Net Endogenous Acid Production Research Articles

Critique on equations of net endogenous acid production (NEAP) and indirect proof of constant organic acid excretion

Critique on equations of net endogenous acid production (NEAP) and indirect proof of constant organic acid excretion

Estimation of the diet-dependent net acid load in 229 worldwide historically studied hunter-gatherer societies

Nutrition scientists are showing growing interest in the diet patterns of preagricultural (hunter-gatherer) humans. Retrojected preagricultural diets are reportedly predominantly net base producing in contrast to the net acid-producing modern Western diets. We examined the dietary net acid load [net endogenous acid production (NEAP)] for 229 worldwide historically studied hunter-gatherer societies to determine how differences in plant-to-animal (P:A) dietary subsistence patterns and differences in the percentage of body fat in prey animals affect the NEAP. With the use of 1) ethnographic data of dietary P:A ratios of hunter-gatherer populations, 2) established computational methods, and 3) knowledge that fat densities of animal foods consumed by hunter-gatherers varied between 3% and 20%, we computed the NEAP for the diets of 229 populations in 4 different models of animal fat densities (model A, 3%; model B, 10%; model C, 15%; model D, 20%). As P:A ratios decreased from 85:15 to 5:95, the NEAP increased from -178 to +181 mEq/d (model A) and from -185 to +120 mEq/d (models B and C). Approximately 50% of the diets consumed by the 229 worldwide hunter-gatherer populations were net acid producing (models B and C). In model D, 40% of the diets were net acid producing. Our data confirm that the NEAP of hunter-gatherer diets becomes progressively more positive as P:A ratios decline. The high reliance on animal-based foods of a worldwide sample of historically studied hunter-gatherer populations renders their diets net acid producing in approximately 40-60% of subgroups of P:A ratios. Only further investigations can show the implications of these findings in determining the NEAP of human ancestral diets.

Differences in bone health and bone biomarkers between exercising male protein supplement users and non-users

Title: Differences in bone health and bone biomarkers between exercising male protein supplement users, and non-users. By R. Warner and L. Doyle, Department of Health, Sport and Exercise Science, Waterford Institute of Technology Background: Increasing protein intake through protein supplements is a growing practice amongst exercising individuals. However there are varying reports in terms of the detrimental(1) and beneficial(2) effects of protein on bone. The effect of high level protein supplementation on bone health in exercising individuals is relatively unexplored. Aim: To investigate the effect of variations in protein intake on bone health and bone biomarkers in exercising males. Subjects and Methods: 50 non-supplement users (25.9 ± 5.1y) and 52 supplement users (25.4 ± 4.9y) were recruited. The average length of time for supplement use was 33 months. All subjects completed a food diary for 3 days which was analyzed using Comp EatTM. Net endogenous acid production (NEAP) was calculated by the method described by Remer et al. (2003). Protein content of supplements consumed was obtained from product labels. Effect of exercise on bone health was calculated using osteogenic index (OI). Bone health (bone mineral density (BMD) and bone mineral content (BMC) and percent lean body mass (LBM) was measured using dual energy xray absorbtiometry (DEXA). Serum samples were analyzed for osetocalcin (S-OC) and crosslaps (S-CTx) using commercially available ELISA kits. Urine was measured for pH using a digital urine analyzer with urinary calcium (U-Ca) and creatinine (U-Cr) levels being measured spectrophotoemetrically. Independent samples t-test or Mann Whitney U test (depending on data normality) were used to test for any differences between supplement users and non-users. Results: There were no significant differences in potential confounders of BMI, OI or percent LBM (P > 0.05) between users and non-users. Protein intake, NEAP and sulphur content of the diet was significantly greater in users than non-users. There were no significant differences in BMD, BMC, urine pH or calcium, serum osteocalcin or crosslaps between users and non-users. This study demonstrates protein supplementation of 33 months duration has no effect on bone health in exercising males. (1)Abelow et al. (1992) (2) Promislow et al. (2002)

Postgraduate Symposium Positive influence of nutritional alkalinity on bone health

