Acid-Base Analysis of Individuals Following Two Weight Loss Diets

ORIGINAL ARTICLE Acid-base analysis of individuals following two weight loss diets

WS Yancy Jr1,2, MK Olsen1,2,3, T Dudley1 and EC Westman2

1Department of Veterans’ Affairs Medical Center, Center for Health Services Research in Primary Care, Durham, NC, USA; 2Department of Medicine, Duke University Medical Center, Durham, NC, USA and 3Department of Biostatistics and Bioinformatics, Duke University Medical Center, Durham, NC, USA

Objective: To examine the effects of low-carbohydrate, ketogenic (LCKD) and low-fat (LFD) diets on acid-base status. Design: Prospective analysis of volunteers from two clinical trials. Participants: 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. Setting: Outpatient research clinic. Intervention: LCKD (initially o20 g of carbohydrate daily) or LFD (o30% of energy from fat, 500–1000 kcal energy reduction) instruction. Measurements: 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 (7standard deviation) age of 43.579.3 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 ¼ 0.03), and the LCKD group experienced a decrease from 7.42 at week 0 to 7.40 at week 24 (P ¼ 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. Conclusion: 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. European Journal of Clinical Nutrition (2007) 61, 1416–1422; doi:10.1038/sj.ejcn.1602661; published online 14 February 2007

Keywords: diet therapy; reducing diets; acid-base equilibrium; acidosis; ketone bodies

