HerbalEGram: Volume 13, Issue 7, July 2016
Editor’s Note: Each month, HerbalEGram highlights a conventional food and briefly explores its history, traditional uses, nutritional profile, and modern medicinal research. We also feature a nutritious recipe for an easy-to-prepare dish with each article to encourage readers to experience the extensive benefits of these whole foods. With this series, we hope our readers will gain a new appreciation for the foods they see at the supermarket and frequently include in their diets.
The basic materials for this series were compiled by dietetic interns from Texas State University (TSU) in San Marcos and the University of Texas at Austin (UT) through the American Botanical Council’s (ABC’s) Dietetic Internship Program, led by ABC Education Coordinator Jenny Perez. We would like to acknowledge Jenny Perez, ABC Special Projects Director Gayle Engels, and ABC Chief Science Officer Stefan Gafner, PhD, for their contributions to this project.
By Hannah Baumana, Genesis Valdesb, and Candace Charlesb
a HerbalGram Assistant Editor
b ABC Dietetics Intern (UT, 2015)
History and Traditional Use
Range and Habitat
Tomato (Solanum lycopersicum, Solanaceae) is, botanically, a fruit. Nevertheless, in the 1893 Nix v. Hedden decision, the United States Supreme Court classified tomatoes as a vegetable, which created an economic advantage for US producers, because taxes were levied on vegetables, but not fruits, imported into the US.1 The Supreme Court decided that “in the common language of the people, whether sellers or consumers of provisions, all these are vegetables … are usually served at dinner … and not, like fruits generally, as dessert.”2 The tomato is a common ingredient in cuisines around the world, and is cultivated as an annual food crop, although technically it is classified as a short-lived perennial.3
A member of the nightshade family, the tomato is related to the potato (Solanum tuberosum), eggplant (S. melongena), bell pepper (Capsicum annuum), and chili pepper (C. frutescens). Tomatoes are colorful, with various tomato cultivars producing fruit that is generally red, orange, and yellow in different sizes and shapes. Tomato plants grow 3-10 feet in height and have a sprawling growth habit, with hairy stems, bright green compound leaves, and small yellow flowers.4,5 The tomato plant produces a fleshy fruit with seeds embedded in a watery matrix that requires delicate care during transport.6
Tomatoes grew wild as a weed in South and Central America, and the size of the original tomato was more comparable to the cherry tomato than the larger varieties.6,7 Aztecs and Incas were among the first to cultivate the tomato due to its resemblance to the green tomatillo (Physalis philadelphica and P. ixocarpa, Solanaceae), one of their cuisine staples.4,6 After arriving in Mexico, Spanish conquistadors were intrigued by the tomato and took seeds to Europe. The tomato spread throughout Europe and made its way into Mediterranean cuisine during the 16th century. Today, the tomato and potato dominate the US vegetable market in dietary intake and economic value.1
Phytochemicals and Constituents
Tomatoes are a good source of vitamin C, vitamin A, folate, potassium, carotenoids, and flavonoids.5 The tomato skin contains 98% of the tomato’s total flavonol content, which includes quercetin and kaempferol. Studies have shown that potassium and vitamin C in the diet lowers blood pressure, which is good because high blood pressure is a risk factor for cardiovascular disease (CVD).8 Tomatoes also contain minerals including phosphorus, magnesium, molybdenum, and calcium.5 Tomato-based products, including tomato paste, contain these same nutrients in varying concentrations depending on how the tomatoes were processed.9
The fruit is dense in lycopene and several other carotenoids, including phytoene, phytofluene, zeta-carotene, beta-carotene, gamma-carotene, and neurosporene.5 Carotenoids give tomatoes their varying colors.10 Tomatoes and tomato products are the richest sources of lycopene in the American diet, representing more than 85% of all dietary sources of lycopene.
Because of its chemical structure, lycopene is one of the most potent antioxidants.11 Lycopene provides many health benefits, including reducing the risk of cellular oxidative damage, inflammation, and modulation of cellular signaling pathways. There is a strong correlation between lycopene/tomato product intake and the reduction of CVD and cancer incidence.5,8 In vitro studies demonstrate that lycopene reduces cellular proliferation induced by insulin-like growth factors in various cancer cell lines, and protects important cellular biomolecules, including lipids, proteins, and DNA.11 Additionally, lycopene can suppress carcinogen-induced phosphorylation of regulatory proteins and stop cell division in cancer cell lines, providing a mechanism to explain putative cancer preventive effects.
