The humble tomato

The healthy tomato

The healthy tomato (photo: Wikimedia)

When you think of tomato you might think of Italy. But you are partly wrong. Although Italy is now a prominent tomato-growing country, the tomato plant initially originated from Mexico and spread around the world following the Spanish colonisation of the Americas. By the way Italy has been displaced by China as the top growing country for tomatoes with Italy only at the sixth place, beaten also by the United States, India, Turkey and Egypt. Italy is even importing tomatoes from China for their food processing industry. The world is about to be turned upside down, don’t you think?

And even if you think of tomato as a vegetable you are again at least partly wrong since botanically it is a fruit. However, legally according to a verdict by the United States Supreme Court as well as for culinary purposes it is considered to be a vegetable. So there you have it.

There are more than 7,500 different varieties of the tomato grown for different purposes and of varying colours. There are small cherry tomatoes, bright yellow tomatoes, Italian pear-shaped tomatoes, and the green tomato, famous for its fried preparation in Southern American cuisine. The tomato plant (Lycopersicon esculentum) belongs to the nightshade family that also includes potato, aubergine and capsicum among many other plants. Many members of the family contain potent alkaloids, and some are highly toxic. We will come back to that since this is a food safety blog, but first to the health aspects.

Tomatoes brimming with healthy compounds

Tomatoes produce lycopene, carotene, anthocyanin, and several other beneficial antioxidants in differing amounts according to the specific variety. The most studied is lycopene, a carotenoid pigment that gives tomatoes and certain other fruits and vegetables their colour.  Although the most common colour of tomato is red, there are indications that the lycopene from orange- and tangerine-colored tomatoes may actually be better absorbed than the lycopene from red tomatoes. That’s because the lycopene in deep red tomatoes is mostly trans-lycopene, and the lycopene in orange/tangerine tomatoes is mostly tetra-cis-lycopene. And if you cook your tomatoes, it makes the lycopene more available.

The benefit of lycopene (Photo: Wikimedia)

The benefit of lycopene (Photo: Wikimedia)

Recent research has linked lycopene with a whole host of beneficial health effects including impacting cardiovascular disease, cancer, diabetes, osteoporosis, infertility, and skin damage. People who have diets rich in tomatoes, which contain lycopene, appear in some studies to have a lower risk of certain types of cancer, especially cancers of the prostate, lung, and stomach. However, not all of the studies have reached the same conclusion. As usual it is likely that the preventive effect of diets high in fruits and vegetables cannot be explained by just one single part of the diet. Tomatoes are sources of other beneficial nutrients, including vitamin C, folate, and potassium, that might contribute to the beneficial effects attributed to lycopene.

Despite accumulating evidence for the benefits of lycopene, the research has so far not convinced the European Food Safety Authority (EFSA) that the compound itself is worthy of health claims. Claims that have been so far rejected by EFSA include skin health, sun tolerance, improving dry skin, prostate functionality, eye health, heart health, healthy ageing, protection from cellular ageing and strengthening the immune system. However, a tomato extract in the form of a dry powder had a health claim for improved blood circulation approved by EFSA in 2009.

The US Food and Drug Administration (FDA) has been equally restrictive in approving health claims for lycopene. They have permitted a highly qualified claim to be used for tomatoes and tomato products which contain lycopene: “Very limited and preliminary scientific research suggests that eating one-half to one cup of tomatoes and/or tomato sauce a week may reduce the risk of prostate cancer. FDA concludes that there is little scientific evidence supporting this claim.”

Nothing good without some bad

Leaves, stems, and green unripe fruit of the tomato plant contain small amounts of the toxic alkaloids tomatine and solanine as well as low amounts of nicotine.

Stems, leaves and unripened tomatoes might be avoided (Photo: Camelia TWU)

Stems, leaves and unripened tomatoes might be avoided (Photo: Camelia TWU)

Tomatine has been shown in animal experiments to cause a profound drop in blood pressure and haemolysis of red blood cells when injected. However, levels of tomatine in foliage and green fruit are generally too small to be dangerous and it is poorly absorbed when eaten. Consumption of large amounts as greens or tea should be avoided. Use of tomato leaves in tea has been responsible for at least one death.  Small amounts of tomato foliage are sometimes used for flavoring without ill effect, and the green fruit is sometimes used for cooking as mentioned above, particularly as fried green tomatoes.

Compared to potatoes the amount of solanine in green or ripe tomatoes is low. Even in the case of potatoes, while solanine poisoning resulting from dosages several times normal human consumption has been demonstrated, actual cases of poisoning resulting from excessive consumption of potatoes that have high concentration of solanine are rare.

Nicotine is a potent parasympathomimetic alkaloid also found in other plants in the nightshade family, including of course the tobacco plant. It is made in the roots and accumulates in the leaves of the plants. Nicotine increases blood pressure and heart rate in humans and can stimulate abnormal proliferation of vascular endothelial cells, similar to that seen in atherosclerosis. On the other side, nicotine has been observed to lower the risk of developing Parkinson’s disease.

On balance

Tomatoes are a treasure of riches when it comes to their antioxidant benefits. It is clear that tomatoes and tomato products in general provide many compounds beneficial to human health and should be important parts of a varied diet. Some caution might be appropriate in relation to unripened fruit and consumption of leaves and stems of the plant is not recommended

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