Two new studies have found what their authors say is scant evidence that changes in diet help cancer patients survive longer or avoid recurrences of the disease.

Many cancer patients and their families see hope in foods popularly believed to help fight cancer, including nutritional supplements. And studies indicate that eating plenty of vegetables and fruits helps prevent certain cancers.

While not disputing that healthy eating has major benefits, the authors of one study said such diets may have little relevance in treating cancer itself. Some nutritional supplements may even be harmful, they added.

The study consisted of an analysis of 59 previous studies of specific dietary modifications. There was little relationship between diet and survival or prognosis, the authors said.

The other study found that neither garlic nor vitamin supplements, both popularly thought to help fight cancer, delays the progression of pre-cancerous gastric lesions to cancer.

Both studies appear in the July 19 issue of the Journal of the National Cancer Institute.

In the first, Steven Thomas of the University of Bristol, U.K. and colleagues investigated a range of dietary changes among patients previously diagnosed with cancer or pre-cancerous lesions. The changes included increased intake both of packaged nutritional supplements and of foods generally considered healthy, such as high-fiber meals.

There was little evidence that these had any effect on disease-free survival, mortality, or recurrence, Thomas’ team argued, adding that it was hard to gauge the effects at all because of a dearth of high-quality studies.

“The large personal expenditure on supplements and dietary modifications by patients with cancer demonstrates an urgent need to understand their effects on cancer outcomes. This vulnerable group of people need to be better informed as diet is one of the few areas of their lives where they may feel that they have some control,” the researchers wrote.

“Encouraging a healthy diet is certainly important because many patients with cancer and preinvasive lesions will live a long time and may die of other diseases related to diet,” they continued. But without better evidence, they added, clinicians shouldn’t tell patients that a healthy diet is “a priority in management of cancer itself.”

The second study found that garlic and vitamin supplements did not reduce the prevalence of precancerous lesions or gastric cancer. But treatment to kill the germ Helicobacter pylori, which causes the cancer, may provide benefits, it found.

In Linqu County, China, gastic cancer causes 42 percent of all cancer deaths, and the bacteria infect two-thirds of adults, said the scientists, Wei-Cheng You of the Beijing Institute for Cancer Research and colleagues.

They tested 3,365 Chinese adults ages 35 to 64 in the county. The researchers found that antibiotics reduced the severity and progression of pre-cancerous gastric lesions. Long-term vitamin and garlic supplementation, though, had no effect on the incidence of gastric cancer or progression of pre-cancerous lesions, the researchers said.

ABOUT THE AUTHOR

Science writer Jack Lucentini is founder and editor of the World Science science news webzine. He has worked as a staff writer at three daily newspapers, and as a freelance science writer for a range of publications including The Washington Post, Discover magazine and The Scientist magazine. He earned his bachelor's degree at Oberlin College in Oberlin, Ohio in 1993.