There is growing evidence that consumption of a Western diet is a risk factor for osteoporosis through excess acid supply, while fruits and vegetables balance the excess acidity, mostly by providing K-rich bicarbonate-rich foods. Western diets consumed by adults generate approximately 50-100 mEq acid/d; therefore, healthy adults consuming such a diet are at risk of chronic low-grade metabolic acidosis, which worsens with age as a result of declining kidney function. Bone buffers the excess acid by delivering cations and it is considered that with time an overstimulation of this process will lead to the dissolution of the bone mineral content and hence to reduced bone mass. Intakes of K, Mg and fruit and vegetables have been associated with a higher alkaline status and a subsequent beneficial effect on bone health. In healthy male volunteers an acid-forming diet increases urinary Ca excretion by 74% and urinary C-terminal telopeptide of type I collagen (C-telopeptide) excretion by 19% when compared with an alkali (base-forming) diet. Cross-sectional studies have shown that there is a correlation between the nutritional acid load and bone health measured by bone ultrasound or dual-energy X-ray absorptiometry. Few studies have been undertaken in very elderly women (>75 years), whose osteoporosis risk is very pertinent. The EVAluation of Nutrients Intakes and Bone Ultra Sound Study has developed and validated (n 51) an FFQ for use in a very elderly Swiss population (mean age 80.4 (sd 2.99) years), which has shown intakes of key nutrients (energy, fat, carbohydrate, Ca, Mg, vitamin C, D and E) to be low in 401 subjects. A subsequent study to assess net endogenous acid production (NEAP) and bone ultrasound results in 256 women aged > or = 75 years has shown that lower NEAP (P=0.023) and higher K intake (P=0.033) are correlated with higher bone ultrasound results. High acid load may be an important additional risk factor that may be particularly relevant in very elderly patients with an already-high fracture risk. The latter study adds to knowledge by confirming a positive link between dietary alkalinity and bone health indices in the very elderly. In a further study to complement these findings it has also been shown in a group of thirty young women that in Ca sufficiency an acid Ca-rich water has no effect on bone resorption, while an alkaline bicarbonate-rich water leads to a decrease in both serum parathyroid hormone and serum C-telopeptide. Further investigations need to be undertaken to study whether these positive effects on bone loss are maintained over long-term treatment. Mineral-water consumption could be an easy and inexpensive way of helping to prevent osteoporosis and could be of major interest for long-term prevention of bone loss.

Mediterranean Diet and High Dietary Acid Load Associated with Mixed Nuts: Effect on Bone Metabolism in Elderly Subjects

To analyze the effect of differing diet on the acid load content on bone metabolism. Multicentric, randomized, single-blind, parallel-group clinical trial. Outpatient clinics. Two hundred thirty-eight elderly men and women aged 60 to 80 at high risk for cardiovascular disease were randomly assigned to three interventional groups: a recommended low-fat diet (control diet group), a Mediterranean diet supplemented with virgin olive oil, or a Mediterranean diet supplemented with mixed nuts. Main outcomes were 12-month changes from baseline in bone formation and resorption markers and bone mass measured according to quantitative ultrasound scanning. The baseline data on the anthropometric, bone densitometry, and biochemical variables did not differ between the three groups. Dietary potential renal acid load (PRAL) and daily net endogenous acid production (NEAP) at baseline did not differ between groups. After intervention, subjects allocated to the Mediterranean diet with mixed nuts had a significant increase of PRAL and NEAP. In comparison, subjects in the Mediterranean diet with nuts group had higher parathyroid hormone (PTH) levels (2.63, 95% confidence interval (CI)=-1.01-6.35, P=.02) and a nonsignificantly higher (0.31, 95% CI=-0.13-0.74, P=.14) urine free deoxypyridoxine:creatinine ratio, a marker of bone resorption, than the control group and the Mediterranean diet with virgin olive oil group. A Mediterranean dietary pattern associated with a high dietary acid load derived from consumption of mixed nuts does not seem to have a much greater effect on bone metabolism biomarkers, with the exception of PTH levels, than a Mediterranean diet without mixed nuts or a control diet in elderly subjects.