Introduction emerging. The most restrictive of these diets lower carbohydrate intake to the point of inducing a shift in metabolism. Low-carbohydrate diets have gained popularity even though The reduced carbohydrate availability stimulates lipolysis, research regarding the metabolic effects of these diets is just producing fatty acids and ketone bodies for use as alternative fuel sources. Nearly all cell types in the human body can use Correspondence: Dr WS Yancy Jr, HSR&D (152), Durham VA Medical Center, these alternative fuels although some (e.g., myocardium) 508 Fulton Street, Durham, NC 27705, USA. prefer fatty acids, whereas others (e.g., brain) can only use E-mail: [email protected] ketone bodies. Ketone bodies are detectable in the serum, Guarantor: WS Yancy Jr. urine, and breath (Azar and Bloom, 1963; Young et al., 1971; Contributors: WSY conceived, designed and coordinated the study; partici- pated in data collection; performed statistical analysis and drafted the paper. Rabast and Kasper, 1978; Rabast et al., 1981), and in fact, MKO and TD performed statistical analysis. ECW conceived and designed the urine and breath ketone body tests are sometimes used to study, provided personnel and funding for laboratory tests and facilitated monitor for adequate carbohydrate restriction by low- recruitment of participants. All authors assisted with interpretation of the data carbohydrate diet followers (Larosa et al., 1980). and contributed to the intellectual content of and approved the final paper. Received 31 May 2006; revised 12 December 2006; accepted 18 December Ketone bodies have an acidic pK and are best known 2006; published online 14 February 2007 for causing ketoacidosis, a serious condition that can cause Diet-acid-base WS Yancy Jr et al 1417 acidemia in diabetic and alcoholic patients. Acidemia is said Intervention to exist when the arterial blood pH is below normal (normal LCKD group. Using handouts based on a popular lay press range is 7.35–7.45 at our facility) (Seifter, 2004). An acidosis is diet book (Atkins, 1998), the investigators instructed parti- the individual process that drives the blood pH downward, cipants to restrict carbohydrate intake, initially to less than although because multiple processes may coexist, an abnormal 20 g of carbohydrate per day. Participants were permitted pH is not required for there to be an acid-base disturbance. unlimited amounts of meat and eggs, and limited amounts Metabolic acidosis occurs when the primary acid-base disorder of hard cheese and vegetables each day (Yancy et al., 2004). is a decrease in serum bicarbonate concentration; this As participants approached their goal weight, they were frequently occurs when bicarbonate is needed to compensate advised to add approximately 5 g of carbohydrates to their for (buffer) acid metabolites (Seifter, 2004). Ketosis, therefore, daily intake each week until they reached a level where is a type of metabolic acidosis and is a condition characterized weight was maintained. The LCKD group also received daily by the enhanced production of ketone bodies, whereas nutritional supplements (multivitamin, essential oils, diet ketonemia is the presence of recognizable concentrations of formulation and chromium picolinate, see Appendix). ketone bodies in the plasma (Hensyl, 1990). Individuals following low-carbohydrate diets that restrict LFD group. Using a commonly available booklet and carbohydrate intake to a level that induces ketogenesis (low- additional handouts, a registered dietician instructed parti- carbohydrate ketogenic diet or LCKD) apparently experience cipants in a diet that had o30% of daily energy intake from ketonemia without illness or known complication. It is fat, o10% of daily energy intake from saturated fat and assumed that the ketonemia induced by these diets is o300 mg cholesterol daily (Anonymous, 1994, 2000). Indivi- tolerated, based on those research studies that have mea- duals were instructed to reduce energy intake by subtracting sured ketone body production (Phinney et al., 1983; Langfort 500–1000 kcal from their calculated weight-maintenance et al., 1996; Volek et al., 2002; Brehm et al., 2003, 2005; energy intake (body weight in lbs Â 10) (Duyff, 1998). Meckling et al., 2004; Yancy et al., 2004; Boden et al., 2005). It is not known, however, if actual acidemia develops. After a Both diet groups. Participants were regularly advised to drink literature search, we were unable to find any studies that at least 6–8 glasses of water or other clear fluids daily. In reported the detailed acid-base effects of these particular addition, participants were encouraged to exercise for 30 min diets (Westman, 1999; Volek et al., 2002; Brehm et al., 2003, at least three times per week, but no formal exercise program 2005; Meckling et al., 2004; Yancy et al., 2004; Boden et al., or incentives were provided. 2005). None of the studies provided arterial blood gas (ABG) analysis results or even full electrolyte panels in order to Primary outcome measures calculate an anion gap, which can be used as an indicator of All measurements were collected at weeks 0, 2, 8, and 24 metabolic acidosis. In light of recent case reports of during regularly scheduled group meetings. ABG analysis ketoacidosis associated with low-carbohydrate diets, this provided the main outcome, serum pH. Arterial puncture information is needed to judge the safety of such diets (Chen was performed in the standard manner at the radial artery et al., 2006; Shah and Isley, 2006). using a heparinized syringe after a modified Allen’s test was The purpose of this study was to use ABG and serum noted to be normal. The arterial blood specimen was chemistry measurements to examine the acid-base status of immediately placed on ice and transported to the laboratory individuals following two weight loss diets, one of which was within 1 h for analysis by a Bayer 855 blood gas analyzer. an LCKD, on an outpatient basis for 6 months. The blood specimen for serum sodium, potassium, chloride, bicarbonate, urea nitrogen, creatinine and glucose was Methods placed in a serum separator tube and remained at room temperature until analysis by a Beckman LX20 analyzer. The Participants anion gap was calculated from serum electrolyte measure- At the initial visit (before starting the diet intervention) for ments in the following manner: anion gap ¼ sodium chlor- each group in a randomized, controlled trial comparing the ide – measured bicarbonate. The blood specimen for serum LCKD with a low-fat diet (LFD) in individuals with ketone bodies came from the serum separator tube and was hyperlipidemia (Yancy et al., 2004) and in a single-arm pilot analyzed by a Bayer Acetest analyzer (sodium nitroprusside study of the LCKD in individuals without hyperlipidemia, reagent, which tests for acetone and acetoacetate) with participants were asked to volunteer for this ancillary study the following ordinal 5-item scale: none, trace (up to that required extra blood specimens (arterial and venous) to 20 mg/dl), small (20 mg/dl), moderate (30–40 mg/dl), or large be taken at return visits. Exclusion criteria were an abnormal (80–100 mg/dl). Urine ketone bodies were analyzed by the modified Allen’s test or any established peripheral vascular same reagent with the following ordinal six-item scale: none, disease, arterial anomaly, skin abnormality, bleeding dia- trace (up to 5 mg/dl), small (5–40 mg/dl), moderate thesis or anticoagulant medication that precluded arterial (40–80 mg/dl), large80 (80–160 mg/dl), and large160 puncture. Each volunteer provided written informed consent (4160 mg/dl). Urine or serum ketone body level was approved by the institutional review board. considered elevated if above ‘none.’ The blood specimen

