Scientists are developing a "super-broccoli" which they hope will help people ward off cancer.
Broccoli contains beneficial chemicals
Broccoli has anti-cancer properties but an Institute of Food Research study has found some people's genetic make-up may minimise the protection they get.
IFR scientists say creating broccoli containing more of the key chemical - sulforaphane - may counter this effect.
They hope it will be ready in three years but recommend eating lots of different green vegetables until then.
Lead researcher Professor Richard Mithen said the key appeared to be a gene called GSTM1, which about half the population don't have.
He said: "Some individuals, who lack the gene, appear to get less cancer protection from broccoli than those who have the gene.
"Our studies suggest that this may be because, if you lack the gene, you cannot retain any sulforaphane inside your body. It is all excreted within a few hours.
"However, if you consume larger portions of broccoli, or broccoli with higher levels of sulforaphane, such as the 'super-broccoli', you may be able to retain as much sulforaphane in your body as those who have the gene.
"Eating larger portions may have additional benefits, since broccoli is also a rich source of other vitamins and minerals."
Broccoli belongs to the crucifer family of vegetables which includes cabbage, cauliflower and Brussels sprouts.
These vegetables contain high levels of glucosinolates, which when eaten break down to release isothiocyanates.
Evidence shows that these isothiocyanates, which include sulforaphane, are among the most powerful anti-cancer agents in the diet.
The "super-broccoli" variety contains 3.4 times more of the compound than standard types.
The researchers suggest it might not all be bad news for those people who lack the GSTM1 gene.
It was possible they gained more cancer protection from other types of crucifers rather than broccoli, they said.
They said the best advice was to eat a mixture of different types of crucifer vegetable.
Josephine Querido, of Cancer Research UK, said: "The research backs current thinking that genetic differences may affect how we absorb nutrients from our food.
"But only 16 people took part in Professor Mithen's study and this is too small a number from which to draw specific conclusions.
"We know that a healthy balanced diet is an important factor in preventing cancer, especially cancers of the digestive system.
"But when it comes to food, there is no one particular 'super' fruit or vegetable that will protect you from cancer.
"Experts have proven that the best way to reduce your risk of many cancers is to eat a healthy balanced diet.
"This should include at least five portions a day of a variety of fruit and vegetables."