Over the last few years it has been increasing evident that Low Carb diets are more effective for weight loss than low fat diets^{1, 9, 10, 11}.  In addition to losing more weight, Low Carb diets also seem to improve lipid profiles.  One study reported that an Atkins-style diet approach, which included a vitamin and nutritional supplements lost more weight than a low fat diet. Along with losing an average of 26 pounds, dieters assigned to the low-carbohydrate plan lost more body fat, and lowered their triglyceride levels and raised their HDL, or good cholesterol, more than the low-fat dieters. The low-fat dieters lost an average of 14 pounds².  Many nutritionists once thought that high fat/high protein diets were more effective for weight loss than low fat diets simply due to reduced caloric intake; however low-carbohydrate diets do more than just curve the appetite but also turn on fat burning genes.

Over the last few years it has been increasing evident that Low Carb diets are more effective for weight loss than low fat diets^{1, 9, 10, 11}.  In addition to losing more weight, Low Carb diets also seem to improve lipid profiles.  One study reported that an Atkins-style diet approach, which included a vitamin and nutritional supplements lost more weight than a low fat diet. Along with losing an average of 26 pounds, dieters assigned to the low-carbohydrate plan lost more body fat, and lowered their triglyceride levels and raised their HDL, or good cholesterol, more than the low-fat dieters. The low-fat dieters lost an average of 14 pounds².  Many nutritionists once thought that high fat/high protein diets were more effective for weight loss than low fat diets simply due to reduced caloric intake; however low-carbohydrate diets do more than just curve the appetite but also turn on fat burning genes.

High Protein/High Fat Diets Turn on Fat Burning Genes.

Several animal and human studies indicate that dietary fats increase the expression of genes regulating fat metabolism in skeletal muscle^{6, 7}.  Plasma fatty acids are increased after a short-term high fat diet and also increase the expression of several key genes associated with fatty acid metabolism³. For example, one study investigated low and high fat diets and changes in enzymes that control fat metabolism in endurance trained men.   Irrespective of training, beta-hydroxyacyl-CoA-dehydrogenase activity (ß-oxidation enzyme controlling fat metabolism) in the thigh muscle was significantly increased by an average of 25% after adaptation to a fat-rich diet and was unchanged after adaptation to a carbohydrate-rich diet⁴.  Another study reported that in athletes in as little as 5 days on a high fat, high protein diet during a 20-min exercise bout, fat oxidation was increased almost 2-fold greater after 5 days of the high fat diet than after the high carbohydrate diet; in conjunction their were significant increases in the fat oxidation enzymes in skeletal muscle after the high fat diet⁷. 

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Catecholamines Increase Brown Adipose Tissue

Adipose tissue is divided into two types: white and brown adipose tissue (BAT).  Extensive work over the last 30 years, principally on rodents, has demonstrated the thermogenic function of BAT. BAT therefore contrasts with white adipose tissue, which stores energy. BAT contributes to an increased metabolism by the generation of heat, which contributes to increased basal metabolism. Brown adipose tissue is rich with sympathetic nerves and mitochondria, and is responsible for a major portion of the thermogenesis. In the resting state, about 90% of the oxygen consumption takes place in the mitochondria²⁹.  Therefore, stimulating mitochondrial activity can increase thermogenesis.  As promising as increasing brown adipose activity sounds, many researchers have given up on activating brown adipose tissue through the use of pharmacological drugs due to rapid loss of brown adipose tissue after birth in humans.  Beta 3-Adrenoceptor agonists are effective thermogenic anti-obesity agents in rodents. Their main sites of action are white and brown adipose tissue, and muscle. Beta 3-Adrenoceptor mRNA levels are lower in human than in rodent adipose tissue, and adult humans have little brown adipose tissue.   A new study however challenges the notion that that brown adipose tissue is lost in adulthood, in fact the researcher's speculated we contain more brown fat than we previously thought however more research needs to be conducted¹².  Brown fat can be increased by chronic cold exposure but also beta-agonists which stimulate sympathetic activity.  Brown adipose tissue is activated by increasing catecholamine levels; it has been shown that adults with pheochromocytomas (tumors of the adrenal gland which produce excess adrenaline) have more brown adipose tissue than normal people¹⁵. Could long term use of supplements or drugs that increase thermogenesis increase brown adipose tissue?  No one knows for sure but it may be possible. Activated BAT rapidly releases fatty acids and produces heat. This is achieved by the numerous mitochondria in brown adipocytes and a specific protein in the mitochondria called UCP (uncoupling protein), which activates respiration and diverts the free energy of oxidation to thermogenesis.