Scientific Update
by Reed Mangels, PhD, RD, FADA
Plant-Based Diets and Risk of Hip Fracture
According to the American Academy of Orthopaedic Surgeons, more than 300,000 people in the United States fracture a hip each year. A hip fracture can result in a loss of mobility and an increased risk of a variety of health issues. Researchers from Spain, Norway, and the United States recently examined the association between plant-based diets and hip fracture risk in older women. The study included more than 70,000 U.S. women who were followed for up to 30 years and who regularly reported on foods they ate and whether they had fractured a hip. In this study, a "plant-based diet" is not a vegetarian/vegan diet but a diet that is high in plant foods. The researchers used a "healthful plant-based diet index" (hPDI) and an "unhealthful plant-based diet index" (uPDI). Healthy plant foods included whole grains, beans, fruits, vegetables, nuts, and vegetable oils. A diet reported to contain more of these foods would receive a higher hPDI score. Less healthy plant foods were identified as fruit juices, sugary desserts, sugar-sweetened beverages, refined grains, and potatoes. A diet reported to contain more of these foods would receive a higher uPDI score. When long-term diet was examined, neither of the plant-based diet indices were associated with hip fracture risk. In other words, women eating diets that were more plant-based were not at a higher risk for hip fracture. When the women's most recent diet was examined, a higher score on the hPDI was associated with a 21% lower risk of hip fracture. A higher score on the uPDI was associated with a 28% higher risk of hip fracture. Additional research is needed to determine why the most recent plant-based diet index was associated with hip fracture while long-term intake was not.
Sotos-Prieto M, Rodriguez-Artalejo F, Fung TT, et al. Plant-based diets and risk of hip fracture in postmenopausal women. JAMA Netw Open. 2024;7(2):e241107.
Plant-Based Diets After a Diagnosis of Prostate Cancer Are Associated with a Lower Risk of Progression
Prostate cancer is the second most common cancer among men in the United States and the second-leading cause of cancer death in American men. Once someone is diagnosed with prostate cancer, could diet affect the risk of recurrence, metastases to bone, or death from prostate cancer? A recent study of more than 2,000 men who had been diagnosed with prostate cancer examined the association between a plant-based diet and prostate cancer progression. Cancer progression means that the cancer recurs, or metastasizes to the bones or that death due to prostate cancer occurs. In this study, a "plant-based diet" is not a vegetarian/vegan diet but is a diet that is high in plant foods. The men completed a survey about foods they commonly ate at a time about 2.5 years after their diagnosis. They were followed for a median of 6.5 years after completing the survey. Based on their responses to the survey, each man received a "plant-based diet index" (PDI) score and a "healthful plant-based diet index" (hPDI) score. A higher PDI score indicated that more healthful and unhealthful plant foods and fewer animal foods were eaten. A higher hPDI score indicated that more healthful plant foods and fewer unhealthful plant foods and animal foods were eaten.
Men with the highest PDI scores had a 47% lower risk of progression of prostate cancer compared to men with the lowest PDI scores. The hPDI scores was not associated with risk of progression. Gleason scores are a grading system for prostate cancer. A Gleason score of 6 indicates low-grade cancer while a score of 8 to 10 indicates high-grade cancer. Among those study subjects who had a Gleason score of 7 or higher at the time that they were diagnosed with prostate cancer, those with the highest hPDI score after diagnosis had a 55% lower risk of progression compared to those with the lowest hPDI score. These results suggest that plant-based diets containing mostly healthful plant foods and few unhealthful plant foods or animal foods are associated with a lower risk of prostate cancer recurrence in those with intermediate or higher grade cancer.
Liu VN, Van Blarigan EL, Zhang L, et al. Plant-based diets and disease progression in men with prostate cancer. JAMA Netw Open. 2024;7(5):e249053.
Dietary Protein, Especially Plant Protein, Is Associated with Better Odds of Healthy Aging in Women
Protein is important for older adults because it helps maintain muscles and thus physical mobility and strength. Adequate protein intake is associated with a reduced risk of hip fractures and loss of cognitive function. A recent study examined the association between protein intake in middle-aged women with healthy aging later in life.
More than 48,000 female nurses were studied beginning in 1984 when their average age was 48.6 years. They were followed for the next 30 to 32 years when their ages ranged from 70 to 93 years. Subjects provided information about their diet when they started the study. At the end of the study, the women were asked about their health. At that time, 3,721 (7.6%) of study subjects achieved what the researchers termed "healthy aging." Healthy aging was defined as a long life without major chronic diseases, with good mental health, and with no diminishment of physical or mental function.
The women who achieved healthy aging were compared to the other women to see if reported intake of protein in midlife was associated with health status. A 3% higher calorie intake from plant protein was associated with 38% higher odds of healthy aging. A 3% higher calorie intake from animal protein was associated with 7% higher odds of healthy aging, and a 3% higher calorie intake from dairy protein was associated with 14% higher odds of healthy aging. This suggests that plant protein is superior to animal or dairy protein in promoting healthy aging.
The researchers did a hypothetical calculation to estimate what would be the likely effect of replacing a small amount of the animal or dairy protein the women reported eating with a similar amount of plant protein. If 3% of total calories coming from animal or dairy protein was replaced with plant protein, the odds of healthy aging would be 38% or 26% higher, respectively. In addition, substituting the same amount of calories from animal protein or dairy protein with plant protein was associated with higher odds of being free of chronic diseases. Plant protein intake in midlife was also favorably associated with mental health status in aging.
The results of this study support the importance of plant protein in middle age to support and promote healthy aging.
Ardisson Korat AV, Shea MK, Jacques PF, et al. Dietary protein intake in midlife in relation to healthy aging—results from the prospective Nurses' Health Study cohort. Am J Clin Nutr. 2024;119(2):271-282.
Calcium Absorption from Vegan Foods
Two foods can contain similar amounts of calcium but have different amounts of calcium absorbed from those foods. For example, only about 6% of the calcium in spinach is absorbed whereas about a third of the calcium in bok choy is absorbed. The amount of oxalate in a food, and to a lesser extent, the amount of phytate in a food, affect calcium absorption. Researchers used information about the amount of calcium, oxalate, and phytate in different foods to develop an algorithm to predict how much calcium adults would absorb from those foods.
The researchers used cow's milk as their standard for comparison. Vegan foods that were evaluated and that are predicted to have a calcium absorption rate similar to or higher than cow's milk include bok choy, broccoli, Chinese cabbage, Chinese mustard greens, kale, orange juice fortified with calcium citrate malate, soymilk fortified with calcium carbonate, and tofu made with calcium sulfate.
Weaver CM, Wastney M, Fletcher A, Lividini K. An algorithm to assess calcium bioavailability from foods. J Nutr. 2024;154:921-927.
