Scientific Update

A Review of Recent Scientific Papers Related to Vegetarianism

Food Choices During the Teen Years May Influence Cancer Risk Later in Life

Breast cancer is the most common form of cancer in women (if you donít count non-melanoma skin cancers). One in eight women in the U.S. will develop breast cancer. New research suggests that dietary choices in adolescence may play a role in determining whether a woman will develop breast cancer. More than 40,000 women, ages 25 to 43 years, were asked about what they ate when they were in high school. Records were kept and the women were studied for the next seven years.

Those women who reported eating the most red meat (beef, pork, lamb, and processed meat like hot dogs) during high school had a 30 to 40 percent greater risk of developing breast cancer, compared to women who reported eating the least red meat during high school. The women in the high red meat group in high school averaged 2.6 servings of meat daily, while women in the lowest red meat group averaged 0.7 servings per day. Even when the results were adjusted for the womenís red meat intake as adults, the increased risk seen with higher red meat intake as a teen persisted. There was an especially strong association between processed meat and hot dogs eaten as a teen and risk of breast cancer. These results may be caused by the cancer-causing chemicals created by cooking meat, to the hormone treatment of meat, or to some as-yet undetermined factor. In any case, these results raise questions about red meatís role in teenage girlsí diets.

Linos E, Willett WC, Cho E, et al. 2008. Red meat consumption during adolescence among premenopausal women and risk of breast cancer. Cancer Epidemiol Biomarkers Prev 17:2146-51.

Fish Not Necessary for DHA

DHA is an omega-3 fatty acid found mainly in oily fish. DHA plays a role in reducing the risk of heart disease and may be involved in other chronic diseases. Vegetarian and vegan diets contain little or no DHA unless fortified foods or supplements are used. Vegan DHA supplements that are derived from microalgae have been developed. Are these supplements equivalent to fish in terms of their DHA? To address this question, researchers studied 32 men and women. Study subjects either ate 2 ounces of salmon (which provided 600 milligrams of DHA) or took capsules containing 600 milligrams of DHA from microalgae daily for two weeks. The subjectsí blood DHA concentrations were measured. Both groups saw an increase in blood DHA levels, and the increase in DHA in both groups was similar. These results suggest that microalgae-derived DHA is as effective as fish in increasing blood DHA levels.

Arterburn LM, Oken HA, Hall EB, et al. 2008. Algaloil capsules and cooked salmon: nutritionally equivalent sources of docosahexaenoic acid. J Am Diet Assoc 108:1204-1209.

New Research on Raw Foods

Despite the interest in raw foods diets, little research has been conducted about them. A small German study examined blood levels of carotenoids in 198 strict raw foods diet followers. Carotenoids are found in fruits and vegetables and include substances associated with a lower risk of diseases like cancer, such as beta-carotene, alpha-carotene, and lycopene. Study subjects ate close to 95 percent by weight of their foods as raw foods and had followed this diet for at least two years.

Because of their high fruit and vegetable intake, people eating a raw foods diet would be expected to have high levels of these carotenoids in their blood. Most study subjects, especially those eating more than 312 pounds of fruits and vegetables per day, had blood beta-carotene levels in the normal range. Surprisingly, however, blood lycopene levels were below the reference values in more than three-quarters of study subjects. This may be because the lycopene from raw foods was not well-absorbed. Cooking foods like tomatoes, which are a good source of lycopene, has been shown to increase lycopene absorption. Other factors that may have affected carotenoid absorption were the amount of fat in the subjectsí diets and whether the high fat foods were eaten at the same meal as foods high in carotenoids. Dietary fat provided an average of 30 percent of calories; the main dietary sources of fat were nuts, seeds, and avocados. Dietary fats have been shown to increase the amount of carotenoids that are absorbed in a meal. Those subjects who ate the lowest amount of fat and oil also had the lowest blood levels of carotenoids. For those eating a raw foods diet to increase carotenoid absorption, especially absorption of the carotenoid lycopene, fat intake may need to be increased. Additionally, fat sources should be at the same meal as good sources of lycopene.

Garcia AL, Koebnick C, Dagnelie PC, et al. 2008. Long-term strict raw food diet is associated with favourable plasma beta-carotene and low plasma lycopene concentrations in Germans. Br J Nutr 99:1293-1300.

Diet Has a Significant Impact on Global Climate Change

One of the most important environmental issues is the increasing level of greenhouse gas production, which is leading to global climate change. Proposals for reducing fossil fuel consumption and CO2 emissions frequently focus on choosing energy efficient vehicles and driving less. These are important steps, but perhaps just as important are our dietary choices.

In 2002, the food production systems accounted for 17 percent of all fossil fuel use in the United States. This number is expected to increase over the coming years. A recent analysis used the fossil fuel needs for irrigation energy, farm machinery, and labor and considered the production of non-CO2 greenhouse gases methane and nitrous oxide resulting from animal waste in evaluating various dietsí environmental impacts. Animal-based diets, whether based on red meat, fish, poultry, or dairy products and eggs, result in a higher greenhouse burden than do vegan diets. A person consuming the average American diet (72 percent of calories from plants, 15 percent from meat/fish/poultry, 11 percent from dairy products, and 1 percent from eggs) is responsible for the release of 1,485 more kilograms per year of CO2 equivalents than a person choosing a vegan diet is. This difference represents more than 6 percent of total U.S. greenhouse gas emissions.

The researchers also compare dietary intake to driving various kinds of vehicles. The difference in greenhouse gas production between eating approximately 20 percent of calories from animal products (a lower level of animal product use than the typical American diet) and a vegan diet is roughly equivalent to the difference between driving a Camry and a Prius. If one chooses a diet high in red meat and animal products (35 percent of calories from animal products), the difference in greenhouse gas production between this type of diet and a vegan diet is equivalent to the difference between driving an SUV and driving a Camry.

Eshel G, Martin PA. 2006. Diet, energy, and global warming. Earth Interact 10:1-17.

Lifestyle Changes, Including a Plant-Based Diet, Improve Activity of a Useful Enzyme

Telomerase is an enzyme that helps to protect chromosomes, the structures that hold our genes. If chromosomes arenít adequately protected, the risk of getting certain cancers and of having the cancer progress more rapidly seems to be higher. Additionally, telomerase repairs the part of the chromosome, the telomeres, that controls longevity. We know that a healthy lifestyle can reduce risk of many chronic diseases, including cancer.

A recent small study suggests that lifestyle changes may improve the activity of the telomerase enzyme and that this could, at least partially, explain the relationship between diet and cancer risk. Dean Ornish, MD, Head of the Preventive Medicine Research Institute, studied 30 men with low-risk prostate cancer. These men did not receive surgery or radiation therapy because their prostate cancer did not appear to be progressing and was not causing symptoms. For three months, the men followed a program that required them to make significant lifestyle changes. They ate a lowfat, near-vegetarian diet (Subjects did use fish oil supplements.) rich in whole grains, fruits, vegetables, dried beans, and soy products. They exercised moderately and practiced techniques, such as yoga, to reduce stress.

Following this three-month period, the menís blood level of telomerase was 29 percent higher than at the start of the study. According to Ornish, this is the first study showing that lifestyle changes can increase telomerase. Since this enzyme may play an important role in reducing risk of cancer development and progression, larger studies will probably be conducted to confirm these potentially important results.

Ornish D, Lin J, Daubenmier J, et al. Nov 2008. Increased telomerase activity and comprehensive lifestyle changes: a pilot study. Lancet Oncol 9(11):1048-57.