Dietary protein, calcium metabolism, and skeletal homeostasis revisited

Abstract

High dietary protein intakes are known to increase urinary calcium excretion and, if maintained, will result in sustained hypercalciuria. To date, the majority of calcium balance studies in humans have not detected an effect of dietary protein on intestinal calcium absorption or serum parathyroid hormone. Therefore, it is commonly concluded that the source of the excess urinary calcium is increased bone resorption. Recent studies from our laboratory indicate that alterations in dietary protein can, in fact, profoundly affect intestinal calcium absorption. In short-term dietary trials in healthy adults, we fixed calcium intake at 20 mmol/d while dietary protein was increased from 0.7 to 2.1 g/kg. Increasing dietary protein induced hypercalciuria in 20 women [from 3.4 ± 0.3 (x -± SE) during the low-protein to 5.4 ± 0.4 mmol/d during the high-protein diet]. The increased dietary protein was accompanied by a significant increase in intestinal calcium absorption from 18.4 ± 1.3% to 26.3 ± 1.5% (as determined by dual stable isotopic methodology). Dietary protein intakes at and below 0.8 g/kg were associated with a probable reduction in intestinal calcium absorption sufficient to cause secondary hyperparathyroidism. The long-term consequences of these low-protein diet-induced changes in mineral metabolism are not known, but the diet could be detrimental to skeletal health. Of concern are several recent epidemiologic studies that demonstrate reduced bone density and increased rates of bone loss in individuals habitually consuming low-protein diets. Studies are needed to determine whether low protein intakes directly affect rates of bone resorption, bone formation, or both.Am J Clin Nutr 2003;78(suppl):584S-92S. KEY WORDSDietary protein, urinary calcium, parathyroid hormone, vitamin D, hypercalciuria, bone, soy INTRODUCTIONAlmost 30 million Americans are affected by osteoporosis, and women are 4 times more likely to suffer from this disease than men (1). The health problem is reaching near-epidemic proportions in the United States and worldwide. Nutrition plays an important role in both the prevention and the pathogenesis of many chronic diseases, including osteoporosis. Numerous studies have established that dietary calcium and vitamin D are critical nutrients for both accruing and maintaining skeletal mass. In contrast, our understanding of how other dietary components, such as protein, affect calcium homeostasis and skeletal metabolism is limited.

Effect of short-term high dietary calcium intake on 24-h energy expenditure, fat oxidation, and fecal fat excretion

“…Moreover, more calcium is probably absorbed in the presence of protein, making less calcium available for binding to fat. 21 A more effective calcium absorption on the HC/HP than on the HC/ NP diet was also suggested by a 66% higher urinary calcium excretion on the HC/HP diet. It was attempted to make the dietary fiber content in all three diets identical, and it is therefore unlikely that the difference in fecal fat excretion can be explained by differences in fiber content.…”

Impacto dos nutrientes na saúde óssea: novas tendências

“…O excesso de lipídeos pode inibir a secreção de GH, pelo aumento nos níveis de ácidos graxos plasmáticos livres (10)(11) .…”

“…O excesso de gordura dietética pode exacerbar este desgaste por inibição da formação de osteoblastos maturos e aumento da adipogê-nese (10) . Entretanto, não existem, ainda, recomendações de lipídeos específicos que possam garantir maximização da MO.…”

Influência de contraceptivos hormonais sobre indicadores de homeostase de zinco e de turnover ósseo em mulheres adultas jovens

“…A alta ingestão proteica observada poderia influenciar negativamente a excreção urinária e o balanço de cálcio, principalmente quando a ingestão desse mineral encontra-se inadequada 33 . Tem sido considerado que a relação de ingestão de cálcio/proteína ideal deve ser ≥20:1 (mg cálcio/g proteína) 34 ; no presente trabalho, as não usuárias de ACH apresentaram uma razão de ingestão cálcio:proteína de aproximadamente 8,1:1 (mg/g) e as +ACH, de 7,4:1 (mg/g), o que poderia prejudicar a manutenção do cálcio no organismo e, consequentemente, o metabolismo ósseo.…”