Why not purple broccoli… (Photo: AJC)
The constant nagging of children to eat their greens often has little effect. But have you ever heard parents urge their children to eat their purples. I didn’t think so, but they probably should. In flowers, bright red and purple colours are used to attract pollinators. In fruits, the colorful skins also attract the attention of animals, which may eat the fruits and disperse the seeds.
If that holds true for children it could be a way of making fruit and vegetables more attractive. And thus encourage increased consumption to reach the goal of 400 g a day set by the World Health Organization. It is clear that there are considerable benefits in increasing consumption of fruit and vegetables for most of us. In many parts of the world, fruit and vegetable consumption is dismal.
But what about health aspects of the purple colour itself?
No lack of praise of purple foods
First you need to know that the colour is caused by anthocyanins that are water-soluble pigments belonging to a parent class of molecules called flavonoids. They may appear red, purple, or blue depending on the pH. Anthocyanins are powerful antioxidants and there is no lack of praise of purple fruit and vegetables on the web. Just a few examples:
- The top benefactor in purple foods is their antioxidant content. The powerful health benefits of antioxidants are only too well known: they neutralise the agents of aging and disease, and keep you looking younger longer.
- A basket filled with luscious blue or dark red fruit and vegetables does much more than look good in still life paintings or on your kitchen counter. It contains a wealth of incredible health benefits.
- There is evidence that purple foods improve heart health, vision, and brain power. Recent studies found that adults who eat purple and blue fruits and vegetables have reduced risk for both high blood pressure and low HDL cholesterol; they are also less likely to be overweight.
- Let’s take a deeper look into these dark nutritional superheroes. Here are five reasons to eat more purple foods: purple foods kill cancer, are ulcer-fighters, are good for your liver and heart, and prevent urinary tract infections.
Convinced? Not so fast. Vegetables and fruits are rich sources of antioxidants. There is good evidence that eating a diet with lots of fruits and vegetables is healthy and lowers risks of certain diseases. But it isn’t clear whether this is because of the antioxidants, something else in the foods, or other factors.
So what are antioxidants?
… or purple carrots …
Antioxidants are man-made or natural substances that may prevent or delay some types of cell damage by counteracting oxidative stress. Free radicals can cause oxidative stress, a process that can trigger the cell damage. Free radicals are highly unstable molecules that are formed during exercise and conversion of food into energy or can be accumulated from a variety of environmental sources, such as cigarette smoke, air pollution, and sunlight. Oxidative stress is thought to play a role in a variety of diseases including cancer, cardiovascular diseases, diabetes, Alzheimer’s disease, Parkinson’s disease, and eye diseases such as cataracts and age-related macular degeneration.
Antioxidants are found in many foods, including fruits and vegetables. They are also available as dietary supplements. Examples of antioxidants include vitamins C and E, selenium, and carotenoids, such as beta-carotene, lycopene, lutein, and zeaxanthin. As well as flavonoids, like the purple anthocyanins.
The flavonoids have long been thought to be nutritionally important for their antioxidant activity, but actually have little or no value in that role. Unfortunately, research has now proven that flavonoids are poorly absorbed by the body, usually less than five percent, and most of what does get absorbed into the blood stream is rapidly metabolised in the intestines and liver and excreted from the body.
But don’t give up yet!
Anthocyanins may indeed benefit human health, but for quite different reasons. The body sees them as foreign compounds and through different mechanisms, they could play a role in preventing cancer or heart disease. They appear to strongly influence cell signaling pathways and gene expression, with relevance to both cancer and heart disease. A relatively modest intake – like the amount found in five to nine servings of fruits and vegetables – is sufficient to trigger a much larger metabolic response.
Flavonoids also increase the activation of existing nitric oxide synthase, which has the effect of keeping blood vessels healthy and relaxed, preventing inflammation, and lowering blood pressure – all key goals in prevention of heart disease.
Both of these protective mechanisms could be long-lasting compared to antioxidants, which are more readily used up during their free radical scavenging activity and require constant replenishment through diet.
So why not go for purple foods
… or spiff it up with a purple spud.
So not too bad after all. Beetroot and eggplant have long been obvious choices, and of course all the berries. But now there are also purple carrots, cabbage, potatoes, onions, sweet potato, maize and asparagus.
The ancestors of the carrot can be traced back to Iran and Afghanistan, and the original carrots were predominantly purple. It was only during the 17th century that western Europeans began cultivating orange carrots.
The purple sweet potato has only been available commercially since 2006, after a North Carolina sweet potato farmer received some as a gift and began to cultivate them on a large scale.
The vividly colored cauliflower variety was achieved after painstaking cross breeding and has a similar flavor to its white cousin.
The purple-black maize is commonly grown in the Andes Mountains and is a popular food in Bolivia, Ecuador, Mexico, and Peru.
Purple kale is cultivated from the dwarf variety of kale, and adds a splash of color to green salads. Like green kale, it has a cabbage-like flavor and a slightly chewy texture.