Now there's a clue. It comes from a study of 601 Connecticut women with non-Hodgkin's lymphoma. Tongzhang Zheng, ScD, head of the division of environmental health sciences at the Yale School of Public Health in New Haven, Conn., collected detailed dietary information from these women and from 717 similar women without cancer.
"What we found is if a person has a higher intake of animal protein, they will have a higher risk of non-Hodgkin's lymphoma," Zheng tells Web. "And people who have a higher intake of saturated fat have an increased risk. On the other hand, if you have higher-than-average intake of dietary fiber -- particularly if you frequently eat vegetables and fruits with a high fiber content -- you have a reduced risk of non-Hodgkin's lymphoma."
The findings appear in the March 1 issue of the American Journal of Epidemiology.
Earlier studies hinted at the same thing. Now, Zheng says, it seems clear that a major factor in the mysterious rise of non-Hodgkin's lymphoma is a diet high in meat, saturated fats, dairy products, and eggs and low in fiber, fruits, and vegetables.
Unbalanced Diet, Unhealthy Body
In the U.S., three kinds of cancer have skyrocketed in recent decades. One is lung cancer, mainly caused by smoking. Another is skin cancer, caused by too much sun. The third is non-Hodgkin's lymphoma. But nobody knows why it's on the rise, says Nancy Mueller [pronounced MULL-er], ScD, associate director of population sciences at Harvard's Dana-Farber Cancer Center.
"Non-Hodgkin's lymphoma is a basket of related diseases," Mueller tells WebMD. "It probably has a set of causal factors that may be related to one another, but not in a simple way. We can't really explain it -- this is a really hard nut to crack. But what is happening to the American is associated with a number of malignancies such as breast, kidney, and colon cancer. Higher body weight is a common theme."
A high-fat diet may indeed be linked to higher body weight. But Zheng says that people eating low-carb diets may also be at risk of non-Hodgkin's lymphoma if they eat too much meat and too few vegetables.
One thing that's known about non-Hodgkin's lymphoma is that people whose immune systems aren't working well -- such as AIDS patients -- are at increased risk. Zheng suggests that immune function depends on proper nutrition.
"Your body is designed to repair things," Zheng says. "But if your body is not getting proper nutrition, how can the immune system continue to function? Everything relates to the nutrients in your dietary intake."
Zheng says that it's not necessary to stop eating meat. Nor it is necessary to gobble up huge quantities of vegetables. A balanced diet, he says, is all that's needed.
His study showed that people who ate more of certain foods tended to have a lower risk of non-Hodgkin's lymphoma. Those foods include:
- Mixed lettuce salad
- Citrus fruits
Improving your diet won't just lower your cancer risk, Mueller notes.
"There is such a confluence between risk factors for cancer and risk factors for heart disease," she says. "Get plenty of exercise, eat a good diet, don't smoke. It is what your mother told you. It's true that this is the basis of a healthy lifestyle. And it's true that this lowers your risk for these big killers, too."