We”re getting mixed messages about food and health. One story tells you to avoid carbohydrates; another says they”re not so bad. You”re advised to limit your intake of alcohol, but you hear that a daily glass of wine will do you good. Red meat was vilified. Now it stars in high-protein diets.
Confused? Horticulture professor Irwin Goldman sympathizes.
Goldman studies compounds
contained in fruits and vegetables and how they affect plants and the people who eat them. His interest lies in sorting out conflicting claims about food and health.
The questions are more complex than they first appear, he says, and finding answers is much more so.
“There are some extremely long-term studies that cost millions of
dollars and take decades,” he notes. “But most researchers have to do
short-term projects. They are very
suggestive and hint at trends, but
they aren”t comprehensive.
“We want to understand the whole system,” he says.
While most of us are aware of the major beneficial nutrients in foods – things like vitamins and minerals – Goldman”s research extends to other, less obvious compounds. For example, one major research question in his lab is why onions contain sulfur compounds and how those compounds affect people.
Goldman knows what sulfur does for the onion plant: It provides a natural form of pest control. He also knows that onions and garlic (another bulb that contains sulfur compounds) have been valued as blood thinners since the time of the Pharaohs.
His research has helped move this knowledge from the realm of home remedies to that of science. Working with John Folts, a UW Medical School cardiologist, Goldman has fed raw onions to dogs and mixed onion juice with human blood samples. The findings are consistent: raw onion juice, even in fairly small amounts, is a potent blood thinner.
The key word here is raw. It turns out that heat destroys the sulfur compounds. Cooked onions have no benefit as a blood-thinning agent and may actually have a negative effect.
This doesn”t mean that cooked onions don”t have health benefits, Goldman is quick to point out. It means that if there are such benefits, they haven”t been uncovered.
Beets are another of Goldman”s research interests. Beets have long been bred for their pigments, which can be used as natural food dyes. A colleague, food scientist Kirk Parkin, has learned that beet pigments can enhance the activity of phase II enzymes, which in turn can protect against certain cancers. Goldman wants to know why and how plants produce the pigments and what happens when people consume them.
“Many compounds affect color, flavor and taste, but which of those affect consumer choices?” he wonders.
He is also looking at ways to enhance food”s medicinal benefits. His research team recently discovered a natural genetic mutation that allows carrots to produce vitamin E. Until then, the sweet potato was the only vegetable known to have that trait. In the future, growers might be able to market carrots with natural vitamin E.
Goldman”s interest extends beyond plant chemistry. He”s also interested in the cultural aspects – the idea of integrating the use of health-enhancing compounds into everyday eating habits, rather than “taking” them as isolated medical treatments. People react to food differently than to medicine, he points out.
“Medicine is a targeted chemical,” he explains, “while people choose food based on their culture, personal biases and personal taste.”
grapes and cranberries may help your heart
High cholesterol levels are a problem for as many as 99 million American adults, according to American Heart Association estimates. The problem has spurred many people to eat less of certain foods, including animal products.
However, one College scientist believes the key to lowering levels of bad cholesterol may lie in eating more of foods, such as grapes and cranberries, that contain a class of compounds called flavonoids.
Animal scientist Jess Reed knows that many people associate cholesterol with heart disease. However, he cautions that “there”s actually a poor link between heart disease and cholesterol, while we know that there is a strong genetic component to the problem.” Atherosclerosis – hardening of the arteries – also plays a role, he adds.
Reed”s research team studies how flavonoids in food affect both high cholesterol and hardening of the arteries.
Flavonoids occur naturally in certain plants, where they contribute to properties such as color, flavor and texture. Many flavonoids are also thought to provide health benefits, such as fighting cancer and heart disease.
When Reed fed cranberry juice powder, which is rich in flavonoids, to pigs with high cholesterol, he found that the levels of LDL – “bad” cholesterol – dropped. “It was comparable to the effect of statins, which are human
cholesterol-lowering drugs,” he says.
