Potassium Bicarbonate Attenuates the Urinary
Nitrogen Excretion That Accompanies an Increase in
Dietary Protein and May Promote Calcium Absorption
Lisa Ceglia, Susan S. Harris, Steven A. Abrams, Helen M. Rasmussen, Gerard E. Dallal,
and Bess Dawson-Hughes
Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University
(L.C., S.S.H., H.M.R., G.E.D., B.D.-H.), Boston, Massachusetts 02111; and United States Department of Agriculture
Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine and Texas Children’s
Hospital (S.A.A.), Houston, Texas 77030
Context: Protein is an essential component of muscle and bone. However, the acidic byproducts of
protein metabolism may have a negative impact on the musculoskeletal system, particularly in
older individuals with declining renal function.
Objective: We sought to determine whether adding an alkaline salt, potassium bicarbonate
(KHCO3), allows protein to have a more favorable net impact on intermediary indices of muscle and
bone conservation than it does in the usual acidic environment.
Design: We conducted a 41-d randomized, placebo-controlled, double-blind study of KHCO3 or
placebo with a 16-d phase-in and two successive 10-d metabolic diets containing low (0.5 g/kg) or
high (1.5 g/kg) protein in random order with a 5-d washout between diets.
Setting: The study was conducted in a metabolic research unit.
Participants: Nineteen healthy subjects ages 54–82 yr participated.
Intervention: KHCO3 (up to 90 mmol/d) or placebo was administered for 41 d.
MainOutcomeMeasures:Wemeasured 24-h urinary nitrogen excretion, IGF-I, 24-h urinary calcium
excretion, and fractional calcium absorption.
Results: KHCO3 reduced the rise in urinary nitrogen excretion that accompanied an increase in
protein intake (P 0.015) and was associated with higher IGF-I levels on the low-protein diet (P
0.027) with a similar trend on the high-protein diet (P 0.050). KHCO3 was also associated with
higher fractional calcium absorption on the low-protein diet (P0.041) with a similar trend on the
high-protein diet (P 0.064).
Conclusions: In older adults, KHCO3 attenuates the protein-induced rise in urinary nitrogen excretion,
and this may be mediated by IGF-I. KHCO3 may also promote calcium absorption independent
of the dietary protein content. (J Clin Endocrinol Metab 94: 645–653, 2009)
Protein is an essential component of skeletal muscle, and severe
protein deficiency causes muscle wasting (1). Studies
have demonstrated a positive association between dietary protein
intake and lean body mass (2, 3), perhaps mediated by the
anabolic hormone, IGF-I (4). Other studies have suggested that
high-protein diets cause increased urinary nitrogen (UNi) excretion
due in part to muscle breakdown from the acidogenic component
of dietary protein (5, 6). Diets rich in protein and low in
fruits and vegetables result in a low-grade, chronic metabolic
acidosis because the metabolism of protein releases noncarbonic
ISSN Print 0021-972X ISSN Online 1945-7197
Printed in U.S.A.
Copyright © 2009 by The Endocrine Society
doi: 10.1210/jc.2008-1796 Received August 14, 2008. Accepted November 20, 2008.
First Published Online December 2, 2008
Abbreviations: BMD, Bone mineral density; CV, coefficients of variation; IGFBP-3, IGF
binding protein-3; NAE, net acid excretion; 25(OH)D, 25-hydroxyvitamin D; UCa, urinary
calcium; UCr, urinary creatinine; UK, urinary potassium; UNa, urinary sodium; UNi, urinary
nitrogen; UNTX, urinary N-telopeptide.
O R I G I N A L A R T I C L E
E n d o c r i n e R e s e a r c h
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acids (e.g. sulfuric acid) into the bloodstream in amounts that
override the alkalinizing effect of potassium in vegetable foods
(7). Conditions of chronic metabolic acidosis, such as chronic
kidney disease and ketogenic weight loss diets, stimulate muscle
breakdown (5,
. Reversal of metabolic acidosis by administration
of alkaline salts has been shown to decrease UNi excretion,
suggesting an attenuation of muscle breakdown (9, 10), but only
one prior study has demonstrated such an effect in healthy adults
on a high-protein diet (11).
