Many of the health benefits associated with eating broccoli require consumption of the whole vegetables, because key phytonutrients are poorly absorbed and are of far less value if taken as a supplement, according to new research.
The study, published in the Journal of Agricultural and Food Chemistry, is said to be one of the first of its type to determine whether some of the healthy compounds found in cruciferous vegetables can be just as easily obtained through supplements.
"The issue of whether important nutrients can be obtained through whole foods or with supplements is never simple," said Emily Ho, associate professor at the Linus Pauling Institute at Oregon State University, USA – who led the research study.
“Consumption of a broccoli supplement results in significantly lower amounts of isothiocyanate metabolites that are excreted in the urine, which is likely due to the lack of myrosinase enzymes in the supplement,” said the researchers.
Without the enzyme, which is found in the whole food, Ho and her team found that that the body absorbs 5 times less sulforaphane metabolites, and 8-fold less of erucin metabolites,
“This finding has significant implications for people who consume broccoli supplements for the chemopreventive benefits and believe they are getting equivalent amounts of the bioactive isothiocyanates as if they were consuming fresh broccoli sprouts,” they added.
The tissue of cruciferous vegetables, such as broccoli, cauliflower, and cabbage, contain high levels of the plant chemicals glucosinolates. These are metabolized by the body into isothiocyanates (such as sulforaphane), which have been suggested to be powerful anti-cancer agents.
As such, the potential health benefits of broccoli have led to a range of commercial supplements on the market.
When eaten as a raw or lightly-cooked food, enzymes in the broccoli help to break down the glucosinolates into two valuable compounds of intensive research interest – sulforaphane and erucin.
Ho noted that small amounts of the myrosinase enzyme needed to break down glucosinolates are found in the human gut, but her teams findings show that they accomplish that task far less effectively than whole food consumption does.
She added that most supplements designed to provide these glucosinolates have the enzyme inactivated, so sulforaphane and erucin are not released as effectively.
There are a few supplements available with active myrosinase – whose function more closely resembles that of the whole food – but they are still being tested and not widely available, noted Ho.
"Some vitamins and nutrients, like the folic acid often recommended for pregnant women, are actually better-absorbed as a supplement than through food," said Ho.
"But the particular compounds that we believe give broccoli and related vegetables their health value need to come from the complete food," she said.
Earlier this year, researchers from the University of Illinois recently reported combining broccoli supplements with broccoli sprouts to boost the absorption of sulforaphane.
“Data from the combination meal were interesting as they identified possible synergy among the sprouts and powder at early time point measurements of plasma and urine recovered metabolites,” wrote the U of I authors in Nutrition and Cancer (doi: 10.1080/01635581.2011.523495 ).
“The results show that combination improved availability, opening the door to development of products with enhanced chemoprotective potential.”
Source: Journal of Agricultural and Food Chemistry
Published online ahead of print, doi: 10.1021/jf202887c
“Comparison of Isothiocyanate Metabolite Levels and Histone Deacetylase Activity in Human Subjects Consuming Broccoli Sprouts or Broccoli Supplement”
Authors: J.D. Clarke, K. Ried, D. Bella, S.J. Schwartz, J.F. Stevens, E. Ho