Study of Diet Due for Imminent Overhaul, Says World-Renowned Researcher

American Institute for Cancer Research
Tuesday, 21 November 2000

"Holistic" Approach to Overall Diet Set To Revolutionize Knowledge of Diet/Cancer Link

A leading international researcher said today that an innovative approach to studying the diet may drastically improve our understanding of the link between what we eat and our risk of contracting illnesses like heart disease and cancer. The key, says Dr. Mariette Gerber of France's National Institute for Medical Research, is to study the overall diet as a network of complex interactions, not as nutrients in isolation.

Dr. Gerber believes that current dietary research is beset by a 'reductionist' viewpoint that needs updating. So-called single-agent studies attempt to isolate and examine the effects of a specific food or a specific nutrient. At issue, says Dr. Gerber, is the basic ability of such research methods to reflect the complexity of real-world diets.

"When researchers focus on one particular nutrient or food, we do so in an attempt to ascertain its precise role in the body," she says. "Unfortunately, there is no guarantee that a nutrient like vitamin C exhibits the same behavior when consumed alone as it may when consumed as a tomato."

In particular, single-agent studies may miss synergistic effects, whereby different nutrients interact to lend increased disease-fighting benefits. Ample epidemiological evidence links healthy diets to reduced risk of chronic disease. Recently, however, studies involving supplements of fiber, beta-carotene, vitamin E and other components of healthy diets have failed to find a link with heart disease or cancer risk.

Dr. Gerber believes these failures have arisen out of a methodology that is too narrowly focused. "Science needs to develop a more holistic view of food intake," she says.

Dr. Ritva Butrum, Vice President for Research at the American Institute for Cancer Research in Washington, DC, agrees. "In America," Dr. Butrum explains, "the term 'holistic' has become popularly associated with 'alternative' or even 'New Age' thinking. That's why Dr. Gerber and other researchers throughout the US and Europe are careful to use the word in its original sense -- as defining a system in which the whole is measurably greater than the sum of its parts."

Butrum believes that over the next few years, holistic or synergistic approaches to studying the diet will supplant the reductionist models that currently dominate scientific literature. She argues that since the human diet is made up of so many different variables, and since diseases like cancer and heart disease are themselves caused by many different factors, any attempts to study how diet affects disease risk must be able to address this complexity. "Such a change is inevitable," Butrum says. "It has already begun."

New Approach Starts with Established Methods

Dr. Gerber offered one example of this new approach in a recent study published in the October 2000 issue of the Journal of the American Dietetic Association. The study was carried out in the Group of Metabolic Epidemiology, National Institute for Medical Research (INSERM) at the Research Cancer Center in Montpellier, France.

In the study, Dr. Gerber and her colleagues began by interviewing 69 men and 77 women about their diets using a food-frequency questionnaire. The researchers then collected and combined these data to score each subject on a Diet Quality Index (DQI) based on current guidelines for disease prevention. A low DQI score reflected a healthier diet, while a high score connoted a poor diet.

Although using a DQI to profile subjects' diets is an established technique, Gerber and her colleagues adapted their DQI so it could accurately reflect the unique makeup of the Mediterranean diet consumed by this study's subjects.

Innovative Combination of Subjects' Blood Data Lends Direct, Unbiased Insight

Now that the researchers had devised a means of representing the Mediterranean diet, the next step was to check it against reliable biomarkers. Biomarkers are measurable biological factors such as the level of specific nutrients found in a subject's blood. They are increasingly used to precisely track and quantify dietary change.

Subjects in Gerber's study had their blood drawn and tested for levels of several dietary nutrients, including fatty acids, vitamin E, and the carotenoids alpha-carotene and beta-carotene. Individually, each of these variables offers researchers a useful measure of food intake. But Gerber and her associates were attempting to measure more than simple intake - they wanted to see if they could track whole dietary patterns.

Her study revealed that by combining data from different biomarkers, a much clearer picture of the subjects' diets did in fact emerge. The resulting "composite index," derived by combining measurements of certain carotenoids, vitamin E and two omega-3 fatty acids in the blood, closely corresponded to the DQIs of study subjects. Gerber believes the biomarker composite represents an important step towards addressing the full complexity of the human diet - and chronic disease. With a few adjustments, it may become a tool that confers an unprecedented degree of precision and real-world practicality to the study of diet and health.

"In this study," she says, "we have shown that by examining these different biomarkers simultaneously, we can accurately reflect and measure multidimensional dietary behavior. Further research will reveal if additional biomarkers like folate or homocysteine may improve the composite even further."

Researcher's Search for New Approach Spurred by Popular Misconceptions

Dr. Gerber and her associates began to look for a means to measure the many changing factors involved with the human diet because they sensed an important message about moderation and overall diet was being overlooked.

"Many people in the world have heard that the so-called 'Mediterranean diet' is healthy and disease-protective," she says. "But there is a distressing tendency to attribute those health benefits to some single part of the diet, such as olive oil or fish or even red wine."

Today, Dr. Gerber's work is showing how overall dietary patterns, not specific foods or nutrients, provide powerful disease-fighting benefits. "Variety is important, and we don't hear enough about its role in overall health. The diet consumed by inhabitants of the Mediterranean basin is one that features a wide variety of vegetables, fruits, whole grains and beans - along with moderate amounts of fish, meats and oils."

Dr. Gerber and her colleagues report feeling an increasing sense of urgency about their work. Every year, she says, more and more Europeans adopt "American-style" diets featuring high-fat, nutrient-poor meals in oversize portions. "Unfortunately, we find ourselves in a race against the clock. We wanted to study the Mediterranean diet and understand why it seems so protective before it vanishes completely," she says.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org