Dietary protein promotes peripubertal bone growth (4, 12)
and has been positively associated with higher bone mass (13, 14)
and lower hip fracture rates in adults (15, 16). However, dietary
protein also appears to have some potentially adverse effects on
calcium and bone metabolism. For example, protein has consistently
been shown to increase urinary calcium (UCa) excretion
(17, 18), whereas it has had varying effects on calcium absorption
(19–24). In addition, experimental increases in amino acid
intakes have been shown to negatively influence bone remodeling
(25). These adverse calcium and bone effects may result from
the metabolic acid load that accompanies a high dietary protein
intake. An acidic environment reduces osteoblastic activity (26),
increases osteoclastic activity (27), and appears to have a direct
physicochemical effect on bone. Studies have found that the
addition of alkaline salts lowered UCa excretion (28, 29) and
biochemical markers of bone turnover during short-term administration
(29, 30), suggesting beneficial effects on bone preservation.
A recent study showed that administration of an alkaline
salt of potassium in rats in combination with a high-protein diet
improved calcium retention but failed to demonstrate beneficial
skeletal effects (31). To our knowledge, there are no similar studies
in humans.
The purpose of this study was to investigate whether the addition
of an alkaline salt of potassium, potassium bicarbonate
(KHCO3), allows dietary protein to have a more favorable impact
on indices of muscle and bone conservation than is observed
in its usual acidic environment. We studied healthy older men
and women because typical age-related declines in renal function
may decrease their ability to compensate for protein-induced
metabolic acidosis, and alkali therapy may prevent this from
occurring.
Subjects and Methods
Study design and subjects
This was a double-blind, randomized, placebo-controlled study that
was conducted at the Metabolic Research Unit at the Jean Mayer United
States Department of Agriculture Human Nutrition Research Center on
Aging at Tufts University. The Tufts Medical Center-Tufts University
Health Sciences Campus Institutional Review Board approved the study,
and written informed consent was obtained from each subject.
Subjects were given up to 90 mmol/d KHCO3 or placebo for 41 d. A
computer-generated randomization scheme was used for block randomization
of subjects within sex and age (50 to 64 and 65 and older) strata.
Subjects underwent a 16-d phase-in to reach a maximal KHCO3 (or
placebo) dose of 90 mmol/d, and then two successive 10-d metabolic diet
periods containing either low (0.5 g/kg d) or high (1.5 g/kg d) protein
in random order, with a 5-d washout period in between on their usual
diets (Fig. 1). Blood, urine, and fractional calcium absorption analyses
were performed after each diet period.
Healthy men and postmenopausal women age 50 and older were
recruited through direct mailings and local newspaper advertisements,
and they were prescreened by telephone. Before study entry, subjects
were screened with a medical history, physical examination, and fasting
blood and urine tests within 6 months of the study start date. Exclusion
criteria included body mass index of 38 kg/m2 of more; vegetarianism;
use of medications including oral glucocorticoids, estrogen, osteoporosis
medications, thiazide diuretics, and nonsteroidal antiinflammatory
drugs; medical conditions including kidney stones, cirrhosis, gastroesophageal
reflux, active hyperparathyroidism, untreated thyroid disease,
significant immune disorders, unstable heart disease, adrenal insufficiency,
primary aldosteronism, Bartter’s syndrome, and diabetes
FIG. 1. Study design. Randomization to placebo or KHCO3 on d 1. Sixteen-day phase-in period followed by two successive 10-d metabolic diets (low protein, 0.5 g/
kg d; or high protein, 1.5 g/kg d) in random order with a 5-d washout period in between.
646 Ceglia et al. Effect of Protein plus KHCO3 on Muscle and Bone J Clin Endocrinol Metab, February 2009, 94(2):645–653
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mellitus; total hip bone mineral density (BMD) T-score below 3.0;
creatinine clearance below 50 ml/min/1.73 m2 of body surface area;
24-h UCa excretion greater than 300 mg/d; abnormal serum calcium;
elevated alkaline phosphatase; and serum 25-hydroxyvitamin D
25(OH)D level below 16 ng/ml.
Twenty-six subjects were screened, and 23 were enrolled. Subjects
were asked to maintain their usual diet, exercise level, and body weight;
to discontinue their own calcium and vitamin D supplements; and to
avoid bicarbonate- or potassium-rich products during the study. Three
individuals randomized to the KHCO3 group discontinued the study for
reasons unrelated to treatment. Twenty subjects (11 in the placebo group
and nine in the KHCO3 group) completed the study. One subject on
placebo was excluded from this analysis because of a suspected acid-base
disorder as indicated by a 10-fold higher net acid excretion (NAE) compared
with the mean in other subjects, a low urine pH, and a 3-fold higher
N-telopeptide level. Characteristics of the 19 subjects included in this
analysis are shown in Table 1.