Diet-Dependent Net Acid Load and Risk of Incident Hypertension in United States Women

Animal and human studies suggest a potential link between acid-base status and blood pressure. Contemporary Western diets yield a daily systemic acid load of varying amounts, yet the association with hypertension has never been explored. We prospectively examined the association between the diet-dependent net acid load (also known as the estimated net endogenous acid production) and the risk of incident hypertension among 87 293 women without a history of hypertension in the Nurses' Health Study II. We also used the ratio of animal protein intake to potassium intake as an alternative evaluation of diet-dependent net acid load. We identified 15 385 incident cases of hypertension during 995 239 person-years of follow-up. After adjusting for potential confounders, women in the top decile of estimated diet-dependent net acid load had an increased risk of hypertension (relative risk: 1.14; 95% CI: 1.05 to 1.24; P for trend=0.01) compared with women in the bottom decile. To test whether the association between estimated diet-dependent net acid load and hypertension is independent of its individual components, an additional adjustment for intakes of protein and potassium was made and resulted in a relative risk of 1.23 (95% CI: 1.08 to 1.41; P for trend=0.003) for the top decile of estimated diet-dependent net acid load. Results of the ratio of animal protein intake to potassium intake were similar with those of estimated diet-depend net acid load. In conclusion, a high diet-dependent net acid load is independently associated with a higher risk of incident hypertension.

Relationship among dietary estimates of net endogenous acid production, bone mineral density and biochemical markers of bone turnover in an Iranian general population

Chronic, low-grade metabolic acidosis due to Western diets may be a risk factor for osteoporosis. The severity can be determined in part by net endogenous acid production (NEAP). In a population-based study, a total of 1028 healthy men and women aged 20–72 years were evaluated for dietary intakes and NEAP estimates with a validated food frequency questionnaire. Dual-energy X-ray absorptiometry (DXA) was used to determine BMD of the lumbar spine (L2–L4), distal third of radius, and proximal femur. Serum CrossLaps, degradation products of the C-terminal telopeptides of type I collagen, and osteocalcin were measured by highly specific ELISA methods. Lower estimates of energy-adjusted rates of NEAP were associated with greater femoral neck BMD ( p = 0.01) in premenopausal women and with greater BMDs at the distal radius ( p = 0.001) and lumbar spine ( p = 0.04) in postmenopausal women. Compared with women in the highest quartile of the estimates of the energy-adjusted rates of NEAP, pre- and postmenopausal women in the lowest quartile had significantly greater means of osteocalcin [9.12 (SD ± 1.62) vs. 5.24 (SD ± 1.41) ng/ml, p = 0.02 and 11.74 (SD ± 1.69) vs. 7.79 (SD ± 2.63) ng/ml, p = 0.002, respectively]. Analysis by quartiles of the estimates of energy-adjusted rates of NEAP did not reveal a relationship between BMD and bone turnover markers in men. In conclusion, we found that a high energy-adjusted rate of NEAP was associated with a significantly lower BMD in women but not in men and the energy-adjusted rate of NEAP had a negative relationship with bone formation.

Bone mineral status and its relation with dietary estimates of net endogenous acid production in Hong Kong Chinese adolescents

Diet composition influences net endogenous acid production (NEAP), which may affect bone health. No studies are available to relate dietary estimate of NEAP to bone health in Chinese adolescents. This study examined the association of dietary estimates of NEAP with bone mineral status in Hong Kong Chinese adolescents. Baseline data on 171 boys and 180 girls aged 10-12 years from the Hong Kong Adolescent Bone Health Cohort Study were presented. Weight, height, Tanner stage and dietary intakes by FFQ were collected. NEAP was estimated from diet using Frassetto's method. Bone area (BA), bone mineral content (BMC) and bone mineral apparent density (BMAD) of total hip, lumbar (L1-L4) spine and whole body were estimated by dual-energy X-ray absorptiometry (DXA). No significant association was observed between BMC or BMAD and energy-adjusted NEAP or other nutrients. BA was significantly and positively associated with BMC at all sites in both sexes. Weight was significantly and positively associated with BMC in hip and spine in both sexes. Height was negatively correlated with hip BMC for boys and whole body BMC for girls. Pubertal stage was significantly and positively associated with BMC in all sites in both sexes. Weight and height contributed most of the variability in BMAD at different sites. The results suggest that anthropometric characteristics and pubertal stage are more influential than dietary NEAP in determining bone mineral status of Hong Kong Chinese adolescents. However, the methodological weaknesses regarding the use of DXA and FFQ in the present sample require attention.

