People who maintain a vegan diet show significant deficits in bone microarchitecture, compared with omnivores; however, resistance training not only appears to improve those deficits but may have a stronger effect in vegans, suggesting an important strategy in maintaining bone health with a vegan diet.
“We expected better bone structure in both vegans and omnivores who reported resistance training,” first author Robert Wakolbinger-Habel, MD, PhD, of St. Vincent Hospital Vienna and the Medical University of Vienna, said in an interview.
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“However, we expected [there would still be] differences in structure between vegans and omnivores [who practiced resistance training], as previous literature reported higher fracture rates in vegans,” he said. “Still, the positive message is that ‘pumping iron’ could counterbalance these differences between vegans and omnivores.”
The research was published online in The Endocrine Society’s Journal of Clinical Endocrinology & Metabolism.
Exercise significantly impacts bone health in vegans
The potential effects of the plant-based vegan diet on bone health have been reported in studies linking the diet to an increased risk of fractures and lower bone mineral density (BMD), with common theories including lower bone- and muscle-building protein in vegan diets.
However, most previous studies have not considered other key factors, such as the effects of exercise, the authors noted.
“While previous studies on bone health in vegans only took BMD, biochemical and nutritional parameters into account, they did not consider the significant effects of physical activity,” they wrote.
“By ignoring these effects, important factors influencing bone health are neglected.”
For the study, 88 participants were enrolled in Vienna, with vegan participants recruited with the help of the Austrian Vegan Society.
Importantly, the study documented participants’ bone microarchitecture, a key measure of bone strength that has also not been previously investigated in vegans, using high-resolution peripheral quantitative CT.
Inclusion criteria included maintaining an omnivore diet of meat and plant-based foods or a vegan diet for at least 5 years, not being underweight or obese (body mass index [BMI], 18.5-30 kg/m2), being age 30-50 years, and being premenopausal.
Of the participants, 43 were vegan and 45 were omnivores, with generally equal ratios of men and women.
Vegan bone deficits disappear with strength training
Overall, compared with omnivores, the vegan group showed significant deficits in 7 of 14 measures of BMI-adjusted trabecular and cortical structure (all P < .05).
Among participants who reported no resistance training, vegans still showed significant decreases in bone microarchitecture, compared with omnivores, including radius trabecular BMD, radius trabecular bone volume fraction, and other tibial and cortical bone microarchitecture measures.
However, among those who did report progressive resistant training (20 vegans and 25 omnivores), defined as using machines, free weights, or bodyweight resistance exercises at least once a week, those differences disappeared and there were no significant differences in BMI-adjusted bone microarchitecture between vegans and omnivores after the 5 years.
Of note, no significant differences in bone microarchitecture were observed between those who performed exclusively aerobic activities and those who reported no sports activities in the vegan or omnivore group.
Based on the findings, “other types of exercise such as aerobics, cycling, etc, would not be sufficient for a similar positive effect on bone [as resistance training],” Dr. Wakolbinger-Habel said.
Although the findings suggest that resistance training seemed to allow vegans to “catch up” with omnivores in terms of bone microarchitecture, Dr. Wakolbinger-Habel cautioned that a study limitation is the relatively low number of participants.
“The absolute numbers suggest that in vegans the differences, and the relative effect, respectively of resistance training might be larger,” he said. “However, the number of participants in the subgroups is small and it is still an observational study, so we need to be careful in drawing causal conclusions.”
Serum bone markers were within normal ranges across all subgroups. And although there were some correlations between nutrient intake and bone microarchitecture among vegans who did and did not practice resistance training, no conclusions could be drawn from that data, the authors noted.
“Based on our data, the structural [differences between vegans and omnivores] cannot solely be explained by deficits in certain nutrients according to lifestyle,” the authors concluded.