Scientific Update
British Study Examines Omega-3 Fatty Acids in Vegetarians and Vegans
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are omega-3 fatty acids that come primarily from fish. Non-fish-eaters get small amounts from eggs, but until the advent of fortified foods and supplements, vegans had to rely on their own production of EPA and DHA. Our bodies can make these from another omega-3 fatty acid, alpha-linolenic acid, that is found in flaxseeds, canola oil, walnuts, and other foods. EPA and DHA production is believed to be limited, however.
A recent study from the UK examined dietary intake and blood levels of EPA and DHA in people who eat fish and people who don't eat fish. The latter category was subdivided into meat-eaters, vegetarians, and vegans. Not surprisingly, fish-eaters had the highest intakes of DHA and EPA; the other groups had very low or no dietary DHA or EPA. Vegans, for example, had intakes of EPA that were 18 percent (women) and 8 percent (men) of the fish-eaters' intakes. Somewhat surprisingly, blood levels of EPA and DHA in non-fisheaters, including vegetarians and vegans, were higher than would be expected based on dietary intake. This suggests that conversion rates of alpha-linolenic acid to DHA and EPA may be higher than would be predicted from earlier studies.
The results of this study must be tempered by its limitations. First, the number of subjects who ate vegan diets - only five men and five women - was quite low. Secondly, a vegan was defined as someone who did not eat meat, poultry, fish, dairy products, or eggs for the 7-day period during which food records were kept. If the subjects ate fish before that, this could have a marked effect on the study results. In addition, blood levels of EPA and DHA were quite variable, so we can't say with any confidence that vegans can effectively convert alpha-linolenic acid to EPA and DHA.
These fatty acids appear to play a role in reducing heart disease risk and possibly dementia, diabetes, and asthma. Additional study is needed to determine whether fish avoiders are more efficient at making their own EPA and DHA.
For more information about omega-3 fatty acids, see pages 22-26 of Vegetarian Journal, Volume XXVI, Issue 1, 2007 (www.vrg.org/journal/vj2007issue1/vj2007issue1.pdf).
Welch AA, Shakya-Shrestha S, Lentjes MAH, et al. 2010. Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the precursor-product ratio of alphalinolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort. Am J Clin Nutr 92:1040-51.
Calcium Supplements May Be Associated with Increased Risk of Heart Attack
Many people, especially those over age 50, take calcium supplements to prevent or treat osteoporosis. Recently, a large study raised concerns that healthy older women who take calcium supplements might be at increased risk for heart attacks. Investigators used a technique called meta-analysis, in which the results of a number of studies are combined, to examine the possible relation between calcium supplements and heart attacks.
The researchers used data from 15 studies in which one group received calcium supplements and one group did not. Use of calcium supplements was associated with a 30 percent increased risk of heart attack, regardless of gender or the amount of the calcium supplement. In people with dietary calcium intakes of less than 800 milligrams per day, calcium supplements were not associated with an increased risk of heart attack. In contrast, those with dietary calcium intakes above 800 milligrams were at a higher risk of heart attack.
Studies where participants took both calcium and vitamin D and were compared to participants not receiving calcium or vitamin D were not included in this analysis. Supplements that combine calcium and vitamin D may not have the same effect as supplements that only contain calcium since vitamin D supplementation has been associated with a reduced mortality.
The researchers conclude, "Given the modest benefits of calcium supplements on bone density and fracture prevention, a reassessment of the role of calcium supplements in the management of osteoporosis is warranted."
For those vegans and vegetarians with low dietary calcium intakes, calcium supplements appear to reduce the risk of fracture (www.vrg.org/journal/vj2007issue4/vj2007issue4.pdf) and should probably be used if dietary calcium is not adequate. For those whose diets are adequate in calcium, additional supplemental calcium may not be advantageous.
Bolland MJ, Avenell A, Baron JA, et al. 2010. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ [Epub ahead of print].
Low-Carbohydrate Diets
High-protein, low-carbohydrate diets have been promoted as weight loss diets. Typically, these diets feature high amounts of animal protein, saturated fat, and total fat; limited carbohydrate; and little fiber. Researchers wondered what effect long-term use of these diets would have on mortality. Two large studies examined the effects of animal-based and plant-based low-carbohydrate diets on mortality in men and women. Study participants were identified as following a low-carbohydrate diet based on records of their eating habits. Dietary records were also used to classify them as using animal-based or more plant-based low-carbohydrate diets.
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Those who followed an animal-based, low-carbohydrate diet that emphasized animal sources of fat and protein had lower intakes of fruits and vegetables; those eating a plant-based, low-carbohydrate diet had higher intakes of whole grains.
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Those who ate a low-carbohydrate diet containing the most animal products had approximately a 20 percent higher mortality than those eating a lowcarbohydrate diet containing fewer animal products. This group also had a higher mortality from cancer and heart disease.
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Those who ate a plant-based, low-carbohydrate diet had a 20 percent lower overall mortality and a lower heart disease-related mortality.
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While amounts of protein, fat, and carbohydrate appeared similar in both low-carbohydrate groups, there were probably large differences in fiber, protein source, vitamins, minerals, and antioxidants that could have affected results.
The researchers determined, "The health effects of a low-carbohydrate diet may depend on the type of protein and fat, and a diet that includes mostly vegetable sources of protein and fat is preferable to a diet with mostly animal sources of protein and fat."
Fung TT, van Dam RM, Hankinson SE, et al. 2010. Low-carbohydrate diets and all-cause and cause-specific mortality. Ann Intern Med 153:289-98.
Vitamin D in Vegetarians and Vegans
Vitamin D appears to play an important role in bone health and may also be protective against several chronic diseases. Vegetarians do not eat some foods that contain vitamin D, such as oily fish and meat. In addition, vegans may avoid fortified foods such as cereals and vegan margarine that are fortified with a form of vitamin D that is derived from lanolin from sheep's wool.
Researchers in the UK wondered whether vegetarians and vegans would have lower dietary and blood vitamin D levels. They examined 1,388 meat-eaters, 210 fish-eaters, 420 vegetarians, and 89 vegans. On average, meat-eaters had the highest dietary intake of vitamin D, followed by fish-eaters, vegetarians, and vegans. Blood levels of vitamin D followed the same pattern—highest in meat-eaters, lowest in vegans. Although the vegans' average vitamin D intake was less than a quarter of the meat-eaters' intake, only 8 percent of vegans had blood vitamin D levels that were considered low enough to increase the risk for bone loss. These results were based on blood drawn in the winter. Because our skin produces vitamin D following sun exposure, blood levels of vitamin D are expected to be lower in the winter when less sun exposure occurs. When blood drawn during the summer and fall was examined, only 5 percent of vegans had low vitamin D levels.
There was a relation between dietary vitamin D levels and blood vitamin D levels in all groups, suggesting that it is important for everyone, including vegetarians and vegans, to have reliable dietary and/or supplement sources of vitamin D. Vitamin D sources for vegans include plant milks fortified with vitamin D and vitamin D supplements.
Crowe FL, Steur M, Allen NE, et al. 2010. Plasma concentrations of 25-hydroxyvitamin D in meat-eaters, fish-eaters, vegetarians, and vegans: results from the EPIC-Oxford study. Public Health Nutr [Epub ahead of print].