Low Estimates of Dietary Acid Load Are Positively Associated with Bone Ultrasound in Women Older Than 75 Years of Age with a Lifetime Fracture

Dietary acid load from Western diets may be a risk factor for osteoporosis. It can be estimated by net endogenous acid production (NEAP). No data currently exists for NEAP estimates and bone indices in the very elderly (i.e. ≥75 y). The aim of this study was to determine the association between NEAP estimates by using the potential renal acid load (PRAL) equation and quantitative bone ultrasound (QUS) measurements at the heel [broadband ultrasound attenuation (BUA)] in Caucasian women. We assessed NEAP and QUS in 401 very elderly Swiss ambulatory women. We evaluated dietary intake and NEAP estimates with a validated FFQ. QUS was measured using Achilles (Lunar). We identified 2 subgroups: 256 women (80.6 y ± 3; BUA, 96.8 dB/MHz) with a fracture history and the remaining 145 (79.9 y SD 2.9; BUA, 101.7 dB/MHz) without. Women who reported having suffered a fracture had lower BUA (P < 0.001) than nonfractured women but did not differ in nutrient intakes and NEAP. Lower NEAP (P = 0.023) and higher potassium intake (P = 0.033) were correlated with higher BUA, which remained significant even after adjustment for age, BMI, and osteoporosis treatment. BUA was positively correlated with calcium (P = 0.016) and BMI (P < 0.001). Women who reported no fractures had no significant correlations between nutrient intake, NEAP, and BUA. Low nutritional acid load was correlated with higher BUA in very elderly women with a fracture history. Although relatively weak compared with age and BMI, this association was significant and may be an important additional risk factor that might be particularly relevant in frail patients with an already high fracture risk.

Effects of a fruit and vegetable intervention trial on net endogenous acid production: results from the US Women's Healthy Eating and Living (WHEL) Study

Effects of a fruit and vegetable intervention trial on net endogenous acid production: results from the US Women's Healthy Eating and Living (WHEL) Study

Acid Base Considerations in Stone-Age Farming Sweet Potato Eaters, Modern-Day Sweet Potato Eaters, and High-Protein Consumers

Net endogenous acid production (NEAP) can be estimated by a primarily anthropometry-dependent organic acid anion (OA) component and the particularly diet-dependent potential renal acid load (PRAL). However, there is evi- dence that certain foods may also impact on the OA component. Here, we discuss measurements of urinary 24-h OA ex- cretion obtained in healthy subjects, against the background of relevant literature with a special focus on former Papuan New Guinea stone-age farmers eating predominantly highland sweet potatoes. Contrary to the reports in Papuans, we ob- served only modest increases of 5-12% in 24-h excretion rates of OAs (including the detoxification product of phenolic and benzoic acids, i.e., hippuric acid) in healthy adults consuming commonly available yellow-fleshed sweet potatoes. This and additional results on OA increases after higher protein intakes suggest that a specification of the NEAP=PRAL+OA model for estimating the diet-dependent acid load to the metabolic system might be useful regarding particular foods and their effects on the OA component.

Estimates of daily net endogenous acid production in the elderly UK population: analysis of the National Diet and Nutrition Survey (NDNS) of British adults aged 65 years and over

Dietary intake has been shown to influence acid-base balance in human subjects under tightly controlled conditions. However, the net effect of food groups on alkali/acid loading in population groups is unclear. The aims of the present study were to: (1) quantify estimates of daily net endogenous acid production (NEAP) (mEq/d) in a representative group of British elderly aged 65 years and older; (2) compare and characterise NEAP by specific nutrients and food groups likely to influence dietary acid loading; (3) determine whether geographical location influenced NEAP. The National Diet and Nutrition Survey dataset, consisting of a 4 d weighed record and anthropometric data, was used to estimate dietary acidity. Dietary under-reporters were excluded by analysing only subjects with energy intakes >/= 1.2 x BMR. NEAP was estimated as the dietary potential renal acid load+organic acid excretion, the latter as a multiple of estimated body surface area. NEAP was lower in women compared with men (P < 0.001), and lower than values reported in a Swedish elderly cohort. Lower dietary acidity was significantly associated with higher consumption of fruit and potatoes and lower consumption of meat, bread and eggs (P < 0.02 to P < 0.001). Lower intakes of fish and cheese were associated with lower NEAP in men only (P < 0.01 to P < 0.001). There were regional differences for NEAP, with higher intakes in Scotland/Northern regions compared with Central/South-Western and London/South-Eastern regions (P = 0.01). These data provide an insight into the acid-generating potential of the diet in the British elderly population, which may have important consequences in this vulnerable group.

