According to this week’s nonsensical nutrition headlines, vegetable oils and tuna are out to get you.

First up, a recent study by Cornell, published in the journal Molecular Biology and Evolution, indirectly linked vegetable oils to heart disease and cancer and directly linked the researchers’ names to outrageous headlines including, “Being a vegetarian could kill you, science warns.”  For some important context, the researchers didn’t measure the kinds of oils consumed or increased health problems among the population studied.  More details on the convoluted path to the comical headlines is available here.

This next one isn’t even a published study.  Now all it takes is a grad school dissertation to result in the headline, “Eating too much tuna may increase risk of breast cancer.”  Here’s the left out details:

• This report includes no primary data.  Rather, it looks solely at associations (canned tuna consumption, blood mercury levels, and breast cancer incidence) within secondary data not originally designed for this purpose.
• The results from this report are unable to provide any evidence of causation.
• Known risk factors for breast cancer – namely family history and genetic predisposition – were not considered.
• The role of omega-3s, which canned tuna is a leading source of in the U.S., and which have been linked to decreased risk of cancer, were not considered.
• The actual source of mercury in the data reviewed for the report is unknown.
• The average levels of mercury in canned tuna in the data reviewed for the report consistently fall below the FDA level of concern (1.0 ppm).
• According to this report, smoking and increased BMI decreased odds of breast cancer, showing the shortcomings of this methodology.

For science-based information on fish and cancer risk, see these takeaways from the reputable, authoritative organization, the American Institute for Cancer Research.

Fish and Cancer Risk: 4 Things You Need to Know

You probably know that fish is part of a healthy diet. Fish — and its healthy fats — are well recognized for their heart health benefits. But research on the role that fish may play in cancer protection is less clear. And if you’re one of the many Americans who enjoys fish, there’s a good chance you also have concerns about its possible contaminants.

When it comes to cancer risk and overall health, here are the fish basics.

1. Nutrition Treasure

Any given serving of fish is packed with protein, and contains B vitamins and minerals including potassium and selenium. One serving (3-ounces) contains from 80 (lean fish like cod) to 150 calories (fattier fish, like salmon).

Higher fat fishes with their omega-3 fatty acids are the ones most linked to heart health benefits. Omega-3 fats are found in fish like salmon, mackerel, herring, lake and rainbow trout, sardines and albacore tuna.

2. Fish and Cancer Risk

AICR’s new report on liver cancer reveals hints that eating fish may protect against this cancer, although the evidence was not strong enough to form a conclusion. Some population studies have also linked higher fish consumption with reduced risk of other cancers, including colon and breast.

In lab studies, the omega 3-fats of fish are well researched. The major omega-3 fats in fish oil are called DHA(docosahexaenoic acid) and EPA(eicosapentaenoic acid). Lab studies have suggested these fats alter colon cell function and may cut down on inflammation.

But when it comes to fish itself linking to reducing cancer risk, more research is needed.

Although fish oil is a popular dietary supplement, for people with no heart disease, the American Heart Association says getting omega-3 fatty acids through foods is best. For cancer protection, AICR recommends that people do not rely on supplements.

3. Health Trumps Contaminants (with caveats)

Almost all fish and shellfish come with at least some contaminants, accumulated in waters with pollutants and pesticides. For most people eating a variety of fish, either farmed or wild-caught, the levels of contaminants are too small to cause harm, according to government guidelines. The 2010 US Dietary Guidelines general recommendation for American adults is to eat about 2 servings (approximately 8 ounces cooked) of a variety of fish and seafood per week.

Some people, including children, breastfeeding women and women who are or who could become pregnant, should steer away from certain types of fish. One toxin of concern is mercury, a heavy metal that can harm an unborn baby or young child’s developing nervous system if enough is consumed. Large fish that live the longest, such as sharks and swordfish, contain the highest amounts. For the specific recommendations visit the EPA’s What You Need to Know about Mercury in Fish and Shellfish. Another good resource on fish selection is the Monterey Bay Aquarium Seafood Watch.

4. Fish – One Part of the Whole

Again and again, research shows that people eating diets with a moderate amount of seafood have lower risk of cancer and other chronic diseases and longer lives.

This could be due to other parts of the diet. For example, if you’re eating more fish for dinner, you may be eating less red and processed meats, which increase colorectal cancer risk. Fish is a staple of several dietary patterns also linked to lower cancer risk, such as the Mediterranean diet. People eating a Mediterranean diet are also eating plenty of beans, whole grains, vegetables and other plant foods, which all play a role in reducing cancer risk.

These healthy fish-containing dietary patterns are also low on sugary foods and drinks and refined grains. Taken together, these diets high in plant foods, moderate in fish and seafood and low in sugar can help people stay a healthy weight. Overweight and obesity is now linked to increased risk of 10 cancers, including postmenopausal breast, liver and colorectal.

For delicious fish and seafood recipes, check out AICR’s Healthy Recipes.

Additional facts about breast cancer prevention are available here.