Of all the micronutrients found in tomatoes, lycopene is certainly the most talked about: we have dedicated a whole article on the health benefits of lycopene so we won't be discussing it in detail here; suffice it to say it is one of the most powerful natural antioxidants and it has been shown by preliminar studies to be protective against several age-related diseases such as colorectal, prostate, breast, endometrial, lung, and pancreatic cancers, as well as some cardiovascular diseases.
There's a very interesting study published in the American Journal of Clinical Nutrition: in patients with colorectal adenomas, a benign tumor that is often a precursor of colorectal cancer, blood levels of lycopene were 35% lower compared to subjects with no adenomas (beta-carotene also was be 25.5% lower, although according to researchers, this difference was not significant). In their final (multiple logistic regression) analysis, only low levels of plasma lycopene (lower than 70 microgram per liter) and smoking significantly increased the likelihood of colorectal adenomas by, respectively, 230% and 302%.
In a study published in the Journal of the National Cancer Institute, animals were fed a lycopene-rich diet and given N-methyl-N-nitrosourea (a powerful carcinogen) and testosterone to induce prostate cancer. Their risk of death from prostate cancer was about the same as rats fed a normal diet.
However, animals given whole tomato powder had a 26% risk reduction of death by prostate cancer. By the end of the study, 80% of the control group and 72% of the animals fed lycopene had died from prostate cancer, versus only 62% of the animals fed whole tomato powder. In addition to this, the groups were subdivided into a calorie-restricted group and a normal-fed group: the calorie-restricted had the best survival rates, with a 32% lower risk of dying from prostate cancer.
As this study shows, a diet low in calories with whole foods is much more effective at improving your health than a high-calorie diet with concentrated supplements such as lycopene.
Another meta-analysis of 21 studies, published in "Cancer Epidemiology Biomarkers and Prevention" confirms that eating tomatoes, especially cooked tomatoes, provides protection against prostate cancer. Please note that meta-analyses are considered the most reliable type of study in medical research, due to the high number of studied subjects and the broader analysis.
This study found that men who ate the highest amount of whole, uncooked tomatoes had an 11% reduction in risk of developing prostate cancer, versus a 19% reduction for those who ate cooked tomatoes. The percentage of risk reduction seems to be quantity-related, since eating fractional amounts of tomatoes provided fractional amounts of risk reduction (e.g. a 3% risk reduction for a 6-ounce serving/day of raw tomatoes).
The Journal of Nutrition published a 3-year study with two groups of subject: on group consisted of subjects with pancreatic cancer, the other one of healthy people of the same age and sex.
After adjusting for other statistical variables such as province, folate intake, calorie restriction etc, the study found that subjects consuming the most lycopene had a 31% reduction in their risk of pancreatic cancer.
The study was also extended to micronutrients very similar to lycopene: those whose diets were richest in beta carotene or total carotenoids reduced their risk of pancreatic cancer by 43% and 42%, respectively.
In addition to lycopene, tomatoes also contain several different antioxidants with health-promoting effects.
For example, tomatoes are an excellent source of the water-soluble vitamin C, and the lipid-soluble vitamin A (through its concentration in beta-carotene). Several independent studies have shown that increased intakes of vitamin C and A help protect against DNA cell damage, an important risk factor for cancers, atherosclerosis and diabetes, as well as many other age-related diseases. Antioxidants work by quenching the oxidant power of free radicals, who are responsible for oxidative stress of the cells and increased DNA mutation rates.
Tomatoes are also a very good source of dietary fiber, which has been shown to reduce "bad" cholesterol levels, regulate blood sugar levels, and help prevent colon cancer. A cup of fresh tomatoes will provide 57.3% of the daily recommended value for vitamin C, plus 22.4% of the DV for vitamin A, and 7.9% of the DV for fiber.
Tomatoes contain important amounts of niacin, vitamin B6, and folate, which are strongly related to a reduction in heart disease risk. Niacin has been used for years as a safe way to lower high cholesterol levels,while potassium has been proven to lower high blood pressure and reduce the risk of heart disease.