Estimated net endogenous acid production and intake of bone health-related nutrients in Hong Kong Chinese adolescents

To examine the daily intake of bone health-related nutrients and to explore the association between diet composition and estimated net endogenous acid production (estimated NEAP) in Hong Kong Chinese adolescents. In total, 171 boys and 180 girls aged 10-12 years of Chinese origin from nine primary schools from the Hong Kong Adolescent Bone Health Cohort Study. The study design used food frequency questionnaire. Mean daily intakes of foods and selected nutrients were estimated. Mean percentage of nutrient intake contributed by different food groups was presented. Frassetto's method was used to calculate the estimated NEAP from the diet's protein to potassium ratio. There was no significant difference in the energy-adjusted intakes of most nutrients between boys and girls, except for intakes of vitamins C and D. Mean protein, sodium and potassium intakes were higher than the Chinese dietary reference intake (DRI), whereas mean intakes of magnesium, calcium and vitamin D were lower than the DRI. Boys had significantly higher estimated NEAP than girls (P=0.0051). Estimated NEAP was significantly positively correlated with meat intake and negatively associated with the consumption of fruits, vegetables, legumes, beverages and dairy products. The results highlight the importance of considering whole diet quality when interpreting the effects of single nutrient or diet's net acid load on bone. The effect on high protein intake and low fruit and vegetable intake on the long-term bone health of Hong Kong Chinese adolescents warrants attention.

The Importance of Calcium, Potassium, and Acid-Base Homeostasis in Bone Health and Osteoporosis Prevention

The Importance of Calcium, Potassium, and Acid-Base Homeostasis in Bone Health and Osteoporosis Prevention

Standardizing Terminology for Estimating the Diet-Dependent Net Acid Load to the Metabolic System

Contemporary Western diets contain acid precursors in excess of base precursors, yielding a daily systemic net acid load of varying amounts, depending on the specific composition of the diet. Increasing evidence suggests that differences in daily net acid load, resulting predominantly from differences in dietary intake, can have deleterious health consequences, with a stepwise increase in severity with increasing magnitude of the net acid load. The daily net acid load’s magnitude (in part by influencing systemic acid–base status) has been shown to induce renal losses of calcium, magnesium, and nitrogen and adversely affects numerous endocrine functions. Investigations have shown detrimental clinical outcome effects for axial and peripheral bone health, particularly in elderly subjects (1) and postmenopausal women (2), as well as healthy children (3,4). Although physiological and biochemical principles support negative effects on bone architecture, muscle wasting, and nephrolithiasis, quantifying clinical outcomes is not straightforward. The long latency period required for subclinical changes to be clinically relevant and the lack of precision of current technology have posed challenges for researchers. For example, dual energy X-ray absorptiometry does not detect moderate changes in architectural-related bone strength parameters thus requiring long-term follow-up or large sample sizes. Additionally, terminological confusions result from investigators’ use of different algorithms for estimating the diet’s daily net acid load, even when the estimates derive essentially from the same input variables. For this reason, a number of plenary speakers at the 2nd International Acid-Base Symposium held in Munich, (8–9 September 2006) tried to reach agreement on terminology related to estimating the diet’s daily net acid load from the composition of the diet, based on accepted physiological principles. The group discussions yielded the following: under ordinary physiological conditions, differences in the amount of net acid produced by the metabolic system per day, which is referred to as the daily net endogenous acid production (NEAP), results predominantly from differences in the relative amounts of the diet’s acid and base precursors absorbed by the gut. Although investigators have devised several algorithms for estimating NEAP from the composition of the diet (see below), the group agreed to refer to the estimated diet-dependent net acid load as ‘‘estimated NEAP’’ and to always specify the algorithm used to obtain the estimated NEAP. For example, Frassetto et al. (5) estimated the diet’s net acid load from the diet’s contents of protein (an acid precursor) and potassium (an index of base precursors from organic anions). They would then specify:

Net endogenous acid production and circulating leptin are associated with potentially bioactive free glucocorticoids in healthy lean women

