November 30, 1996Addicted to Java? Don't press it!
Many coffee aficionados eschew the filtered brew, arguing that filters remove some of a bean’s savory flavor. What filtering really does -- besides screening out gritty grounds -- is eliminate coffee’s oils, rich in alcohols known as diterpenes. Two of these alcohols, cafestol and kahweol, can elicit a number of unhealthy changes in the blood of regular coffee drinkers.
The newest diterpene effect to be identified -- an increase in blood levels of an enzyme that is normally associated with damage to liver cells -- emerged in a 6-month long Dutch trial with healthy, coffee-loving volunteers.
Rob Urgert and his colleagues at Wageningen Agricultural University in the Netherlands recruited 46 men and women to participate in the experiment. All of the volunteers received a locally popular blend of coffee and strict instructions on how to brew two batches of it each day.
Urgert’s group directed half the men and women to pour boiling water through 33 grams of ground beans sitting in a cone-shaped filter until the dripping brew filled a half-liter jar.
The remaining volunteers were told to pour their boiling water and ground beans together into a French press -- also known as cafetière -- coffee maker. The top of this type of pot is fitted with a large plunger. The volunteers were told to stir the mix and then to let the grounds steep for 2 to 5 minutes before they pushed the plunger down. (This effectively stops the brewing and traps any floating grounds so that they won’t enter the cup.) The coffee was then decanted into another bottle.
The participants, all healthy and between the ages 19 and 69, were told to drink almost a liter of the coffee daily for 24 weeks. Every 2 to 4 weeks, the scientists brought the volunteers in for blood tests that measured concentrations of cholesterol, triglycerides, and a host of liver enzymes.
A report of the study, published in today’s British Medical Journal, shows that men and women who drank the filtered coffee exhibited no changes over the course of the trial in any of the assayed blood constituents. Previous studies by Urgert’s group had shown that such a filter effectively removes all of the coffee-oil’s diterpenes. Those who drank coffee made by the French press method, however, displayed a host of undesirable changes.
For instance, levels of one liver enzyme (alanine aminotransferase) nearly doubled early in the trial. This enzyme serves as a marker of potential stress to the liver, Urgert explains. "If there is some change in liver cell integrity, the concentration of these enzymes in the blood can rise."
Fortunately, he notes, the enzyme rise among cafetière coffee drinkers was far less than that in persons with liver disease. Moreover, his data indicate, the rise in these enzymes is transient. Levels were already falling by the end of 24 weeks and continued to fall further during the 12 weeks after the trial ended.
However, Urgert told Science News Online, the enzyme findings remain interesting because "until now there have been very few foods identified as having such an effect on liver cells."
The Dutch nutrition scientists also observed a sharp, transitory 26 percent rise in serum triglyceride levels among the men and women drinking French-pressed coffee. Like the liver-enzyme changes, however, the triglycerides fell as the study progressed. By the end of 24 weeks, their concentrations had already returned to levels recorded before the start of the study.
Of far greater concern, Urgert believes, were increases of between 9 and 14 percent in the concentrations of low-density-lipoprotein (LDL) cholesterol -- the so-called bad cholesterol -- in volunteers drinking the pressed brew. An increase this large in LDLs, a risk factor for heart disease, might over a lifetime elevate an individual’s chance of developing coronary disease by up to 20 percent, he notes. Also observed in several shorter studies by this group, this potent elevation in LDL concentrations shows no sign of attenuating with time.
"These [diterpenes] are amazingly predictable," Urgert observes. "If you knew much you gave to Dutch volunteers, you could almost exactly predict their change in LDL cholesterol."
This link to persistent LDL increases "should also apply to Turkish coffee, which contains similar amounts of cafestol and kahweol per cup," the researchers point out. Significant LDL increases might also accompany heavy consumption of Italian espresso, they add. However, owing to the small size of espresso cups, one would have to drink some 25 cups per day.
The good news: Grandma’s old metal percolator basket will filter out the diterpenes almost as effectively as do the new generation of filtering drip coffee makers.
What if you mix your coffee up from instants? No problem. Analyses of 19 different instant coffees marketed in Europe, the United States, and North Africa -- including 6 decaffeinated brands -- turned up only "minimal" quantities of the diterpenes in the brewed drinks.
That doesn’t mean that some forms of coffee are completely innocuous. A study conducted in California, a few years back, showed that drinking at least two cups a day throughout life can increase the risk that an individual will suffer from osteoporosis in old age.
Tea drinkers, by contrast, can take heart in their habit. The diterpenes that caused LDL and other changes in the new study are not found in other hot beverages. Most regular (not herbal) teas also are rich in a class of compounds known as flavonoids. These can largely halt oxidative changes in the blood -- changes that can transform dietary fats into artery-clogging plaque.
References:
Barrett-Connor, E., J.C. Chang, and S.L. Edelstein. 1994. Coffee-associated osteoporosis offset by daily milk consumption. Journal of the American Medical Association 271(Jan. 26):280.
Urgert, R., et al. 1996. Comparison of effect of cafetière and filtered coffee on serum concentrations of liver aminotransferases and lipids: Six month randomized controlled trial. British Medical Journal 313(Nov. 30):8.
Urgert, R., et al. 1995. Levels of the cholesterol-elevating diterpenes cafestol and kahweol in various coffee brews. Journal of Agricultural and Food Chemistry 43(August):2167.
Related Reading:
Raloff, J. 1995. New support for tea’s heart-y benefits. Science News 148(Dec. 9):399.
_____. 1995. Coffee: Brewing’s link to cholesterol. Science News 148(Sept. 16):182.
_____. 1995. Filtered coffee friendlier to the heart. Science News 147(Feb. 4):72.
_____. 1991. Heart disease worries? Watch the decaf. Science News 140(Sept. 14):165.
Rosmarin, P.C., W.B. Applegate, and G.W. Somes. 1990. Coffee consumption and serum lipids: A randomized, crossover clinical trial. American Journal of Medicine 88(April):349.
S., M. 1996. Tonic in a teapot? FDA Consumer 30(March):25.
Salvaggio, A., et al. 1991. Coffee and cholesterol, an Italian study. American Journal of Epidemiology 134:149.
Superko, H.R., et al. 1991. Caffeinated and decaffeinated coffee effects on plasma lipoprotein cholesterol, apolipoproteins, and lipase activity: A controlled, randomized trial. American Journal of Clinical Nutrition 54:599.
van Rooij, J., et al. 1995. A placebo-controlled parallel study of the effect of two types of coffee oil on serum lipids and transaminases: Identification of chemical substances involved in the cholesterol-raising effect of coffee. American Journal of Clinical Nutrition 61(June):1277.
Zock, P.L., et al. 1990. Effect of a lipid-rich fraction from boiled coffee on serum cholesterol. The Lancet 335(May 26):1235.
Sources:
Rob Urgert
Department of Nutrition
Wageningen Agricultural University
Bomeneg 2, 6703 HD
Wageningen, the Netherlands
E-mail: rob.urgert@et3.voed.wau.nl
This week's Food for Thought has been prepared by Janet Raloff, senior editor of Science News.
Food for Thought Archives
copyright 1996 ScienceService