Slimming soybeans are on the horizon

"We found that soybeans rich in beta-conglycinins limit lipid accumulation in fat cells by inhibiting an enzyme called fatty acid synthase. What's more, we have identified the specific peptides (digested proteins) that do this, and we are now beginning to understand the mechanism behind it. This is exciting research because it could lead to the development of nutraceuticals to fight obesity," said de Mejia, a U of I associate professor of food science and human nutrition.

The study was also the first to establish the anti-inflammatory properties of soy high in this type of protein. "The peptides fight inflammation by blocking key enzymes in the body's immune response," said the scientist.

de Mejia said that soy contains, among others, two types of protein, glycinins and beta-conglycinins, and the most important factor influencing a soy cultivar's healthful effects is the proportion in which they occur. Her research shows that soy that is low in glycinins and high in beta-conglycinins is preferred for its ability to inhibit lipid accumulation and inflammation.

"Using the latest molecular marker-assisted breeding techniques, soybeans with the right composition can be tagged and later identified using a simple leaf tissue sample. This would make it possible to create high-yielding cultivars that contained the 'slimming' trait for soybean farmers to grow in their fields," she said.

How did de Mejia discover that certain soybeans had this slimming effect? She had learned from her previous research that administration of soy protein caused weight loss in laboratory rats, but she wanted to know exactly why it happened.

She incubated human fat cells in the lab, treated them with soy hydrolysates from 15 soy genotypes containing varying amounts of beta-conglycinin, and then measured the amount of fat that accumulated.

"As we increased the concentration of beta-conglycinin, we saw more inhibition of lipids and less accumulation of fat. Further testing showed that this occurred because fatty acid synthase, an enzyme responsible for synthesizing lipids, had been suppressed.

"We also found that fat cells exposed to digests made from the 'slimming' soybeans increased the synthesis of adiponectin, a hormone that enhances insulin sensitivity and fat metabolism," she said.

She then compared the activity of beta-conglycinins with glycinins and found that hydrolysates from beta-conglycinins inhibited almost 50 percent of lipid accumulation in the fat cells. Glycinins did not inhibit lipid accumulation at all, she said.

In a separate study, her team identified specific soy peptides that inhibit fatty acid synthase, and they were able to learn exactly how it happens.

de Mejia and her colleagues are now taking their research a step further by performing human trials with soy milk that is high in beta-conglycinins.

"For years we've known that soy protein is a good source of essential amino acids. Soy helps us maintain muscle mass, and its peptides make people feel full so they don't eat as much," she said.

"Now it appears that products made from soybeans selected for this particular protein profile may also help limit fat accumulation. Food manufacturers will be able to create soy products targeted at consumers who are trying to maintain their ideal weight," she said.

The first study appeared in a recent issue of Molecular Nutrition and Food Research. Cristina Martinez-Villaluenga and Vermont P. Dia of the University of Illinois, Mark Berhow of the Agricultural Research Service, and Neal A. Bringe of The Monsanto Company are co-authors.

It was supported by Monsanto, whose geneticists provided the 15 soy genotypes; the USDA Cooperative State Research, Education and Extension Service (CSREES); and a Marie Curie International Outgoing Fellowship for Career Development.

The study that identifies the specific peptides and the mechanism by which they inhibit fatty acid synthase appears in FEBS Journal.