It wouldn’t be summer without plump, juicy heirloom tomatoes piled high on a table at the farmers’ market, or containers of cherry tomatoes as sweet as raspberries reappearing in supermarkets for the season. Eating a rainbow of produce is an effective—and tasty—way to ensure intake of a wide array of nutrients and phytochemicals; and just within the tomato family itself, you can find red, green, yellow, orange, and purple varieties.
With their low carbohydrate content, fiber, and complement of nutrients, tomatoes fit nicely into many different nutritional strategies, including vegetarian, low-carb, and Paleo-style diets. Due to tomatoes’ natural sweetness, people on very low carbohydrate diets sometimes avoid them, but this isn’t necessary. Tomatoes—particularly when they’re in season—are sweet, but although they have a slightly higher glycemic index than, say, spinach and broccoli, their glycemic load is extremely low. This means it would take a very large amount of tomatoes to have an adverse impact on blood sugar, although, of course, individual sensitivity to carbohydrate varies. They are a good source of vitamin C, vitamin K1, beta-carotene, and potassium.
Tomatoes are perhaps most touted for their antioxidant phytochemical, lycopene – best known for its role in men’s health (lycopene is the most abundant carotenoid found in the prostate gland). This great antioxidant has other beneficial roles worth mentioning. Lycopene may help prevent sunburn, and studies have shown it also has the potential to be mildly hypocholesterolemic via naturally inhibiting HMG CoA reductase, as well as increasing LDL receptor synthesis. Interestingly, lycopene concentration is higher in tomato products—such as tomato paste and tomato sauce—than in fresh tomatoes. As a fat-soluble carotenoid, the body absorbs lycopene best when taken with some fat—in case anyone needed an excuse to drizzle a fresh tomato salad with a little olive oil, or sprinkle some cheese over tomato sauce and zucchini noodles.
As if their flavor and nutrient content weren’t good enough reasons to eat tomatoes, there’s another beneficial substance hiding in tomatoes, tucked away like a little secret: melatonin! Yes, it’s true: tomatoes contain a small amount of melatonin, and it seems to have a similar function in plants as it does in humans: regulation of the circadian rhythm. A study in which multiple tomato cultivars were grown in the same greenhouse, but some were grown in full sunlight while others were shaded, found that the shaded tomatoes had as much as 135% more melatonin than the non-shaded ones, suggesting that light exposure plays a role in their melatonin content, just as melatonin synthesis is regulated by photo-exposure in people. Some researchers have pointed to the bioactive phytochemicals in various plants as being a key factor contributing to the healthfulness of the Mediterranean diet. In looking at select foods common in certain Mediterranean countries, they noted tomatoes, olive oil, wines, and grape skins, for their melatonin content, which, while small, might still be one part of the multifactorial picture underlying the benefits of this traditional cuisine. At about 250ng/g of dry weight, the melatonin content of tomatoes isn’t enough to act as a sleep aid, but it’s an interesting bit of trivia nonetheless.
Don’t limit yourself to the more common red tomatoes. Other varieties bring enhanced nutritional properties, such as purple tomatoes, which have a higher anthocyanin and antioxidant content. Plant breeders recognize these as providing a longer shelf life and protection against certain plant pests, but they’re helpful for human health, as well. Yellow tomatoes also have something to offer beyond their sweet taste. While the lycopene in red tomatoes has been shown to be helpful in fighting prostate cancer, serum from rats fed yellow tomatoes—which contain no lycopene—has been shown to beneficially influence expression of Connexin43 (Cx43), a protein that regulates cell growth, on human prostate cancer cells in vitro.
With summer upon us, enjoy the bounty of tomatoes the season offers and enjoy experimenting in the kitchen with this wonderful food. You can find such a great variety of recipes, both hot and cold, where tomatoes add a splash of flavor, a touch of color, and of course, nutrition galore.
Note: As a Sicilian American my family’s whole life revolved around tomatoes. Every autumn my grandfather bought hundreds of cases of plum tomatoes which he my grandmother and all the aunts cooked, prepped and canned for the entire coming year. I say hundreds because there were 10 families and each of those 10 needed enough jars to make “gravy” every Sunday. I also remember my NoNa taking tomatoes onto the roof to make tomato paste–another time consuming process worth the time and energy it took to make. When they passed the family no longer canned the tomatoes; and buying them in cans just about killed them–but they adjusted to the “modern times” of 1965.