Health

Seeing red: the healthful qualities of the humble tomato

There’s no doubting the importance of the fruit

Revellers pelt each other during the annual tomato festival in Buñol, Spain. Photograph: Jose Jordan/AFP/Getty Images

George Winter
Fri Mar 29 2019 - 06:01

"You may find goggles useful," La Tomatina website counsels. This is because, every August, thousands of participants flock to the Spanish town of Buñol to chuck more than 100 metric tons of overripe tomatoes at each other. Goggles offer a degree of protection against such high-speed incoming fruits, but scientists generally agree that the health benefits of tomatoes – posh name Lycopersicon esculentum – are best conferred when consumed, rather than when splattered all over your face.

There's no doubting the popularity and dietary importance of the tomato. For example, Mike Neary – director of horticulture at Bord Bia – says that 33,000 tons of them are sold annually in Ireland; the Irish retail market is valued at €111 million each year; and 96 per cent of households buy tomatoes about 43 times a year. The tomato's dietary importance derives from the antioxidant, anti-inflammatory and anti-cancer properties it contains by virtue of being enriched with a wide range of beneficial compounds and micronutrients.

Cancer

Twenty years ago, a report in the Journal of the National Cancer Institute noted interest in the tomato as a food with possible anti-cancer properties, mainly due to the antioxidant properties of a carotenoid called lycopene, which is also found in fruits such as papayas and watermelons. Of 72 observational studies that were identified and evaluated, 35 yielded statistically significant results and "the evidence for a benefit was strongest for cancers of the prostate, lung and stomach". However, observational studies themselves cannot establish a cause-effect relationship, and although the report authors implicated lycopene as a possible beneficial factor, they advocated further study.

In 2018, American researchers reported on a systematic review of 30 studies, including more than 260,000 participants, into the relationship between dietary tomato consumption and prostate cancer. They stated: "Higher total tomato consumption was associated with a reduced risk of prostate cancer", asserting that their study "further supports the protective role of tomatoes and lycopene in prostate carcinogenesis".

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Cardiovascular disease

As for a protective role of tomatoes in cardiovascular disease, a 1997 report of a 10-country study in the American Journal of Epidemiology concluded that "lycopene, or some substance highly correlated which is in a common food source, may contribute to the protective effect of vegetable consumption on myocardial infarction risk".

But in 2016 a report in the journal Nutrients summed up its findings in the study's title: Tomato Sauce Enriched with Olive Oil Exerts Greater Effects on Cardiovascular Disease Risk Factors than Raw Tomato and Tomato Sauce: A Randomized Trial.

Although the authors’ conclusion was self-evident, they also cited evidence suggesting that the lower risk for developing cardiovascular disease “was more strongly associated with tomato intake with all its components than with isolated lycopene intake, suggesting that other compounds may also be involved in the protective cardiovascular effects of tomato.”

Perhaps this is unsurprising, given the array of micronutrients hosted by tomatoes – including folic acid, vitamins C and E, fibre, carotenoids, potassium, magnesium and polyphenols – which might well act in concert to exert their beneficial effects.

Central nervous system

Given that the possible protective roles for tomatoes/lycopene in cancer and cardiovascular disease may be related to their compounds' anti-inflammatory properties, it is reasonable to infer that they may also be involved in modifying certain central nervous system diseases. This was explored in a study published this year in the journal Biomedicine & Pharmacotherapy and entitled A Review for the Pharmacological Effect of Lycopene in Central Nervous System Disorders.

The authors cite animal studies showing that lycopene can exert prophylactic and/or therapeutic effects in different type of disorders, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and epilepsy. For example, it’s known that oxidative stress can promote Alzheimer’s progression, and in a mouse model of the disease a recent study showed that an eight-week treatment with lycopene appeared to attenuate nerve damage. Similarly, with some present-day Parkinson’s research focussing on inhibiting oxidative stress, mouse studies in a Parkinson’s model have shown that seven days of lycopene treatment can reduce the concentration of certain indicators of oxidative stress.

Possible side effects

Given the health benefits conferred by tomatoes, it is unsurprising, as Bord Bia’s Mike Neary points out, that tomatoes are the number one category in value terms of fresh products sold in Irish supermarkets in the vegetable/salad category, and that the average annual volume purchased by individual buyers in supermarkets is 20kg.

However, as a recent review published this year notes, "both the excessive and sometimes regular consumption of this vegetable [sic] can cause distinct side effects in [the] human body." For example, consumption of tomatoes and/or tomato-based products is one of the main causes of heartburn, and the authors observe: "In one survey, tomato and tomato juice consumption were higher in [heartburn] patients when compared to healthy controls." The authors speculate that citric and malic acids, found in tomatoes, are potent triggers of acid reflux in susceptible individuals.

Finally, for those wishing to attend the Official La Tomatina after party, it will cost €20.00, and, with “booze flowing, this is going to be a truly unforgettable night”.

Er … could I just have a tomato juice, please?

Mike Neary