European Journal of Clinical Nutrition Diet-acid-base WS Yancy Jr et al 1418 for serum lactate was obtained in a sodium fluoride arterial blood sample could not be obtained, resulting in 27 (stabilizer)/potassium oxalate (anticoagulant) tube and kept participants in the LCKD group. There were no statistically on ice until analysis by a Beckman LX 20 analyzer. In this significant differences in baseline characteristics between assay, lactate is converted into pyruvate and hydrogen diet groups (Table 1). The mean age was approximately 43 peroxide by lactate oxidase, followed by a peroxidase years; the majority of participants were women and of white indicator reaction. race. The mean body mass index (BMI) was 36 kg/m2. In both diet groups, participants who completed follow-up appeared to be older, more likely to be male, and more likely to be of Statistical analysis white race compared with those who did not complete Linear mixed-effects models (PROC MIXED in SAS) including follow-up but these differences did not reach statistical fixed and random effects were used to analyze the effect of significance (Table 1). the diet group assignment on weight loss and each of the laboratory measurements. Linear mixed-effects models are a flexible class of models that can be used to analyze expected Body weight mean change over time, making efficient use of all available By mixed model analysis, using data from all participants, measurements (Cnaan et al., 1997). The random effects part including those who discontinued the study, the mean of the model takes into account the natural heterogeneity of weight change was À16.3 kg for the LCKD group and À6.4 kg the subjects as well as the lack of independence that occurs for the LFD group (Po0.001 for comparison). in repeated measurements from a single subject. Further- more, in these models, we used an unstructured covariance matrix for the repeated measurements (i.e., no function of Laboratory measurements time). This type of structure allows for unequal correlations Using a mixed-model analysis to examine blood test changes between consecutive time points, making it more ideal (than over the 24-week duration, the LFD group experienced a an ANOVA-type model) for unequally spaced time points. statistically significant change only in arterial blood pH from The fixed effects included in the models were duration of a mean of 7.43 at week 0 to 7.40 at week 24 (P ¼ 0.03, see intervention (i.e., week of visit, treated as a class variable), Table 2). In the LCKD group, mean arterial blood pH diet group, and the interaction between week of visit and decreased from 7.42 at week 0 to 7.40 at week 24 diet group. The correlation between serum pH and the (P ¼ 0.01). Combining measurements at all time points for concentration of serum ketone bodies was examined using both diet groups, arterial blood pH ranged from 7.34 to 7.48 Spearman’s rank order correlation coefficient for ordinal with seven of 126 (five of 88 from LCKD group) measure- data. A P-value of o 0.05 was considered statistically ments less than 7.38. No individual in the LCKD group had a significant. Analyses were performed using SAS Statistical measurement below 7.37 at any time point (Figure 1a and b). Software, Version 8.02. (SAS Institute, Cary, NC, USA) and In the LCKD group, there were statistically significant, but S-Plus 7 (Insightful Corp., Seattle, WA, USA). clinically insignificant, decreases in serum sodium, potassium, and chloride over the 24 weeks (P ¼ 0.002, 0.01 and 0.04, respectively). Serum bicarbonate did not change Results significantly over the 24 weeks in either diet group. For both diet groups, bicarbonate levels ranged from 18.5– Participants 32.0 mmol/l with four of 131 (two of 92 from LCKD group) Forty participants volunteered for the study, 28 from the measurements less than 22 mmol/l. The calculated anion gap LCKD group and 12 from the LFD group. One participant also did not change significantly from week 0 to week 24. In from the LCKD group was not enrolled because baseline both diet groups, anion gap ranged from 3.4 to 16.0 with

Table 1 Baseline characteristics

Characteristic Low carbohydrate diet group Low fat diet group

Enrollees (n ¼ 27) Completers (n ¼ 21) Non-completers (n ¼ 6) Enrollees (n ¼ 12) Completers (n ¼ 7) Non-completers (n ¼ 5)

