New USDA Study Shows Plant
Sterols Lower Cholesterol
By Jim De
April 18, 2000
WASHINGTON, Apr. 18--People who
already eat a low-fat diet to reduce cholesterol might lower it more by
consuming a soybean extract with high levels of substances called plant
sterols, according to preliminary new research,
Agricultural Research Service
Administrator Floyd P. Horn said today. Volunteers in the research study ate
the soybean sterols as an ingredient in low- and reduced-fat salad dressings.
"The research is preliminary but offers new evidence that soybean and
other plant extracts containing sterols can increase the cholesterol-lowering
benefits of a healthy low-fat diet," said Horn. "People who want to
reduce their cholesterol through diet may see better results by including
low-fat foods having added sterols as part of their low-fat diet."
study's lead researcher, chemist Joseph T. Judd of
USDA's Agricultural Research Service in
Beltsville, Md., presented the findings today at the
2000 meeting in San Diego.
Horn said cholesterol reductions nearly doubled in the study's 53 men and
women volunteers, when their low-fat diet included two daily servings (4
tablespoons total) of salad dressing containing soybean sterols. The volunteers
consumed the sterols--2.2 grams or about ½ teaspoon--daily for three weeks
of the six-week study period in 1999.
Judd led the study at ARS'
Beltsville Human Nutrition
Research Center. The study was partly funded by Lipton through a
cooperative research agreement with ARS. A manuscript is being prepared for
submission to a peer-reviewed scientific publication.
Plant sterols are ingredients in a number of fat-based foods on the market
including salad dressings and margarines. Potential dietary benefits of plant
sterols, including cholesterol reduction, have been studied for decades. Judd
said the Beltsville study was unique in examining plant sterols as an
ingredient in low-fat foods and as part of a tightly controlled low-fat diet.
Most studies have looked at sterol effects in higher fat foods.
The soybean extracts used in the Beltsville study are compounds known as
sterol esters. Their molecular structure is similar to cholesterol. Judd said
sterol esters most likely lowered the volunteers' cholesterol by limiting its
The volunteers began the study with their levels of "bad" (LDL)
cholesterol in the mildly elevated range. For six weeks, they ate all their
meals at the Beltsville center. For three of those weeks, their daily diet
included 2.2 grams of soybean sterols as an ingredient in salad dressing. On
the low fat diet alone--without plant sterols--the volunteers' total and
"bad" cholesterol levels dropped 7.3 and 8.4 percent, respectively.
With the sterols, the reductions were nearly double: 14.1 and 18.2 percent.
"I was surprised at the magnitude of the effect," said Judd, with the
Beltsville center's Diet and Human Performance Laboratory. "And, the
volunteers' levels of 'good' (HDL) cholesterol stayed the same."
Overall fat intake in the study diet amounted to 32 percent of total
calories. A 36-percent fat diet is about the average for American adults.
Curiously, five of the 53 volunteers lowered their cholesterol only during
the part of the study that included sterol esters. "Many people with high
cholesterol," Judd noted, "do not respond to a low-fat diet alone and
rely on cholesterol-lowering drugs. The question is, could dietary plant
sterols also help these kinds of people?"
Judd conducted the study with physiologist David Baer of the
Diet and Human
Performance Laboratory; chemist Beverly Clevidence, who leads the center's
Laboratory; and nutrition scientists Shirley Chen and Gert Meijer of
"We want to learn how plant sterols could affect cholesterol in people
eating their own diets," Judd said. "So, we plan to extend our
investigation of plant sterols to study about 100 free-living volunteers who
will eat their usual diets instead of a controlled diet."
The sterols used in the study already occur--in low concentrations--in many
raw and refined vegetable-based foods including vegetable oils. A typical
American diet provides approximately 0.25 g of plant sterol per day. "It
would be impractical to try to consume 2.2 grams a day of sterols from refined
oils or other foods," Judd said.
Scientific contacts: Joseph T. Judd and David Baer, Diet and Human
Performance Laboratory, ARS Beltsville Human Nutrition Research Center,
Beltsville, Md., phone (301) 504-9014, fax 504-9098,