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The role of brown fat in metabolic health

Not all body fat is bad. As it turns out, the more brown fat you have, the merrier. New research on 198 Asian preschool children from the GUSTO cohort has found that young children with more brown fat or brown adipose tissue had a healthier metabolic profile – these kids had a lower body mass index, less fat in the abdomen and less harmful fat in the liver and muscle tissue.

By Mya Thway Tint

Girl eating cookie

Fat is not created equal. Just as there are different types of dietary fat, the human body also has different types of fat cells. Fat or adipose tissue is composed of white and brown fat – white fat stores excess energy while brown fat dissipates excess energy or fat storage as heat through a process called thermogenesis.

Brown fat or brown adipose tissue (BAT) was traditionally believed to be present abundantly only in infants and to progressively regress following infancy. Recently, studies have shown that BAT persists into adulthood. However, it’s noted that less brown fat can be found in obese individuals. BAT has since received a great deal of attention as an appealing target to combat obesity and metabolic diseases – such as diabetes – due to its ability to use body fat stores as fuel.

Boosting metabolism with brown fat
Research suggests that BAT is a major contributor to the regulation of energy metabolism in the body. Brown fat, when activated, increases thermogenesis by stimulating fatty acid oxidation and thereby increasing energy dissipation. BAT also possesses a great capacity for glucose uptake from the circulation, thereby keeping blood sugar levels balanced and improving insulin sensitivity – both of which are beneficial to an individual’s health. These properties suggest that brown fat might have an important role in whole-body metabolism.

Measuring BAT
The most commonly used method for estimating activity and quantity of brown fat in humans has been positron emission tomography (PET) combined with computed tomography (CT), which involves significant doses of radiation. Therefore, most previous studies on brown fat were done in patients requiring PET/CT scans for medical indications, limiting its applicability to the general population and to its use in children.

We investigated the influence of brown fat on adiposity in 198 young Asian preschool children (at 4.5 years of age) from the Growing Up in Singapore Towards healthy Outcomes (GUSTO) study using magnetic resonance imaging (MRI), an alternative technique to identifying brown fat without radiation. Our study is the first to examine brown fat in relation to metabolic health in a cohort of children from a general population.

The current available applied methods to identify brown fat in humans are PET/CT and infrared thermography. These techniques generally detect activated brown fat, but do not detect inactive or weakly activated brown fat. Our findings confirm that identification and quantification of brown fat is possible with MRI and strengthen the proposition of MRI as an alternative imaging technique to characterise brown fat without any form of activation. This paves a new and effective way for future studies in identifying brown fat in healthy populations, children and in longitudinal studies without applying methods involving radiation.

Findings from GUSTO
In GUSTO, we observed that young children with more brown fat had a lower body mass index. These children also had less fat in the abdomen as well as less harmful fat in the liver and muscle tissue. The composite scores representing fat in the liver (i.e. fatty liver index and metabolic syndrome scores) were also lower in children with higher/more brown fat. These factors have been found to predict an increased risk of diabetes and heart disease in adulthood.

The observed inverse relationship between brown fat and liver fat supports the potential role of brown fat in the development of non-alcoholic fatty liver disease – a condition with excessive fat accumulation in the liver. A possible mechanism underlying these findings is the ability of brown fat to dissipate stored excessive fat, thereby suppressing liver fat accumulation and consequently reducing the risk of developing non-alcoholic fatty liver disease.

We also observed that gender and ethnicity modified these associations. Compared to boys, girls had a higher proportion of brown fat and seemed to benefit more from the protective effect of brown fat as there was a stronger inverse association between brown fat and abdominal adiposity. Interestingly, Indian children had higher brown fat as well as higher abdominal adiposity compared to Malay and Chinese children. The observed differences imply that the protective effect of brown fat may vary among different ethnic groups and by gender.

Can BAT combat obesity and chronic metabolic diseases?
Within the GUSTO study, comprehensive data has been collected on these children, which provides us with an excellent opportunity to continue studying brown fat and its implications in health and disease. Our findings add to the limited information in the literature on brown fat in young children. Furthermore, GUSTO draws from the three major Asian ethnic groups that represent 50 percent of the global population, which increases the relevance of these findings to global efforts aimed at addressing the prevention of non-communicable diseases.

A novel finding in this study was the ability to show an inverse relationship between brown fat under physiological conditions and metabolic profile in early childhood without involving activation of brown fat. The fact that these differences are observed in preschool age children points to underlying genetic and early environmental factors which can have important future metabolic implications.

As we continue our work to better understand the role of brown fat, the factors influencing brown fat in children and look into possible interventions to increase brown fat, we also plan to track the profile of BAT in these children longitudinally to determine the long-term health implications of brown fat on the development of obesity and related metabolic disorders.


ABOUT DR MYA THWAY TINT

Dr Mya Thway Tint is a research scientist at the Singapore Institute for Clinical Sciences (SICS) and a senior research fellow with the Department of Obstetrics and Gynaecology at the NUS Yong Loo Lin School of Medicine. Her research focuses on the developmental influences of offspring's metabolic risk and bone health in reproductive-age women and children. She is involved in the GUSTO, S-PRESTO and NiPPeR studies.

Posted in : Human Development