Age, years, mean (s.d.) 43.8 (10.2) 45.2 (9.8) 38.7 (10.8) 42.8 (7.3) 44.4 (7.1) 40.6 (7.7) Gender, female 70% 67% 83% 75% 57% 100% Race, White 74% 81% 50% 75% 86% 60% Weight, kg, mean (s.d.) 103.3 (13.8) 102.1 (14.0) 107.4 (13.6) 99.6 (18.9) 100.1 (19.1) 98.9 (20.8) BMI, kg/m2, mean (s.d.) 36.0 (4.9) 35.6 (5.0) 37.1 (4.6) 36.0 (5.7) 35.2 (6.0) 37.2 (5.8)

Abbreviations: BMI, body mass index; s.d., standard deviation. There were no statistically significant differences in baseline characteristics between diet groups, or between completers vs non-completers.

European Journal of Clinical Nutrition Diet-acid-base WS Yancy Jr et al 1419 b a Low Carbohydrate Diet Group value mg/dl. P 0.6 ¼ w a 7.45 0.9 (0.8) 0.5 1.4 (0.8) 0.8 6.1 (3.6) 0.6 0.03 (0.010) 0.02 (0.09) 0.2 0.21 (0.18)0.71 (0.55) 0.7 0.008 0.18 (0.23) 0.8 À À À À À À À À

7.40 pH 12)

¼ 7.35 n

mg/dl; divide glucose (mmol/l) by 0.0555 0 2 8 24 ¼ Time in Weeks

b Low Fat Diet Group mol/l) by 76.26 m

7.45 Week 0 Week 2 Week 8 Week 24 Change

7.43 (0.006) 7.42 (0.007) 7.42 (0.005)4.09 7.40 (0.11) (0.009) 4.09 (0.10) 4.17 (0.13) 4.08 (0.08) 1.13 (0.16) 1.01 (0.10) 1.10 (0.08) 0.93 (0.09) 7.40 pH 137.0 (0.5) 136.8 (0.5)102.9 (0.7) 136.9 (0.5) 101.7 (0.8) 136.1 (0.6) 103.6 (0.7) 101.5 (0.6) w w w w w a mg/dl; divide creatinine ( ¼

7.35 0.8 (0.5) 7.0 (0.7) 7.5 (0.7) 7.1 (0.7) 7.2 (0.7) 0.2 (0.9) 0.3 1.1 (0.5) 3.8 (2.1) 66.4 (3.3) 60.3 (4.0) 64.1 (4.1) 60.3 (4.4) 1.6 (0.5) 0.16 (0.06) 0.29 (0.12) 0.17 (0.15) 5.32 (0.17) 5.05 (0.13) 4.85 (0.12) 5.22 (0.16) 0.02 (0.007) À À À À À À À À 0 2 8 24 Time in Weeks Figure 1 (a–b). Individual arterial blood pH measurements over time by diet group. 27) LFD ( ¼ n sevenof 131 (seven of 92 from LCKD group) measurements greater than 11. In the LCKD group, serum lactate decreased over the 24 weeks from a mean of 1.23 to 0.94 mmol/l (P ¼ 0.02), whereas urea nitrogen increased from a mean of kPa.

¼ 5.11 to 6.21 mmol/l (P ¼ 0.002); serum creatinine did not change significantly. In comparisons between diet groups, the 24-week change in blood urea nitrogen in the LCKD group was statistically different from that of the LFD group (1.11 vs –0.71 mmol/l, P ¼ 0.008). There were no other

Week 0 Week 2 Week 8 Week 24 Change statistically significant differences between groups (Table 2). (mm Hg) by 0.1333 27.2 (0.6) 25.7 (0.4) 25.7 (0.5) 27.5 (0.4) 0.3 (0.5) 27.1 (0.8) 27.1 (0.7) 26.1 (0.7) 27.5 (0.6) 0.4 (0.8) 0.9 5.11 (0.29) 5.96 (0.24) 5.93 (0.29) 6.21 (0.33) 1.11 (0.33) 5.64 (0.43) 4.86 (0.39) 4.57 (0.42) 4.89 (0.56)