Objective: Recent evidence suggests that endogenous glucocorticoids may be suppressed by adipocyte-derived leptin and elevated by dietary acidity. Therefore we examined whether these factors might be predictors of potentially bioactive free glucocorticoids (sum of urinary free cortisol [UFF] and urinary free cortisone [UFE], UFF+UFE), independently of adrenocortical activity. Methods: Body composition, plasma cortisol, plasma leptin, 24-h urinary excretion rates of net acid (NAE), total nitrogen, UFF+UFE, and further major glucocorticoid metabolites were examined cross-sectionally in 30 healthy adults (15 females; 22–44 yr old; BMI: 20–25kg/m2). All glucocorticoids were analyzed by RIA and leptin by ELISA. Adrenocortical activity (overall daily cortisol secretion) was assessed by the sum of the 3 major urinary glucocorticoid metabolites tetrahydrocortisone + tetrahydrocortisol + 5a-tetrahydrocortisol (C21) and daily diet-dependent acid load by NAE. Results: Plasma leptin (mean±SD, 2.8±1.6 vs. 7.6±4.9 ng/mL) and percent body fat (%BF, 16.8±4.2 vs. 26.9±4.9%) were lower (P<0.01) and body surface (BS)-corrected C21 higher (P<0.01) in males, whereas plasma cortisol and BS-corrected UFF+UFE were statistically undistinguishable between the sexes. Both UFF+UFE and C21 correlated positively with %BF and leptin in males (P<0.05), but not in females. After adjusting for adrenocortical activity (C21), NAE was a positive (P=0.011) and leptin a negative (P=0.046) predictor of UFF+UFE in females (total explained variability R2=0.71). In males only C21 explained variation of UFF+UFE (R2=0.49, P=0.004). Conclusion: Our findings indicate that – at least in females – variability of potentially bioactive glucocorticoids is not only explained by individual adrenocortical activity, but may also be affected by circulating leptin and diet-dependent daily acid load.

Acid-Base Status Affects Renal Magnesium Losses in Healthy, Elderly Persons

Magnesium and calcium deficiency in humans is related to a number of pathological phenomena such as arrhythmia, osteoporosis, migraine, and fatal myocardial infarction. Clinically established metabolic acidosis induces renal losses of calcium. In normal subjects, even moderate increases in net endogenous acid production (NEAP) impair renal calcium reabsorption but no information is available whether this also influences renal magnesium handling. The aim of the study was to examine the relation between NEAP and renal magnesium excretion in healthy, free-living, elderly subjects. The subjects (age 64 ± 4.7 y, n = 85) were randomly selected from the population register in Gothenburg (Sweden). Magnesium, calcium, and potassium were measured in 24-h urine samples and NEAP was quantified as renal net acid excretion (NAE). NAE was positively correlated with excretions of magnesium (R2 = 0.27, P < 0.0001) and calcium (R2 = 0.30, P < 0.0001) but not potassium. When 24-h urinary magnesium excretion was adjusted for 24-h urinary potassium excretion, a biomarker for dietary potassium intake, the association between magnesium excretion and NAE remained significant (R2 = 0.21, P < 0.0001). The significant association between potassium-adjusted magnesiuria and NAE suggests that the acid-base status affects renal magnesium losses, irrespectively of magnesium intake. Magnesium deficiency could thus, apart from an insufficient intake, partly be caused by the acid load in the body.

Anthropometrics Provide a Better Estimate of Urinary Organic Acid Anion Excretion than a Dietary Mineral Intake-Based Estimate in Children, Adolescents, and Young Adults

