Effects of dietary essential fatty acids on active thermogenin content in rat brown adipose tissue

Rats were fed diets providing either 0.3% (low EFA), 3% (control) or 10% (high EFA) of the energy as essential fatty acids. (All diets provided 20 energy percent of fat.) Both the experimental groups had a lower body weight than the controls. Small differences were found between the groups in many traditional parameters of brown adipose tissue activity (wet weight, protein content, mitochondrial content, cytochrome c oxidase activity). A specific increase in the mitochondrial concentration of the 32,000-dalton GDP-binding protein thermogenin was observed in the high EFA group (from 0.30 to 0.45 nmol/mg). When the thermogenin content of the animal was expressed per gram body weight, the content was more than doubled (from 22 to 47 pmol/g body weight) in the high EFA group, but was unaltered in the low EFA group. It is concluded that the effect of low EFA is nonspecific and due to a general decrease in health status. The effects of high EFA are, however, specific and resemble the changes observed in animals exhibiting diet-induced thermogenesis. It is suggested that the animals fed high amounts of essential fatty acids are in a state of decreased metabolic efficiency and this may be at least in part an explanation for their low body weight.