According to the research findings:
- Eating soy in childhood may make women less likely to get breast cancer.
- Men who eat fish frequently may be less likely to get colorectal cancer.
However, the researchers warn, it's too soon to make dietary promises about the cancer prevention qualities of soy and fish from these studies.
Soy & Breast Cancer
The study looking at soy was based on interviews with 1,500 women aged 20-55 of Chinese, Japanese, and Filipino descent. The women were living in Los Angeles, San Francisco, and Hawaii.
Researchers included the National Cancer Institute's Larissa Korde, MD, MPH.
The researchers questioned the women -- and their mothers, when possible -- about how much soy they ate as kids, teens, and adults.
They found that women with the highest childhood soy intake were 58% less likely to get breast cancer than those with the lowest intake.
In this study, women with the highest childhood soy intake ate soy -- mainly tofu -- a little more than twice a week. Those with the lowest childhood soy intake ate soy about once a month, Korde says.
Women who ate the most soy as teens or adults were about 25% less likely to have breast cancer than those who skimped on it.
The study results weren't affected by family history of breast cancer and were "strikingly consistent," Korde says.
She calls the findings "provocative" but says they need to be replicated.
Meanwhile, the researchers aren't telling anyone to load their kids' diets with soy.
Men, Fish, and Colorectal Cancer
The second study found that men who eat fish frequently may be less likely to develop colorectal cancer than those who rarely eat fish.
The researchers included Megan Phillips, a graduate student at the Harvard School of Public Health.
The study reviewed data on about 22,000 men from the Physicians' Health Study. In that large health study, in 1983, the men reported how often they ate fish and shellfish over the course of a year.
Over the next 18 years, 501 of the men developed colorectal cancer.
"What we found was that men who ate the most fish -- and that was five or more servings per week of fish -- compared to the least fish -- less than one time per week -- had a 40% lower risk of developing colorectal cancer," Phillips says.
She notes that previous studies haven't always found the same thing when it comes to fish consumption and colorectal cancer.
"I think it's premature to make a recommendation for how much fish men should eat to reduce their risk of colorectal cancer," she says.
"But I do think it provides possibly another reason for men to include fish in their diet in addition to the benefit that we know about for heart disease," she says.
"The best recommendation at this time is a balanced diet," Elizabeth Platz, ScD, MPH, told reporters in a teleconference.
A healthy diet includes fruits, vegetables, and plant-based proteins -- and balances calories consumed with calories burned, she says.
Platz is an associate professor in the epidemiology department at Johns Hopkins Bloomberg School of Public Health in Baltimore.