Diet Induced Thermogenesis Clinical Trial
Official title:
The Thermic Effect of Some Plant Foods Native to Scotland: A Pilot Study.
Weight gain occurs because of imbalances in energy balance favouring energy intake. Whilst
over 50% of a person's energy requirement goes towards the maintenance of physiological
functions, around 40% is used for physical activity. In addition to this, around 10-15% of
energy is spent on what is termed as Diet Induced Thermogenesis (DIT). Diet Induced
Thermogenesis is the increase in energy expenditure following a meal, and represents the
energy utilised for the digestion and metabolism of food. Some nutrients such as proteins
require more energy to digest and therefore produce a greater DIT than others. In addition to
this, some food components are able to independently stimulate calorie burning. For example
caffeine, chilli, ginger and green tea have been shown to induce calorie burning through DIT.
Therefore the inclusion of such foods in the diet could increase energy expenditure and
thereby help in weight control.
The objective of this study is to determine the DIT effects of some plant foods that are
native to Scotland (blackberries, blueberries, red raspberries, wild garlic and sea
buckthorn). These foods have been shown to contain compounds that stimulate DIT. If found to
be effective, these foods could then be used to develop dietary strategies for weight control
in Scotland.
Obesity prevalence is increasing around the world and the United Kingdom is no exception.
Latest statistics show that approximately 25% of the UK population is obese and is predicted
to rise to 70% by 2020 if present trends continue. Obesity is particularly widespread in
Scotland where approximately 62% of the population are of a BMI over 25kg/m2. Curtailing
obesity rates is a public health priority as excess weight is also the greatest predictor of
other co-morbidities such as cardiovascular disease, cancer and diabetes, and hence
collectively exerts a significant toll on the health and economic burden of the country.
Weight gain occurs primarily due to an imbalance in energy balance status where energy intake
outweighs expenditure. Energy expenditure (EE) in adults consists of three components: basal
metabolism (50-70% of EE), physical activity (30-40% of EE) and diet induced thermogenesis
(DIT). The latter is described as the thermic effect of food and is the increase in EE above
Basal Metabolic Rate after a meal, and usually ranges between 3-10% of total EE (depending on
the composition of the meal). Whilst cornerstone approaches to weight control have focused on
strategies to reduce energy intake and increase physical activity, the still escalating
obesity levels show that this approach is ineffective in the long term possibly due to poor
long-term compliance to dietary regimes and adequate physical activity. Thus it is being
increasingly recognised that the most sustainable long-term strategy for reducing obesity is
making small diet and lifestyle changes that would positively influence energy regulatory
mechanisms targeted at preventing a positive energy balance. It is also now recognised that
genetic predispositions to a slow mechanism characterised by a slow metabolic rate and
capacity for fat oxidation also determines an individual's propensity to weight gain.
Furthermore, studies have shown that weight loss and reduced food intake result in an
attenuation of EE possibly due to the loss of lean mass and improved metabolic efficiency.
The regular consumption of high DIT foods which could increase EE and fat oxidation whilst
circumventing these energy sparing mechanisms may have significant potential in long-term
weight control. Indeed studies demonstrating pronounced obesity in mice whose DIT mechanism
were inactivated indicates the important role thermogenesis plays in weight control
Food components such as chilli (capsaicin), ginger, mustard, pepper, caffeine, green tea
(flavanols) and medium-chain triglycerides have been demonstrated as increasing DIT. The
thermogenic effects of these compounds have been shown to be mainly via the sympathetic
nervous system. Pharmacological agents such as ephedrine and salicylate as well as food
constituents such as methylxanthines (theophylline and caffeine) and caffeine have been shown
to possess sympathomimetic properties and induce fat oxidation and thermogenesis in effector
cells by stimulating the release of noradrenalin. Flavanoids such as green tea catechins have
also been shown to stimulate this pathway. Sympathetically released noradrenalin has been
shown to activate Beta3adrenoceptors and thereby induce thermogenesis and fat oxidation in
peripheral tissues as well as activate uncoupling protein (UCP1) that mediates thermogenesis
in brown adipose tissue (BAT). Plant phenolics have also been shown to demonstrate
thermogenic effects, particularly Oleuropein, green tea catechins, Kaempferol, flavanol
glycosides, stilbenes and quercetin.
The objective of the present pilot study is to assess the thermogenic effects of some plant
foods native to Scotland that contain the above phytochemicals. Specifically, the study will
investigate the thermogenic effects of berries (blackberries [Rubus sp.], blueberries
[Vaccinium corymbosum] and red raspberries [Rubus idaeus L]), wild garlic (Allium ursinum)
and sea buckthorn (Hippophae rhamnoides). Blackberries, blueberries and raspberries have been
shown to be rich in flavonoids and phenolics including catechins and raspberry ketones which
have been suggested to be thermogenic. These berries are also rich in anthocyanins such as
cyanidin-3-glucoside which has been shown to potentially promote thermogenesis by
upregulating UCP1. Furthermore, blueberries have been shown to be a good source of stilbenes
such as resveratrol and pterostilbene which have demonstrated thermic effects elsewhere.
Similarly, sea buckthorn has been reported to contain catechins, epicatechins and flavonols
such as isorhamnetin, quercetin and kaempferol. Sea buckthorn is also rich in carotenoids,
especially those with provitamin A activity that have been shown to upregulate the expression
of UCP1 and thereby influence thermogenesis. Wild garlic contains Sulphur containing
compounds such as alliin and Allicin derivatives (diallyldisulphide) that in studies using
garlic have shown thermogenic activity by enhancing noradrenalin secretion and stimulating
brown adipose tissue. Indeed the total thiosulfinate content in wild garlic has been shown to
be comparable to garlic.
The presence of thermogenic compounds in these plant products logically suggests that they
may have a thermic effect in humans and this forms the rationale for the present study. No
studies have investigated the thermic effects of these foods in humans and their therapeutic
potential in weight control from a thermogenesis perspective. The proposed pilot study will
provide preliminary data on the thermic effects of these Scottish foods and provide a basis
for future research.
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