Acid-base analysis of individuals following two weight loss diets.
OBJECTIVE
To examine the effects of low-carbohydrate, ketogenic (LCKD) and low-fat (LFD) diets on acid-base status.


METHODS
Prospective analysis of volunteers from two clinical trials.


METHODS
Subset of 39 volunteers from a randomized trial comparing the effects of an LCKD with an LFD, and a single-arm trial of an LCKD.


METHODS
Outpatient research clinic.


METHODS
LCKD (initially <20 g of carbohydrate daily) or LFD (<30% of energy from fat, 500-1000 kcal energy reduction) instruction.


METHODS
Arterial blood gas analysis, serum chemistries (electrolytes, urea nitrogen/creatinine, glucose, ketone bodies, lactate), anion gap, and urine ketone bodies measured at weeks 0, 2, 8, and 24.


RESULTS
Participants had a mean (+/-standard deviation) age of 43.5+/-9.3 years; 28 (72%) were female, 29 (74%) were Caucasian. Using linear mixed-model analysis to examine blood test changes from baseline to 24 weeks, the LFD group experienced a decrease in arterial blood pH from a mean of 7.43 at week 0 to 7.40 at week 24 (P=0.03), and the LCKD group experienced a decrease from 7.42 at week 0 to 7.40 at week 24 (P=0.01). The lowest pH measurements observed were 7.34 in the LFD group and 7.37 in the LCKD group. Although serum bicarbonate appeared to decrease from baseline at weeks 2 and 8 in the LCKD group, the change at 24 weeks was not statistically significant in either diet group, and only four of 131 (two of 92 from the LCKD group) measurements were less than 22 mmol/l. The proportion of participants with elevated urine and serum ketone body levels rose in the LCKD group only, was highest at week 2, and decreased over the subsequent time points.


CONCLUSIONS
In individuals following an LCKD or an LFD, blood pH decreased mildly and the LCKD group experienced a small, transient decrease in serum bicarbonate in conjunction with mild ketosis. This suggests that an LCKD induced a mild compensated metabolic acidosis, but no individual showed evidence of significant metabolic derangement.
Yancy
W S
WS
Department of Veterans' Affairs Medical Center, Center for Health Services Research in Primary Care, Durham, NC 27705, USA. yancy006@mc.duke.edu
Olsen
M K
MK
Dudley
T
T
Westman
E C
EC
D000136:Acid-Base Equilibrium / Q000502:physiology*; D000138:Acidosis / Q000453:epidemiology / Q000209:etiology; D000328:Adult; D001774:Blood Chemical Analysis; D001784:Blood Gas Analysis; D050528:Diet, Carbohydrate-Restricted; D018752:Diet, Fat-Restricted; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007657:Ketone Bodies / Q000032:analysis*; D016014:Linear Models; D008297:Male; D009765:Obesity / Q000178:diet therapy* / Q000378:metabolism; D011446:Prospective Studies; D015431:Weight Loss / Q000502:physiology*
D007657:Ketone Bodies