2 Urine and serum ketone body measurements for each time

CO point by diet group are displayed in Table 3. At week 0, most p participants in both diet groups had negative urine and serum ketone body measurements. Urine and serum ketone body measurements remained negative for almost all LFD , multiply 2

mol/l (46–107) 64.8 (2.2) 70.2 (2.7) 68.6 (2.8) 61.0 (2.8) group participants throughout follow-up. For the LCKD CO m p Mean (standard error) ABG and chemistry measurements at each timepoint group, most participants had ketone bodies detectable in the urine at weeks 2, 8, and 24, although the percentage , mm Hg (35–45) 37.9 (0.6) 36.5 (0.6) 37.1 (0.5) 38.3 (0.7) 0.4 (0.7) 38.9 (0.9) 38.1 (0.9) 38.8 (0.8) 39.2 (1.1) 0.3 (1.1) 0.9 2 0.05.

value in final column is for the comparison between groups of the changes by linear mixed-model analysis. decreased over time. The majority of LCKD participants also o CO P- Change is the mean change within group fromP week 0 to week 24 by linear mixed-model analysis. p Potassium, mmol/l (3.5–5.4) 4.23 (0.07)Measured bicarbonate, mmol/l 4.06 (22–32) (0.06)Anion gap 4.06 (0.09) 4.07 (0.05) 7.9 (0.4) 7.5 (0.4) 9.6 (0.5) 7.1 (0.5) Chloride, mmol/l (101–111) 103.1 (0.4) 102.4 (0.5) 101.9 (0.5)Urea nitrogen, mmol/l 102.0(2.9–8.2) (0.3) Creatinine, Lactate, mmol/l (0.5–2.2) 1.23 (0.10) 0.90 (0.07) 0.95 (0.06) 0.94 (0.05) To convert Glucose, mmol/l (3.6–6.1) 4.84 (0.12) 4.54 (0.08) 4.59 (0.09) 4.67 (0.10) To convert from System International (SI) into conventional units, divide urea nitrogen (mmol/l) by 0.357 Table 2 Measurement (normal range)pH (7.35–7.45) 7.42 (0.004) 7.40 (0.005) 7.41 LCKD (0.004) ( 7.40 (0.006) Abbreviations: ABG, arteriala blood gas; LCKD, low-carbohydrate,b ketogenic diet; LFD,w low-fat diet. Sodium, mmol/l (134–144) 138.2 (0.4) 135.7 (0.3) 137.1 (0.3) 136.7 (0.4) had ketone bodies detectable in the serum at weeks 2 and 8,

European Journal of Clinical Nutrition Diet-acid-base WS Yancy Jr et al 1420 Table 3 Urine and serum ketone measurements at each timepoint

Urine ketones (%) LCKD LFD

Week 0 Week 2 Week 8 Week 24 Week 0 Week 2 Week 8 Week 24 (n ¼ 26) (n ¼ 22) (n ¼ 22) (n ¼ 21) (n ¼ 12) (n ¼ 11) (n ¼ 11) (n ¼ 7)

None 73a 01443759173100 Trace (up to 5 mg/dl) 23 0 23 33 25 9 27 0 Small (5–40 mg/dl), 4 14 18 0 0 0 0 0 Moderate (40–80 mg/dl) 0 45 14 14 0 0 0 0 Large80 (80–160 mg/dl) 0 23 18 5 0 0 0 0 Large160 (4160 mg/dl) 0 18 14 5 0 0 0 0

Serum ketones (%) Week 0 Week 2 Week 8 Week 24 Week 0 Week 2 Week 8 Week 24 (n ¼ 27) (n ¼ 22) (n ¼ 22) (n ¼ 21) (n ¼ 12) (n ¼ 9) (n ¼ 11) (n ¼ 7) None 100 36 27 86 100 100 91 100 Trace (up to 20 mg/dl) 0 5 50 5 0 0 9 0 Small (20 mg/dl) 0 41 23 5 0 0 0 0 Moderate (30-40 mg/dl) 0 18 0 5 0 0 0 0 Large (80–100 mg/dl) 0 0 0 0 0 0 0 0

