Effects of a High-Protein Diet Replacement on Energy Homeostasis in Healthy Adults

  • Author / Creator
    Lemos Pinto Oliveira, Camila
  • Lifestyle modifications that induce energy deficit, such as diet and physical activity are considered the cornerstone of weight management. The overall purpose of this research was to compare the effects of an acute nutritional intervention comprised of a high-protein (HP) diet replacement versus a standard North American dietary pattern on selected components of energy metabolism, metabolic blood markers, appetite sensations, and appetite-related hormones in healthy, normal-weight adults of both sexes.
    Three studies are presented as part of two complementary randomized, controlled, cross-over clinical trials conducted separately in men and women. Two studies explored the impact individuals undergoing two isocaloric nutrition interventions: a) high-protein total diet replacement (HP-TDR): 35% carbohydrate, 40% protein, and 25% fat achieved through a nutritional supplement; b) control (CON): 55% carbohydrate, 15% protein, and 30% fat. Participants received the prescribed diets for 32 hours while inside a whole-body calorimetry unit (WBCU). The first dietary intervention randomly offered in the WBCU was designed to maintain energy balance and the second matched what was offered during the first stay.
    The last study was a sub-analysis involving the isocaloric breakfasts during the WBCU stay: a) high-protein meal replacement (HP-MR): 30% carbohydrate, 43% protein, and 27% fat achieved through a nutritional supplement; b) CON: 55% carbohydrate, 15% protein, and 30% fat. Following the breakfast, participants performed a moderate-intensity aerobic exercise session. The following physiological changes were compared between groups: energy expenditure, energy balance, macronutrient oxidation rates and balances, metabolic blood markers, appetite sensations, and appetite-related hormones. Body composition was assessed at baseline using dual-energy X-ray absorptiometry.
    In total, forty-three healthy, normal-weight adults (56% males) were included. Compared to the CON diet, the HP-TDR produced higher total energy expenditure (HP-TDR: 2143 ± 268 kcal/day; CON: 2061 ± 243 kcal/day; p<0.001), protein (HP-TDR: 91 ± 40 g/day; CON: 53 ± 20 g/day; p<0.001) and fat oxidation rates (HP-TDR: 79 ± 17 g/day; CON: 71 ± 16; p=0.013), and lower carbohydrate oxidation rate (HP-TDR: -48 ± 33 g/day; CON: 22 ± 26 g/day; p<0.001). Moreover, a HP-TDR led to a lower energy (-112 ± 85 kcal/day; p<0.001), fat (-22 ± 20 g/day; p<0.001), and carbohydrate balances (-69 ± 44 g/day; p<0.001), and higher protein balance (90 ± 32 g/day; p<0.001).
    In the HP-TDR, only females experienced lower 24-h area under the curve for prospective food consumption, and higher composite satiety score after breakfast day 1, before lunch, and before dinner. Compared to the CON diet, the change in appetite-related hormones from fasting day 1 to fasting day 2 during the HP-TDR intervention was smaller for peptide tyrosine-tyrosine (PYY) and greater for leptin. Moreover, postprandial levels of glucagon-like peptide 1 (GLP-1) and PYY were higher in the HP-TDR.
    In the last study, compared to the CON breakfast, the HP-MR produced higher fat oxidation (1.07 ± 0.33 g/session; p=0.003) and lower carbohydrate oxidation (-2.32 ± 0.98 g/session; p=0.023) and respiratory exchange ratio (-0.01 ± 0.00; p=0.003) during the exercise. After the exercise, increases in hunger were lower during the HP-MR condition. Changes in blood markers from the fasting state to post-exercise during the HP-MR condition were greater for insulin, PYY, and GLP-1, and lower for low-density lipoprotein cholesterol, triglyceride, and glycerol.
    The major findings of this thesis were that, compared to a North American dietary pattern, a HP diet replacement improved selected components of energy metabolism favoring body weight and fat losses at rest and during exercise, partly improved individual’s metabolic profile, and elicited changes in appetite sensations and appetite-related hormones that reflected decrease hunger and increased satiety. Additionally, females and males responded differently to the dietary interventions with respect to appetite sensations and appetite-related hormones. Overall, females’ response to the HP diet replacement was more pronounced in terms of appetite sensations, while in males this response was mostly related to appetite-related hormones. Findings from this research contribute to the body of literature pertaining to the effects of a HP diet replacement and physical activity. Collectively, they provide further insight into the potential role of these strategies for weight maintenance and prevention of obesity.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.