Claim: Broccoli contains a lot of iron

As always, iron is an important nutrient for human health and broccoli is supposed to provide us with that nutrient. Broccoli contains about 0.67 mg of iron per 100 g. That would be 7.44% of the daily requirement for men, 4,46% for women. So far so good until the antinutrients kick in.

The bioavailability of iron from broccoli is 9.7%, which is better than spinach, but not by a lot. So effectively 100 g of broccoli will provide 0.74% of iron for men, and 0.47%. A meager amount of iron, especially considering that iron deficiency anemia is already quite common.

The culprit is the generally worse bioavailability of elemental iron. Oxalates play a minor role since broccoli is low in oxalate.

Claim: Broccoli is high in potassium

Also similar to spinach is the claim for high potassium content. At 293 mg per 100 g broccoli has about half the amount of potassium of spinach with a similar bioavailability of ~50%. This means broccoli will indeed provide you with a reasonable amount of potassium. Fair enough.

Claim: Broccoli and Vitamin K

Broccoli contains about 141 mg of vitamin K per 100 g, but as always it’s not that simple. First of all, bioavailability from broccoli is below 10%, resulting in 14 mg absorbed. Second is the form of vitamin K. While animal foods contain the form of Vitamin K2, plant foods on the other hand contain the form Vitamin K1. Although little is known about the bioavailability of Vitamin K2 in numbers, it is generally considered more bioavailable.

There are also many sub-forms of Vitamin K2 like MK4 and MK7 (menaquinones) which all have different sources and effects, but there is only murky evidence and quite some debate which ones are better or worse.

That being said, it isn’t really known what 14 mg of Vitamin K1 are going to do, or if it’s enough or not. The current requirements put it at ~100 mg per day for adults, with no upper limit defined.

Claim: Broccoli provides a lot of calcium

Broccoli on paper contains 40 mg of calcium per 100 g. Though this is even less than would be in spinach, broccoli has a much higher bioavailability of ~48% due to being a low-oxalate vegetable. So all things considered, broccoli is probably a much better source of calcium than spinach. But compared to that, a single 50 g egg weights in at 25 mg of calcium. Egg prevails.

Further claims: Vitamin C, Folate

At 108 µg of folate per 100 g it is somewhat lower than spinach. But fiber entraps the folate and makes it less bioavailable unless broken down (e.g. blending or extensively cooking it) and cooking does directly destroy ~50% of the folate contained. So in the end it may not be as effective as you’d hope, unless you’re downing raw broccoli smoothies.

Vitamin C on the flipside is crazy high in broccoli covering almost 70-100% per 100 g. But when boiled a lot of it is lost, so keep that in mind. But if I were scared of not getting enough vitamin C, I’d still rather eat some fruit than (raw) broccoli to cover that need.

Glucosinolates

This is where the article I mentioned really gets ahead of itself, claiming “glucosinolates strengthen your immune system and help prevent cancer“. It also claims that glucosinolates “has antifungal and antibacterial properties that your body needs for detoxification“. What are they even thinking of making definitive health claims like that?

They don’t even link any sources, which doesn’t really surprise me because there are probably none available. Let me guess, it’s probably some epidemiological “nutrition science” nonsense again.

Glucosinolates are bitter tasting and are supposed to deter you from eating the plant. They are released as a reaction when the plant is damaged aka chewed or cut. And that’s a good thing since they are toxic. You don’t want to eat that stuff.

Glucosinolates form Isothiocyanates in the gut which interfere with the production of thyroid hormones. Thiocyanates inhibit the absorption of iodine into the thyroid leading to decreased production of thyroxine. Oxazolidine-2-thiones also suppress iodine uptake and thyroxine release. Sulforaphane (and some others) are also often claimed to have anti-cancer properties or other health effects, with absolutely zero evidence to back this up.

The website goes as far as claiming that raw broccoli is better because cooking destroys the glucosinolates (and the folate and vitamin C).

Broccoli for protein

I really struggle to understand this point, but I’ve seen it time and time again. Broccoli contains about 3 g of protein per 100 g. How in the world is that supposed to be a reasonable source of protein? Obviously it’s not complete protein either, just forget it and eat some meat.