Vazquez Rocha, Lucia del Carmen
(2019)
Dietary manipulation of brown adipose tissue (BAT) thermogenesis in healthy adult volunteers.
PhD thesis, University of Nottingham.
Abstract
Brown adipose tissue (BAT) is one of the three different types of adipose tissues found in mammals and is only present in small amounts in the adult human (~100 g), of which the main site is the supraclavicular neck region. As BAT possess a unique mitochondrial uncoupling protein (UCP1), it can have a pronounced influence on energy balance due to the capacity of UCP1 to uncouple aerobic respiration that results in the free flow of protons across the inner mitochondrial membrane thereby bypassing the need to convert ADP to ATP. One of BAT’s main functions is to transfer energy from food into thermal energy, and this is primarily regulated through the sympathetic nervous system (SNS). The activation of non-shivering thermogenesis in BAT can be measured indirectly by thermal imaging (TI). Two important factors that influence the activity of BAT are diet and cold. My thesis aimed to investigate the effect of cold and individual dietary compounds, i.e. galacto-oligosaccharide (GOS) prebiotic and extra virgin olive oil (EVOO) on BAT thermogenesis in healthy adult volunteers by using TI. In mice, the end product of microbial fermentation of the GOS-prebiotic, short chain fatty acids (SCFA), and the phenol content in EVOO (oleuropein aglycone) have both been shown to increase UCP1 expression in BAT, and therefore, promote thermogenesis.
In my first pilot study, one individual was exposed to seven days of intermittent cold exposure that significantly increased BAT supraclavicular temperature. Then to study the influence of the GOS-prebiotic on BAT function, two studies were performed. The first was a feasibility study that recruited 14 participants and aimed to establish whether daily consumption of a GOS-prebiotic was practical and feasible as part of a daily routine. Each participant was studied before and during GOS-prebiotic consumption, i.e. at 0, 7 and 14 days. All participants were readily able to consume the GOS-prebiotic each day. However, there was no detectable difference in BAT temperature after 7 or 14 days of consumption. The second study was a randomised controlled trial to further assess the effect of GOS-prebiotic. It involved 63 participants, divided into three groups; one received the prebiotic, another a placebo (maltodextrin) and another did not receive any supplement. There were two study
sessions, before and after consumption, i.e. at 0 and 14 days. Again, there was no effect of the GOS-prebiotic on BAT temperature after 14 days. Finally, I examined the effect of EVOO by examining 58 participants, who were divided into two groups one consumed 25 ml of EVOO for 21 days and the other was a control group. There was no effect of EVOO on BAT temperature after 21 days.
In conclusion, adding potential thermogenic compounds to the diet appear to not affect BAT thermogenesis as determined by TI. Future studies should examine the effect of longer-term use of other dietary compounds, e.g. tea catechin or caffeine, and its impact on BAT thermogenesis. Cold challenges seem to be more effective in increasing BAT thermogenesis assessed with TI than diet. However, the sample size was too small to consider it significant. More studies are needed with more participants per group to demonstrate causality.
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