Category Archives: Alkaline Diet

Protein Sulfur Associated with Lower Bone Density in Postmenopausal Women – 2008

Abstract

A positive association of lumbar spine bone mineral density with dietary protein is suppressed by a negative association with protein sulfur.

Dietary protein is theorized to hold both anabolic effects on bone and demineralizing effects mediated by the diet acid load of sulfate derived from methionine and cysteine. The relative importance of these effects is unknown but relevant to osteoporosis prevention. Postmenopausal women (n = 161, 67.9 +/- 6.0 y) were assessed for areal bone mineral density (aBMD) of lumbar spine (LS) and total hip (TH) using dual X-ray absorptiometry, and dietary intakes of protein, sulfur-containing amino acids, and minerals using a USDA multiple-pass 24-h recall. The acidifying influence of the diet was estimated using the ratio of protein:potassium intake, the potential renal acid load (PRAL), and intake of sulfate equivalents from protein. aBMD was regressed onto protein intake then protein was controlled for estimated dietary acid load. A step-down procedure assessed potential confounding influences (weight, age, physical activity, and calcium and vitamin D intakes). Protein alone did not predict LS aBMD (P = 0.81); however, after accounting for a negative effect of sulfate (beta = -0.28; P < 0.01), the direct effect of protein intake was positive (beta = 0.22; P = 0.04). At the TH, protein intake predicted aBMD (beta = 0.18; P = 0.03), but R2 did not improve with adjustment for sulfate (P = 0.83). PRAL and the protein:potassium ratio were not significant predictors of aBMD. Results suggest that protein intake is positively associated with aBMD, but benefit at the LS is offset by a negative impact of the protein sulfur acid load. If validated experimentally, these findings harmonize conflicting theories on the role of dietary protein in bone health.

Thorpe M, Mojtahedi MC, Chapman-Novakofski K, McAuley E…
J. Nutr. Jan 2008
PMID: 18156408 | Free Full Text

Animal Protein Increases Bone Loss and Fracture in Postmenopausal Women – 2001

Abstract

A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women. Study of Osteoporotic Fractures Research Group.

Different sources of dietary protein may have different effects on bone metabolism. Animal foods provide predominantly acid precursors, whereas protein in vegetable foods is accompanied by base precursors not found in animal foods. Imbalance between dietary acid and base precursors leads to a chronic net dietary acid load that may have adverse consequences on bone. We wanted to test the hypothesis that a high dietary ratio of animal to vegetable foods, quantified by protein content, increases bone loss and the risk of fracture. This was a prospective cohort study with a mean (+/-SD) of 7.0+/-1.5 y of follow-up of 1035 community-dwelling white women aged >65 y. Protein intake was measured by using a food-frequency questionnaire and bone mineral density was measured by dual-energy X-ray absorptiometry. Bone mineral density was not significantly associated with the ratio of animal to vegetable protein intake. Women with a high ratio had a higher rate of bone loss at the femoral neck than did those with a low ratio (P = 0.02) and a greater risk of hip fracture (relative risk = 3.7, P = 0.04). These associations were unaffected by adjustment for age, weight, estrogen use, tobacco use, exercise, total calcium intake, and total protein intake. Elderly women with a high dietary ratio of animal to vegetable protein intake have more rapid femoral neck bone loss and a greater risk of hip fracture than do those with a low ratio. This suggests that an increase in vegetable protein intake and a decrease in animal protein intake may decrease bone loss and the risk of hip fracture. This possibility should be confirmed in other prospective studies and tested in a randomized trial.

Sellmeyer DE, Stone KL, Sebastian A, Cummings SR
Am. J. Clin. Nutr. Jan 2001
PMID: 11124760 | Free Full Text


More recent studies and randomized trials have discredited the conclusions of this study.

There are two published comments on this study. The full text is available for both.

Protein intake and bone health: the influence of belief systems on the conduct of nutritional science.
Heaney RP
PMID: 11124741 | Free Full Text

Dietary ratio of animal to vegetable protein and rate of bone loss and risk of fracture in postmenopausal women.
Sebastian A, Sellmeyer DE, Stone KL, Cummings SR
Am. J. Clin. Nutr. Sep 2001
PMID: 11522569 | Free Full Text

Hypothesis: Animal Protein Associated with Hip Fracture – 1992

Abstract

Cross-cultural association between dietary animal protein and hip fracture: a hypothesis.

