A study that took a big-picture look at environmental health risks found that a majority of cancers around the world are connected to three activities that we know are bad for us: smoking, eating meat products, and drinking alcohol.

The study, published in the journal Nutrients, analyzed data from 2008 to see how often 21 types of cancers occurred in 157 countries, 87 of which had reliable cancer data. William Grant, study author and director at the Sunlight, Nutrition, and Health Research Center in San Francisco, wanted to see whether these cancer rates correlated with various risk factors such as age, a country’s gross domestic product, and type of diet.

The high-quality data provided by the 87 countries showed that smoking and consumption of animal products were responsible for over half of all the cancer incidence rates. Some trends were notably different for males and females; smoking affected males twice as much as eating animal products, while females showed the opposite pattern. Excluding lung cancer rates, smoking, and animal products accounted for 70 percent of the variation of cancer rates between countries.

Overall, 30 percent of cancer deaths, which was around 7.5 million in 2008, were caused by five “leading behavioral and dietary risks,” Grant explained in the study. These risks are high body mass index, low fruit and vegetable intake, lack of physical activity, tobacco use, and alcohol use.

Animal products had a particularly strong correlation with various types of cancer because this kind of diet promotes body growth as well as tumor enlargement, Grant explained in a statement. Specifically, the kinds of cancer affected by this dietary factor include female breast, uterine, kidney, ovarian, pancreatic, prostate, testicular, thyroid, and multiple myeloma.

Grant noted that Japan serves as an example of how alteration in diet can affect both body growth and the incidence of cancer. While the older Japanese population is considerably shorter than westerners, the younger generation has become just as tall due to an increase in the number of calories that they derive from animal products, which is typically a more western diet. As a result, the types of cancers that were more common in Western countries have now been on the rise for the past two to three decades in Japan.

The Food and Agriculture Organization of the UN provided the dietary data, which allowed Grant to assess changes in eating habits that began in 1980. This was important because, according to Grant, the amount of time between changes in diet and peak cancer rates is approximately 20 years.

"This is an important study showing strong relationships between meaty diets and cancer risk. There's a clear-cut lesson there for national food policies." Neal Barnard, of the George Washington University School of Medicine, commented in the study’s press release.

Mark McCarty, research director of the non-profit Catalytic Longevity, also commented in the release, saying, “This compelling new study clarifies the over-riding impact of smoking and animal product consumption as environmental determinants of global cancer risk. In fact, it’s the most impressive evidence I’ve yet encountered indicting animal products per se as a major cancer risk factor.” He added that the bright side of these findings is that they stem from lifestyle choices that people can control.

Studies finding a correlation between diet and cancer rates go as far back as 1907 when researchers found that meat eating ethnic groups, such as Germans, Irish, Scandinavians, and Slovenians had much higher cancer rates than their vegetarian counterparts in China and Italy. Another study has found that Seventh-Day Adventists, who have a vegetarian diet, have lower cancer rates than the typical meat-eating American.

Source: Grant W. A Multicountry Ecological Study of Cancer Incidence Rates in 2008 with Respect to Various Risk-Modifying Factors. Nutrients. 2014.