The food industry sees the potential value of compounds like flavonoids, says Reed. Marketers of food supplements, the fastest-growing area of the food industry, often tout their products” flavonoid properties. For example, cranberry tablets are marketed to treat urinary tract infections.
“This area of research is very important and will expand as we learn more about the link between nutrition and health,” Reed says.
Researchers face a huge challenge when it comes to the diversity of compounds in food. For example, there are 14 different classes of flavonoids. Any given food, such as grapes or cranberries, might contain four classes (anywhere from six to 20 different compounds). And because flavonoids are not essential nutrients, their absence doesn”t trigger observable deficiency symptoms, making them hard to study.
“The dilemma is that traditional
scientific approaches are founded on reducing an idea to testable experiments,” Reed says. “However, in modern biochemistry that means getting down to individual molecules. We have to recognize that these problems are not simple, and do not lie with any one compound.”
Humble vegetables may help fight cancer
They may not appear on nouvelle cuisine menus in trendy restaurants, but some of food scientist Kirk Parkin”s favorite vegetables deserve star status in our daily diets. Parkin and his colleagues are finding that extracts from “everyday” veggies contain ingredients that may help our bodies produce
Parkin studies green beans, corn, green onions and other vegetables, seeking components that can boost the body”s production of cancer-fighting phase II enzymes. These proteins help detoxify carcinogens, converting them to less harmful chemicals that the body can more easily eliminate.
“We had been studying some of
the biochemical aspects of flavor gen-eration in freshly minced onion and
garlic and found that the chemistry of the flavor compounds was even more interesting because it was not well
documented,” Parkin says.
Previous research had suggested that these same fresh-flavor compounds also had biological activities relevant to human health, he says.
“Our program has since evolved
to primarily focus on health-
promoting agents in common
fruits and vegetables.
“Consumption of vegetables is known to confer health benefits, such as the reduced risk of developing vitamin deficiencies, heart diseases and cancer,” Parkin says. “Vegetables contain phenolic antioxidants, which protect against cancer mediated by free radical mechanisms, and also induce antioxidant, protective enzyme activities in bodily tissues. These enzymes have multiple functions, including detoxification, neutralization of the effects of free radicals, and recycling
For example, Parkin”s lab has isolated three fractions from green beans that elevate levels of quinine reductase, a phase II enzyme, in cancerous mouse-liver cell cultures. Green bean fractions raised enzyme levels fivefold. Sweet corn extracts raised them thirteenfold, while kale extract bumped them eightfold. The vegetable fractions are also efficient antioxidants, knocking out free radicals that can disrupt cell function.
Wisconsin is a major producer of many “everyday” vegetables. In 2002 the state produced more than 300,000 tons of green beans for processing and nearly 600,000 tons of sweet corn. Parkin sees several ways in which the vegetable industry could benefit from the discovery of health-promoting agents in common vegetables.
For example, plant breeders or molecular biologists might be able
to develop germplasm with enhanced levels of those compounds. And if researchers learn more about what
happens to these compounds during processing, they might be able to modify processing to enhance or maintain levels of the compounds.
This could add value to Wisconsin”s vegetable industry, he says. It could also add value to what”s now being thrown away.
“Selected agricultural waste streams may be rich enough in health-promoting agents that efforts to recover and process waste may become more economically feasible,” says Parkin.
The discovery of one health-promoting bioactive agent could lead to others, Parkin says. The same agent may be known to exist in other foods. Or it may be a member of a diverse class of compounds, others of which could also have healthful effects.
Researchers used to ignore nonnutritive constituents of vegetables, assuming they were biologically inert, Parkin notes. But recent discoveries of links between diet and the incidence
of cancer and heart diseases have convinced many researchers that nonnutritive constituents may help prevent the development of these diseases.
“As genetic tools continue to become available to diagnose enhanced risks of individuals for specific diseases, I believe there will be the opportunity to use diet in specific ways for specific individuals to help manage those risks,” Parkin says. “What may limit our ability to do this is a lack of information on which dietary components are most effective at helping reduce these risks. That is a major
reason why we are committed to doing the work we do.”