Food and diet

Broccoli compounds may help combat chronic diseases

"Eating broccoli could lower your risk of having coronary heart disease, type 2 diabetes and several types of cancer, a new study suggests," the Daily Mail reports.

But there is little hard evidence to back up this claim – the study it reports on involved plants, not humans.

Phenols, which are compounds found in broccoli and other cruciferous vegetables, have been linked for years to a lower risk of heart disease, certain cancers, type 2 diabetes and asthma.

They are thought to play a part in reducing oxidative stress – cell damage caused at the molecular level – and inflammation in cells, although the way they do this is unclear.

Because of their potential health-giving properties, plant scientists would like to produce fruits and vegetables with higher levels of phenols.

This study looked at a type of broccoli bred specifically for high phenol content, and mapped which genes and gene sequences were most consistently linked to high phenol production.

However, the study also showed variation between the levels of phenol in different growing conditions, across different years. That suggests it's not as simple as tweaking genes – environmental factors also influence phenol content.

Despite the Mail's headline to the contrary, no type of "genetically tweaked" broccoli has been tested on animals, let alone humans.

Broccoli and other types of green vegetables are recommended as part of a healthy diet, but this study does not provide evidence the vegetable directly reduces the risk of these chronic diseases.  

Where did the story come from?

The study was carried out by researchers from the University of Illinois and the International Institute of Tropical Agriculture in Tanzania, and was funded by the Hatch Multistate Project.

It was published in the peer-reviewed journal, Molecular Breeding.

The Mail focuses on the old news that phenols in broccoli are linked to a lower risk of certain diseases, which was first reported in studies during the 1990s and 2000s.

The reporting is confused and poorly focused. The point of the new study – the researchers' hopes they may be able to breed vegetables with higher levels of phenols – is mentioned, but not in the headline or first few paragraphs.

The fact that this story seems to champion the idea of genetically enhanced broccoli also seems at odds with the newspaper's often-stated editorial policy against so-called "Frankenstein foods": genetically modified, or GM, foods.

What kind of research was this?

This is a plant-breeding study that used molecular and genetic markers to identify certain traits.

The potential health benefits of phenolic compounds found in fruit and vegetables have been extensively studied.

The biological pathways involved in the production of phenols within plants are also quite well understood.

This study aimed to better understand the genetics associated with the production of the highest phenol levels, as well as the environmental factors that could influence this.

The ultimate aim is to breed plants that could be most beneficial for human health.    

What did the research involve?

Researchers crossed two types of broccoli – one alabrese-type and one black broccoli, both of which had high levels of phenols – to create a new hybrid.

They grew it from seed on three different years in different states. During the growing season, they harvested broccoli florets at different points in the plant's growth, freeze-dried and ground them, then used chemical tests to determine their levels of phenols.

The researchers had bred the experimental broccoli with genetic markers, so they could map specific "candidate genes" to see which were most consistently associated with plants that had higher levels of phenols.

They then analysed the results to see what patterns emerged from the interplay of environment and genes.

What were the basic results?

In brief, the researchers found phenol levels varied in the broccoli both within the same year and between different years, suggesting that factors such as the amount of light and the temperature affected the plants' phenol production.

They also identified three candidate genes that played a key role in the early stages of phenol production, which occurred consistently across different years and growing environments.

How did the researchers interpret the results?

The researchers said the results showed that "both genetic and environmental factors play a significant role" in the amount of phenol produced by a plant.

They say the "complex regulatory network" of factors that affect whether specific genes activate phenol production "may at first glance appear to hinder the ability of breeders or growers to enhance phenolic compound accumulation".

However, they go on to say similar work with tomatoes show it may be possible.

They admit that "substantial environmental effects … are a challenge", but suggest that controlled environments such as greenhouses may enable growers to target optimal conditions for growing phenol-rich vegetables.


The "news" that broccoli may protect against some types of disease because they have high levels of phenol compounds is nothing new. We've known about the link between diets rich in phenolic compounds and the lower risk of heart disease since 1995.

This study looks instead at the mechanisms within broccoli plants that regulate how much phenol a plant produces.

Perhaps unsurprisingly, this varies a lot and seems to be affected both by the plant's genetic make-up and the environmental conditions in which it is grown.

The research may help food growers to increase the amount of phenol compounds in vegetables – including veg other than broccoli – using breeding programmes, genetic modification or controlled growing conditions, such as greenhouses.

However, this research is just one step on the pathway to that. More research will be needed to put these tentative findings into practice.

Also, this study does not involve people and in itself provides no direct evidence that eating large amounts of broccoli – high phenolic or otherwise – will directly influence your risk of cancer, heart disease, diabetes or any other chronic diseases.

Anyone wanting to increase the phenol content in their diet can do so by eating not just broccoli, but many other fruits and vegetables, including green vegetables, tomatoes, beans, berries and stone fruits.

Better still, why not try growing some in your garden or allotment? For more info, read some tips for growing your own fruit and vegetables

NHS Attribution