Diet, supplements, and physical activity
Usual nutrient intakes were assessed by food frequency questionnaire
(32) before subjects started the study pills. During the two 10-d metabolic
diet cycles, all food and caloric beverages were provided by the Metabolic
Research Unit as a 3-d cycle menu. Each subject was studied on a lowand
a high-protein diet. The low-protein diet contained 0.5 g/kg d of
protein from natural foods, mainly meat. The high-protein diet contained
an additional 1.0 g/kg d of dietary protein, as lean meat. The
contents of the daily diet, calculated with version 4.05 of the University
of Minnesota Food and Nutrient Database 34, are shown in Table 2.
Phosphorus intake was higher on the high-protein diet because meat
contains significant amounts of phosphorus.Wechose not to balance the
phosphorus in the two diets to simulate the real-life setting. During the
study, caffeine-containing beverages were limited to 12 ounces daily, and
alcohol was not permitted. Subjects came in at least three times per week
to eat a meal, pick up their food, and be weighed. The research dietitian
assessed adherence to the diet by reviewing self-report food intake checklists
and returned uneaten food and food containers at each visit. Adjustments
in the foods provided were made to optimize adherence and
maintain body weight. Each day during the study, subjects took a supplement
tablet containing 600mgof calcium, 266mgof phosphorus, 125
IU of vitaminD3, 50mgof magnesium (Posture D;USRhodia, Cranbury,
NJ) and a multivitamin (CVS brand) containing 400 IU of vitamin D3
with the evening meal.
Leisure, household, and occupational activity were assessed on d 1
and 41 with the Physical Activity Scale for the Elderly (PASE) questionnaire
(33).
Study capsules and dosing schedule
Capsules containing 7.5 mmol of KHCO3 and matching placebo
capsules were made by a local compounding pharmacy. Subjects started
on three capsules daily (one after each meal), and gradually increased the
dose by three capsules every 3 d to a maximum daily dose of 12 capsules
(90 mmol/d; four capsules after each meal with 8 ounces of water), which
they took thereafter throughout the study. If a subject developed gastrointestinal
distress on the pills, the dose was cut back by three capsules
per day, and escalated again 3 d later, as tolerated. A safety serum potassium
level was drawn after the 16-d phase-in, but no hyperkalemia
was observed.
TABLE 1. Subject characteristics before study entry
Placebo
(mean SD)
KHCO3
(mean SD)
n 10 9
Females (n) 8 5
Age (yr) 62 7 62 9
Height (cm) 164.15 6.27 164.78 8.74
Weight (kg) 64.08 3.73 72.38 12.50
BMI (kg/m2) 23.9 2.3 26.6 3.7
Lean body mass (kg) 40.45 5.63 43.39 11.51
Total hip T-score 0.43 0.72a 0.08 0.74
25(OH)D (ng/ml) 26.20 6.75 23.11 6.25
PTH (pg/ml) 46.5 7.7b 47.4 10.4b
Serum calcium (mg/dl) 9.11 0.37 9.12 0.19
24-h UCa (mg) 102.9 55.5 115.5 61.1
24-h UCa/Cr (mg/g) 87.4 45.3 99.9 40.0
Total energy intake (kcal/d) 1491.5 412.1 1558.0 551.8
Dietary protein intake (g/d) 69.1 22.1 73.0 29.9
Dietary potassium intake (mg/d) 2909.1 650.0 2605.7 1023.6
Dietary calcium intake (mg/d) 697.9 258.4 898.6 635.2
Dietary sodium intake (mg/d) 2830.0 997.1 2471.3 1091.9
PASE score 175.3 49.3c 167.9 74.1c
To convert values for 25(OH)D to nmol/liter, multiply by 2.5; serum PTH to pmol/
liter, multiply by 0.11; serum calcium to mmol/liter, multiply by 0.25; UCa to
mmol, multiply by 0.025; UCa/Cr ratio to mmol/mol, multiply by 2.82.
a Total hip T-score measurements available on eight subjects in the placebo
group.
b PTH levels were drawn on eight KHCO3 and eight placebo subjects
approximately 5 months before the start of the study.
c PASE was available for eight subjects in the KHCO3 group and nine subjects in
the placebo group.