Historical and Commercial Uses
The tomato was not a popular food when introduced to Europe and was originally grown as an ornamental plant. The Solanaceae family famously contains some plants that are poisonous, such as deadly nightshade (Atropa belladonna) and black henbane (Hyoscyamus niger), which made many people suspicious of the bright red fruit.4,6 Europeans overcame their fear of the tomato by the late 18th century, but conflicting information persists in modern times regarding tomato leaves.6,12 The leaves were believed to be as poisonous as the fruit — once thought to be toxic as well — but scientific literature remains undecided on the leaves’ actual toxicity to humans and animals.12 Some chefs and home cooks have reported no adverse effects while cooking with and consuming tomato leaves, but evidence remains largely anecdotal on both sides.
Though little research exists on tomato’s efficacy for skin conditions, such as acne or sunburn, folk remedies recommend preparations of tomato mixed with other ingredients, such as avocado (Persea americana, Lauraceae), honey, yogurt, or lime (Citrus x latifolia, Rutaceae) juice, applied to the face or other afflicted areas.13
As tomato consumption spread throughout Europe, it gained more acceptance as a versatile food, which inspired Italians to begin mass-producing and canning tomatoes (known as pomodoro, or “golden apple” in Italian) by the early 19th century. The US soon followed, and by the 1830s, ketchup (catsup) became the “national condiment.”4 Currently, the tomato has a wide variety of uses and is one of the most popular vegetables worldwide. In the US, the tomato is the most commonly consumed vegetable.1 The average American consumes nearly 18 pounds of fresh tomatoes and almost 69 pounds of processed tomato products every year.10The Economic Research Service of the US Department of Agriculture estimates that of total raw tomato processing, 35% is processed into sauces, 18% into tomato paste, 17% into canned tomatoes, 15% into juices, and 15% into ketchup. The tomato was the first genetically-engineered food, modified to maintain the firmness of the fruit for longer periods of time during transport.7
The tomato and tomato products have gained greater attention because of the increasing research surrounding their antioxidant and anti-inflammatory properties.9
Tomatoes have a variety of nutrients and compounds that may contribute to the prevention of CVD and certain cancers by decreasing inflammation. Recent studies have identified lycopene as a beneficial compound that reduces inflammation and oxidation. Oxidative stress at the cellular level leads to the damage of cell membranes and eventually causes inflammation. The chemical transfer of electrons of ascorbic acid (vitamin C) and alpha-tocopherol (vitamin E) prevents damage to fat cells, therefore indirectly preventing inflammation.
Lycopene and Inflammation
Vitamin C and vitamin E may work in combination with lycopene to increase beneficial effects. Researchers observed a greater production of anti-inflammatory cytokines with the combination of the three compounds (lycopene, ascorbic acid, and alpha-tocopherol) compared to the individual compounds or a combination of two.14 (Cytokines are chemical messengers produced by immune cells to communicate with damaged cells and initiate immune response.) This indicates that consuming tomato provides greater health benefits versus isolated single compounds.
Tomato products may also benefit overweight or obese individuals.15 After 20 days of consuming 330 mL of tomato juice daily while otherwise maintaining their normal diet, overweight and obese women had a decrease in the concentration of certain inflammatory factors compared to baseline and compared to the control group, possibly decreasing the risk of inflammatory conditions such as CVD, diabetes, and other chronic diseases.
Chronic inflammation is associated with an increased risk of degenerative diseases like cancer. In healthy human subjects, dietary supplementation with lycopene for just one week increased serum lycopene levels and reduced oxidation of lipids, proteins, lipoproteins, and DNA, whereas subjects with diets free of lycopene supplementation or tomato products showed low blood levels of lycopene and increased lipid oxidation.11 Blood and tissue levels of lycopene were inversely associated with risks of breast cancer and prostate cancer. Several epidemiological studies have found that high intake of tomatoes/tomato products was linked to lower incidences of gastrointestinal (GI) cancer and a 50% reduction in cancer death rates in an elderly US population.16 In a review of 72 epidemiological studies, 57 (79%) confirmed an inverse association between tomato intake and risk of several different types of cancer, measured by serum lycopene levels and predisposition to cancer.