Age-adjusted female hip fracture incidence has been noted to be higher in industrialized countries than in nonindustrialized countries. A possible explanation that has received little attention is that elevated metabolic acid production associated with a high animal protein diet might lead to chronic bone buffering and bone dissolution. In an attempt to examine this hypothesis, cross-cultural variations in animal protein consumption and hip fracture incidence were examined. When female fracture rates derived from 34 published studies in 16 countries were regressed against estimates of dietary animal protein, a strong, positive association was found. This association could not plausibly be explained by either dietary calcium or total caloric intake. Recent studies suggest that the animal protein-hip fracture association could have a biologically tenable basis. We conclude that further study of the metabolic acid-osteoporosis hypothesis is warranted.

Abelow BJ, Holford TR, Insogna KL
Calcif. Tissue Int. Jan 1992
PMID: 1739864


This study from 1992 was one of the earlier proposals that animal protein may cause osteoporosis. The hypothesis has since been discredited.

Review: Protein + Calcium May Benefit Bones – April 2011

Abstract

Dietary protein and bone health: harmonizing conflicting theories.

A precise understanding of the role of dietary protein in bone health has been evasive despite decades of research. It is known that a dietary acid load is harmful to bone, and sulfur-containing amino acids are metabolized to provide such an acid load. It is also known that protein elevates urine calcium loss. However, recent clinical studies and a meta-analysis have indicated either no effect or a modest benefit associated with higher protein intakes. These contradictory considerations may be explained by the existence of a two-faced relationship between protein and bone, with simultaneous positive and negative pathways. In opposition to the negative effects of dietary acid load, protein may exert positive effects related to improving calcium absorption, increasing insulin-like growth factor 1, or improving lean body mass, which, in turn, improves bone strength. Putative mechanisms behind these pathways are reviewed here, and some limitations in the historical literature as well as suggested measures to counter these in the future are identified. When positive and negative pathways are considered in tandem, protein may offer modest benefits to bone in the presence of adequate dietary calcium and acid-neutralizing fruits and vegetables.

Thorpe MP, Evans EM
Nutr. Rev. Apr 2011
PMID: 21457266

Protein and Energy Deficiencies May Increase Bone Loss in Rats – 2008

Abstract

Influence of high and low protein intakes on age-related bone loss in rats submitted to adequate or restricted energy conditions.

Low energy and protein intake has been suggested to contribute to the increased incidence of osteoporosis in the elderly. The impact of dietary protein on bone health is still a matter of debate. Therefore, we examined the effect of the modulation of protein intake under adequate or deficient energy conditions on bone status in 16-month-old male rats. The animals were randomly allocated to six groups (n = 10/group). Control animals were fed a diet providing either a normal-protein content (13%, C-NP) or a high-protein content (26%) (C-HP). The other groups received a 40% protein/energy-restricted diet (PER-NP and PER-HP) or a normal protein/energy-restricted diet (ER-NP and ER-HP). After 5 months of the experiment, protein intake (13% or 26%) did not modulate calcium retention or bone status in those rats, although a low-grade metabolic acidosis was induced with the HP diet. Both restrictions (PER and ER) decreased femoral bone mineral density and fracture load. Plasma osteocalcin and urinary deoxypyridinoline levels were lowered, suggesting a decrease in bone turnover in the PER and ER groups. Circulating insulin-like growth factor-I levels were also lowered by dietary restrictions, together with calcium retention. Adequate protein intake in the ER condition did not elicit any bone-sparing effect compared to PER rats. In conclusion, both energy and protein deficiencies may contribute to age-related bone loss. This study highlights the importance of sustaining adequate energy and protein provision to preserve skeletal integrity in the elderly.

Mardon J, Habauzit V, Trzeciakiewicz A, Davicco MJ…
Calcif. Tissue Int. May 2008
PMID: 18437274

Review: Protein Recommended Intake – 2008

Abstract

Amount and type of protein influences bone health.

Many factors influence bone mass. Protein has been identified as being both detrimental and beneficial to bone health, depending on a variety of factors, including the level of protein in the diet, the protein source, calcium intake, weight loss, and the acid/base balance of the diet. This review aims to briefly describe these factors and their relation to bone health. Loss of bone mass (osteopenia) and loss of muscle mass (sarcopenia) that occur with age are closely related. Factors that affect muscle anabolism, including protein intake, also affect bone mass. Changes in bone mass, muscle mass, and strength track together over the life span. Bone health is a multifactorial musculoskeletal issue. Calcium and protein intake interact constructively to affect bone health. Intakes of both calcium and protein must be adequate to fully realize the benefit of each nutrient on bone. Optimal protein intake for bone health is likely higher than current recommended intakes, particularly in the elderly. Concerns about dietary protein increasing urinary calcium appear to be offset by increases in absorption. Likewise, concerns about the impact of protein on acid production appear to be minor compared with the alkalinizing effects of fruits and vegetables. Perhaps more concern should be focused on increasing fruit and vegetable intake rather than reducing protein sources. The issue for public health professionals is whether recommended protein intakes should be increased, given the prevalence of osteoporosis and sarcopenia.

