Abstract
BackgroundA plant-based diet is a dietary pattern high in plant-foods and low in animal foods. As the evidence for the numerous health and environmental benefits of plant-based diets continues to grow, concerns about their nutritional adequacy and effects on certain health aspects, such as muscle health, persist. Additionally, there is limited knowledge of how feasible it is to implement plant-based diets in a clinical setting. This thesis systematically examines the current research on plant-based diets and muscle health; then investigates the nutritional and behavioural practices of plant-based eaters and explores how plant-based diets can be implemented in an Australian clinical setting.
Methods
This PhD consists of a mixed methods design over four phases. Phase one involved a systematic review that examined the literature on the effect of vegetarian diets on muscle mass and muscle strength in adults, compared with omnivorous diets Phase two was a cross-sectional study that examined the nutrient and discretionary food intake in Australian vegan adults. Sixty-six adult vegans completed a four-day semi-weighed food diary on two occasions. Intake from diet and supplements and diet alone was compared to Australian Nutrient Reference Values. for selected nutrients. The contribution of Discretionary Food intake to total energy intake was examined. Phase three qualitatively explored the experiences and practices of contemporary vegans. An interpretive approach was used to conduct semi-structured, qualitative interviews with 18 Australian vegan adults. Phase four was an 8-week feasibility study. Acceptance and adherence to a plant-based vegan diet. were evaluated among 20 patients who received dietary counselling at an outpatient cardiology clinic.
Results
A systematic review of three intervention and eleven observational studies revealed that 5 of the 12 studies that reported muscle mass found no statistical difference in muscle mass between participants consuming an omnivorous versus vegetarian diet. One observational study reported higher muscle mass for vegetarians. Of the studies that reported muscle strength (n = 5), 3 reported no difference between participants consuming an omnivorous versus vegetarian diet.
Macronutrient intake of 66 Australian adult vegans aligned with the acceptable macronutrient distribution ranges Total protein intake aligned with measures of adequacy and guidelines for optimal protein intake. Nutrients most at risk in our sample were vitamin B12, calcium, iodine, selenium, zinc and long-chain omega-3 fatty acids. Supplementation did not fully resolve under-consumption. Discretionary Foods contributed 24.2 ± 11.8% to total energy intake.
Motivations for adopting a vegan diet are driven by a reinforcing interplay between ethical, environmental, health, and personal concerns. Transitioning to a vegan diet presents practical challenges; however, these are perceived as relatively easy to overcome. Long-term adherence to a non-normative diet is challenged by interpersonal relationships, cultural, and social pressures.
After 8 weeks, 55% (n=11) of patients of an outpatient cardiology clinic were classified as fully adherent to a plant-based vegan diet. Mean score for the plant-based vegan diet score (increased from 20.3±8.7 at baseline to 38.9±5.8 at week 8. Mean total cholesterol body mass index body mass and waist circumference significantly decreased (p<0.001) after 8 weeks on the plant-based vegan diet The plant-based vegan diet score satisfied the feasibility criteria of speed, ease of use, alignment with dietary education, capacity to assess adherence and usefulness to assess relationship between adherence and outcome measures. The PBVD was rated as either “moderately” or “extremely” acceptable by 80% of patients
Conclusions
The findings of this thesis suggest that vegetarian diets can support muscle mass and strength comparable to omnivorous diets, although further high-quality research is needed to clarify their long-term impact on muscle health. Evidence from dietary intake and qualitative insights indicates that plant-based diets are theoretically adequate but require tailored education and supplementation strategies to address nutrient gaps. These findings may support the development of targeted nutrition interventions that not only emphasise health benefits but also address practical and psychosocial barriers, leading to improved adherence and sustainability. Overall, this research highlights the potential for plant-based diets to be integrated into clinical practice as a feasible and acceptable option, contributing to both individual health and broader environmental goals.
| Date of Award | 2025 |
|---|---|
| Original language | English |
| Supervisor | Michelle Minehan (Supervisor) & Cathy KNIGHT-AGARWAL (Supervisor) |