Abstract
BackgroundModern diets have been suggested to increase systemic acid load and net acid excretion. In response, alkaline diets and products are marketed to avoid or counteract this acid, help the body regulate its pH to prevent and cure disease. The objective of this systematic review was to evaluate causal relationships between dietary acid load and osteoporosis using Hill's criteria.MethodsSystematic review and meta-analysis. We systematically searched published literature for randomized intervention trials, prospective cohort studies, and meta-analyses of the acid-ash or acid-base diet hypothesis with bone-related outcomes, in which the diet acid load was altered, or an alkaline diet or alkaline salts were provided, to healthy human adults. Cellular mechanism studies were also systematically examined.ResultsFifty-five of 238 studies met the inclusion criteria: 22 randomized interventions, 2 meta-analyses, and 11 prospective observational studies of bone health outcomes including: urine calcium excretion, calcium balance or retention, changes of bone mineral density, or fractures, among healthy adults in which acid and/or alkaline intakes were manipulated or observed through foods or supplements; and 19 in vitro cell studies which examined the hypothesized mechanism. Urine calcium excretion rates were consistent with osteoporosis development; however calcium balance studies did not demonstrate loss of whole body calcium with higher net acid excretion. Several weaknesses regarding the acid-ash hypothesis were uncovered: No intervention studies provided direct evidence of osteoporosis progression (fragility fractures, or bone strength as measured using biopsy). The supporting prospective cohort studies were not controlled regarding important osteoporosis risk factors including: weight loss during follow-up, family history of osteoporosis, baseline bone mineral density, and estrogen status. No study revealed a biologic mechanism functioning at physiological pH. Finally, randomized studies did not provide evidence for an adverse role of phosphate, milk, and grain foods in osteoporosis.ConclusionsA causal association between dietary acid load and osteoporotic bone disease is not supported by evidence and there is no evidence that an alkaline diet is protective of bone health.
Highlights
Modern diets have been suggested to increase systemic acid load and net acid excretion
Some critical reviews of the acid ash hypothesis have been undertaken with regards to bone health, to our knowledge, no systematic review has been done to assess the strength of the evidence of the acid ash hypothesis in terms of the etiology of osteoporosis
Random intervention studies were included if a) acid-base intake was manipulated through supplemental salts or through foods to decrease the diet acid load for, b) at least 24-hours to avoid variability due to diurnal variation, and c) outcomes related to bone health or osteoporosis were evaluated
Summary
Modern diets have been suggested to increase systemic acid load and net acid excretion. Alkaline diets and products are marketed to avoid or counteract this acid, help the body regulate its pH to prevent and cure disease. Marketers claim that alkaline diets and According to the acid-ash hypothesis, high dietary protein intakes are detrimental to bone health since protein is an important “acid generating” diet component, and structural bone mineral is dissolved to release bicarbonate to neutralize acid and avoid systemic acidosis [9,14,15,16]. Some critical reviews of the acid ash hypothesis have been undertaken with regards to bone health (in terms of the biochemistry [22,23,24,25], the role of protein [26,27], and phosphate [28], calcium balance [29], and the hypothesis in general [30]), to our knowledge, no systematic review has been done to assess the strength of the evidence of the acid ash hypothesis in terms of the etiology of osteoporosis
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