Abbreviations; LCKD, low-carbohydrate, ketogenic diet; LFD, low fat diet. aEach cell contains the percentage of individuals in one diet group with measurements performed at one timepoint who had the specified ketone reading. Columns might not add exactly to 100% due to rounding.

but by week 24, the proportion of LCKD participants with ketonemia by measurement of serum b-hydroxybutyrate in ketone bodies detectable in the serum had decreased to 15%. subjects following a low-carbohydrate diet (Azar and Bloom, The serum pH did not correlate with the concentration of 1963; Young et al., 1971; Rabast and Kasper, 1978; Rabast serum ketone bodies in either diet group (LCKD: r ¼À0.197, et al., 1981; Volek et al., 2002; Brehm et al., 2003, 2005; P ¼ 0.07; LFD: r ¼À0.206, P ¼ 0.2) (Figure 2a and b). Meckling et al., 2004; Yancy et al., 2004; Boden et al., 2005). Furthermore, some data suggest an inverse relationship such that urinary ketone body levels increase as carbohydrate Discussion intake decreases (Young et al., 1971). However, the data also show significant subject to subject variability in urinary In this study, there was a statistically significant, yet ketone body response even when subjects are provided clinically small, decrease in mean serum pH for followers strictly uniform diets (Azar and Bloom, 1963). Most of the of either an LCKD or an LFD. No individual on the LCKD had recent studies of the LCKD note that the level of ketosis a serum pH measurement below 7.37, with the lower limit of decreases with time; (Volek et al., 2002; Brehm et al., 2003, normal range being 7.35. Despite previous case reports of 2005; Meckling et al., 2004; Yancy et al., 2004; Boden et al., acid-base disturbance in two individuals following similar 2005) this effect occurs in studies of both short (14 days) diets, we did not observe this disturbance in our sample of (Boden et al., 2005) and longer (6 months) (Brehm et al., participants (Shah and Isley, 2006; Chen et al., 2006). In the 2003; Yancy et al., 2004) duration. It is unclear whether this LCKD group, mean serum bicarbonate decreased and mean effect is a result of the body’s increased efficiency over time anion gap increased early in the study but then returned to at utilizing ketone bodies for energy or a decrease in the baseline, indicating that a compensated metabolic acidosis production of ketone bodies over time, presumably from may occur soon after initiation of an LCKD. Accordingly, the adding carbohydrates back into the diet. However, one proportion of LCKD participants with elevated urine and inpatient study that closely controlled carbohydrate intake serum ketone body levels was highest early in the study and at 21 g daily also observed this effect over 2 weeks of daily decreased over time. Regardless of duration on the diet, the urine ketone body measurements, suggesting that the former serum pH did not appear to be related to the concentration hypothesis at least plays a role (Boden et al., 2005). Notably, of serum ketone bodies. This likely reflects that the buffering the present study allowed the LCKD dieters to restrict capacity of the body can accommodate the relatively low carbohydrate intake to the typical level of ketogenesis longer concentrations of ketone bodies (as compared with diabetic than what is recommended in several popular lay-press diet or alcoholic ketoacidosis) that have been observed in books, which employ this restrictive phase for only the first 2 individuals following an LCKD. weeks of the weight loss process. As ketosis is a goal in the most restrictive low-carbohydrate Comparing laboratory changes between diet groups, there diets, some low-carbohydrate diet followers use urinary was a statistically significant increase in blood urea nitrogen ketone strips to verify sufficient carbohydrate reduction. in the LCKD group, but not the LFD group. This effect has Several studies have confirmed ketonuria by urine dipstick or been reported in other studies of the LCKD and may result

European Journal of Clinical Nutrition Diet-acid-base WS Yancy Jr et al 1421 a Low Carbohydrate Diet Group These changes occurred in conjunction with a mild ketosis. These data suggest that an LCKD induces a mild compensated metabolic acidosis. However, none of the individuals displayed evidence of a significant metabolic 7.45 derangement.

