Reference
Cramer JM, Jeffery EH. Sulforaphane absorption and excretion following ingestion of a semi-purified broccoli powder rich in glucoraphanin and broccoli sprouts in healthy men. Nutr Cancer. 2011;63(2):196-201.
Design
Subjects were randomly assigned to a 4-by-4 crossover design with a 2- or 3-day washout between experimental meals.
Participants
Four healthy men, aged 18 to 30 years
Study Medication and Dosage
The test meals contained either 2 grams of air-dried broccoli sprouts, 2 grams of broccoli powder or both together. These were mixed into a bowl of Kashi Go Lean Crunch cereal with yogurt.
Outcome Measures
Blood and urine samples were analyzed for sulforaphane and isothiocyanate levels.
Key Findings
Broccoli sprouts produced the highest 24-hour recovery of sulforaphane (74%) while the combination of sprouts and broccoli powder produced 49% and the broccoli powder alone only 19%.
Practice Implications
Given the quantity of research that suggests the phytochemical sulforaphane plays a desirable role in promoting health, we should encourage our patients to consume foods or supplements that will provide this chemical. This study by Cramer and Jeffery adds valuable information on how to do so.
Cruciferous plants use sulforaphane to ward off bacterial, viral, and fungal infections. Despite this antibiotic-like effect, Sulforaphane probably triggers benefit in people via a hormetic effect: “At the subtoxic doses ingested by humans that consume the plants, the phytochemicals induce mild cellular stress responses.”2
Plants often store their noxious chemicals in inert form, activating them only as needed. In the case of sulforaphane, as in many other parallel plant systems, the activating enzymes are stored in nearby cell vacuoles and are released when the cells are damaged. An example that patients easily relate to is the reaction in onions. Once chopped or chewed, onions quickly undergo a reaction releasing a sharp smell and odor. Garlic is another example; damage to the plant releases the enzyme alliinase. This enzyme catalyzes the reaction in which alliin is converted into allicin. In the case of cruciferous vegetables, glucoraphanin is the stored form of the chemical and requires the enzyme myrosinase for it to be converted into sulforaphane. Thus to get sulforaphane from the diet requires the chemical reaction between glucoraphanin and the enzyme myrosinase. If cruciferous vegetables are cooked before they are eaten, the heat destroys the myrosinase enzyme, and very little sulforaphane is produced. Fermentation by intestinal bacteria can also catalyze this reaction but not very efficiently.
Nutritional supplements that contain cruciferous vegetable concentrates have become popular. Unless otherwise stated, assume they contain only glucoraphanin and not sulforaphane. While attracting consumer attention and sounding healthy, they provide little benefit. That is, unless they contain myrosinase enzyme with which to catalyze the reaction to sulforaphane.
As suppliers begin to add cruciferous vegetable extracts to their product lines, we should question them about myrosinase content or sulforaphane yield.
Tang et al, in their bladder cancer study from June 2005, illustrate the value of active sulforaphane. In looking for correlations in diet and cancer recurrence, they found no association between consumption of cooked cruciferous vegetables and bladder cancer recurrence. On the other hand, individuals who ate one or more servings of raw broccoli per month had less than half the risk of their cancer returning compared to those that ate broccoli less often.3 Remember, cooking destroys myrosinase, and without it, very little sulforaphane is produced.
Cramer and Jeffrey used air-dried broccoli sprouts to provide the myrosinase enzyme in this study. About 4/5 of the glucorophanine in the broccoli sprouts is converted into sulforaphane during eating and digestion because the sprouts contain active enzyme. Combining broccoli sprout powder with enzyme-empty broccoli powder allowed the enzymes from the sprouts to convert about half of the glucoraphanin in the inert powder into sulforaphane. Consuming just broccoli powder still produced a little sulforaphane through intestinal fermentation; about one-fifth of the glucoraphanin us converted. Obviously it would be to anyone’s advantage to consume myrosinase whenever eating foods containing glucoraphanin.
Myrosinase is available in a number of food sources. Daikon radishes, common in Japanese salads, contain significant amounts of myrosinase, but most is in the skin, a part of the plant typically not eaten.4 Myrosinase is also present in rapeseed but is purposefully deactivated by heating before the seeds are pressed to make canola oil. Just because the chemicals produced by this enzyme provide medical benefit does not mean that we like the way they taste.
This current study by Cramer and Jeffrey highlights the importance of myrosinase. Powdered or cooked vegetables, even if they contain glucoraphanin, are of little benefit unless converted to sulforaphane. As suppliers begin to add cruciferous vegetable extracts to their product lines, we should question them about myrosinase content or sulforaphane yield. We should encourage testing for and labeling the enzyme levels for these products. If myrosinase is not present, these powders provide little benefit. Watch for products containing myrosinase. Someday, we may add myrosinase to digestive enzyme formulas taken when eating cruciferous vegetables. Such a practice may increase the potential benefits of these foods.