TABLE 2. Daily nutrient contents of the 10-d low-protein and
high-protein metabolic diets in the two groups
Placebo
(mean SD)
KHCO3
(mean SD)
Energy (kcal/d)
Low 1990.7 142.3 2168.1 240.9
High 2160.9 72.9 2401.1 271.0a
Total fat (g/d)
Low 105.4 8.7 117.7 16.0a
High 84.0 3.8 100.6 16.0a
Total carbohydrate (g/d)
Low 238.7 16.0 251.4 20.7
High 255.6 6.6 265.8 16.1
Total protein (g/d)
Low 32.1 2.02 36.1 5.2a
High 96.7 5.7 109.2 17.7a
Protein (g/kg d)
Low 0.50 0.01 0.50 0.02
High 1.51 0.02 1.51 0.04
Total dietary fiber (g/d)
Low 15.6 1.4 16.2 2.1
High 14.8 0.4 15.2 1.1
Calcium (mg/d)b
Low 586.1 6.3 583.8 13.7
High 602.0 4.9 590.1 10.3a
Phosphorus (mg/d)b
Low 688.3 50.6 739.8 63.6
High 1125.0 55.4 1210.4 133.4
Magnesium (mg/d)b
Low 197.5 12.6 209.3 21.4
High 244.1 9.0 254.0 21.7
Sodium (mg/d)
Low 2496.7 140.0 2624.3 143.4
High 2565.0 106.9 2704.7 139.5a
Potassium (mg/d)
Low 2298.5 128.2 2396.4 235.0
High 2348.9 43.0 2504.4 225.3a
a Differs from the placebo group within diet P 0.05.
b Each subject also received a supplement containing 600 mg calcium, 266 mg
phosphorus, and 50 mg magnesium.
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Biochemical measurements
Blood was drawn after a 12-h overnight fast and between 0700 and
1000 h. All samples from individual subjects were batched for analyses,
with the exception of the serum potassium measurement on d 17 (a safety
measurement). Serum 25(OH)D was measured with RIA kits from Diasorin
(Stillwater, MN) with coefficients of variation (CV) of 5.6–7.7%.
Serum intact PTH, IGF-I, IGF binding protein-3 (IGFBP-3), and osteocalcin
were measured by chemiluminescent immunoradiometric assays
on an automated immunoassay system, (IMMULITE 1000, Diagnostic
Product Corporation, Los Angeles, CA). The CV for this assay ranged
from 3.0–9.0%. Serum calcium, potassium, phosphorus, and 24-h urinary
sodium (UNa), potassium (UK) and creatinine (UCr) were measured
on an automated clinical chemistry analyzer (Olympus AU400; Olympus
America Inc., Melville, NY). The CVs for these assays ranged from 3.0–
6.0%. The 24-h UCa was measured by direct-current plasma emission
spectroscopy (Beckman SpectraSpan VI Direct Current Plasma Emission
Spectrophotometer; Beckman Instruments, Fullerton, CA) with a CV of
3–5%. Twenty-four-hour urinary N-telopeptide (UNTX) was measured
by ELISA (Wampole, Princeton, NJ), with a CV of 5.6–7.7%. Twentyfour-
hour UNi was measured with a model FP-2000 nitrogen/protein
determinator (LECO, St. Joseph, MI), which employs a Dumas combustion
method and detection using a thermal conductivity cell. It measures
nitrogen with a precision of 15 ppm. Twenty-four-hour NAE was
measured by a modification of the Jorgensen titration method (34), as
described by Chan (35): NAE titratable acid NH4
HCO3
.
Briefly, titratable acid HCO3
was assessed after addition of HCl,
boiling the sample, and then titrating the sample to neutral pH. To measure
the NH4
, formol was added to the sample to release the H from
NH4
, and the sample was again titrated to neutral pH. All titrations
were carried out with a TIM 900 Titration Manager (Radiometer Analytical,
Loveland, CO). The precision of NAE measurements in our
laboratory was determined by analyzing aliquots of a single 24-h urine
collection on 15 different days. The aliquots were stored frozen at 20
C and thawed only once. The CV of these measurements was 10.1%.