Vitamin B6 and folate are both needed by the body to convert homocysteine into other molecules: high levels of homocysteine are associated with an increased risk of heart attack and stroke (this substance tends to damage blood vessel walls). In a cup of tomatoes, you'll get 11.4% of the recommended daily value for potassium, 5.6% for niacin, 6.8% of the DV for folate and 7.0% of the DV for Vitamin B6.
A study conducted at Brigham and Women's Hospital in Boston, tracked 40,000 middle-aged and older women who were free of both cardiovascular disease and cancer when the study began. These subjects were divided in two groups and tracked for 7 years, during which the first group was fed 7 to 10 servings each week of tomato-based products such as pizza, tomato sauce, raw tomatoes and tomato sauces.
This group was found to have a 29% lower risk of cardiovascular disease compared to the second group (women eating less than 1.5 servings of tomato products weekly). Women who ate more than 2 servings per week of oil-rich tomato products, such as tomato sauce and pizza, fared even better, with a 34% risk reduction in cardiovascular disease.
A European study, published in the European Journal of Nutrition, tracked a group of 12 healthy women who ate tomato products resulting in at least 8mg/day of lycopene, for three weeks. After this period, their LDL cholesterol was much more resistant to free radical oxidation, which is a recognized conditio sine qua non for the formation of atherosclerotic plaques.
A study published in Italy, in the Journal of Agricultural and Food Chemistry, found that drinking a glass of tomato juice daily can reduce the levels of TNF-alpha (an important marker of inflammation) almost 35% in less than one month.
The trial (double-blind) divided 26 young healthy volunteers into two groups. In three 26-day segments, the first groupfirst was given a placebo juice (same taste and flavor but no active compounds), then nothing, then a daily glass of tomato. The second group got the tomato juice first, then nothing, then placebo. Study subjects continued to eat their normal diet. After a period of 26 days, the first two groups had undergone a 34% reduction of TNF-alpha blood levels, while the placebo group found no reduction.
The presence of inflammatory markers such as TNF-alpha have been correlated to nearly all chronic degenerative diseases, such as atherosclerosis, cardiovascular disease, several cancers, osteoporosis and Alzheimer's disease.
The protective effect of tomato juice is to be found in the powerful mix of antioxidants: a glass contains 5.7 mg of lycopene, 1 mg beta-carotene, 3.7 mg of phytoene, 2.7 mg of phytofluene, and 1.8 mg of the alpha-tocopherol fraction of vitamin E.
In an Australian study published in the Journal of the American Medical Association, 20 people with type 2 (insulin-resistant) diabetes were given 250 ml (about 8 ounces) of tomato juice or a tomato-flavored placebo daily. Subjects had no history of thrombosis or coagulopathies and were taking no medications that would affect blood clotting.
After 3 weeks, platelet aggregation was significantly reduced among those drinking tomato juice, while nothing happened in the subjects receiving placebo.
Dietary strategies have traditionally been good at reducing cardiovascular disease risk factors such as cholesterol, but currently there is no dietary strategy aimed at reducing high platelet activity: that's why tomatoes might be the only candidate to achieve this effect.
This tomato-rich diet provides beneficial effects to all those with a higher risk of thrombosis, such as people with high cholesterol, those who undergo surgical procedures, women who take oral contraceptives and smokers. Just be sure to choose tomato juice with a low sodium content, since sodium has the opposite effect of hardening vessel walls and increasing risk of blood clotting.
In a study published in the British Journal of Nutrition, 21 healthy subjects followed a diet free of tomato products for 3 weeks, followed by a high tomato diet (1 ounce ketchup and 13.5 ounces tomato juice daily). At the end of the high tomato diet period, the subjects' total cholesterol levels had dropped an average of 5.9%, with LDL (bad) cholesterol reduced by 12.9%. Blood samples also showed an increases in lycopene, beta-carotene and other carotenoids, as well as a 13% increase in the ability of LDL cholesterol to resist oxidation. (Silaste ML, Alfthan G, et al., Br J Nutr.).