Plant-Based Proteins Necessary for Healthy Bones

Kim J, Kim B, Lee H, Choi H, Won C. The relationship between prevalence of osteoporosis and proportion of daily protein intake. Korean J Fam Med. 2013;34(1):43-48. 

 

This cross-section study of the Korean population involved the Korean National Health and Nutrition Examination Survey IV (KNHANES IV, 2008–2009) and bone mineral density (BMD) measurements using DXA (DISCOVERY-W fan-beam densitometer, Hologic, Inc., Bedford, MA, USA). BMD of the lumbar spine (L1–L4) and femoral neck were measured. Percentage of calories from protein in the diet was obtained through a 24-hour recall reporting.

 

A total of 6,952 people (3,100 men, 3,852 women) all had dual energy X-ray absorptiometry (DEXA) scans, were older than 19 years old, and were osteoporosis treatment naïve. Participants were of 3 groups based on daily protein intake (<10%, 10–20%, and >20%). With variables weighted statistically, this allowed for 35,256,072 people to be included in the analysis. Applying this method of analysis allows for a large group to be assessed for prevalence of a chronic disease—in this case, osteoporosis in the Korean population.

 

BMD of T-score ≤ -2.5 was the cutoff for diagnosis of osteoporosis. Optimal protein intake for Korean adults is considered to be 7–20% of total calories. Statistical analysis included consideration of variables for age, level of education, alcohol intake, current smoking, physical activity level, obesity, thyroid disease, menopause, and hormone replacement therapy (HRT).

 

Of the women in this population, 9.3% had osteoporosis (1,622,181 of 17,291,639), and 2.9% of the men had it (523,817 out of 17,964,433). Both gender groups with osteoporosis were found to be older, had lower incomes, and were less educated than the normal-BMD group. Weight, height, body mass index (BMI), total caloric intake, protein intake, and calcium intake were all lower in the osteoporosis groups. In both women and men, it was found that the high-protein intake group proportionately had less lumbar osteoporosis, with all variables and statistical adjustments. It was also statistically significant that men were seen to be more prone to osteoporosis in the femur with the group of highest proportion of protein in the diet.

 

Higher animal protein levels are associated with osteoporosis in this study and others.^1,2 Phyto-based proteins, polyphenols and other compounds found in fruits and vegetables, like soybeans, wasabi, Satsuma oranges, sargassum algae and others, are associated with stimulating osteoblastic activity, decreasing osteoclastic activity of the bones, and could be preventive of osteoporosis.^1,3

 

 

This current study is helpful in recognizing that protein is necessary for healthy bones, but not too much animal source proteins. It has been seen before that the possibility of low-level metabolic acidosis, which is influenced by increased animal protein intake and low plant based diet could be a big factor with aging and osteoporosis.² With a high protein diet, the acids produced might be buffered with calcium from the bones. There are other postulated theories about this as well involving growth factor affecting calcium and phosphate metabolism.⁴ The exact amounts of protein needed in the diet for healthy bones may vary based on ethnicity (Asian vs. Caucasian), calcium intake and other risk factors and concomitant diseases.

 

In this study is that protein levels were defined as a percentage of the total dietary intake and not in another measure, such as grams/day of protein. This is a bit confounding in determining just how much is too much protein in the diet, although a percentage of the total calories is possibly more reflective of a real diet, as opposed to protein numbers by themselves. In the study, however, it could have been given with both parameters for protein measurement-proportion and grams per day.

 

In regards to men and the greater occurrence of femur osteoporosis in the highest protein group, this is particularly disturbing. It was postulated in the study commentary that this could be explained by the difference between cortical bone, making up 75% of the femoral neck, whereas trabecular bone is 70-100% of the lumbar vertebrae. Further, in a review article cited below, age-related bone loss may be different between men and women based on different structures in the trabecular bone that are affected with age.⁵

 

The prevention of osteoporosis is very important as life expectancies have increased, and the incidence of bone fractures from osteoporosis has increased with aging populations.^1,2,5–7 There is some indication as well that increased calcium intake along with higher protein diets may protect the bones from excess bone loss from acid leaching calcium from protein metabolism to be neutralized and excreted by the body.^2,4 People with lower protein diets were found to have lower BMD in this study and others. At least in the Korean population a high enough protein level is important for making healthy bones. As to what this level might be, it remains a question. In two other studies cited in this study, a US study found that women who had > 95 grams of protein per day had more risk for forearm fractures than those whose level was <68 grams/day.⁴ The other, a Norwegian study, found that lower calcium and high protein intake levels were associated with higher levels of fracture.⁸ The question of adequate protein and calcium levels in osteoporosis is worthy of further research. From this study, it does appear that an adequate high level of protein is necessary for healthy bone formation.