Broccoli sprouts

Broccoli sprouts are broccoli seeds left to germinate for a few days, then eaten whole, root and seed leaves included. They matter to anyone reading about sulforaphane for one reason: they carry more of its precursor, glucoraphanin, than any other common food. This section covers what that claim rests on, what human trials of sprouts have found, and how to grow and handle them.

Why do broccoli sprouts have more sulforaphane than broccoli?

They hold far more glucoraphanin, and the plant turns glucoraphanin into sulforaphane when its tissue is broken. In 1997 a Johns Hopkins group reported that 3-day-old sprouts of certain broccoli and cauliflower cultivars contained 10 to 100 times more glucoraphanin than the mature plants of the same cultivars.

Two limits apply to that figure. It is a ratio within each cultivar, and it spans a tenfold range, so it says little about any given packet of seed. The same paper found that extracts of the sprouts reduced mammary tumors in rats treated with a carcinogen. That is an animal result, and it does not show the same effect in people.

The age in that figure is not incidental. A 2002 study measured glucosinolates across an eleven-day developmental span and found the ungerminated seed richest, with content falling as the sprout grew, which is why the convention is to harvest in the first few days. That evidence, and what it means for when to harvest broccoli sprouts, is set out on the growing page.

This site does not quote a per-gram glucoraphanin figure for sprouts without the assay behind it, because published values vary widely between seed lots and methods. Measured values, each with its method, go into the sulforaphane content by food table as they are verified. For how the precursor works, see glucoraphanin.

How do you get the sulforaphane out of broccoli sprouts?

Chewing is what releases it. An intact sprout keeps glucoraphanin and the enzyme myrosinase in separate cells. Chewing, chopping or blending brings them together, and only then does sulforaphane form.

A 2001 study in healthy volunteers tested this directly. Excretion of sulforaphane metabolites was higher when people chewed fresh sprouts thoroughly than when they swallowed them whole. The same study estimated that the ready-formed compounds were about six times more bioavailable than the glucoraphanin precursor, which must first be split, either by plant enzyme or by gut bacteria.

Boiling destroys myrosinase. In that study the researchers boiled sprouts on purpose to make an enzyme-free preparation, so boiled sprouts deliver glucoraphanin without the enzyme that converts it. The how much sulforaphane per day page gives the recovery figures, with methods, for preparations with and without active enzyme.

Chewing, heat, blending and mustard seed are the four preparation steps that have been tested in people, each with a measured result. How to eat broccoli sprouts takes them one at a time, and covers whether washing does anything for safety.

What have human trials of broccoli sprouts found?

A handful of randomized trials have fed people sprouts or sprout products. All were small or short, and all measured markers in blood, breath, stool or urine, not illness.

In one trial, 48 adults infected with Helicobacter pylori were randomly assigned to 70 g of broccoli sprouts a day or the same weight of alfalfa sprouts for eight weeks. The broccoli sprout group had lower urea breath test and stool antigen results, both markers of how heavily the stomach is colonized, and lower serum pepsinogens, markers of stomach inflammation. The values returned to where they started two months after the sprouts stopped.

In another, 81 people with type 2 diabetes were randomly assigned to 10 g or 5 g of broccoli sprout powder a day, or placebo, for four weeks. Only 63 were included in the analysis. At 10 g a day, fasting insulin and HOMA-IR, a calculated index of insulin resistance, fell, with a treatment effect of p = 0.05. That is at the edge of statistical significance, in a small group, over a month. The same randomization produced two further papers on lipid and oxidative stress markers, and none of the three states the sulforaphane content of the powder they used.

In Qidong, China, 200 healthy adults drank a hot-water infusion of 3-day-old sprouts, or a control infusion with almost no glucoraphanin, each night for two weeks. Urinary aflatoxin-DNA adducts did not differ between the two groups. Among people who drank the sprout infusion, those who excreted more sulforaphane metabolites had lower adduct levels, and metabolite levels varied widely from person to person. A later and larger Qidong trial, using a sprout beverage for 12 weeks, is described on the dosage page.

What does not exist is a trial showing that eating broccoli sprouts prevents cancer, diabetes or any other disease in people. The nearest thing is a 2025 randomized placebo-controlled trial of a concentrated sprout extract in 74 adults with prediabetes, which fell short of its own prespecified target with a 0.2 mmol/l reduction in fasting blood glucose over 12 weeks. Every human trial of sprouts and sprout extracts is tabulated by what it measured under sulforaphane benefits.

How many broccoli sprouts should you eat per day?

No official amount exists. The trials above give scale: 70 g of fresh sprouts a day in the H. pylori trial, and 5 or 10 g of dried sprout powder in the diabetes trial. Those are the amounts researchers chose to test, and neither trial was designed to find a best amount.

A gram weight of sprouts also does not fix a sulforaphane dose, because glucoraphanin content varies between seed lots and conversion depends on chewing and on active enzyme. Every daily amount tested in people, from 20 g to 200 g, is listed with its trial size on how much broccoli sprouts per day.

Are raw broccoli sprouts safe?

Raw sprouts have a documented record of food poisoning. A review by US public health researchers counted 33 outbreaks linked to seed and bean sprouts from 1998 to 2010, with 1,330 people reported ill. Salmonella caused 28 of them, Shiga toxin-producing E. coli four, and Listeria one.

That count covers all sprout types, not broccoli alone. In 15 of the 18 outbreaks with information available, growers had not followed FDA guidance, but three came from growers who appeared to follow it. The authors concluded that seed disinfection reduces the risk and does not eliminate it.

In the Qidong infusion trial, the researchers reported no safety or tolerance problems over two weeks. For what trials of sulforaphane products have recorded, see sulforaphane side effects.

How do you grow broccoli sprouts?

In a jar, from seed sold for sprouting, with a rinse and drain twice a day for three to five days. Drainage decides whether a batch works. The step-by-step method, and how to tell root hairs from mold, is in how to grow broccoli sprouts.