Plant-based diets without adequate calcium and vitamin D intake may pose a risk for bone health, according to researchers at the University of Helsinki.
During the study, 136 adults adhered to one of three diets for 12 weeks. One diet corresponded to the average Finnish diet, where approximately 70% of the protein is derived from animals and the rest of the protein is from cereal products. In the second diet, half of the protein was derived from plant products, and the other half was derived from animal products. The third included 30% animal protein and 70% plant-based protein.
Sources of animal protein, both red and white meat as well as dairy products, were partially replaced with plant-based proteins by adding a diverse range of legumes, nuts, seeds, and cereal products. Fluid dairy products, which are fortified with vitamin D in Finland, were partially replaced with plant-based drinks not fortified with calcium or vitamin D. The amount of cheese was lower in the diets that included more plant-based protein compared to the diet rich in animal protein. All diets included the same amount of fish and eggs.
According to the study, both bone formation and resorption increased when part of the animal protein in the diet was replaced with plant protein, which may in the long term be detrimental to bone health, the researchers said. These findings are in line with those recently published from the large EPIC-Oxford population-based study, according to which vegetarians were found to have a greater risk of bone fractures over a follow-up period of 18 years compared to people on a mixed diet, the researchers said.
The researchers suggest that the changes in bone metabolism as well as calcium and vitamin D intakes are probably caused by the low amount of dairy products and, consequently, the low amount of calcium and vitamin D consumed. Due to the study design applied, the study subjects were not allowed to use vitamin or mineral supplements during the study period.
“The results could be different if fluid dairy products had been replaced with plant-based drinks fortified with vitamin D and calcium. Then again, the average vitamin D intake was also below the recommended level in the group where subjects consumed the animal protein-rich diet, but not to the same extent as in the other groups,” said Suvi Itkonen of the Department of Food and Nutrition, Faculty of Agriculture and Forestry.
When adopting an increasingly plant-based diet, the researchers said, it is important in terms of bone health to ensure adequate calcium and vitamin D intake. In the case of vitamin D, the researchers added, the recommended intake for adults is 10 micrograms per day. This amount includes total intake from both food and vitamin supplements.
“When consuming plant-based drinks and yogurt-like products, it is essential to choose the option fortified with calcium and vitamin D. If the daily diet contains no margarines, dairy products, or plant-based drinks fortified with vitamin D, and if fish is consumed less than two to three times per week, it’s important to ensure adequate vitamin D intake, especially in the dark season, by taking a daily vitamin D supplement,” Itkonen said.
The study, “Partial Replacement of Animal Proteins with Plant Proteins for 12 Weeks Accelerates Bone Turnover Among Healthy Adults: A Randomized Clinical Trial,” was published by The Journal of Nutrition.