SCIENTIFIC UPDATE
By Reed Mangels, PhD, RD, FADA
Prostate Cancer and Alpha-Linolenic Acid: An Update
More than 10 years ago (www.vrg.org/journal/vj2005issue1/2005_issue1_sciupdate.php), we reported on a study that found that those men whose diets were highest in alpha-linolenic acid had an increased risk of developing advanced prostate cancer. These results were concerning because alpha-linolenic acid — a fat found in walnuts, flaxseeds, flaxseed oils, hemp, chia, and other foods — is something that vegans are encouraged to seek out since it is an omega-3 fatty acid. Other omega-3 fatty acids, like DHA and EPA, come from fish, although vegan sources are available. In 2005 we recommended, "Until more information is available, the results of this study suggest that men who are at increased risk of prostate cancer should not use high amounts of alpha-linolenic acid."
A recent study revisits the question of alpha-linolenic acid's role in prostate cancer. This study followed close to 50,000 men from 1986 to 2010 and asked them about their diet and the occurrence of prostate cancer over that time. During the study period, widespread screening for Prostate-Specific Antigen (PSA) began. This test allows for earlier detection and treatment of prostate cancer. Also during the study period, food sources of alpha-linolenic acid changed. In the study's early years, trans-alpha-linolenic acid (a trans-fat) was found in deep-fried foods and foods containing partially hydrogenated oils. Because of the health problems associated with trans-fats, hydrogenated oil was removed from the list of food additives "generally recognized as safe." This meant that, later in the study, men were eating lower amounts of trans-alpha-linolenic acid.
In the early years of the study, it found that alpha-linolenic acid was associated with an increased risk of advanced prostate cancer. Later, after PSA screening was common and trans-alpha-linolenic acid was not being added to foods, a higher intake of alpha-linolenic acid was no longer associated with a higher risk of advanced prostate cancer. Perhaps only trans-alpha-linolenic acid increases risk of advanced prostate cancer. Another possibility is that PSA screening is identifying prostate cancer earlier before it becomes advanced. Based on this study's results, it does not appear necessary for men to limit their intake of alpha-linolenic acid from foods. This study did not examine high doses of alpha-linolenic acid like those found in dietary supplements.
Wu J, Wilson KM, Stampfer MJ, Willett WC, Giovannucci EL. 2018. A 24-year prospective study of dietary a-linolenic acid and lethal prostate cancer. Int J Cancer. 142:2207-2214.
Bean Biofortification
Iron deficiency is very common worldwide, especially in women and children in developing countries. One proposed means for reducing the occurrence of iron deficiency is to fortify staple foods with iron. This fortification is being done through conventional plant breeding as well as by genetic modification. Conventional breeding, in which plants are selected for iron accumulating traits, has been used to develop iron-biofortified millet, rice, and beans.1 In some cases, this fortification has led to beans that contain twice as much iron as unfortified beans.2 This kind of biofortification of beans with iron also seems a promising way to increase iron intakes of vegans and other vegetarians.
Unfortunately, along with the higher iron concentrations, these fortified beans also seem to have higher concentrations of phytates. These phytates are notorious for binding iron in the human intestinal tract and keeping it from being absorbed. Removing or significantly reducing the phytate concentration of iron biofortified beans has markedly increased the amount of iron absorbed from them.2 In addition to breeding beans to increase their iron content, selective breeding could also be done to reduce the concentration of phytates.2 This could result in beans that are good sources of easily absorbed iron. Stay tuned — someday we may have beans that are high in iron and low in phytates.
1 Tan GZH, Das Bhowmik SS, Hoang TML, et al. 2017. Finger on the pulse: pumping iron into chickpea. Front Plant Sci. 8:1755.
2 Petry N, Egli I, Gahutu JB, et al. 2014. Phytic acid concentration influences iron bioavailability from biofortified beans in Rwandese women with low iron status. J Nutr. 144:1681-1687.
Medication Use and Cancer Screening Practices of Vegetarians and Meat Eaters
We know that vegetarians and vegans eat differently from non-vegetarians, but are there other differences among these groups? A recent study examined some health-related behaviors in vegetarians and non-vegetarians living in the U.K. More than 30,000 men and women were studied. Based on their responses to dietary questionnaires, they were identified as being meat-eaters (ate any amount of meat), fish-eaters (did not eat meat but did eat fish), vegetarians (did not eat meat or fish but did eat dairy products and/or eggs), or vegans (did not eat meat, fish, dairy products, or eggs). Study participants were asked about their use of medications and about whether they participated in cancer screenings. Non-meat-eating women (includes fish eaters, vegetarians, and vegans) were less likely to use hormone replacement therapy than were women who ate meat, with the lowest usage seen in vegan women.
Non-meat-eaters were less likely to use any medication than were meat eaters. Approximately 56% of meat-eaters used at least one prescribed medicine, while only 28% of vegans used at least one prescribed medicine. The use of alternative therapies was not assessed.
Vegetarian and vegan women were less likely to participate in breast cancer screening than were meat eaters; there was no significant difference between the groups in rates of screening for cervical cancer. Vegetarian, but not vegan, men were less likely to be screened for prostate cancer.
The U.K. has different recommendations and practices with regard to screening for cancer than the U.S. does, and this could lead to different results in vegetarians in the United States. To learn more about current recommendations for cancer screening in the United States, see www.cdc.gov/cancer/dcpc/prevention/screening.htm.
Tong TYN, Appleby PN, Bradbury KE, et al. 2017. Cross-sectional analyses of participation in cancer screening and use of hormone replacement therapy and medications in meat eaters and vegetarians: the EPIC-Oxford study. BMJ Open. 7:e018245.
Italian Vegetarian Food Guide Includes Information for Pregnant and Lactating Women
As there are no official government recommendations to help vegetarians plan their diets, Italian scientists decided to develop their own food guide for adult vegetarians. Their plan includes calorie levels from 1,200 to 3,200 calories and includes meal plans for pregnant and breastfeeding women. The Italian guide includes six food groups: grains, protein-rich foods, vegetables, fruits, nuts and seeds, and fats. The plan also features a calcium-rich food group, which includes foods highest in calcium from all the groups except for fats. It has an omega-3-rich food group, which includes foods from the nuts and seeds group and the fats group. The plan recommends a specific number of servings of foods from each group, depending on calorie level and whether a woman is pregnant or breastfeeding. For example, an adult who needs 2,000 calories a day and who is not pregnant or breastfeeding is told to eat 10 servings of grains, 3 servings of protein-rich foods, 6 servings of vegetables, 2.5 servings of fruits, 2 servings of nuts and seeds, 2 servings of fats, 6 servings of calcium-rich foods, and 2 servings of omega-3-rich foods. Vitamin D supplements are recommended when there is little or no sunlight exposure. Supplemental DHA is recommended for pregnant and lactating women. Vitamin B12 supplements are recommended since many fortified foods are not available in Italy.
This food guide makes sensible recommendations. You can read more about it at http://jandonline.org/article/S2212-2672(17)31397-7/fulltext.
Baroni L, Goggi S, Battino M. 2017. VegPlate: A Mediterranean-based food guide for Italian adult, pregnant, and lactating vegetarians. J Acad Nutr Diet. [Epub ahead of print].
Previous Scientific Updates Can Be Read Online
If you are interested in reading previous Scientific Updates that we've run in Vegetarian Journal over the years, be sure to visit our website here: http://www.vrg.org/journal/ScientificDepartment.htm.
