There is currently much debate about the role of added sugar in our diet in relation to weight gain and obesity. In particular, sugar-sweetened beverages are thought to be articularly problematic, with some claims that ' liquid calories' are not sensed by the petite control system. Research findings spanning over 3 decades have shown that this not the case - these studies have used a procedure in which participants consume a drink containing sugar, or a control drink (water, or a drink sweetened with a low-energy sweetener), and subsequently eat a meal in which their food intake is measured covelily. This 'preload, test-meal procedure' has shown that consuming sugar in a drink does suppress appetite, but not sufficiently to fully 'compensate' for the calories in that drink. This thesis focused on aspects of study design in relation to the preload, test-meal procedure. Five experiments were conducted (testing a total of349 participants, eating a total of 698 test meals). The energy compensation (EC) for sugar in the traditional (commonly-used) cross-over design was modest when a sugar-sweetened beverage was matched to a low-energy sweetened beverage in terms of flavour, appearance and volume (37%, p = .048). Analyses suggested that this design may underestimate compensation due to a 'carry-over' effect, possibly arising from learning about the satiety effect of the sweet drink served on the first occasion carrying over to influence satiety experienced for the (higher or lower energy) sweet drink served on the second occasion. Consistent with this, compensation was greater when in another experiment water (familiar as nonsatiating, and different in taste and appearance to the sugar-containing drink) was used as a control- EC was 91 % (p = .009). The improved EC in this experiment was more apparent in men (123%) than in women (39%). In two further experiments, the satiety effects of sugar were examined in betweensubjects designs after controlling for baseline meal intake. Using this approach to avoid carry-over effects, the EC of sugar versus low-energy sweetener was 63% (p = .01). Again, EC was greater in men (109%) than in women (16%). This gender difference was not explained by differences in cognitive control of eating between men and women (i.e., women were not more likely than men to endorse restraint, meal planning, etc. as reasons for ending their meal). Another between-subjects design study varying the viscosity of a sugar versus low-energy sweetener preload showed that, contrary to current claims, EC for sugar in a drink was not less than EC for sugar consumed in semi-solid Gelly) and solid (candy) foods. Taken together, this thesis shows that the satiating effect of sugar in a drink has been underestimated by previous research. Nonetheless, it is likely that use of low-energy sweeteners will reduce energy intake, and therefore the risk of overweight and obesity, because they, like the use of fat replacers, reduce dietary energy density.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:680129 |
| Date | January 2014 |
| Creators | Gadah, Nouf Saleh |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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