The role of elevated net endogenous acid production (NEAP) in the causation of osteoporosis, muscle wasting, and kidney stones is currently under discussion. The aim of this study was to examine whether urinary organic acid anion excretion, a major component of NEAP, is predicted primarily by anthropometric- (OA(anthro)) or diet- (OA(diet)) based estimates. Dietary intakes, anthropometric data, and 24-h urinary excretion rates of organic acids (24h-OA(urine)) were determined cross sectionally in healthy children (6-7 y; n = 217), adolescents (13-14 y; n = 91), and young adults (18-22 y; n = 82). OA(anthro) was computed from body surface area and OA(diet) calculated using a published algorithm based on dietary intakes of mineral anions and cations. There was a significant increase (P < 0.0001) in 24h-OA(urine) across the age groups that was no longer discernible after correction for body surface area. In almost all sex-stratified subsamples, OA(anthro) had a higher correlation with 24h-OA(urine) than OA(diet). Multiple regression analyses, using energy-corrected diet variables, revealed that OA(anthro) was consistently the primary predictor of 24h-OA(urine) (R(2) varying from 0.15 to 0.39) and dietary fat and protein were sporadic predictors. In accordance with the observed age independency of 24h-OA(urine) after body surface area correction, our findings indicate that OA(anthro) is a better estimate of 24h-OA(urine) in healthy children, adolescents, and young adults than OA(diet). This further confirms that the (principally diet-dependent) NEAP comprises a component, i.e., organic acid anions, that is reasonably predictable by anthropometrics. Consequently, the other component, i.e., the potential renal acid load, appears to be the primary parameter that characterizes the diet-induced acid load.

Measurement of net acid excretion by use of paper strips

Objective Net endogenous acid production, reflected in the steady state as net acid excretion (NAE), is implicated in bone loss because it is positively associated with urinary calcium loss. Protein is one of the main sources of dietary acid load, whereas fruit and vegetables provide alkaline potassium salts that counteract the dietary acid load. This study investigated whether a pH paper strip measurement of overnight (i.e., first void) urine would reflect 24-h NAE, measured as excretion rates of titratable acid minus bicarbonate plus ammonium. Methods Twenty-three subjects collected 24-h urine in two parts: day (∼7 am to 11 pm) and overnight (∼11 pm to 7 am). At first void, subjects recorded pH using paper strips. Subjects recorded intake and 20 subjects provided fasting urine collected from 7 to 9 am. Results The pH paper strip measurements of first void urine was significantly correlated with 24-h titratable acid minus bicarbonate ( r = −0.466, P < 0.025) but not with 24-h NAE. We examined the association of dietary protein, potassium, protein:potassium ratio, and sodium with NAE, with fasting morning urinary calcium excretion, an indirect measurement of bone loss, and with urinary cross-links, a direct measurement of bone resorption. Of these, only sodium intake (measured as 24-h urine excretion) and urine potassium:sodium ratio showed a significant relation (with fasting calcium excretion). Conclusions We did not find that the first void urine pH by paper strip measurement provided an index of daily net endogenous acid production as reflected in 24-h NAE. In our sample of young adults, daily sodium intake positively correlated with bone resorption, as reflected in fasting urine calcium, whereas daily NAE did not.

Low dietary potassium intakes and high dietary estimates of net endogenous acid production are associated with low bone mineral density in premenopausal women and increased markers of bone resorption in postmenopausal women2–4

The Western diet may be a risk factor for osteoporosis. Excess acid generated from high protein intakes increases calcium excretion and bone resorption. Fruit and vegetable intake could balance this excess acidity by providing alkaline salts of potassium. Algorithms based on dietary intakes of key nutrients can be used to approximate net endogenous acid production (NEAP) and to explore the association between dietary acidity and bone health. We investigated the relation between dietary potassium and protein, NEAP (with an algorithm including the ratio of protein to potassium intake), and potential renal acid load (with an algorithm including dietary protein, phosphorous, potassium, magnesium, and calcium) and markers of bone health. Measurements of bone mineral density (BMD) (n = 3226) and urinary bone resorption markers (n = 2929) at the lumbar spine and femoral neck were performed in perimenopausal and early postmenopausal women aged 54.9 +/- 2.2 y (x +/- SD) in 1997-1999. BMD (g/cm(2)), free pyridinoline (fPYD), and free deoxypyridinoline (fDPD) were expressed relative to creatinine. Dietary intake was assessed with a food-frequency questionnaire. Comparison of the highest with the lowest quartile of potassium intake or the lowest with the highest NEAP showed a 6-8% increase in fPYD/creatinine and fDPD/creatinine. A difference of 8% in BMD was observed between the highest and lowest quartiles of potassium intake in the premenopausal group (n = 337). Dietary potassium, an indicator of NEAP and fruit and vegetable intake, may exert a modest influence on markers of bone health, which over a lifetime may contribute to a decreased risk of osteoporosis.