Study design, population and setting:
This was a single-center, retrospective cohort study, conducted in accordance with Strengthening The Reporting of Observational Studies in Epidemiology (STROBE) guidelines [28]. The study population included bariatric patients who were referred to our milk-based meal replacement programme. During the programme, patients attended the bariatric clinic every two weeks for 24 weeks (14 visits in total), met the nurse, dietitian and physician at each visit, had blood tests performed and had weight, height and blood pressure measurements taken. All baseline and follow-up measures for the programme were conducted in the Bariatric Medicine Clinic at the Centre for Diabetes, Endocrinology and Metabolism in Galway University Hospitals (GUH).
Inclusion and Exclusion criteria:
Male and female patients aged 18 years or older, referred to the bariatric service for assessment of severe obesity were eligible for inclusion. Our clinical practice is to define severe obesity as a body mass index (BMI) ≥40 kg m-2 (or ≥35 kg m-2 with co-morbidities such as type 2 diabetes or obstructive sleep apnea syndrome). Patients must have been willing to attend all the 14 scheduled intervention visits. Females of childbearing potential who were pregnant, breast-feeding or intended to become pregnant or were not using adequate contraceptive methods were not considered eligible for the programme. Those with a recent myocardial infarction (within six months), untreated arrhythmia, untreated left ventricular failure, recent cholelithiasis (within the past year), hepatic or renal dysfunction, type 1 diabetes, untreated major psychiatric disorders, eating disorders, cancer, previous bariatric surgery, a BMI <35 kg m-2 or those deemed unlikely to attend for the full programme (e.g. frequent clinic non-attendance) were excluded from the programme. Excess alcohol consumption, defined as more than 21 units per week for men and more than 14 units per week for women, was also an exclusion criterion. Moreover, patients were requested to avoid any alcohol whatsoever during the six-month intervention. Patients with a history of lactose intolerance or allergy to milk or other dairy products were excluded from participation in the milk diet.
Ethics approval:
The study was approved by the Galway University Hospitals’ Central Research Ethics Committee in December 2017 (ref CA 1900). As the programme was part of standard clinical care for patients attending our service between 2013 and 2016 and was not a prospective research study, we did not prospectively obtain written informed consent from patients to use their data for research purposes. Considering recent changes in European legislation regarding the use of personal data (the General Data Protection Regulation (GDPR)), we have only used data in this study from the subgroup of patients who agreed to this retrospectively and provided written informed consent.
Intervention:
The milk-based low energy liquid diet (LELD) consisted of three continuous eight-week phases, each with fortnightly visits to the bariatric medicine clinic, as previously described [21]. During the first (weight loss) phase from weeks one to eight inclusive, an exclusively milk-based liquid diet was prescribed, consisting of approximately 2.5 liters per day of semi-skimmed milk (depending on calculated protein requirements [29, 30]) divided in seven portions throughout the day in equal doses, with additional sodium replacement, vitamin, mineral and fiber supplementation, equating to approximately 1200 kcal/day. The dietary composition of 100 mL of semi-skimmed milk included protein (3.5 g), carbohydrate (5 g, of which sugars 5 g) and fat (1.5 g). Throughout this phase, renal and liver profiles were assessed every two weeks and the patients were seen by a physician, bariatric nurse and dietitian at each visit. During the second phase (weight stabilization) from weeks nine to sixteen inclusive, there was a gradual re-introduction of low-calorie meals from a set menu over eight weeks, according to protocol under the supervision of the bariatric dietitian with fortnightly visits continuing. During the third phase (weight maintenance) from weeks 17 to 24 inclusive, the milk component of the diet was stopped completely and a standard isocaloric diet was restarted, based on individualized meal plans, under the supervision of the bariatric dietitian.
Measurements:
Weight was measured on a Tanita® scale and height with a Seca® wall-mounted stadiometer, according to departmental standard operating procedures. After an overnight fast, bloods were drawn for glucose, liver, renal and lipid profiles. All blood samples were processed locally in the Galway University Hospitals’ Department of Clinical Biochemistry (certified to ISO 15189 2007 accreditation standard). ALT was quantitated using the Roche Cobas® 8000 enzymatic assay with spectrophotometric detection. The decrease in absorbance at 340nm is directly proportional to the concentration of ALT. Inter-assay precision at a mean ALT concentration of 28 iu/l, 121 iu/l and 210 iu/l was 5.4%, 1.6% and 2%, respectively. All of the above measures were preformed fortnightly throughout the programme. Normal ALT reference ranges were taken from the American College of Gastroenterology (ACG) clinical guidelines for the evaluation of abnormal liver chemistries (29 to 33 iu/l in men, and 19 to 25 iu/l in women) [31].
SPSS version 25 was used for all statistical analyses. Summary data were presented as means and standard deviations for normally distributed data and medians and interquartile ranges for skewed data, while categorical variables were presented as numbers and percentages.
In addition to analyzing ALT levels across the entire cohort we also classified the patient population into two groups according to baseline ALT levels as ‘normal’ (patients with normal baseline ALT levels), and ‘high’ (patients with elevated baseline ALT levels). For baseline characteristics, the independent samples t-test, was used to compare normally distributed variables between groups, while non-normally distributed variables were compared using the Mann-Whitney U test. Pearson’s chi square was used to compare proportions of categorical variables.
The Wilcoxon signed-rank test was used to compare changes in ALT levels from baseline to week 2, and from baseline to week 24, respectively. Changes in ALT overtime in weeks 0, 2, 4, 6, 8, 16, and 24 were analyzed using the Friedman test. Changes over time in weight, BMI, excess body weight percentage (EBW%), HbA1c, total, LDL and HDL cholesterol and triglycerides were analysed using repeated measures ANOVA.