7.40 pH Acknowledgements

The authors thank Keith Tomlin, Bill Bryson, and Juanita Hepburn for assistance with data collection. Dr Yancy is 7.35 supported by Health Services Research Career Development Award RCD 02-183-1 from the Department of Veterans 0 up to 20 20 30-40 80-100 Affairs, Washington, DC, USA Serum Ketones (mg/dL) b Low Fat Diet Group References

Anonymous (2000). The practical guide: identification, evaluation and 7.45 treatment of overweight and obesity in adults. National Institutes of Health, National Heart, Lung, and Blood Institute, North American Association for the Study of Obesity, U.S. Department of Health and Human Services. Public Health Service: Bethesda, MD. Anonymous (1994). Step by step. Eating to lower your high blood 7.40 pH cholesterol. American Heart Association, U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health. National Heart, Lung, and Blood Institute: Bethesda, MD. Atkins RC (1998). Dr. Atkins’ New Diet Revolution. Simon & Schuster: 7.35 New York! Azar GJ, Bloom WL (1963). Similarities of carbohydrate deficiency 0 up to 20 20 30-40 80-100 and fasting. II. Ketones, nonesterified fatty acids, and nitrogen excretion. Arch Intern Med 112, 338–343. Serum Ketones (mg/dL) Boden G, Sargrad K, Homko C, Mozzoli M, Stein TP (2005). Effect of a Figure 2 (a–b). Correlation between arterial blood pH measure- low-carbohydrate diet on appetite, blood glucose levels, and ments and serum ketone bodies by diet group. The serum pH did insulin resistance in obese patients with type 2 diabetes. Ann not correlate with the concentration of serum ketone bodies in either Intern Med 142, 403–411. diet group (LCKD: r ¼À0.197, P ¼ 0.07; LFD: r ¼À0.206, P ¼ 0.2). Brehm BJ, Spang SE, Lattin BL, Seeley RJ, Daniels SR, D’Alessio DA (2005). The role of energy expenditure in the differential weight loss in obese women on low-fat and low-carbohydrate diets. J Clin from an increase in dietary protein or a decrease in Endocrinol Metab 90, 1475–1482. Brehm BJ, Seeley RJ, Daniels SR, D’Alessio DA (2003). A randomized intravascular volume. Another interesting finding that trial comparing a very low carbohydrate diet and a calorie- occurred in the LCKD group only was a statistically restricted low fat diet on body weight and cardiovascular significant reduction in lactate. This is consistent with a risk factors in healthy women. J Clin Endocrinol Metab 88, presumed overall shift from glycolysis (anaerobic, lactate- 1617–1623. Chen TY, Smith W, Rosenstock JL, Lessnau KD (2006). A life- producing) to fat metabolism (aerobic). threatening complication of Atkins diet. Lancet 367, 958. One limitation of our study is that the small sample size Cnaan A, Laird NM, Slasor P (1997). Tutorial in biostatistics: using might explain the lack of significant changes observed in the the general linear mixed model to analyse unbalanced repeated LFD within-group analyses and in comparisons between the measures and longitudinal data. Stat Med 16, 2349–2380. Duyff RL (1998). The American Dietetic Association’s Complete Food and two diet groups. Additionally, because this was an outpatient Nutrition Guide. Chronimed Pub: Minneapolis, MN. diet intervention, dietary intake was not explicitly con- Hensyl WR (ed). (1990). Stedman’s Medical Dictionary. Williams and trolled and measurements were made infrequently. More Wilkins: Baltimore. accurate assessment of how much and when carbohydrate Langfort J, Pilis W, Zarzeczny R, Nazar K, Kaciuba-Uscitko H (1996). restriction affects acid-base status might be obtained from an Effect of low-carbohydrate-ketogenic diet on metabolic and hormonal responses to graded exercise in men. J Physiol Pharmacol inpatient study. However, our study more likely represents 47, 361–371. these effects in a more real-world setting. Larosa JC, Fry AG, Muesing R, Rosing DR (1980). Effects of high- In conclusion, in individuals following an LCKD or an LFD protein, low-carbohydrate dieting on plasma lipoproteins and body weight. J Am Diet Assoc 77, 264–270. for 24 weeks, mean blood pH decreased slightly with a mild Meckling KA, O’Sullivan C, Saari D (2004). Comparison of a low-fat transient decrease in serum bicarbonate and a mild transient diet to a low-carbohydrate diet on weight loss, body composition, increase in anion gap observed only in the LCKD group. and risk factors for diabetes and cardiovascular disease in free-

