SCIENTIFIC UPDATE
By Reed Mangels, PhD, RD, FADA
Vegetarian Diets & Weight Loss
A group of researchers combined the results of 12 studies where vegetarian diets were used for weight loss. They found that, overall, subjects assigned to vegetarian diets lost more weight than those assigned to control (non-vegetarian) diets. Those on vegan diets lost more weight, compared to control subjects, than did those on lacto-ovo vegetarian diets. These results suggest that vegetarian diets, especially vegan diets, can be an effective way to lose weight. Better results were seen in studies where subjects limited their calorie intake than in studies where subjects were simply placed on a vegetarian diet.
Huang RY, Huang CC, Hu FB, Chavarro JE. 2015. Vegetarian diets and weight reduction: a meta-analysis of randomized controlled trials. J Gen Intern Med. 2015 Jul 3. [Epub ahead of print]
Red Meat and Diabetes
According to the Centers for Disease Control and Prevention (CDC), diabetes cost the United States $245 billion in 2012 (the most recent year that costs are available). This huge expenditure is due both to the treatment-related expenses and to disabilities and early death due to diabetes. There are many factors that increase risk of type 2 diabetes. One easily modifiable factor is red meat consumption. Researchers in Germany developed a risk score for diabetes, based on a number of factors that have been shown to affect the risk for diabetes. Eating 5 ounces or more of red meat daily increased the risk of diabetes, about as much as having a parent with diabetes.
What is it about red meat that makes it a risk factor for type 2 diabetes? Researchers looked at more than 2500 adults, some of whom had diabetes. They asked participants about their eating habits and measured substances in their blood. They found that higher red meat consumption was associated with a higher risk of developing type 2 diabetes; these results were similar to other studies. Red meat included both unprocessed beef, veal, pork, and lamb and processed meats like sausage, bacon, and ham. Higher levels of the storage form of iron, ferritin, were seen in subjects who consumed more red meat and were associated with a higher risk of diabetes, as were higher concentrations of certain fats in the blood. The researchers hypothesize that oxidative stress due to higher iron intakes may be one reason for the higher risk of diabetes seen with higher intakes of red meat.
Mühlenbruch K, Ludwig T, Jeppesen C, et al. 2014.Update of the German Diabetes Risk Score and external validation in the German MONICA/KORA study. Diabetes Res Clin Pract. 104:459-66.
Wittenbecher C, Mühlenbruch K, Kröger J, et al. 2015. Amino acids, lipid metabolites, and ferritin as potential mediators linking red meat consumption to type 2 diabetes. Am J Clin Nutr. 101:1241-50.
Iron Absorption
It's fairly common for vegetarians to be told that getting enough iron on a vegetarian diet is challenging. That's because the form of iron found in plants may not be as easy for us to absorb. The main reason for this is that beans, whole grains, nuts, and vegetables contain substances called phytates. These phytates bind up with iron in the human intestinal tract and keep iron from being absorbed. A recent study suggests that there is more to the story of phytates and iron absorption. Researchers put 14 women on a diet high in phytates and 14 women on a low-phytate diet for 8 weeks. All of the women had low iron stores as shown by their low blood ferritin concentrations (ferritin is the storage form of iron). Although the women were not vegetarians, their low ferritin concentrations were typical of many vegetarians. The women on the high phytate diet ate whole wheat grain products (cereal, pasta, tortillas, bread), brown rice, beans, soy products, and nuts while the women on the low-phytate diet ate refined grains, eggs, cheese and other low-phytate foods. Phytate intake was markedly higher in the high phytate group; iron intakes were similar in the two groups. We would expect to see lower iron absorption in the high-phytate group. This did not happen; iron absorption was actually higher in the high-phytate group. These results suggest that, in women with suboptimal iron stores, regular use of a high-phytate diet does not have a large effect on iron absorption. If these results are confirmed by other studies, changes may need to be made to the RDAs for iron, which call for higher iron intakes by vegetarians.
Armah SM, Boy E, Chen D, Candal P, Reddy MB. 2015. Regular consumption of a high-phytate diet reduces the inhibitory effect of phytate on nonheme-iron absorption in women with suboptimal iron stores. J Nutr. 2015;145:1735-9.
Partially Hydrogenated Oils No Longer Recognized as Safe
In January 2006, the U.S Food and Drug Administration (FDA) began requiring that the amount of trans-fat in foods be listed on the Nutrition Facts label. Trans-fat, found in processed foods that contain partially hydrogenated oil, is linked to an increased risk of heart disease. Food companies reduced the amount of trans-fat in products such as cookies, crackers, snack foods, and margarine, but some of these products still contain partially hydrogenated oil. The FDA recently removed partially hydrogenated oil from the list of food additives "generally recognized as safe," commonly called the GRAS list. This means that partially hydrogenated oils will not be recognized as safe for use in human foods. FDA is providing a 3-year compliance period, during which companies are expected to phase out use of partially hydrogenated oils. In the meantime, consumers should check the ingredient listing for partially hydrogenated oils.
FDA. June 2015. Final determination regarding partially hydrogenated oils. Federal Register. 80 FR 34650.
Comparisons between Vegetarians and "Conscientious Omnivores"
The term "conscientious omnivores" was introduced in a book by bioethicist Peter Singer and activist Jim Mason to describe individuals who consume only meat or fish that has met certain ethical standards. For example, a conscientious omnivore may avoid factory farmed meat. Do conscientious omnivores differ from vegetarians in ways other than their food choices? A recent study examined more than 500 adults, 18% identified as conscientious omnivores for health reasons, 8% as conscientious omnivores for ethical reasons, 16% were vegetarian (not vegan) for health reasons, 21% were ethical vegetarians, 14% were vegans for health reasons, and 23% were ethical vegans. Study subjects completed a questionnaire about their attitudes and practices. Those following their diet for ethical reasons reported fewer dietary violations and were more disgusted by factory farmed meat compared with those following their diet primarily for health reasons. The exception was the vegans who reported the same disgust with meat whether they were motivated by health or ethics. Compared to vegetarians and vegans, conscientious omnivores violated their diet more often and felt less guilt about violating their diet. They also had more difficulty following their diet and believed less in animal rights. The researcher who conducted this study offered several possible explanations for conscientious omnivores' seemingly lower commitment to their diet. One is that they do not look at animals in the same way that vegetarians do. Another possibility is that it is more difficult to explain their diet – they eat meat but only meat produced in a certain way. Restaurants, caterers, and others may not understand the difference between "ethical" and "unethical" meat. Additionally, there is no consistent definition of "humane" practices in use of animals for food. Perhaps these results can be used to develop strategies for promotion of vegetarian eating as an ethical choice.
Rothgerber H. Can you have your meat and eat it too? Conscientious omnivores, vegetarians, and adherence to diet. Appetite. 2015;84:196-203
Vegetarian Dietitians More Apt to Endorse Dietary Changes to Slow Climate Change
Dietary choices have been identified as having an important role in mitigation of global warming. Dietitians could convey this information to the public and potentially influence climate change. A study of 570 registered dietitians examined their awareness and behaviors related to climate change. Approximately 75% of respondents said that they believed that climate change is an important issue. However, only 38% were involved in activities that promote diet as a way to mitigate climate change. Vegetarian and vegan dietitians were more likely than nonvegetarian dietitians to be involved in these activities. Dietitians who felt knowledgeable about plant-based diets and those who believed that animal products are not essential for a healthy diet were also more likely to promote dietary change.
Hawkins IW, Balsam AL, Goldman R. 2015. A survey of registered dietitians' concern and actions regarding climate change in the United States. Front Nutr. 2:21.
