Protein Supplementation With Isocaloric Carbohydrate Reduction Spares Calcium

  1. Protein Supplementation With Isocaloric Carbohydrate Reduction Spares Calcium

    Just got this article from Medscape Physician News. Thought I'd share.

    Protein Supplementation With Isocaloric Carbohydrate Reduction Spares Calcium

    News Author: Laurie Barclay, MD
    CME Author: Désirée Lie, MD, MSEd

    March 19, 2004 — Contrary to popular belief, protein supplementation with isocaloric reduction in carbohydrates does not increase calcium wasting but rather may have favorable effects on the skeleton, according to the results of a small study published in the March issue of the Journal of Clinical Endocrinology and Metabolism.

    "Currently there is no consensus on the impact of dietary protein on calcium and bone metabolism," write Bess Dawson-Hughes, MD, from the U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University in Boston, Massachusetts, and colleagues. "This study was conducted to examine the effect of increasing protein intake on urinary calcium excretion and [on] circulating levels of [insulin-like growth factor-I] IGF-I and biochemical markers of bone turnover in healthy older men and women."

    Thirty-three subjects with usual protein intakes of less than 0.85 g/kg/day were randomized to receive high (0.75 g/kg) or low (0.04 g/kg) protein supplements daily for nine weeks. Calorie intake remained stable because subjects were advised to reduce their carbohydrate intake accordingly.

    Both groups had similar changes in urinary calcium excretion throughout the study. Compared with the low protein group, the high protein group had significantly higher levels of serum IGF-I (P = .008) and lower levels of urinary N-telopeptide (P = .038) during the period of days 35 to 49 or 63.

    Study limitations include incomplete baseline data on some measurements and small sample size.

    "Increasing protein intake from 0.78 to 1.55 g/kg/day with meat supplements in combination with reducing carbohydrate intake did not alter urine calcium excretion, but was associated with higher circulating levels of IGF-I, a bone growth factor, and lowered levels of urinary N-telopeptide, a marker of bone resorption," the authors write. "In contrast to the widely held belief that increased protein intake results in calcium wasting, meat supplements, when exchanged isocalorically for carbohydrates, may have a favorable impact on the skeleton in healthy older men and women."

    The U.S. Department of Agriculture supported this study.
    J Clin Endocrinol Metab. 2004;89:1169-1173

  2. calcium is still needed when dieting to compensate for increased bone turnover, consider this study which uses better markers, IMO:

    High dairy-protein versus high mixed-protein energy restricted diets - the effect on bone turnover and calcium excretion in overweight adults.

    Bowen J, Noakes M, Clifton P.

    Clinical Research Unit, CSIRO Health Sciences and Nutrition, PO Box 10041, Adelaide, SA 5000.

    Background - A moderate exchange of some dietary carbohydrate for protein appears to have metabolic and weight loss advantages in human studies. This dietary strategy raises safety concerns for bone health. The impact of dietary calcium in high protein diets on bone turnover has not been investigated. Objective - This study examined the effect of protein source and calcium content in high protein, energy restricted diets on calcium excretion and bone metabolism in 50 overweight adults (BMI 33.4 +/- 2.1 kg/m(2)). Design - The parallel study consisted of a 12-week energy restriction phase followed by a four-week energy balance phase. Subjects were randomised to one of two isoenergetic (5.5 MJ/d, 34% energy from protein, 41% from carbohydrate and 24% from fat) diets; high dairy protein (DP, 2400mg Ca/d) or high mixed protein (MP, 500mg Ca/d). Outcomes - Energy restriction was the primary determinant of weight loss (-9.7 +/- 3.8 kg, P<0.01) with no significant effect of protein source. Twenty-four hour calcium excretion decreased during both interventions (-1.09 +/- 0.23 mmol/day, P<0.009). By week 16 the MP diet had a 40% larger increase in deoxypyridinoline (a bone turnover marker) compared to the DP diet (P=0.008). Osteocalcin (a marker of bone formation) increased from week zero to 16 in the MP diet only (+2.22 ng/ml P=0.001). Conclusions - Overall, the DP diet has a modest advantage over MP diet by reducing the accelerated bone turnover associated with weight loss.

    PMID: 15023671 [PubMed - in process]

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