Efekt velmi nízko sacharidové vysoko tukové diety a vysoce intenzivního intervalového tréninku na vybrané ukazatele kvality života

Mgr. Dominik ŠINDLER

Disertační práce

Effect of a very low-carbohydrate, high-fat diet and high-intensity interval training on selected quality-of-life indicators

Abstract:

The global rise in obesity and metabolic disorders has intensified interest in lifestyle-based interventions that go beyond conventional diet and exercise. Among these, very low-carbohydrate high-fat (VLCHF) diets and high-intensity interval training (HIIT) have gained popularity due to their benefits in weight loss, insulin sensitivity, and cardiovascular fitness. While their physiological effects are well-documented, less is known about their psychosocial impacts, quality of life outcomes, and long-term sustainability-factors crucial for lasting behavioural change. This dissertation explores the influence of VLCHF and HIIT on selected quality of life indicators through three interconnected studies: a systematic review, a randomized controlled trial (RCT), and a qualitative follow-up. The first study is a systematic review of 16 RCTs examining the effects of carbohydrate-restricted diets, including VLCHF and ketogenic diets, on psychological outcomes in adults. The review identified four key domains: quality of life, mental health, mood, and fatigue. Overall, these diets did not negatively affect psychological well-being and were at least comparable to other dietary approaches. Some studies even suggested psychological benefits, particularly with interventions lasting 12 weeks or more. Notably, the review highlighted a lack of research on the combined effects of dietary and exercise interventions, as well as the role of social factors-gaps addressed in the subsequent studies. Building on these findings, the second study involved a secondary analysis of an RCT assessing the individual and combined effects of VLCHF and HIIT on psychological indicators in adults with overweight or obesity. Sixty-eight participants were randomized to VLCHF, HIIT, combined VLCHF+HIIT, or control groups for a 12-week intervention. Participants completed validated psychological questionnaires before and after the program (SF-12, SWLS, PSS). While most outcomes showed no significant differences between groups, life satisfaction (SWLS) improved significantly in the combined group compared to the HIIT-only group. These findings support the conclusions of the systematic review and suggest potential added value of combining VLCHF and HIIT. The third study complements the quantitative findings through a qualitative exploration of long-term adherence. In a follow-up study conducted nearly four years post-intervention (median [IQR] = 3.9 [3.7; 4.3] years), 32 participants were interviewed using semi-structured interviews to explore their lived experiences, barriers, and enablers in maintaining these lifestyle changes. Thematic analysis revealed five key themes: (1) short- vs. long-term vision for change, (2) diet effectiveness as a catalyst, (3) social support inside and outside the home, (4) personal needs guiding exercise sustainability, and (5) the evolving social climate. Interestingly, increases in body composition variables (fat mass, visceral fat, lean and total mass) were observed only in the VLCHF group. The findings emphasize the importance of motivation, social support, individualized strategies, and gender-sensitive approaches in sustaining lifestyle interventions. In summary, this dissertation provides an integrated understanding of the psychological and behavioural effects of VLCHF and HIIT. Both interventions, individually and in combination, appear psychologically safe in the short term and may offer benefits in specific contexts. Long-term success, however, depends on alignment with individual motivations, social environments, and contextual adaptability-factors that should guide future research and intervention design.

Abstract:

The global rise in obesity and metabolic disorders has intensified interest in lifestyle-based interventions that go beyond conventional diet and exercise. Among these, very low-carbohydrate high-fat (VLCHF) diets and high-intensity interval training (HIIT) have gained popularity due to their benefits in weight loss, insulin sensitivity, and cardiovascular fitness. While their physiological effects are well-documented, less is known about their psychosocial impacts, quality of life outcomes, and long-term sustainability-factors crucial for lasting behavioural change. This dissertation explores the influence of VLCHF and HIIT on selected quality of life indicators through three interconnected studies: a systematic review, a randomized controlled trial (RCT), and a qualitative follow-up. The first study is a systematic review of 16 RCTs examining the effects of carbohydrate-restricted diets, including VLCHF and ketogenic diets, on psychological outcomes in adults. The review identified four key domains: quality of life, mental health, mood, and fatigue. Overall, these diets did not negatively affect psychological well-being and were at least comparable to other dietary approaches. Some studies even suggested psychological benefits, particularly with interventions lasting 12 weeks or more. Notably, the review highlighted a lack of research on the combined effects of dietary and exercise interventions, as well as the role of social factors-gaps addressed in the subsequent studies. Building on these findings, the second study involved a secondary analysis of an RCT assessing the individual and combined effects of VLCHF and HIIT on psychological indicators in adults with overweight or obesity. Sixty-eight participants were randomized to VLCHF, HIIT, combined VLCHF+HIIT, or control groups for a 12-week intervention. Participants completed validated psychological questionnaires before and after the program (SF-12, SWLS, PSS). While most outcomes showed no significant differences between groups, life satisfaction (SWLS) improved significantly in the combined group compared to the HIIT-only group. These findings support the conclusions of the systematic review and suggest potential added value of combining VLCHF and HIIT. The third study complements the quantitative findings through a qualitative exploration of long-term adherence. In a follow-up study conducted nearly four years post-intervention (median [IQR] = 3.9 [3.7; 4.3] years), 32 participants were interviewed using semi-structured interviews to explore their lived experiences, barriers, and enablers in maintaining these lifestyle changes. Thematic analysis revealed five key themes: (1) short- vs. long-term vision for change, (2) diet effectiveness as a catalyst, (3) social support inside and outside the home, (4) personal needs guiding exercise sustainability, and (5) the evolving social climate. Interestingly, increases in body composition variables (fat mass, visceral fat, lean and total mass) were observed only in the VLCHF group. The findings emphasize the importance of motivation, social support, individualized strategies, and gender-sensitive approaches in sustaining lifestyle interventions. In summary, this dissertation provides an integrated understanding of the psychological and behavioural effects of VLCHF and HIIT. Both interventions, individually and in combination, appear psychologically safe in the short term and may offer benefits in specific contexts. Long-term success, however, depends on alignment with individual motivations, social environments, and contextual adaptability-factors that should guide future research and intervention design.

Keywords

very low-carbohydrate high-fat diet, high-intensity interval training, quality of life, excessive weight, obesity

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 16. 4. 2025

Zveřejnit od: 31. 12. 2999

Obhajoba závěrečné práce

• Vedoucí: doc. PhDr. Lukáš Cipryan, Ph.D., doc. PhDr. Lukáš Cipryan, Ph.D.

OSTRAVSKÁ UNIVERZITA

Pedagogická fakulta

Doktorský studijní program / obor:
Kinantropologie / Kinantropologie