Effects of an Evening PROtein PrEload on Metabolic Health in Night ShIfT Workers (PROPENSITy)

Participants are assigned in random order to two conditions, for 12 days each. The interventions are 1) a 30g whey protein preload consumed 1-1.5 hr prior to their main evening meal every day for 12 days. No other advice will be given. 2) an identical mixed-nutrient drink matched for caloric content, taste and palatability consumed 1-1.5 hr prior to their main evening meal every day for 12 days(placebo). Conditions are separated by a 2-week washout period, during which participants will be encouraged to maintain their habitual diet and physical activity levels. Metabolic testing will be performed at baseline, and at the end of both conditions.

Inclusion criteria

• Female
• Night shift workers (with a minimum of 6 months in their current shift work schedule)
• 35-65 years
• BMI 28.0-35.0 kg/m2; waist circumference > 80cm
• Weight stable in the past 6 months

Exclusion criteria

• Those working standard day time hours only, or those who work less than three to four night shifts per fortnight on average
• Personal history and/or diagnosis of: diabetes, cancer, major psychiatric disorders, liver disease, gastro-intestinal surgery or disease (including malabsorption), eating disorders, anaemia, insomnia or cardiovascular disease, and/or any other condition deemed unstable by the study physician
• Taking medications known to alter body composition or metabolism, including (but not limited to): any medication used to lower blood glucose or antidiabetic medications (metformin, sulfonylureas, Glucagon-like peptide-1 (GLP-1) analogues [i.e. exenatide], thiazolidinediones or DPP-IV inhibitors [i.e. 'gliptins']), medications affecting weight, appetite or gut motility (i.e. diuretics, domperidone, cisapride, orlistat, phentermine, topiramate)
• Participants who are taking stable doses (i.e. > 12 months) of androgenic medications (i.e. testosterone) or SSRI's will not be excluded. Personal history/diagnosis (self-reported) of diabetes (type 1 or 2), major psychiatric disorders (schizophrenia, major depressive disorder, bipolar disorder, eating disorders), gastrointestinal disorders, haematological disorders (i.e. thalassemia, iron-deficiency anaemia) insomnia, or any other medical condition, deemed unstable by the study physician
• Pregnant, planning a pregnancy or breastfeeding
• Those who have lost or gained >5% of body weight in the last 6 months
• Those who consume four or more standard drinks on a single occasion at a 'daily or almost daily' occurrence
• current smokers of cigarettes/marijuana/e-cigarettes/vaporisers
• unable to comprehend the study protocol (i.e. due to English language or cognitive difficulties)