AbstractUsing interdisciplinary methods, the aim of this thesis was to understand the glycaemic and appetitive impacts of two simple nutritional behaviours: manipulating hydration status, and consuming high or low sugar breakfasts. Through a heat-tent and fluid restriction dehydration model, Chapters 2 and 3 tested whether hypohydration altered glycaemic regulation, and psychological and physiological appetite, respectively (n = 16) in a randomised crossover fashion. Overall, these studies showed that hypohydration induced the expected physiological response (e.g. reduction in body mass, increased serum osmolality), but did not alter fasted or postprandial glycaemia or insulinaemia. Further, hypohydration did not cause changes in hunger or satiety assessed via visual analogue scales, ad libitum energy intake, and postprandial plasma ghrelin concentration, but did increase thirst and reduce pre-meal salt desire.
Once it was established that hydration status does not alter glycaemic regulation or desire for sugar, and therefore would not confound a breakfast intervention due to overnight fluid abstention and differing rates of morning rehydration, Chapters 4 and 5 investigated sugar at breakfast. Chapter 4 was a cross-sectional analysis of those at high risk of, or newly diagnosed with type 2 diabetes (n = 147). Multilevel modelling was used to establish whether skipping breakfast, consuming a low sugar breakfast, or consuming a high sugar breakfast altered energy or sugar intake later in the day. No association was found between low sugar at breakfast and total daily energy intake, though a high sugar breakfast was associated with slightly higher total daily energy intake compared to skipping breakfast. Post-breakfast energy intake was lower in those consuming a low sugar breakfast compared to skipping breakfast. Additionally, low sugar at breakfast was associated with lower total daily sugar intake compared to skipping breakfast. Following this, Chapter 5 compared three weeks of iso-energetic low sugar (plain) porridge to high (30 % by weight) sugar (sweet) porridge in healthy adults (n = 29) using a randomised crossover design. No differences were found in markers of energy balance (body mass, energy intake, energy expenditure) between the plain and sweet breakfasts. After the sweet breakfast, desire for sugar significantly reduced, but returned to baseline desire levels by lunch. The sweet breakfast was associated with higher total daily sugar, but similar post-breakfast sugar intake. No differences were found between plain and sweet breakfasts in Δ plasma glucose, triacylglycerol, cholesterol, or serum insulin concentrations.
Altogether, this series of studies highlights that manipulating hydration status or sugar at breakfast can alter state desires (e.g. for salt or sugar), but are insufficient stimuli to alter glycaemic and appetite regulatory pathways, at least acutely or in the medium term. These studies emphasise the need to investigate these outcomes holistically, as isolating one mechanism may give a skewed interpretation of the net effect of homeostatic pathways.
|Date of Award||2019|
|Sponsors||Economic and Social Research Council|
|Supervisor||James Betts (Supervisor), Dylan Thompson (Supervisor), Laura Johnson (Supervisor) & Lewis James (Supervisor)|