Web edition: December 1, 2005
Over the past few years, many studies have linked an increased risk of debilitating illnesssuch as heart disease or diabeteswith chronically elevated blood concentrations of a protein typically associated with inflammation. In many cases, people with the indicated illnesses didn't even have a particularly level of inflammation. The good news: A new trial finds that eating plenty of fruits and vegetables reduces concentrations of the worrisome protein.
In the new trial, researchers recruited people to eat a low-produce diet for a month and then increase that dietary component. The inflammation markerC-reactive protein (CRP)was slightly elevated in the participants while they ate few fruits and vegetables, says study leader Bernhard Watzl of Germany's Federal Research Center for Nutrition, in Karlsruhe. He points out that the recruits were not suffering from major infections but that some were overweight. A host of studies has demonstrated that body fat can trigger chronic inflammation (SN: 2/28/04, p. 139: Available to subscribers at http://www.sciencenews.org/articles/20040228/bob9.asp). Whatever the source of CRP, research has linked artery-clogging atherosclerosisand risk of heart attackto excess blood concentrations of the protein (SN: 4/20/02, p. 244: Available to subscribers at http://www.sciencenews.org/articles/20020420/fob4.asp).
The study found that when the participants changed from a diet low in produce to one high in such foods, they experienced a significant drop in blood CRP. However, no statistically significant relationship emerged between blood concentrations of any immune cell or of other components of the immune system and the number of servings of fruits and vegetables people had eaten.
Watzl says his team had actually been expecting to find that feeding adults large quantities of fresh produce would rev up their immune systems. The study was exploring the connections among diet, immune system effects, and cancer risk. Earlier work by his team had suggested that people eating little produce have weakened immune defenses against cancer.
The new findings, however, suggest a different potential explanation, involving inflammation, for why people who eat the most fruits and vegetables typically have the lowest incidence of cancers of the breast, lung, and gastrointestinal tract.
Watzl's team recruited 63 healthy, nonsmoking men to take part in a 2-month study. All were around age 30, had similar body-mass indexes, and reported no history of taking vitamin supplements.
During the study's first 4 weeks, the men were instructed to eat normally except for their fruit and vegetable intake. The trial limited consumption of these foods, or juices made from them, to just two servings per day. One serving of solid food was 100 grams (3.5 ounces). A serving of juice was 200 milliliters (6.8 ounces).
During the next 4 weeks, the volunteers were told to consume no fruits, veggies, or juices except those provided by the researchers. The participants were divided into three groups that received two, five, or eight servings of these foods per day.
The most startling impact of getting eight servings of produce and juice per day was a drop in blood CRP. In men going from two servings to eight servings per day, CRP concentrations fell by one-third. No statistically significant change occurred in men going from two to five servings.
"Our intervention study is the first to show that [blood] CRP concentrations can be modulated by the consumption of vegetables and fruits," the authors report in the November American Journal of Clinical Nutrition.
The researchers attribute the CRP decrease in the eight-servings-per-day group to increases in the men's consumption of foods rich in the carotenoids alpha- and beta-caroteneplant pigments with antioxidant properties. Although carotenoids impart color to a host of red, orange, and yellow fruits and vegetables, alpha-caroteneat least in the German diettraces primarily to the consumption of carrots, Watzl notes. He says his new data suggest that carrots may largely explain the CRP benefit.
Several studies in recent years have shown that eating carotenoid-rich foods, such as tomato juice or carrot juice, can stimulate the immune system. To gauge that effect in the current study, the researchers measured, at the beginning and end of each phase of the new trial, blood concentrations of white blood cells and several immune-system chemicals. However, concentrations of neither the cells nor chemicals varied significantly during the trial.
Watzl concludes that the reason his team found no impact of the high-produce diet on any of the men's immune systems is probably because eating fruits and vegetables will stimulate the immune system only in people whose diets are below some critical threshold in certain plant-based compounds.
Alas, he notes, "our subjects were quite well nourished." Dietary history data for the men showed most had been routinely consuming 350 milliliters of fruit juice daily prior to taking part in the new study.
"In my opinion," Watzl says, "the reason that we didn't see major changes in immune function is likely related to very high concentrations of vitamins, like vitamin C, and carotenoids in the [recruits'] blood" when they entered the study. In fact, the men's vitamin C concentrations didn't notably drop in the lowest-fruits-and-veggies group until about 8 weeks into the trial, he says, suggesting a person would have to eat a low-produce diet far longer than that to seriously deplete his or her stores of such nutrients.
Indeed, Watzl points out, a constant frustration to nutrition researchers is that most people who volunteer to take part in their studies are "too healthy or have too high an intake of certain nutrients" to reflect the population generally, much less people who are poorly nourished.
"In this study," the nutritionist notes, "we did not really restrict the intake of carotenoid-rich vegetables" severely: The lowest intake of produce or juices was two servings per day. That's why Watzl's aim in his next study is look at carotenoid impacts after "extended periods of carotenoid depletion."
If carrots fight CRP, then this could be just the side dish to keep that inflammation marker in check. So, we are again providing the recipe for this year-round favorite in my household. The salad can be hot or not, depending on whether you choose to add a dash of Tabasco sauce. Adults tend to appreciate the unexpected kick far more than kids do.
I tend to be a little heavy-handed with the condiments, but for each pound of peeled and grated carrots, mix in at least:
Then blend in olive or canola oil (canola has less saturated fat), about 1/3 cup. Also add at least 1/4 cup of freshly squeezed lemon juice. Stir thoroughly.
This salad tastes best when prepared an hour ahead of time and set out at room temperature, so the flavors can meld. It keeps up to 5 days in the refrigerator.
Institute of Nutritional Physiology
Federal Research Centre for Nutrition and Food
Web site: [Go to]
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