Higher Protein Intake with Energy Restriction in Overweight/obese Adults: Effects on Body Composition, Metabolic Health, and Indices of Sleep

The increased prevalence of obesity and metabolic syndrome calls for effective dietary strategies to alleviate those epidemics and to reduce health-care costs in the US. Consuming a higher protein diet during energy restriction (ER) was shown to be effective to improve whole body composition. However, the effects of milk protein-based high protein diets on whole and regional body composition and cardio-metabolic risks during ER have not been assessed. Chapter 2 assessed the effects of higher protein intake achieved using milk protein isolate (MPI) on body composition and metabolic health during ER. We conducted a 20-wk randomized, double-blind study (1-wk pre-study assessment, 3-wk weight maintenance baseline, and 16-wk ER intervention with 750 kcal·d -1 energy deficit) with 44 subjects (12M:32F, age 52 ± 1 y, BMI 31.4 ± 0.5 kg·m-2, mean ± SE) assigned to either a normal (NP, n=23) or high (HP, n=21) protein diet (0.8 vs. 1.5 g protein•kg-1 baseline body mass•d-1). The HP diet had 0.7 g•kg-1•d-1 MPI. At weeks 4 and 20, whole (DXA) and regional (MRI) body compositions and cardio-metabolic risk factors (fasting glucose and insulin, lipid profile, and blood pressure (BP), oral glucose tolerance, inflammation, and 24-h ambulatory BP) were measured. HP consumed more protein than NP as reflected by 67% higher 24-h urinary urea nitrogen excretion. Higher protein intake did not influence changes in the measured parameters, except BP and plasma triglycerides (TGs). 24-h systolic and diastolic BPs decreased in HP, but remained stable in NP. TG decreased more in HP than NP. Over time, subjects lost body mass, FM, FM%, LM, and gained LM%. They also lost thigh and calf intermuscular (IMAT) and subcutaneous (SubQ) adipose tissue areas, muscle area (MA), and gained MA%. Other metabolic syndrome parameters all improved over time. Both diet and sleep were shown to be related to metabolic health. Numerous cross- sectional studies also indicated an association between protein intake and indices of sleep (i.e. duration, quality, and patterns) but causal relationship were not elucidated. Chapter 3 assessed the effect of protein intake during dietary energy restriction on indices of sleep in overweight/obese adults in two randomized controlled feeding studies. For study 1, 14 participants (3M:11F, aged 56±3 y, BMI 30.9±0.6 kg·m-2, mean±SE) consumed energy-restricted diets (750 kcal/d deficit) with either beef/pork (BP, n=5) or soy/legume (SL, n=9) as the main protein source for three consecutive 4-week periods with 10 (control), 20 or 30% of total energy from protein (random order). At baseline and the end of each period, global sleep score (GSS) was assessed using the Pittsburgh Sleep Quality Index (PSQI) questionnaire. The design of study 2 is described in Chapter 2; and sleep measurement is a secondary outcome. PSQI was administered during baseline week 3 and intervention weeks 4, 8, 12, and 16. GSS ranges from 0-21 arbitrary units (au) with a higher value representing worse GSS during the preceding month. For study 1, higher protein quantity improved GSS, independent of protein source. GSS was higher when 10% versus 20% protein was consumed with 30% protein as intermediate. For study 2, at baseline, GSS was not different between NP and HP. Over time, GSS was unchanged for NP and improved for HP. In conclusion, adequate protein (achieved using mixed sources) and MPI-based higher protein diets supported weight loss-induced improvements in body composition and indices of metabolic syndrome, and the higher protein diet enhanced reductions in BP and TG. In addition, consuming a greater proportion of energy from protein while dieting may improve sleep in overweight and obese adults