Calcium absorption
Calcium absorption was measured in each subject on the last day of
each metabolic diet period using dual tracer stable isotope technique
(36). A 2-wk interval was needed between these measurements to clear
much of the stable isotopes after the first administration (thus the 5-d gap
between the two diet cycles). On the last day of each diet cycle, subjects
arrived at the center after an overnight fast, had a peripheral iv catheter
placed, and were given breakfast. Toward the end of breakfast, subjects
were given 44Ca(15mgfor subjects weighing80 kg and 23mgfor those
80 kg) that had been mixed in 240 ml of calcium-fortified Minute Maid
orange juice (340 mg of calcium). The breakfast and tracer drink combined
contained a total of 400 mg of calcium. Two hours after breakfast,
42Ca (1–1.5 mg for subjects weighing 80 kg and 2.3 mg for those
weighing 80 kg) was infused iv over 2 min. A 24-h urine collection
began immediately after the oral tracer was administered with breakfast.
When the collection was completed, an aliquot was prepared and analyzed
by the method of Chen et al. (37). The 42Ca/44Ca ratio was measured
by a magnetic sector inductively coupled plasma mass spectrometer
(ICP-MS, Bremen, Germany). Fractional calcium absorption was
determined as the ratio of the cumulative oral tracer recovery to the
cumulative iv tracer recovery in the 24-h urine collections obtained after
dosing. The precision of this method is less than 1%. The stable isotopes
were purchased from Trace Sciences International Corp. (Richmond Hill,
Ontario, Canada). The isotopic enrichments for these tracers were greater
than 95%. Tracers were prepared by the Tufts Medical Center Research
Pharmacy and were tested for sterility and pyrogenicity before use.
Dual-energy x-ray absorptiometry
BMD of the total hip and whole skeleton and whole-body soft-tissue
composition were measured at the beginning of the study with a model
Prodigy dual-energy x-ray absorptiometry scanner (GE-Lunar, Madison,
Whey Isolat). CVs were less than 1% for the hip BMD and lean body mass,
as described previously (38).
Statistical analysis
For the analyses of the dietary protein effect, urine measurements
were not corrected for creatinine because UCr excretion is dependent
upon protein intake; in analyses of the KHCO3 effect, urine measurements
were expressed as a ratio to UCr. Subject characteristics in the
KHCO3 and placebo groups and unadjusted differences between groups
were compared using t-tests for two independent samples. Paired t-tests
were used to assess the effects of dietary protein on outcome variables in
the placebo group. Pearson correlation coefficients were used to describe
linear associations. Analysis of covariance was used to compute and
compare means adjusted for various variables across groups. Two-sided
Pvalues less than 0.05 were considered to indicate statistical significance.
Statistical analyses were conducted with SPSS version 15.0 (SPSS Inc.,
Chicago, IL).
Results
The placebo group included a few more women; as a result, a
trend toward lower body weight was observed in this group (P
0.061; Table 1), and intakes of total energy and some nutrients
were lower (Table 2). Otherwise, characteristics of the two
groups did not differ significantly.
Neither body weight nor physical activity changed significantly
during the study in either treatment group (P 0.270), and changes
in these measures did not differ between groups (P 0.545). The
25(OH)D levels at the end of the study were similar in the two
groups (27.93.3 ng/ml in the placebo group, 26.33.9 ng/ml in
the KHCO3 group, P 0.353). Adherence (mean SD) to study
pills for the placebo and KHCO3 groups was 95 8% and 94
8%, respectively, during the 41-d study period. Adherence to the
FIG. 2. UCa (A) and fractional calcium absorption (B) on the low- and high-protein
diets in the placebo group (n 10). Each line with open circles represents an
individual subject. The line with the black-filled square is the mean. The P value for
the difference between levels of protein: P 0.016 (A); P 0.913 (B).
648 Ceglia et al. Effect of Protein plus KHCO3 on Muscle and Bone J Clin Endocrinol Metab, February 2009, 94(2):645–653
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dietary supplements during the same period was 99 1% in the
placebo group and 97 8% in the KHCO3 group.
Effects of dietary protein
The effects of dietary protein on indices of muscle and bone
metabolism were examined in the 10 placebo subjects. In these
subjects, an increase in dietary protein intake was associated
with significant increases in NAE (by 12.6 8.1 mEq/liter; P
0.001), UNi (by 9.1 2.2 g; P 0.001), IGF-I (by 24.3 18.1
ng/ml; P0.002), andUCa(by 44.847.9 mg; P0.016) (Fig.
2A) and a decrease in PTH (by6.98.8 pg/ml; P0.037). In
contrast, changes in fractional calcium absorption (Fig. 2B),
IGFBP-3, serum calcium, phosphorus, osteocalcin, and UNTX
were not statistically significant.
