find out the entire spectrum of molecules that are important to health," said Merrill.