Consumption of 20 grams per day of the black soybean powder for four weeks also led to increases in nitric oxide levels, a potent vasodilator, and reductions in markers of oxidative stress, according to findings published in Nutrients.
“Therefore, daily intake of black soybean is possible to improve vascular stiffness and to reduce the risk of CVD,” wrote scientists from Kobe University and Fujicco Co. Ltd.
Building the science
The new study builds on an earlier open-label study by the same researchers that used test cookies providing 30 grams per day of the black soybean powder for eight weeks. The new study examined the effects of a smaller dose (20 grams per day) for a shorter duration (four weeks) in a randomized, single blind, placebo controlled, crossover trial with 22 healthy adults aged between 30 and 60.
Participants were randomly assigned to consume cookies with either 20 g of roasted black soybeans powder (“Hikariguro” cultivar) or 20 g of flour as a placebo. A four-week “washout” period separated the two interventions.
The results showed vascular function improved in the black soybean cookie group, compared to placebo. Indeed, “In the black soybean group, vascular age became about 3 years younger at the end of the trial, compared to that at the beginning of the trial [and …] significantly younger than that of the placebo group at the end of the trial,” wrote the researchers.
“After the intake of the black soybean cookie, lowered vascular age was observed in 14 of 22 participants whose vascular ages were higher than their chronological age before the trial,” they added.
Improvements in vascular waveform, waveform score, and peripheral vascular health were also recorded after four weeks for the black soybean group, compared to placebo.
Significant decreases were also observed for systolic blood pressure in the black soybean group compared to baseline levels and compared to the placebo.
Consumption of the soybean cookies also resulted in increases in levels of polyphenols in the plasma and urine, and this accompanied significant reductions in levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker for oxidative stress and DNA damage, compared with placebo.
Commenting on the potential bioactives that may contribute the effects, the researchers noted that the black soybean is a good source of polyphenols, such as (−)-epicatechin and cyanidin-3-O-glucoside, which may play a role in boosting nitric oxide levels and reducing levels of oxidative stress.
The researchers also noted that soy protein (“approximately 36% of dry soybeans by weight”) and fiber may also play a role in promoting cardiovascular health.
“These nutrients and polyphenols might coordinately play a role in the improvement of vascular function. Therefore, black soybean is an attractive functional food for prevention and/or improvement of vascular function. Daily intake of black soybean may contribute to maintaining human health,” they wrote.
2020, 12(9), 2755; doi: 10.3390/nu12092755
“Black Soybean Improves Vascular Function and Blood Pressure: A Randomized, Placebo Controlled, Crossover Trial in Humans”
Authors: Y. Yamashita et al.