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Can brown fat tissue be targeted for fat burning? Current findings on this topic were presented at the 67th German Congress of Endocrinology. Some statistics highlighted the need. Approximately 53% of the German population (almost 47% of women and 60% of men) are overweight (including obesity). Obesity is present in 19% of adults. The condition not only results in a shorter life expectancy but also increases the risk for cancer, diabetes, and cardiovascular diseases.
"The current treatment focuses on reducing energy intake, for example, through GLP-1 [glucagon-like peptide 1] agonists, which induce a feeling of satiety and significantly reduce body weight," explained PD Tim Hollstein, MD, of the Institute of Diabetes and Clinical Metabolic Research at the University Hospital Schleswig-Holstein in Kiel, Germany. But the effect of weight loss injections only lasts for the duration of their application, and they are expensive.
"A potentially more sustainable treatment option would be to increase energy expenditure," said Hollstein. He explained the role of brown fat tissue at a press conference for the German Society of Endocrinology (DGE) Congress.
While white fat tissue stores energy and can make up to 50% of a person's body mass, brown fat tissue (brown adipose tissue [BAT]) burns energy to generate heat. The many mitochondria in brown fat tissue give it its characteristic brown color. "Brown fat tissue is like a heater for our body and kicks in when we are cold," said Hollstein.
Brown fat tissue is primarily found in babies who cannot generate heat through muscle shivering. It has only been known for about 15 years that adults also possess brown fat. PET scans have shown that women generally have a higher amount of BAT and a higher energy intake capacity. The chance of discovering brown fat tissue was lower in older patients (P < .001), at higher outside temperatures (P = .02), in older patients with higher body mass index (P = .007), and if the patients were taking beta-blockers (P < .001).
An average person has about 100-300 g of brown fat tissue, mainly around the neck and collarbone and along the spine. Interestingly, just 50 g of active BAT can burn up to 300 kcal/d. "That's roughly equivalent to a chocolate brownie," said Hollstein. Lean individuals have more active BAT than overweight people, suggesting that BAT plays a role in our body weight.
In addition to its "heating function," BAT also produces hormones, so-called "batokines," which influence metabolism and organs such as the heart and liver. An example of a batokine is the hormone fibroblast growth factor 21, which promotes fat burning in the liver and can protect against fatty liver.
Recent studies have shown that BAT is activated not only by cold but also by food intake. BAT thus contributes to so-called "diet-induced thermogenesis," which is the energy the body needs for digestion. Some people have a higher digestive energy than others, despite having the same food intake. They burn excess calories and can thus protect themselves from being overweight.
"There are people who have a more wasteful metabolism and people who have a more economical metabolic type, meaning they have less brown fat," explained Hollstein. Interestingly, BAT also seems to induce a feeling of satiety in the brain, which could be significant for regulating food intake.
According to Hollstein, batokines probably have diverse effects and influence not only satiety and inflammatory processes but also cardiovascular diseases, diabetes, and fatty liver. It is important to research what distinguishes patients who have a lot of brown fat tissue from those who have little.
BAT can be trained and increased through regular cold exposure, which subsequently melts body fat. In a Japanese study, acute cold exposure (19 °C) for 2 hours increased energy consumption. Cold-induced increases in energy consumption correlated strongly with BAT activity, regardless of age and fat-free mass. Daily 2-hour cold exposure at 17 °C for 6 weeks led to a parallel increase in BAT activity.
"You can train brown fat tissue through cold exposure, which also leads to improvements in metabolism and a slight loss of fat mass, but the effect is very small," explained Hollstein. The changes in metabolism are significant. Blood lipid levels improve, insulin sensitivity increases, and inflammation values decrease, according to Hollstein.
Evidence also indicates that capsaicin contained in chili peppers can activate brown fat tissue. However, the effects are small, and so far, there is no evidence that consumption can help with weight loss.
Because permanent cold and daily consumption of chili peppers are not a real option, especially because the effects on BAT are rather small, research is being conducted to find drugs that activate brown fat tissue.
Preliminary results come from the United States. Mirabegron, originally developed for an overactive bladder, can selectively activate BAT and boost metabolism. A single injection of mirabegron activated BAT and increased energy consumption in the short term. Plasma levels of high-density lipoproteins cholesterol and apolipoprotein A1 increased, as did the total amount of bile acids.
The hormone adiponectin, which has antidiabetic and anti-inflammatory properties, also increased and was 35% higher after the study's completion. An intravenous glucose tolerance test showed higher insulin sensitivity, glucose efficiency, and insulin secretion.
After 4 weeks of therapy in healthy women, brown fat tissue increased, but the participants did not lose weight or body fat.
New studies have also identified the widely used drug salbutamol as a BAT activator. However, the problem with both drugs is that they have side effects such as a faster heartbeat and increased blood pressure.
As Hollstein reported, attempts have also been made to transplant brown fat tissue into overweight mice. However, in most cases, the brown fat tissue was converted into white fat.
In Hollstein's estimation, BAT offers enormous potential in the treatment of obesity and related metabolic diseases, and its activation could make a significant contribution to combating the obesity epidemic. "I believe that brown fat tissue will occupy us even more in the future. In combination with weight loss injections, increased energy consumption through brown fat tissue could have synergistic effects," he concluded.
Sourced from Medscape
