Can eating small fish whole protect against dying from cancer?

For this study, researchers analyzed food frequency questionnaire data from more than 80,000 participants — about 34,500 men and 46,000 women — between the ages of 35 and 69 in Japan. Based on the questionnaires, scientists noted how frequently study participants ate small fish whole.

Researchers followed the participants for an average of nine years, during which about 2,400 participants died with about 60% attributed to cancer.

At the study’s conclusion, scientists discovered there was a significant reduction in all-cause and cancer death among female participants who habitually ate small fish whole.

When researchers factored in lifestyle habits that may impact mortality risk, such as smoking, BMI, and alcohol consumption, they found female participants who ate small fish frequently were less likely to die from any cause.

According to the researchers, it is common practice in Japan to eat small fish — including small horse mackerel, whitebait, Japanese smelt, and sardines — whole, including the organs, bones, and head.

“Previous studies have revealed the protective effect of fish intake on health outcomes, including mortality risks,” explains Chinatsu Kasahara, graduate student (Ph.D. candidate) at the Nagoya University Graduate School of Medicine in Japan and lead researcher of this study. “However, few studies have focused on the effect of the intake of small fish specifically on health outcomes. I was interested in this topic because I have had the habit of eating small fish since childhood. I now feed my children these.”

Smaller fish have the benefits of being sustainable as they are not normally overfished like larger fish and generally have lower levels of mercury.

“I regularly recommend the consumption of small fish due to their impressive nutritional value and low levels of toxic mercury compared to large fish,” Molly Rapozo, RDN, registered dietician nutritionist & senior nutrition and health educator at Pacific Neuroscience Institute in Santa Monica, CA, who was not involved in this study, told Medical News Today.

“Small fish are a component of traditional Japanese and Mediterranean diets, which are both touted for their longevity,” she said.

In addition to being a healthy protein source, small fish also provide a variety of nutritional benefits including omega-3 fatty acids and micronutrients such as calcium, vitamin A, iron, zinc, and vitamin B12.

“The health benefits that have been associated with fish overall such as being a rich source (of) essential and protective nutrients such as protein and healthy fats such as omega-3 fatty acids, as well as a source (of) calcium from the bones and a host of other vitamins and minerals has been pretty consistent in the research,” Monique Richard, MS, RDN, LDN, a registered dietitian nutritionist and owner of Nutrition-In-Sight explained to MNT.

“Often when someone is eating small cold-water fish sources they are also choosing other foods that complement the health benefits offered by fish such as fruits, vegetables, and whole grains,” Richard continued.

“Tiny fish do not typically lend themselves well to being battered, deep fried, and served with french fries but are more delicate as well as naturally portion controlled. They tend to be more rich and flavorful in taste to the palate which lends itself to slower eating, savoring the bites and possibly needing less to feel satisfied,” she said.

“This study adds to the existing evidence of fish consumption and cancer mortality. We’ve seen in previous studies that regular fish intake is associated with a reduced risk of gastrointestinal cancers, as well as being a potential benefit for cancer survivors who have diets high in oily fish.”
— Molly Rapozo, RDN

“This kind of research is important because what we eat has a significant impact on chronic disease. Lifestyle changes, such as food choices, are an opportunity to decrease the risk of early death and disability. Evidence-based dietary strategies offer a practical approach to reducing the burden of chronic diseases, including cancer, and improving longevity,” Rapozo said.

MNT also spoke with Anton Bilchik, MD, PhD, surgical oncologist, chief of medicine, and director of the Gastrointestinal and Hepatobiliary Program at Providence Saint John’s Cancer Institute in Santa Monica, CA, about this study.

Bilchik said he found the study interesting that eating small fish whole may offer protective factors against the development of cancer.

“But I think that this is very early in terms of … what exactly it means, what’s a whole small fish in terms of the anti-cancer chemicals, vitamins, and the big buzzword in cancer right now is inflammation. So within a whole fish, are there various compounds and vitamins that have an anti-inflammatory effect? But there’s still a lot to be worked out,” he said.

Because many young people are being diagnosed with cancer, particularly colorectal cancer, Bilchik said it is important for researchers to continue to find new ways of protecting the body from cancer, including through what we eat.

“The usual causes such as obesity, smoking, family history, are not commonly found in these young people that are being diagnosed,” he explained. “And so the only other potential linker can be looked at is diet at a young age — whether these individuals that are getting early onset cancer, such as colorectal cancer, are eating processed food, are being exposed to environmental factors that may influence cancer at a young age.”

“So there’s a lot of work that needs to be done to better understand why so many young people are being diagnosed with cancers, particularly colorectal cancer,” Bilchik added.

While eating small fish whole may be a normal dietary practice in Japan, the same cannot be said for other countries such as the U.S. or those in Europe.

When thinking about cold-water fish that is lower in mercury, heavy metals, and other contaminants, but also is fairly versatile, tasty, and readily available, Richard said to remember the acronym SMASH — sardines, mackerel, anchovies, salmon, and herring.

Richard recommends adding a serving of 3 to 4 ounces of fish or four to five small fish to:

• a piece of whole-grain toast or crackers
• on top of a salad
• folded into a whole grain such as farro, buckwheat, long-grain or brown rice, or quinoa
• added to vegetable soups, stews, or pastas
• mashed up as a spread or pâté

“A plethora of options are now available in most grocery stores with canned or jarred variations using spices, oil, herbs, or a combination of enhancements. Get out there and experiment — SMASH may be the new spice of life!” Richard added.