Fat burning by brown fat cells: the holy grail of fat reduction
White adipose tissue (WAT), i.e. white fat, is the fat tissue responsible for fat accumulation. In humans comprises the vast majority of fat tissue.
In contrast, brown adipose tissue (BAT, i.e. brown fat) actually burns fat for the production of heat in the body under the influence of a protein called UCP1. In humans it only comprises a small amount of fat tissue.
Ever since the discovery of BAT the focus has been on stimulating that tissue to burn fat for energy and help with the fight against overweight/obesity and cellulite. White adipose tissue was previously considered inert to UCP1 and therefore it was thought to be a waste of time to stimulate that tissue with UCP1.
Beige fat: neither brown nor white - but a great target for fat reduction
As we mentioned above, brown fat generates heat because it expresses a mitochondrial protein called uncoupling protein UCP1. In contrast, white fat does not produce UCP1 and therefore does not burn fat.
However, hundreds of studies in the last few years have shown that there exists an intermediate type of fat which is neither brown nor white, but something in-between, aptly named "beige fat".
Beige fat is basically a subtype of white fat that likes to behave like brown fat. Contrary to what previously was thought impossible, this type of white fat responds to UCP1 stimulation and oxidises fatty acids (in plain terms, burns fat) for heat production. But this happens only if whitev fat is stimulated by cAMP (cyclical adenosine monophosphate).
The good news is that cAMP production can easily be stimulated by adrenaline and noradrenaline, which are in turn produced in large amounts during vigorous exercise. cAMP production is also stimulated by a host of lipolytic herbal extracts which are already widely used for fat reduction and cellulite removal, both topical (anti-cellulite creams) and oral (nutritional supplements) form. Forskolin and sclareolide are two such cAMP-stimulating herbal extracts isolated from indian coleus and clary sage, respectively.
Irisin and beige fat: the holy grail of fat reduction, redefined
The even more exciting finding is that white fat cells can turn into beige fat cells under the influence of the newly discovered hormone irisin (named after Iris, the Greek messenger goddess). This hormone is produced during exercise and is known to convert white fat to beige fat.
This means that exercise does not only lead to fat loss via fat and carb-burning on the muscles. It also changes your fat tissues from fat storing facilities into fat-burning cellular "furnaces".
It also means that the herbal extracts mentioned above do not only cause a temporary fat release via cAMP, but they can potentially change the nature of the fat tissue that they are applied on, towards the fat burning type. Not bad!
Newly discovered "beige" fat cells can be a target for novel fat reduction creams and treatments
And the news is getting even better. Researchers have found that what previously thought to be brown fat tissue (i.e. a tissue which is rarely found on human body) is actually beige fat tissue (i.e. normal white fat which had been changed towards the BAT phenotype via the stimulation of UCP1, cAMP, irisin or even other unknown factors).
Take home message:
I would like to go a bit further and suggest that an anti-cellulite/spot fat reduction cream with ingredients that act on cAMP (e.g. forskolin, sclareolide) can convert white fat into brown fat and help with slimming and cellulite reduction.
In addition, any substance that inhibits the breakdown of cAMP by phosphodiesterases, such as caffeine, theophylline, and many other substances, may also help in that direction.
And of course, any natural chemical that helps boost UCP1 levels directly, such as fucoxanthin, is also welcome as an anti-cellulite cream ingredient.
As a last speculation, I would say that prolonged application of such creams (3-6 months) will have a better chance of changing WAT into BAT, than the usual 2-3 week temporary application of anti-cellulite/local fat reduction products by most women.
[Source: Beige adipocytes Are a Distinct Type of Thermogenic Fat Cell in Mouse and Human]