TABLE 3. Serum and urine biochemistry at the end of the low- and high-protein diets and changes in these measurements with
an increase in dietary protein in the two groups
Low protein (mean SD) High protein (mean SD) Change (mean SD)
Serum
IGF-I (ng/ml)
Placebo 95.9 31.7 120.2 33.2 24.3 18.1
KHCO3 136.4 41.3a 139.4 25.3b 3.0 25.6c
IGFBP-3 (g/ml)
Placebo 4.12 0.69 4.24 0.72 0.12 0.44
KHCO3 4.57 1.09 4.57 0.70 0.00 0.54
Osteocalcin (ng/ml)
Placebo 6.2 2.6 6.9 4.3 0.6 3.6
KHCO3 6.7 3.8 6.6 2.9 0.1 2.6
PTH (pg/ml)
Placebo 46.2 10.6 39.3 12.8 6.9 8.8
KHCO3 35.2 13.8 38.8 13.3 3.6 8.9c
Calcium (mg/dl)
Placebo 9.15 0.40 9.00 0.27 0.14 0.39
KHCO3 9.02 0.21 8.96 0.54 0.07 0.60
Phosphorus (mg/dl)
Placebo 3.71 0.40 3.49 0.42 0.22 0.38
KHCO3 3.57 0.52 3.43 0.55 0.13 0.37
24-h urine
UCr (g)
Placebo 1.03 0.25 1.20 0.29 0.17 0.42
KHCO3 1.04 0.39 1.30 0.39 0.26 0.21
24-h urine corrected for creatinine
UNi/Cr (g/g)
Placebo 4.2 0.8 11.3 2.2 7.1 2.4
KHCO3 5.9 3.0 9.7 2.4 3.8 3.0c
UCa/Cr (mg/g)
Placebo 101.0 48.4 121.3 70.9 20.3 52.4
KHCO3 108.7 60.4 110.0 62.1 1.3 26.8
UNTX/Cr (nmol/mmol)
Placebo 41.0 15.2 40.4 19.1 0.6 14.0
KHCO3 37.1 10.5 35.1 7.0 2.0 5.8
UNa/Cr (mEq/g)
Placebo 99.1 28.5 93.8 24.1 5.2 37.4
KHCO3 136.4 42.8a 107.3 25.2 29.2 34.9
UK/Cr (mEq/g)
Placebo 53.9 15.1 49.5 17.7 4.3 18.7
KHCO3 140.2 55.0a 110.9 28.2a 29.3 38.1
NAE/Cr (mEq/g)
Placebo 10.2 9.1 33.9 8.2 31.9 24.3
KHCO3 55.0 34.6a 23.1 22.0a 23.7 12.4
Calcium absorption
Fractional calcium absorption (%)
Placebo 16.6 7.6 16.3 5.2 0.27 7.6
KHCO3 23.7 6.3a 23.5 10.0d 0.3 7.0
To convert values for IGF-1to g/liter, multiply by 1.0; osteocalcin to g/liter, multiply by 0.17; serum PTH to pmol/liter, multiply by 0.11; serum calcium to mmol/liter,
multiply by 0.25; serum phosphorus to mmol/liter, multiply by 0.32; UCr to mmol, multiply by 8.84; UNi/Cr to mmol/mmol, multiply by 4.04; UCa/Cr ratio to mmol/mol,
multiply by 2.82.
a Differs from placebo group within diet at P 0.05.
b Differs from placebo group within diet at P 0.05.
c Change differs from placebo group at P 0.05.
d Differs from placebo group within diet at P 0.064.
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Effects of KHCO3
Supplementation with KHCO3 had the expected effects of
lowering NAE and increasing UK on both diets (Table 3). The
muscle, calcium, and bone indices during each diet cycle and the
changes in these indices with an increase in dietary protein were
compared across the two treatment groups (Table 3). The rise in
UNi to creatinine ratio (UNi/Cr) with an increase in protein
intake was less in theKHCO3 group than the placebo group (P
0.015; Fig. 3). KHCO3 supplementation was also associated
with higher IGF-I levels on the low-protein diet (P0.027), with
a similar trend on the high-protein diet (P 0.050). There was
no statistically significant difference in IGFBP-3 levels between
the KHCO3 group and the placebo group (Table 3). Notably,
adjustment for IGF-I level on either diet eliminated the statistically
significant effect of KHCO3 on the change in UNi with an
increase in protein intake (P 0.125 for treatment effect after
adjustment). In addition, in all 19 subjects, the change in UNi
with an increase in protein intake was inversely correlated
with IGF-I level both on the low-protein diet (r0.650; P
0.003; Fig. 4, top left) and the high-protein diet (r0.480;
P 0.036; Fig. 4, top right).
