Introduction
Roux-en-Y gastric bypass (RYGB) is a commonly performed bariatric procedure. In the USA alone, more than 50,000 RYGBs are performed each year, i.e., approximately 45% of all bariatric procedures [
1]. RYGB is even more widely used in the Nordic countries and presently accounts for 82% of all bariatric surgery in the Scandinavian Obesity Registry, SOReg, [
2]. Gastric bypass leads to profound changes in eating behavior and metabolism, in turn leading to dramatic weight reduction and often the disappearance of obesity-related comorbidities [
3]. Although these effects lead to increased life expectancy and improved quality of life, the operation has also been reported to have side effects [
4,
5]. RYGB has been reported to cause more rapid and enhanced absorption of alcohol resulting in a faster rise and higher peak blood alcohol concentrations [
6‐
8]. In a retrospective population-based cohort study, Östlund et al. found that gastric bypass patients postoperatively used more inpatient care for alcohol-related disease compared with patients operated with gastric band or vertical banded gastroplasty [
9]. In another prospective cohort study of RYGB patients, the presence of alcohol use disorders increased in the second postoperative year compared to the year prior to surgery [
10].
So far, alcohol consumption in bariatric patients has been assessed with different questionnaires, e.g., the Alcohol Use Disorders Identification Test (AUDIT) [
11]. Since self-reported alcohol consumption can be biased, an alternative approach would be to assess alcohol consumption with a specific alcohol marker, e.g., phosphatidylethanol (PEth). PEth is a collective term for a group of abnormal phospholipid homologs, the most prevalent being PEth 16:0/18:1, formed in the membranes of erythrocytes only in the presence of ethanol [
12]. Being an alcohol metabolite, the theoretical specificity of PEth as an alcohol marker is 100% [
12]. There is a correlation between alcohol consumed and PEth value [
13,
14]. PEth has a half-life of approximately 1 week, thus reflecting alcohol consumption during several weeks before sampling [
15,
16].
The present study was designed to examine alcohol consumption level in obese patients selected for RYGB and investigate whether gastric bypass induces a change in consumption level as estimated with a specific and sensitive alcohol marker.
Results
All operations were performed according to standard protocols. There were no major complications and postoperative hospital time was 1.1 days. Patient anthropometric and weight loss data for both groups are shown in Table
1. There were statistical differences between the groups according to gender, age, anthropometric, and weight loss data, but not in PEth results neither at baseline (
p = 0.53) nor at 1-year FU (
p = 0.41).
Table 1
Anthropometric and weight loss data for groups 1 and 2. In group 1, PEth result was blinded for the surgeon and the patient and in group 2, increased PEth result preoperatively lead to special counseling
Gender, female n (%) | 84 (64) | 175 (82) | 160 (50) | < 0.000 | p = 0.005/p < 0.000 |
Age (years) mean (SD) | 47 (8.9) | 42 (11) | 40 (14) | < 0.000 | p < 0.000/p = 0.335 |
BMI at baseline (kg/m2) mean (SD) | 43 (6.3) | 42 (5.7) | | 0.036 | |
BW at baseline (kg) mean (SD) | 127 (22) | 119 (21) | | 0.001 | |
BW at FU1y (kg) mean (SD) | 93 (17) | 80 (16)2 | | < 0.000 | |
BW loss first year (kg) mean (SD) | 34 (14) | 39 (12)2 | | < 0.000 | |
%EWL first year mean (SD) | 66 (22) | 85 (22)2 | | < 0.000 | |
Discussion
The obesity epidemic has made RYGB common since bariatric surgery is the only treatment achieving long-term weight reduction [
21]. Considering the large number of patients operated, it is important to address possible drawbacks with the surgical procedure, e.g., altered alcohol metabolism and increased risk for alcohol use disorders.
Since self-reported alcohol consumption can be unreliable, there is a need for methods that can provide objective information about patients´ alcohol use [
22‐
24]. PEth is an alcohol marker with high sensitivity in groups with excessive alcohol consumption (96–100%) [
13,
14,
25]. The clinical sensitivity has been more varied in groups with low or moderate alcohol consumption, largely due to differences in sensitivity between analytical methods [
14,
16,
26,
27]
. Hence, it has been reported that PEth can be used as a marker for low or moderate alcohol consumption using a method with improved analytical sensitivity [
28]. In the present study, we used PEth as an objective marker of alcohol consumption level and of potential changes in its level after RYGB.
