Original Academic Latitude Academic Latitude 2024-06-16 08:10 Shanghai
Fat is a less popular ingredient for people who are concerned about body management, and when the excess energy is stored in the form of fat, the abdomen and buttocks will continue to increase due to fat accumulation. In addition to this, some internal organs can also be surrounded by fat, which affects organ function, and these "bad" fats are all white adipose tissue (WAT).
In the fat classification, there is also a type of "good" adipose tissue, which is called brown adipose tissue (BAT) because of its brown appearance, and is usually concentrated in adults near the shoulder blades, neck, and spine. The main function of BAT is to regulate temperature, which converts energy from food into heat, helping to maintain an individual's normal body temperature when it is cold.
Image source: 123RF
Over the years, scientists have found that BAT not only helps with weight loss, but also supports healthy metabolism and reduces the risk of diabetes and cardiovascular disease. But is this really the case?
The research team from the Howard Hughes Medical Institute found that it may not be so simple, their study published in "Cell" showed that BAT in addition to thermogenesis will also absorb some surrounding nutrient molecules, such as glucose, fatty acids, and BAT also ingests many branched-chain amino acids (BCAAs), these molecules will be processed to release some organs and tissues need polypeptides, lipids, play an important role in maintaining healthy metabolism, inhibiting inflammation, BAT has a completely independent of thermogenesis metabolic benefits.
BCAAs, including leucine, valine, and isoleucine, are mainly derived from eggs, meat, and milk, and proper levels of BCAAs help maintain muscle growth and hormone production, but too much BCAAs are associated with an increased risk of diabetes and obesity. In past experiments, the research team has found that individuals who lack BAT are less efficient at removing BCAAs from their blood, which also makes them more likely to become obese.
In the new study, the research team furthered previous findings by wanting to know how BAT would deal with BCAAs and what the implications were. First, BAT samples from mice showed that BCAA is the main nitrogen donor of BAT, and the nitrogen produced by BAT mitochondrial metabolism is used to synthesize glutamate, proline, and glutathione, a process that requires mitochondrial BCAA vectors.
▲Schematic diagram of the study (Image source: Reference [1])
The authors attempted to block the function of mitochondrial BCAA vectors in mice, when the absorption of BCAA by BAT in mice was reduced, and the amino acids and peptides they synthesized from it also decreased. Due to the loss of an important BCAA depletion pattern, BCAA levels in the serum of experimental mice were significantly higher than in wild-type mice.
From the physiological point of view, the experimental mice developed significant insulin resistance, and this effect occurred independently of energy expenditure, which also indicates that insulin resistance was exacerbated by impaired BCAA consumption. As BAT reduces the absorption and breakdown of BCAAs, it also produces less glutathione, which could have helped reduce oxidative stress in the liver, but the experimental mice lost this protective effect of BAT, and the liver's ability to control blood sugar was also weakened, accelerating the onset of insulin resistance.
▲The increase in the activity of BAT can increase the production of glutathione (Image source: Reference [1])
In addition to mice, the authors also tested the response of some human volunteers, who also released more glutathione due to increased BAT activity after spending a period of time in appropriate cold conditions, suggesting that humans and mice have a similar mechanism in the metabolism of BAT BCAA.
It is worth mentioning that the BAT of obese mice cultured on a high-fat diet also reduced the catabolism of BCAAs and the release of BCAA-derived metabolites less, which also added a new potential source of obesity harm.
Resources:
[1] Anthony R.P. Verkerke et al, BCAA-nitrogen flux in brown fat controls metabolic health independent of thermogenesis, Cell (2024). DOI: 10.1016/j.cell.2024.03.030