Fractional calcium absorption was higher in the KHCO3
group than the placebo group on the low-protein diet (P
0.041), and there was a similar trend on the high-protein diet
(P 0.064, Table 3). In all 19 subjects, fractional calcium absorption
and IGF-I were positively correlated on the high-protein
diet (r 0.507; P 0.027; Fig. 4, bottom right) but not on the
low-protein diet (r 0.216; P 0.374; Fig. 4, bottom left). The
change in fractional calcium absorption with an increase in protein
had no association with the change in IGF-I with an increase
in protein (r 0.079; P 0.747; n 19).
The UCa to creatinine ratio (UCa/Cr) did not differ significantly
in the two groups on either diet (Table 3), and the change
in UCa/Cr with an increase in protein intake also did not differ
significantly in the two groups (P0.252; Table 3). Adjustment
for UNa to creatinine (UNa/Cr) excretion did not substantially
alter these results.
The groups did not differ in mean serum PTH on either diet,
and the groups had mixed changes in PTH with an increase in
protein (Table 3). We did not observe significant effects of either
KHCO3 treatment or protein intake on serum calcium, phosphorus,
or markers of bone turnover (Table 3). UNa/Cr was
higher in the KHCO3 group than the placebo group on the
low-protein diet (P 0.037; Table 3), but not on the highprotein
diet.
Adverse effects
Two subjects in the KHCO3 group reported transient gastroesophageal
complaints (one had epigastric discomfort and
one had two episodes of emesis).
Discussion
Supplementation with 90 mmol/d KHCO3, which resulted in a
net alkali-producing intake, reduced by almost 50% the rise in
UNi excretion that accompanied increased protein intake in
healthy older men and women. In our subjects, who were on
fixed protein intakes and had stable weight and physical activity,
this reduction in UNi excretion can be considered an indicator of
reduced muscle wasting. These findings add to those from a study
by Frassetto et al. (11) in which 60–120 mmol of KHCO3 daily
for 18 d in 14 healthy postmenopausal women on constant highprotein
diets (about 1.6 g/kg d) resulted in a significant reduction
in totalUNiexcretion from 14.00.6 to 13.20.5 g/d (P
0.001).
The fact that IGF-I was higher in the KHCO3 group than the
placebo group after each metabolic diet period suggests that it
was increased by KHCO3 supplementation. IGFBP-3 levels in
the KHCO3 group did not differ significantly from the placebo
group. These results are consistent with a study in which healthy
adults given ammonium chloride to induce metabolic acidosis
had significant decreases in serum IGF-I and no change in
IGFBP-3 (39). That decrease in IGF-I was attributed to an impaired
hepatic IGF-I response to circulating GH, similar to that
seen in prolonged fasting and in protein deprivation. Our study
provides the first evidence that ingestion of alkali may increase
serum IGF-I levels in healthy older men and women. Because
adjustment for IGF-I eliminated the significant effect of KHCO3
treatment on protein-induced increases in nitrogen excretion,
our study also provides evidence that IGF-I may be the mediator
of a beneficial KHCO3 effect on muscle.
Calcium absorption on low protein was greater in the
KHCO3 group than the placebo group with a similar trend on
high protein, suggesting that it may be increased by KHCO3.
However, Sebastian et al. (29) studied 18 women on and then off
FIG. 3. Dot plot of the change (high–low protein diet) in UNi/Cr by treatment
group. Each open circle represents the change for an individual subject. The cross
() represents the mean change in each group. P for difference between
groups 0.015.
650 Ceglia et al. Effect of Protein plus KHCO3 on Muscle and Bone J Clin Endocrinol Metab, February 2009, 94(2):645–653
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KHCO3 and observed no change in calcium absorption 12 d after
theKHCO3 treatment was stopped. The positive correlation that
we observed between calcium absorption and IGF-I suggests that
IGF-I may mediate a positive effect of KHCO3 on calcium absorption.
IGF-I has been shown to promote calcium absorption
in aged female rats (40), but there are no comparable data in
humans. Contrary to our expectations, given our diet-induced
rise in IGF-I and previous evidence that protein promotes an
increase in calcium absorption (22), we did not observe an effect
of increased protein intake on calcium absorption. Differences in
our results are not likely to be methodological because we used
a dual-tracer stable isotope method as used in the prior study
(22). Possible explanations are that Kerstetter et al. (22) kept
phosphorus content constant, whereas we allowed it to increase
on a high-protein diet, and that both studies were quite small.
