Glucose control, cardiorespiratory fitness, and dietary composition in healthy men.

Moller, Johanna Christina (2020-12)

Thesis (M Sport Sc)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: The prevalence and incidence of type 2 diabetes mellitus (T2DM) is worrisome and places a great burden on health care systems worldwide, while negatively affecting the quality of life of countless individuals. Continuous glucose monitoring (CGM) has not only improved the quality of diabetes care, but has also identified differences in the glucose profiles of individuals with otherwise seemingly healthy glucose control. The question arises whether CGM and the measurement of glycaemic variability would be more sensitive in identifying individuals who are at risk for imminent insulin resistance and subsequent T2DM. It may have significant clinical value if it can be determined if free-living glycaemic variability is closer related to lifestyle factors, such as diet and exercise, than the traditional measures of glucose control. Hence, this study investigated glucose control and glycaemic variability during free-living conditions in apparently healthy men in relation to cardiorespiratory fitness (CRF) and dietary glycaemic load (GL). Twenty-seven apparently healthy men of varying CRF levels and aged between 30 –47years, were included in the study. The participants underwent at least 7 days of CGM, while logging all food and drink. A modified treadmill Vam-éval ramp test was completed to measure peak aerobic exercise capacity. Each participant had blood samples drawn for the measurement of HbA1c and completed a 2-h 75 g oral glucose tolerance test (OGTT) during which [glucose] and [insulin] was measured every 30 minutes. Inferential statistical analysis was done using Excel, while Cohen’s effect sizes were calculated to describe the magnitude of differences between sub-groups. CFR was best correlated to insulin sensitivity (HOMA-IR: r= -0.74; Matsuda index: r= 0.72), while dietary GL correlated most strongly with MAGE (r= 0.45). A K-means cluster analysis of the dietary macronutrient composition of the participants revealed three groups: high carbohydrate-low fat, low carbohydrate-high fat, and high-carbohydrate-high fat. The high carbohydrate-low fat cluster had the highest glycaemic variability, while the insulin levels were highest in the high carbohydrate-high fat cluster. No differences between clusters were found in traditional glucose control measures. The variation in the OGTT [insulin] was significantly more than the variation in [glucose]. Glycaemic variability indices did not identify more at-risk individuals than were identified with the traditional measures of glucose control. This study could not vouch for early health risk detection among healthy, non-diabetic individuals using CGM. The results, however, showed that dietary macronutrient composition elicited larger differences in glycaemic variability, than in glucose control. Overall, it was evident that increases in insulin secretion occurs before there are any sustained increases in glucose levels.This study provides evidence for the importance of both CRF and diet in the maintenance of metabolic health, as well as the importance of measuring insulin concentrations. Healthy, glucose tolerant individuals are not necessarily protected against hyperinsulinaemia after a high-carbohydrate meal. It is proposed that attention should shift from the measurement of glucose to the measurement of insulin for early risk detection -at least until future longitudinal studies are able to link risk to different glycaemic variability profiles.

AFRIKAANSE OPSOMMING: Die voorkoms en groeikoers in die voorkoms van tipe 2 diabetes mellitus (T2DM) is kommerwekkend, plaas groot druk op gesondheidsorgstelsels wêreldwyd, en verlaag die lewenskwaliteit van ontelbare individue. Deurlopende glukose monitering (DGM) het die kwaliteit van diabetesbehandeling baie verbeter en het verskille geïdentifiseer in die glukose profiele van gesonde individue wat andersins blyk om gesonde glukose beheer te hê. Die vraag ontstaan of DGM en die meet van glisemiese variasie meer sensitief is om individue te identifiseer met verhoogde risiko vir toekomstige insulienweerstandigheid en gevolglike T2DM. Indien vrylewende glisemiese variasie nader verwant aan leefstyl faktore (dieet en oefening) is as tradisionele maatstawwe van glukose beheer, kan dit betekenisvolle kliniese waarde inhou. Die doel van hierdie studie was om glukose beheer and glisemiese variasie gedurende vrylewende omstandighede in oënskynlik-gesonde mans, te ondersoek, asook die verband van hierdie parameters met kardiorespiratoriese fiksheid (KRF) en glisemiese lading (GL).Sewe en twintig oënskynlik-gesonde mans, met verskillende vlakke van KRF en tussen 30 –47 jaar oud, was by die studie ingesluit. Elke deelnemer het ten minste 7-dae se DGM deurgaan, waartydens hy dagboek gehou het van alle kos-en drank-inname. ‘n Gemodifiseerde trapmeul Vam-éval toets is voltooi om piek aerobiese oefenkapasiteit te bepaal. Elke deelnemer het bloed laat trek vir die meet van HbA1c en het ook ‘n 75 g, 2-uur modelinge glukose toleransie toets afgelê waartydens [glukose] en [insulien] elke 30 minute gemeet is. Afleidende statistiese analise is met behulp van Excel gedoen, terwyl Cohen se effekgroottes bereken is om die grootte van verskille tussen sub-groepe te beskryf. KRF het die beste met insuliensensitiwiteit gekorreleer (HOMA-IR: r= -0.74; Matsuda indeks: r= 0.72), terwyl GL die sterkste met MAGE gekorreleer het (r= 0.45). ‘n K-gemiddelde bondel analise is op die makronutriënt samestelling van die deelnemers se diëte gedoen om drie groepe te identifiseer: hoë koolhidraat-lae vet, lae koolhidraat-hoë vet, en hoë koolhidraat-hoë vet. Die hoë koolhidraat-lae vet groep het die hoogste glisemiese variasie getoon, terwyl die insulienvlakke van die hoë koolhidraat-hoë vet groep die hoogste was. Geen verskille in tradisionele glukose beheer is tussen die groepe gevind nie. Die variasie in die [insulien] van die glukose toleransie toets was betekenisvol meer as die variasie in [glukose]. Die glisemiese variasie maatstawwe het nie meer individue met verhoogde risiko geïndentifiseer as die tradisionele maatstawwe van glukose beheer nie. Hierdie studie kon nie ‘n saak uitmaak vir die vroeë risiko bepaling in gesonde, nie-diabetiese individue met behulp van DGM nie. Die resultate wys wel dat die makronutriënt samestelling van ‘n dieet gepaardgaan met groter verskille in glisemiese variasie, as glukose beheer. Oor die algemeen was dit duidelik dat verhogings in insulienvlakke voor volgehoue verhogings in glukosevlakke voorkom. Hierdie studie wys op die belangrikheid van KRF vir dieet vir die handhawing van metaboliese gesondheid. Gesonde, glukose tolerante individue is nie noodwendig beskerm teen hoë vlakke van insulien ná ‘n hoë-koolhidraat maaltyd nie. Dit word voorgestel dat die aandag verskuif word vanaf die meet van glukose na insulien vir vroeë risiko-identifisering –ten minste totdat longitudinale studies risiko kan verbind met verskillende glisemiese variasie profiele.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/109362
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