Heaney RP, Layman DK
Am. J. Clin. Nutr. May 2008
PMID: 18469289 | Free Full Text

Protein Increases Calcium Absorption and Retention From a Low-Calcium Diet – 2009

Abstract

Dietary protein and calcium interact to influence calcium retention: a controlled feeding study.

The effect of meat protein on calcium retention at different calcium intakes is unresolved. The objective was to test the effect of dietary protein on calcium retention at low and high intakes of calcium.In a randomized controlled feeding study with a 2 x 2 factorial crossover design, healthy postmenopausal women (n = 27) consumed either approximately 675 or approximately 1510 mg Ca/d, with both low and high protein (providing 10% and 20% energy) for 7 wk each, separated by a 3-wk washout period. After 3 wk, the entire diet was extrinsically labeled with (47)Ca, and isotope retention was monitored by whole-body scintillation counting. Clinical markers of calcium and bone metabolism were measured.
High compared with low dietary protein significantly increased calcium retention from the low-calcium (29.5% compared with 26.0% absorbed) but not the high-calcium diet (18% absorbed). For the low-calcium diet, this effect nearly balanced a protein-related 0.5-mmol/d greater urinary calcium excretion. Protein-related calciuretic effects were independent of dietary calcium. Testing at 1, 2, 3, 5, and 7 wk showed no long-term adaptation in urinary acidity or urinary calcium excretion. High compared with low dietary protein decreased urinary deoxypyridinoline and increased serum insulin-like growth factor I without affecting parathyroid hormone, osteocalcin, bone-specific alkaline phosphatase, or tartrate-resistant acid phosphatase.
In healthy postmenopausal women, a moderate increase in dietary protein, from 10% to 20% of energy, slightly improved calcium absorption from a low-calcium diet, nearly compensating for a slight increase in urinary calcium excretion. Under practical dietary conditions, increased dietary protein from animal sources was not detrimental to calcium balance or short-term indicators of bone health.

Hunt JR, Johnson LK, Fariba Roughead ZK
Am. J. Clin. Nutr. May 2009
PMID: 19279077 | Free Full Text

Review: Protein Protects Bone in Women – October 2002

Abstract

Elderly women need dietary protein to maintain bone mass.

Excess dietary protein is considered a risk factor for osteoporosis owing to the potential for renal acid load. Researchers who conducted a recent prospective study of older adults reported that animal protein had a protective role for bone, especially in elderly women, whereas plant protein was negatively associated with bone mineral density. An interaction between protein and calcium suggested protein alone was not the important factor. Other studies confirm the beneficial effect of increasing dietary protein intake in older women to reduce bone mineral density loss and risk of fracture, suggesting that emphasis should be placed on promoting adequate protein intake in elderly women.

Bell J, Whiting SJ
Nutr. Rev. Oct 2002
PMID: 12392151

Review: Protein – March 2003

Abstract

Protein and bone health: literature review and counselling implications.

For decades, public health promotion campaigns on bone health have emphasized the importance of adequate calcium and vitamin D intakes, as well as weight-bearing physical activity. However, no obvious consensus has emerged on the role of dietary protein. To identify what agreement does exist in the literature, in this article we review the theoretical basis for protein’s role in bone health, assess some recent cross-sectional and prospective studies, and generate recommendations for practice. There is general agreement in the literature that higher protein intake increases urinary calcium loss; the body compensates for this loss by increasing calcium absorption in the gut, providing that calcium intake is sufficient. A possible explanation for calcium loss, the “acid-ash” hypothesis, is discussed, and suggestions are made about food choices that may counter the calciuric effect of protein. A survey of cross-sectional and prospective studies shows equivocal results, with confounding variables complicating the analysis. Both deficient and excessive protein intakes have been shown to affect bone health negatively, although lower and upper thresholds have not been determined. Practical advice on achieving bone health is given, with an emphasis on the use of Canada’s Food Guide to Healthy Eating in setting dietary goals.

Cloutier GR, Barr SI
Can J Diet Pract Res 2003
PMID: 12631403