Our null finding is in agreement with prior balance studies (23,
24), two isotopic studies (19, 20), and a radiotracer study (21).
In healthy adults,KHCO3 and other alkali therapy have been
found to reduce UCa excretion in the setting of acidogenic diets
(28, 29). The hypocalciuric effect of KHCO3 is presumably due
to its neutralization of the acidic environment known to release
calcium from bone as a buffer (30). There was a small decrease
in UCa excretion in the KHCO3 group compared with the placebo
group, but this reduction was not large enough to be statistically
significant in this study. We did, however, confirm previous
observations that increased dietary protein intake leads to
increased calcium excretion (18, 22). The source of the calciuria
does not appear to be from increased intestinal absorption; other
possibilities include altered endogenous fecal calcium excretion
and bone. Notably, the studies that have documented calciuria
have generally been short in duration.
Wedid not confirm prior reports of a beneficialKHCO3 effect
on markers of bone turnover (29, 30) and detected no effect of
increased dietary protein intake on osteocalcin and UNTX, in
agreement with some (21, 22, 31), but not other prior studies (29).
This pilot study had some important strengths, including the
fact that the dose of KHCO3 effectively neutralized the proteinrelated
acid load, our subjects’ adherence to and persistence in
the study were high, and we used the gold-standard dual-tracer
stable isotope method for measuring calcium absorption. We
FIG. 4. Top left, IGF-I on low protein and change (high–low protein) in UNi (r 0.650; P 0.003; n 19). E, Placebo; F, KHCO3. Top right, IGF-I on high protein
and change (high–low protein) in UNi (r 0.480; P 0.036). Bottom left, IGF-I on low-protein diet and fractional calcium absorption on low protein (r 0.216; P
0.374). Bottom right, IGF-I on high protein and fractional calcium absorption on high protein (r 0.507; P 0.027).
J Clin Endocrinol Metab, February 2009, 94(2):645–653 jcem.endojournals.org 651
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chose a parallel arm design to study the KHCO3 effect. A crossover
design, as used to study the dietary protein effect, would
have added power to observe a KHCO3 effect; however, we
wanted to avoid potential carryover effects of KHCO3, which
has no well-established washout period. The primary limitation
of this study was that we did not have baseline samples for the
KHCO3 and placebo groups for study endpoints. In addition, the
small sample size may have prevented us from detecting some
clinically meaningful effects. Lastly, our findings pertain to highdose
KHCO3 supplementation that caused a net alkali-producing
intake; thus,wecannotcommenton the degree to which these
findings may vary at other doses.
In conclusion, supplementation with KHCO3 attenuates the
UNi excretion that accompanies an increase in dietary protein,
suggesting that the net effect of dietary protein on muscle may be
enhanced by reducing its accompanying acid load. KHCO3 supplementation
was also associated with higher fractional calcium
absorption, independent of protein intake. Moreover, the
KHCO3-induced nitrogen sparing and enhanced calcium absorption
appear to be mediated by IGF-I, which was higher on
the KHCO3 supplementation. A higher protein intake increased
UCa excretion, but not calcium absorption. Larger long-term
studies are needed to establish whether KHCO3 supplementation
is a worthwhile strategy for reducing age-related muscle
wasting and bone loss and to test the hypothesis that IGF-I is a
mediator of such effects.
Acknowledgments
We thank the Metabolic Research Unit at the Jean Mayer United States
Department of Agriculture (USDA) Human Nutrition Research Center
on Aging at Tufts University and the staff at the USDA/Agricultural
Research Service Children’s Nutrition Research Center at Baylor College
of Medicine for their work on the study.
Address all correspondence to: Lisa Ceglia, M.D., Jean Mayer USDA
Human Nutrition Research Center on Aging at Tufts University, 711
Washington Street, Boston, Massachusetts 02111. E-mail: lisa.ceglia@
tufts.edu. Reprints will not be available.
L.C. was supported by Grant DK007651. This research was supported
by the Unilever Corporate Research, Bedfordshire, United Kingdom.
This work was also supported by the USDA/ARS under agreement
no. 58-1950-7-707. Any opinions, findings, conclusions, or recommendations
expressed in this publication are those of the author(s) and do not
necessarily reflect the view of the USDA.
Disclosure Statement: The authors have nothing to disclose.
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