Weight-loss Maintenance and Metabolic Health in Pre-diabetic Adults: Impact of protein content of two ad libitum low-fat diets of varying protein and carbohydrate composition

Abstract

Background - Obesity rates are increasing worldwide in parallel with the rates of Type 2 diabetes mellitus (T2DM). Lifestyle (diet and exercise) interventions are the cornerstone of T2DM prevention. Aim –To investigate the effects of 2 ad libitum diets (with a focus on protein content) on weight-loss maintenance and metabolic outcomes at 6-Month of a lifestyle intervention, after an initial 2 month period of low-energy diet (LED) induced weight-loss. Methods – 136 pre-diabetic and overweight adults aged 25-45 and 55-70 years were enrolled into a randomised controlled trial during July 2013-Jan 2014. All participants had impaired glucose tolerance (IGT, based on an oral glucose tolerance test (OGTT). Those achieving an 8% weight-loss target during an initial 8-wk LED phase (~4MJ/d) were randomised into 1 of 2 dietary intervention groups over 4 months for weight maintenance: high protein, low-glycaemic index (HP-LGI; 25%EI protein, 45%EI CHO, GI<50), or moderate protein, moderate GI (MP-MGI; 15%EI protein; 55%EI CHO, GI 56-70). LED group meetings were provided at weeks 0, 2, 4 and 6. Weight maintenance group meeting providing dietary counselling took place at wk 8, 10, 12, 16, 20, 26. Plasma glucose, weight, fat mass, fat-free mass, blood pressure, heart rate and lipid profile were measured at Baseline, Post-LED and 6-Month. Glucose tolerance and dietary intake (using 4-day diet records) were assessed only at Baseline and 6-Month. Completers analysis was carried out; and the groups were blinded and randomised as Group α and Group β. Results – 70 (51.5%) participants (74% female; 73% Caucasian, 9% Maori, 18% minority groups) completed the 6 month study. Post-LED - Mean (±SD) weight-loss for all (n=70) was 11.9 ± 3.9kg (range 6.6-24.5kg) (p<0.0001), with significant improvements in all parameters including fasting plasma glucose (except HDL-C). Weight maintenance (6- Month)-, Both diet groups maintained body weight, with mean (±SD) weight change from Post-LED of only -0.12 ± 5.6kg for Group α and +1.09 ± 4.6kg for Group β (p=0.3260). Diet: Group α had a much greater increase in %EI protein from Baseline than Group β (6.2% vs. 2.5%, p=0.0244), and are hypothesised in this blinded trial to be the higher protein diet group (HP-LGI). There were no differences in dietary fibre intake (assessed as a proxy for GI) between groups (p=0.4611). Participants who attended 4-6/6 weight maintenance group meetings had a lower FPG at 6-Month (5.45 ± 0.5mmol/L) compared to those who did not attend any of the group meetings (5.93±0.4mmol/L) (p=0.0078). Conclusions –High protein and moderate protein diets both successfully maintained weightloss at 4 months, following 8-week LED induced weight-loss. Attending most of weight maintenance group meetings as opposed to none is associated with lower FPG. Key words: high protein diets, weight-loss maintenance, pre-diabetes, Type 2 diabetes prevention