There is a correlation between PEth and alcohol consumption level, PEth likely reflecting the exposition to alcohol over time, i.e., average blood alcohol concentration during several weeks before sampling [
13,
14]. However, in addition to the amount of alcohol consumed, body mass also influences blood alcohol concentration as indicated in the Widmark’s formula [
29].Weight loss will lead to a reduction not only in adipose tissue but also in total body water, which was shown in a study on six obese women treated with bariatric surgery [
30]. The weight development curves for our two patient groups show drastic reductions in body weight suggesting corresponding reductions in total body water as well. PEth values showed a significant increase between baseline and 1-year FU in group 2. Although not statistically significant (
p = 0.068), a similar tendency between baseline and 1-year FU was seen in group 1 (Fig.
1). Since ethanol is distributed in total body water, the same amount of ethanol consumed will result in higher blood ethanol concentrations postoperatively and consequently to increased PEth values
. The increased PEth results at 1-year FU can thus be due to the decrease in total body water and does not necessarily need to be a consequence of increased alcohol consumption. The weight reduction at 1-year FU was more pronounced in group 2 compared with group 1 (Table
1). This may at least partly explain the significant increase in PEth values at 1-year FU seen in group 2 but not in group 1.
In group 1, there is a significant increase in PEth results at 2-year FU, which is in line with King et al., where the alcohol consumption increased at the 2-year FU according to AUDIT [
10]. Weight data for our 2-year FU are not available, but other studies show that weight reduction has ceased already at 1-year FU [
4]. The results in group 1 suffer from 28% drop-out rate. The drop-outs had significantly higher PEth results at 1-year FU compared to the patients with complete FU (Table
3), so it is possible that the frequency of PEth ≥ 0.05 μmol/L at 2-year FU would have been higher if more patients had completed the study. Hence, this may indicate an increase in alcohol consumption between 1 and 2 years postoperatively. Nonetheless, neither patient group reached the PEth values obtained in the reference group of healthy blood donors.
It seems reasonable that further changes postoperatively can contribute to increased blood alcohol concentrations, resulting in higher PEth despite unaltered alcohol intake. Gastric emptying of liquid seems to be faster after RYGB resulting in a faster absorption of alcohol [
31]. In two different studies, RYGB patients were their own controls and were given the same dose of alcohol pre- and postoperatively. Increased peak alcohol level and longer time to reach zero concentration were seen postoperatively compared to preoperatively [
7,
8]. Another possible mechanism that can contribute to an increased alcohol exposure is the decreased contact with gastric mucosa and thereby to the action of gastric alcohol dehydrogenase after RYGB. In a study on patients after total gastrectomy compared with controls, gastric alcohol dehydrogenase proved to be responsible for a significant part of the first pass metabolism of alcohol [
32].
Almost half of the blood donors in the reference group had PEth results ≥ 0.05 μmol/L. In the study by Kechagias et al., study participants consumed 1 or 2 glasses of wine/day for 3 months. This consumption corresponds to 1.3 or 2.7 alcohol units/day (one unit = 12 g alcohol) and resulted in a median PEth concentration of 0.022 μmol/L after 3 months [
28]. Moderate alcohol consumption is defined slightly different in different countries. In the USA, the upper limit for moderate drinking is one drink (one drink = 14 g alcohol) per day for women and up to two drinks per day for men, while in Sweden, the corresponding limits are 9 and 14 units (12 g/unit) per week [
33,
34]. This indicates that a significant proportion of the blood donors in the reference group consumed more than moderate amounts of alcohol.
It seems plausible that the weight of the blood donors reflects the “normal” weight in the Swedish population. The prevalence of BMI > 30 is estimated to be 15% in Sweden [
35]. Most likely, there is a difference in body weight and total body water content between the patients and the reference group, probably less pronounced at FU as a consequence of the weight reduction. The proportion of PEth results ≥ 0.05 μmol/L is at all time points lower in the patient groups compared with the reference group (Fig.
1). This must not necessarily mean that the patient groups have a lower absolute alcohol intake than the reference group, but rather that their average blood alcohol concentrations were lower.
There was no significant difference in the proportion of PEth ≥ 0.05 μmol/L between groups 1 and 2 neither at baseline nor at the 1-year FU. It is not possible to evaluate whether the preoperative information on PEth in group 2 influenced the outcome.
There are some shortcomings of the present study such as the high drop-out rate and missing body weights at 2-year FU in group 1. Measurement of total body water pre- and postoperatively in the patient groups as well as in the reference group would have been of interest for the interpretation of PEth results. Another point of concern is the FU time; long-term follow-up is advantageous to fully elucidate patterns of alcohol intake after RYGB. However, the fact that we used an objective marker for assessment of alcohol intake provides support for the reliability of our results.