Studies Find Certain Foods May Lower Risk of Some Cancers
We eat for energy and sustenance and tend to choose foods we consider tasty. Growing evidence shows that a plant-based dietary pattern is associated with a lower risk of many cancers. Many plant foods are not only nutritious, but also may have specific anticancer properties. Researchers at Ohio State University are studying how certain phytochemicals or combinations of bioactives found in tomatoes, soy and berries can reduce the risk of certain cancers. They’re cultivating farm-fresh food and creating novel food products that may help prevent some types of cancer. And, rumor has it, these concoctions are quite palatable.
The studies center on foods that are carefully processed into juices, breads and confections, with care not to alter their phytochemical profile. OSU is a land-grant university with plenty of farmland for agricultural experiments, much of which has been integrated into cancer prevention efforts. Dr. Steven Clinton, professor in the division of medical oncology at OSU’s School of Medicine, talked about food-based cancer prevention strategies in an animated NCI Stars in Nutrition lecture to a packed Lipsett Amphitheater recently.
Various studies have shown that components in tomatoes—particularly lycopene, the major carotenoid that gives tomatoes their red color—may reduce the risk of prostate cancer. Whether one consumes tomato juice, sauce or soup, said Clinton, carotenoids and other bioactive compounds in these foods enter the blood and alter concentrations in the target tissue.
In a recent OSU study, rodents fed tomatoes had increased lycopene levels and decreased cancer risk. But in a control group where 80 percent of the animals developed cancer, when certain carotenoid enzymes such as lycopene were eliminated, efficacy declined.
“We’re beginning to see in an animal model, very carefully controlled, how a genetic variation, as extreme as it may be, can alter how a dietary component impacts the cancer risk,” said Clinton, also the John B. and Jane T. McCoy chair in cancer research at the OSU Comprehensive Cancer Center. “We’re seeing dramatic and interactive effects between the tomato components, androgens [hormones that stimulate prostate cancer cell growth] and gene expression patterns.”
Through the magic of food science, technology and plant genetics, OSU investigators created a tomato juice with soy protein, teaming up to choose tomatoes that are easy to process, free of pesticides and rich in carotenoids. Clinton admitted it took quite a few iterations to make this tomato-soy juice taste good.
Each 6-ounce can of their tomato-soy juice has 22 mg of lycopene and 33 mg of soy isoflavones (plant-based estrogens). In several mouse models, tomato products reduced the incidence of prostate cancer and its progression. In human studies where men consumed 2 cans daily over several weeks, prostate cancer risk decreased. Tomato phytochemicals also affected pathways related to androgen signaling, mimicking what happens when doctors put men on hormone therapy, said Clinton.
Studies are ongoing to evaluate the hundreds of metabolites and dozens of genes in tomatoes. There’s great interest in the tangerine tomato, which has polycyst lycopene that rodents and humans seem to more readily absorb.
“There’s enormous variety in bioavailability and metabolism,” said Clinton, much of which may be due to genetic heterogeneity of the population. Research is now progressing rapidly in human studies that extract carotenoids to evaluate their absorption and distribution.
OSU lab studies show that soy inhibits prostate and bladder cancer in animal models. Some studies show compounds in soy actually inhibit critical processes related to cancer progression.
The researchers also created a soy bread. Clinton noted there were challenges upscaling production to make hundreds of loaves in uniform batches for clinical trials. Then came numerous tests to optimize appearance, taste and overall consumer acceptability.
The lab’s soy bread contains 60 mg of soy isoflavone in 2 slices. The team has a tasty soy-almond version as well, since almonds allow for cleavage of soy isoflavones during cooking that may aid in nutrient absorption. Data from one human study revealed how people metabolize soy; men consuming the bread showed positive immune outcomes.
The team also created a yeast-based soy bread. Yeast makes more vitamin D when exposed to light, said Clinton, and vitamin D may affect colon carcinogenesis.
“If we make our bread whole wheat soy-vitamin D bread, now you also have this amazing opportunity to manipulate possibly the colonic microbiome in a way that potentiates the anticancer immune effects that may be there from both soy and vitamin D,” said Clinton.
Another OSU horticulture project is the black raspberry, which happens to grow well in Ohio. Black raspberries are rich in polyphenols—which may stop cancer cells from spreading—and anthocyanins, plant pigments with antioxidant effects.
Several animal studies have shown that black raspberries, whether eaten or applied topically, have oral cancer-fighting properties. The berries inhibited oral carcinogenesis significantly in the hamster cheek pouch and rat tongue model.
“By and large, black raspberries, regardless of the genes, the time of harvesting and location, all contain substantial bioactives,” said Clinton. “But they are impacted statistically and significantly by genetics as well as growing conditions and stages of ripeness.”
Investigators also created a sweet treat—black raspberry confections, including gummies, hard candies and white chocolate-coated candies that, Clinton said, have made great Christmas gifts.
But the focus of the berry studies is a nectar. An OSU team harvests the black raspberries, freeze-dries and vacuum-packs them into sterile containers so the nectar doesn’t require refrigeration. Thus preserved, it can retain its polyphenol profile for 6 months at room temperature, so it can safely travel for clinical studies.
The investigators have identified more than 4,000 compounds in freeze-dried black raspberry powder and nectar. They are trying to determine which compounds to study, which are absorbed and whether the metabolites reach the colon.
“All of these issues are going to be part of deciphering how a food product impacts the cancer process,” said Clinton.
One team has taken the berry study abroad, to China, where cancer of the esophagus is prevalent. In fact, half of all esophageal squamous cell carcinoma in the world occurs in China, in large part due to carcinogens in food and tobacco.
In a rat study that included a carcinogen-treated group as well as a group that received cancer-preventing drugs and a group that ingested black raspberry powder, those consuming the powder had more benign tumors. The latter group targeted several anticancer biomarkers better than the group receiving chemo drugs, said Clinton. “This [result] really has us stimulated to see if we can move this forward to human studies.” Currently, a randomized phase II human clinical trial is under way in China using freeze-dried strawberries.
The goal, said Clinton, is to collect the necessary evidence to justify conducting large trials in high-risk populations and integrate food-based strategies into the cancer-prevention effort.