Increased lycopene intake from various tomato products has been shown to correlate with a reduced risk of developing prostate cancer.11 Lycopene’s prostate cancer-prevention benefits are thought to stem from mechanisms of inhibiting proliferation, anti-androgen and antigrowth factor effects, and decreasing levels of oxidative damage to DNA and T-cells.9 In fact, consumption of 10 or more servings per week showed a 35% reduction in risk of even the most aggressive types of prostate cancer. Epidemiological evidence confirms the relationship between tomato/lycopene consumption and prostate cancer risks. A survey of 51,529 male health professionals between 40 and 75 years old found that consuming more than two servings a week of tomato products resulted in a dose-dependent risk reduction in incidence of prostate cancer. Greater risk reduction is associated with tomato sauce consumption than with lycopene supplementation alone.9
More than 70 million Americans have some form of CVD, which accounts for 38% of all deaths in the US.9 Higher concentrations of lycopene in fat tissue were noted to be protective against CVD. When tomatoes/tomato products are removed from the diet, the antioxidant capacity of plasma decreases, and then increases when they are added back. Consuming tomato products daily for two-four weeks increases antioxidant enzyme defenses and has been shown to reduce plasma lipid peroxides and the susceptibility of low-density lipoprotein (LDL) to oxidation.17 In 2004, researchers reported an inverse association for women consuming more than seven servings per week of tomato-based products and CVD. This association was not observed with lycopene supplementation alone.
Different tomato products contain various concentrations of lycopene and other nutrients. Tomato paste is one of the most lycopene-rich tomato products. A 2012 study examined the effect of tomato paste in the endothelial function of 19 young, healthy individuals.9 After consuming 70 g of tomato paste daily for 15 days, researchers reported that subjects experienced a significant increase in flow-mediated dilation and a significant decrease in total oxidative stress (TOS) compared to baseline. This may indicate that the decrease of TOS increases endothelial function, therefore decreasing the risk of future CVD.
The bioavailability of a compound refers to the amount that is absorbed and used by the body. Thus, increased bioavailability means increased activity and possible benefits from that compound. Tomatoes are one of the few fruits or vegetables whose nutrients are absorbed more readily when cooked. When tomatoes are processed, lycopene becomes more bioavailable, especially when heat is used, which softens cell walls in tomato tissues, and other dietary lipids are present during processing.11,17
The popular combination of tomatoes with olive oil may be as healthy as it is delicious. Researchers observed subjects who consumed tomatoes in conjunction with olive oil and those who consumed tomatoes alone.18 The results found significantly increased plasma concentrations of lycopene in the olive oil group. The dietary sources that deliver the most concentrated sources of lycopene are processed tomato products including tomato juice, ketchup, paste, sauce, and soup.19 Consuming lycopene from whole food products, including tomatoes, instead of in supplement form, confers the benefits from the interaction with and enhancement from different constituents.17
Macronutrient Profile: (Per 1 large tomato [approx. 182 g])
1.6 g protein
7.08 g carbohydrate
0.36 g fat
Secondary Metabolites: (Per 1 large tomato [approx. 182 g])
Excellent source of:
Vitamin C: 24.9 mg (41.5% DV)
Vitamin A: 1,516 IU (30.3% DV)
Very good source of:
Vitamin K: 14.4 mcg (18.0% DV)
Potassium: 431 mg (12.3% DV)
Molybdenum: 9 mcg (12.0% DV)
Manganese: 0.21 mg (10.5% DV)
Good source of:
Dietary Fiber: 2.2 g (8.8% DV)
Vitamin B6: 0.15 mg (7.5% DV)
Folate: 27 mcg (6.8% DV)
Niacin: 1.08 mg (5.4% DV)
Magnesium: 20 mg (5.0% DV)
Vitamin E: 0.98 mg (4.9% DV)
Thiamin: 0.07 mg (4.7% DV)
Phosphorus: 44 mg (4.4% DV)
Iron: 0.5 mg (2.8% DV)
Riboflavin: 0.04 mg (2.4% DV)
Zinc: 0.31 mg (2.1% DV)
Calcium: 18 mg (1.8% DV)
DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet.
Recipe: Gazpacho Salad
Adapted from The New Spanish Table21