TARRYTOWN, NY--America's major medical research institutions are failing to conduct the nutritional research needed to make a major public health impact on cancer and other diseases, says Peter Greenwald, MD, director of the division of cancer prevention and control at the National Cancer Institute.
TARRYTOWN, NY--America's major medical research institutions arefailing to conduct the nutritional research needed to make a majorpublic health impact on cancer and other diseases, says PeterGreenwald, MD, director of the division of cancer prevention andcontrol at the National Cancer Institute.
The value system of most research centers is focused on gettingmore and more precise data on the molecular level, Dr. Greenwaldsaid. Nutritional research does not appear as attractive becauseit offers less precise information. But, he noted, approximateanswers to nutritional questions can have a huge impact on health:"This is a very complex area, and you can't always expectprecise, mechanistic answers to these questions."
Dr. Greenwald spoke at a symposium celebrating the 25th anniversaryof the American Health Foundation, which is largely devoted tonutritional research. Another speaker, Leonard Cohen, PhD, directorof nutritional endocrinology at the foundation, listed questionsabout the role of nutrients in cancer causation that he said urgentlyrequire answers:
1. Is all dietary fat bad or is there a threshold below whichintake is safe? "If there is a threshold, it's very criticalto find out what it is," Dr. Cohen said. "But we don'tknow whether the threshold would be the same for every personand every age group."
2. What are the effects of different kinds of fat? "Eskimosget 60% of their calories from fat, far more than most Americans,yet they have a low incidence of cancer. Their fat comes in theform of omega fatty acids, which are not a major factor in theAmerican diet," he said.
3. How much and what kinds of fiber protect against cancer?
4. How do fiber and fat interact?
5. What is the role of exercise?
6. How does dietary fat intake affect gene expression?
Dr. Greenwald said that he believes Dr. Cohen's priorities areimportant, since there is "strong evidence that diet is drivingthe incidence rate of many cancers." Such evidence linksnot only fat intake (see below) but also total dietary calorieswith cancer occurrence, he said. For example, a summary of 12epidemiologic studies in Western countries found a 50% increasein breast cancer occurrence among postmenopausal women with thehighest fat and calorie intake.
Dr. Greenwald questioned the results of one major study that contradictsthe fat-cancer link--the ongoing study of 90,000 US nurses beingconducted by Walter Willett, MD, of Harvard University. The studyhas found no relationship between reported fat intake and breastcancer in the nurses.
Dr. Greenwald said he could question the results because Dr. Willetthad been thorough enough to conduct a more intensive study ofa subgroup of the nurses, to verify their self-reported levelsof fat intake.
A detailed questionnaire on daily diet filled out by a subsampleof the nurses found that 47% of those listed in the lowest quintilefor fat intake underestimated their intake considerably on thebasic study report, and there were large measurement errors inevery quintile.
Issues about fat, fiber, and cancer can be resolved only by furtherresearch that goes into the nutritional intricacies of the effectof fat on the body, Dr. Greenwald said.
There were 46,000 breast cancer deaths in the United States lastyear. "If Americans had the same breast cancer death rateas the Japanese, who eat a very low-fat diet, there would havebeen only 11,000," Dr. Greenwald said in his talk.
"If we could match the Greeks, who eat a low saturated fat'Mediterranean diet,' rich in, among other things, olive oil,the number of breast cancer deaths would have been 29,000,"he said.