European Journal of Clinical Nutrition Diet-acid-base WS Yancy Jr et al 1422 living, overweight men and women. J Clin Endocrinol Metab 89, Shah P, Isley WL (2006). Ketoacidosis during a low-carbohydrate diet. 2717–2723. N Engl J Med 354, 97–98. Phinney SD, Bistrian BR, Wolfe RR, Blackburn GL (1983). The human Volek JS, Sharman MJ, Love DM, Avery NG, Gomez AL, Scheett TP metabolic response to chronic ketosis without caloric restriction: et al. (2002). Body composition and hormonal responses to a physical and biochemical adaptation. Metabolism 32, 757–768. carbohydrate-restricted diet. Metabolism 51, 864–870. Rabast U, Kasper H, Schonborn J (1978). Comparative studies in Westman EC (1999). A review of very low carbohydrate diets. obese subjects fed carbohydrate-restricted and high carbohydrate J Clinical Outcomes Management 6, 36–40. 1,000-calorie formula diets. Nutr Metab 22, 269–277. Yancy Jr WS, Olsen MK, Guyton JR, Bakst RP, Westman EC (2004). A Rabast U, Vornberger KH, Ehl M (1981). Loss of weight, sodium and low-carbohydrate, ketogenic diet versus a low-fat diet to treat water in obese persons consuming a high- or low-carbohydrate obesity and hyperlipidemia: a randomized, controlled trial. Ann diet. Ann Nutr Metab 25, 341–349. Intern Med 140, 769–777. Seifter JL (2004). Acid-base disorders. In: Goldman L, Ausiello DA Young CM, Scanlan SS, Im HS, Lutwak L (1971). Effect of body (eds). Cecil Textbook of Medicine 22nd edn W.B. Saunders: composition and other parameters in obese young men of Philadelphia. pp 688–695. carbohydrate level of reduction diet. Am J Clin Nutr 24, 290–296.

Appendix (2 mg), grape seed extract (40 mg), green tea (80 mg). Nutritional supplement ingredients (Atkins nutritionals, Inc.) Unspecified amounts of lecithin extracts, garlic, arginine, Multivitamin formula (administered per day in 6 capsules): licorice, bromelain, pantethine, spirulina, inulin, lactoferrin, Vitamin A as acetate (3000 IU), vitamin A as b-carotene bioperine, and acidophilus. w/mixed carotenoids (1200 IU), vitamin C (360 mg), vitamin Essential oil formula (administered per day in 3 capsules): D-3 (400 IU), vitamin E (300 IU), vitamin B1 (50 mg), flaxseed oil (1200 mg), borage seed oil (1200 mg), fish oil

vitamin B2 (50 mg), niacin (40 mg), vitamin B6 (50 mg), (1200 mg), vitamin E (15 IU). folate (1600 mg), vitamin B12 (800 mcg), vitamin K (10 mcg), Diet formula (administered per day in 6 capsules): Citrin biotin (600 mcg), pantothenic acid (120 mg), calcium (2700 mg), chromium (1200 mcg), soy extract (9000 mg),

(500 mg), magnesium (250 mg), zinc (50 mg), selenium methionine (1500 mg), L-carnitine (3000 mg), vitamin B6 (200 mcg), manganese (10 mg), chromium (600 mcg), (120 mg), pantethine (120 mg), asparagus (300 mg), parsley molybdenum (60 mcg), potassium (20 mg), inositol hexani- (300 mg), kelp (120 mg), spirulina (300 mg), potassium cotinate (100 mg), choline bitartrate (100 mg), para-amino citrate (594 mg), magnesium (360 mg), L-glutamine benzoic acid (100 mg), vanadyl (80 mcg), n-acetyl-l-cysteine (450 mg), Dl-phenylalanine (900 mg), L-tyrosine (450 mg), (120 mg), pantethine (150 mg), quercetin (100 mg), boron piperine (30 mg).

European Journal of Clinical Nutrition