SCIENTIFIC UPDATE
By Reed Mangels, PhD, RD
Animal Product-Based, Low Carb Diets Associated with Shorter
Lifespan
Low carb diets are frequently touted as a way to lose weight or to improve overall
health. In reality, although some short-term weight loss may occur, these diets are
associated with a higher risk of death. Beginning in 1987, researchers enrolled more
than 15,000 U.S. middle-aged adults in a study that continued for about 25 years.
The study subjects were asked about their diet periodically. Records were kept of
which subjects died during the study period. Those subjects who had the lowest (less
than 40% of calories) and the highest (more than 60%) intakes of carbohydrates were
markedly more likely to die than were subjects whose carbohydrate intake was in the
middle — around 50-55% of calories coming from carbohydrates. The researchers
calculated that a 50-year old person whose diet had less than 30% calories from
carbohydrate would reduce their projected life expectancy by four years compared to
what would be expected if their diet had more carbohydrate. A very high carbohydrate
diet had a similar but smaller effect — a reduction in projected life
expectancy of 1.1 years. The researchers hypothesized that many of the very high
carbohydrate diets were high in refined carbohydrates (sugars, white bread, white
rice, etc.) and not high in whole grains. This study found that, if dietary
carbohydrate was reduced and animal-based protein and fat were used to replace
carbohydrate, risk of death increased. If plant-based protein and fat replaced
carbohydrate, risk of death decreased. This study suggests that, if someone chooses
to reduce carbohydrate, it's better to replace it with plant-based protein and fat.
Low carb-high animal product diets aren't a good choice.
Seidelmann SB, Claggett B, Cheng S, et al. 2018. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. Lancet Public Health. 3(9):e419-e428.
Vitamin B12 in Vegan Women's Breast Milk
Getting enough vitamin B12 is especially important for infants and young children
because of this vitamin's role in nervous system development. Breastfed infants rely
on their mothers' milk to supply vitamin B12. A recent study found that the
concentration of vitamin B12 in breast milk from vegans was similar to that of
non-vegans. This study examined 26 vegans, 22 lacto-ovo or lacto vegetarians, and 26
non-vegetarians. All but two of the vegans used a vitamin B12 supplement.
Approximately 20% of all the women had milk vitamin B12 concentrations that were
described as low; however, the adequate concentration of vitamin B12 in breast milk
has not been firmly established. Vegans were no more likely to have low milk vitamin
B12 concentrations than were non-vegans. This study suggests that vegans who use
vitamin B12 supplements will have breast milk vitamin B12 concentrations similar to
those of non-vegans.
Pawlak R, Vos P, Shahab-Ferdows S, Hampel D, Allen L, Perrin M. 2018. Vitamin B-12 content in breast milk of vegan, vegetarian, and non-vegetarian lactating women in the United States. Am J Clin Nutr. 146: 1125?1131.
Supplements and Fortified Non-Dairy Milks Provide Vitamin B12 to
Vegetarians
Where do vegetarians get vitamin B12? A study of Seventh-day Adventists examined
practices of 728 adults. Vegans (defined as never or rarely eating meat, fish,
dairy, and eggs) were 9% of the study subjects, 28% were lacto-ovo vegetarians
(defined as never or rarely eating meat or fish), and the remainder were
non-vegetarians. Overall, about 60% of study subjects used a vitamin B12 supplement.
Those using vitamin B12 supplements had significantly higher blood vitamin B12
concentrations than those not using supplements. As might be expected, vegetarians
and vegans had a higher intake of vitamin B12 from fortified foods than did
non-vegetarians. Non-dairy milks fortified with vitamin B12 had a positive effect on
blood vitamin B12 concentrations in those subjects who did not use vitamin B12
supplements. On average, fortified foods supplied enough vitamin B12 to meet
recommendations for vitamin B12. These results suggest that this population of
vegans and vegetarians is aware of the need for adequate vitamin B12 and is using
supplements and fortified foods to supply this essential nutrient.
Damayanti D, Jaceldo-Siegl K, Beeson WL, Fraser G, Oda K, Haddad EH. 2018. Foods and supplements associated with vitamin B12 biomarkers among vegetarian and non-vegetarian participants of the Adventist Health Study-2 (AHS-2) Calibration Study. Nutrients. 10(6). pii: E722.
Linking Dietary Choices to Climate Change
Researchers at the University of Michigan and Tulane University developed a new
database, dataFIELD, to better approximate the environmental impacts of dietary
choices.1 This is the first attempt to estimate the total greenhouse gas
emissions and comprehensive energy demand (amount of energy needed to create a
product) from self-selected diets (what people actually eat) in the U.S.
The researchers found that, on average, 4.7 kilograms of carbon dioxide are produced per day from the food a person in the U.S. eats. This greenhouse gas comes from food production, transportation, and ingredient processing. Compare this to the average passenger car emission of 404 grams (0.404 kilograms) of carbon dioxide per mile.2 This study suggests that, in the U.S., meat is responsible for 56.6% of the total greenhouse gas emissions from diet, followed by dairy, which is responsible for 18.3%.1 Vegetables, grains, legumes, and fruits each individually account for less than 3% of the total greenhouse gas emissions from diet.
The environmental impact of the highest greenhouse gas producing diets is eight times higher than that of the lowest greenhouse gas producing diets. Almost three-quarters of the greenhouse gas emissions attributed to the highest greenhouse gas producing diets are due to meat, specifically beef. According to the researchers, "If the top quintile of diets (representing 44.6 million Americans on a given day) shifted such that their associated GHGE [greenhouse gas emissions] were aligned with the mean [average] impact, this would represent a one-day reduction in GHGE of 0.27 million metric tons CO2 eq. (mmt), equivalent to eliminating 661 million average passenger vehicle miles on a given day."1
Dietary change, meaning lower calorie intake and/or less meat and dairy consumption, is an effective way to reduce greenhouse gas emissions and thus climate change.
1 Heller MC, Willits-Smith A, Meyer R, Keoleian GA, Rose D. 2018. Greenhouse gas emissions and energy use associated with production of individual self-selected US diets. Environ Res Lett. 13(4):044004.
2 EPA. Greenhouse gas emissions from a typical passenger vehicle. www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle. Accessed 25 June 2018.
By Amy Dell, VRG Intern
Eat More Plant Foods to Reduce Cancer Risk Says Expert Panel
The World Cancer Research Fund Network recently issued their third evidence-based
report on cancer prevention. The expert panel that developed these recommendations
concluded that a marked reduction in cancer occurrence worldwide could be achieved
by "avoidance of tobacco in any form, together with appropriate diet and nutrition,
physical activity, and maintaining a healthy weight." Specifically, the report calls
for eating a diet high in plant foods and making whole grains, fruits, vegetables,
and legumes a major part of the usual daily diet. Processed meat should be
completely avoided, and red meat, if eaten, limited to no more than three servings a
week. While the report did not specifically endorse vegan diets, it clearly made a
case for eating mainly whole, plant-based foods to reduce the risk of cancer.
World Cancer Research Fund/American Institute for Cancer Research. Diet, Nutrition, Physical Activity and Cancer: a Global Perspective. Continuous Update Project Expert Report, 2018. Available at www.dietandcancerreport.org
