LOMA LINDA, Calif. — Remember the oat bran craze? Get ready for walnuts.
In a study bound to generate interest among nutritionists and cardiologists--not to mention health-conscious consumers--researchers at Loma Linda University report that walnuts reduce cholesterol levels in the blood and protect against heart disease.
The study found that men who ate a diet rich in walnuts showed a 16% drop in so-called bad LDL cholesterol, although their "good" HDL cholesterol also dropped--by 5%. More important, however, is that the study found a beneficial 12% decrease in the ratio of bad to good cholesterol among men who ate the walnut diet.
But some nutrition and heart experts expressed skepticism about the usefulness of the study, which appears in today's New England Journal of Medicine and was financed by the California Walnut Commission, an agency that helps market walnuts.
According to these experts, it would be nearly impossible--and unwise--for consumers to duplicate the walnut diet, in which 20% of the calories came from walnuts. The diet included 3 ounces of the nuts a day--slightly more than 68 pounds a year if eaten on a daily basis--and even the study's authors acknowledged that the diet is impractical.
"It was an extreme diet; they made everything out of walnuts," said Walter Willett, a professor at the Harvard School of Public Health who studies the links between nutrition and disease. "I definitely would not recommend that as a pattern."
Willett also noted that other nuts may be equally beneficial--a statement with which the study's authors concurred.
Other experts, meanwhile, said they fear that consumers will rush out and add walnuts--high in polyunsaturated fat--to their diets, rather than substitute walnuts for other types of fat, as was done in the Loma Linda study. Several recalled the hoopla about oat bran during the 1980s, after studies showed it helped lower cholesterol; the oat bran boom went bust when further studies showed it had only a small cholesterol-lowering effect.
"I have this worry about some guy who just finishes this enormous filet mignon and has a hot fudge sundae and then orders walnuts, saying, 'This will cover me, this is the magic bullet,' " said Dr. William Castelli, director of the Framingham Heart Study. "That's not what they found in this study. You have to substitute."
The lead researcher on the Loma Linda study, Dr. Joan Sabate, said he shares those concerns--although he added that even a one-ounce portion of walnuts a day, if substituted for other fats, could reduce the risk of heart attack by 8% to 10%.
"Our study was an experimental situation," Sabate said at a press conference Wednesday. "I wanted to prove or disprove if walnuts, in fact, lower cholesterol. By no means do I recommend three ounces of walnuts (daily) for the general population."
The study involved 18 men between the ages of 21 and 43; all were Seventh-day Adventists, who generally avoid smoking and drinking and thus have a lower risk of heart disease. The men were put on tightly controlled diets for 61 days.
After one week during which all the study subjects ate a diet designed to lower cholesterol, the group was split in two. Half the men continued on the same low-cholesterol diet. The other half went on the walnut diet. They ate the same diet as the first group, but substituted three ounces of walnuts a day for certain fatty foods, such as potato chips and meat, as well as oils, margarine and butter.
The nuts were served as snacks, mixed in salads and breakfast cereals and cooked in dinner entrees. Walnuts accounted for 55% of the fat, 14% of the protein and 10% of the fiber in the diet.
After four weeks, some members of each group switched diets. When the results were analyzed, the researchers found that while both diets lowered total blood cholesterol levels, the walnut diet accounted for a far more significant drop, the scientists said.
When Sabate and his colleagues set out to investigate the link between nuts and heart disease, they sought funding from several organizations. When the walnut commission agreed to pay for the study, the researchers decided to examine walnuts, although Sabate acknowledged that other nuts may be equally beneficial.
"I'm interested in all kinds of nuts," Sabate said. "But I can only study one at a time."
Although one watchdog group criticized the researchers for accepting money from those who had a financial stake in the outcome, it is fairly common for food industry groups to finance studies involving their products. Ethics experts say this is not a conflict of interest, as long as the funding source is disclosed and the money comes with no strings attached.
"Who else is going to fund such studies?" asked Willett, the Harvard researcher.