Flaxseed Outperforms Soy in Reducing Cholesterol, Liver Fat Levels

BELTSVILLE, Md.--Flaxseed meal proved to be more beneficial than soy protein concentrate against high triglyceride levels and liver fat composition in an animal model of obesity, as noted in the April issue of the Journal of the American College of Nutrition (22, 2:157-64, 2003) (www.jacn.org). Sam J. Bhathena, Ph.D., and colleagues from the U.S. Department of Agriculture (USDA) Beltsville Human Nutrition Research Center compared the effects of dietary soy protein, flaxseed meal or casein (control) on plasma and liver lipids in a genetic model of obesity, Type II diabetes and insulin resistance.

"We are very interested in obesity and diabetes and whether flax and soy have any beneficial effect," Bhathena told INSIDER. "From several studies we have found soy and flax have a beneficial effect [on both]."

Bhathena and his team fed lean and obese rats diets containing 20 percent of energy from casein, soy protein or flaxseed meal for six months. Plasma was analyzed for total cholesterol, LDL cholesterol, triglyceride and total protein, and livers were analyzed for steatosis, which is characterized by fat deposits in the liver. Fatty liver composition indicates a higher circulation of fat in the bloodstream, according to Bhathena, which is a negative occurrence.

In lean rats, plasma total cholesterol was reduced by 26 percent with soy protein and by 20.3 percent with flaxseed meal compared to casein. Flaxseed meal also significantly lowered plasma triglyceride in both lean (33.7 percent) and obese (37 percent) rats compared to casein-fed rats. In obese rats, flaxseed meal reduced cholesterol levels by 41 percent, including reductions in both LDL and HDL cholesterol.

While reduced LDL cholesterol is beneficial, reduced HDL is not a positive finding of this study, according to Bhathena. "But this is what we have observed," he said. "Unfortunately, [flaxseed] reduces good cholesterol, and that's unfortunate. Many people have not seen that effect and have reported HDL cholesterol either remains the same or is increased. Our results differ somewhat from others. But that was only with the flaxseed. With soy, [HDL cholesterol] remains almost identical--there was no statistically significant difference."

In terms of liver composition, researchers found a significantly greater fat accumulation in the livers of obese rats compared to those of lean rats, regardless of dietary protein type. However, flaxseed meal significantly lowered fat deposition in the livers of both lean and obese rats compared to rats fed casein or soy protein, although researchers did not determine a mechanism of action for this effect.

Researchers concluded that the triglyceride- and cholesterol-lowering effects of flaxseed meal may have important therapeutic implications in patients with high triglycerides and cholesterol, and deserve further study in humans with high levels. Bhathena and his colleagues are currently writing a paper regarding the effects soy and flaxseed had on diabetes, insulin resistance and obesity.