While it is possible that a type II error was committed and the reduction in RER was a real effect, it is also possible that the fish oil treatment increased fat oxidation at other

times during the day such #selleck compound library randurls[1|1|,|CHEM1|]# as during exercise [35], or during the post-prandial period [36]. A potential shortcoming of the present study was not using dietary records to monitor the subjects’ intake during the study. Although there are several potential problems with the use of dietary records (for a review of inaccuracies with self-recorded diet records see [37]), they would have provided us with some insight into the dietary habits of the subjects during the study. It therefore remains a possibility that the fish

oil supplements resulted in the subjects changing their normal dietary habits. Although increasing dietary fat does not generally cause a decrease Tipifarnib in voluntary fat intake [38], it has been shown that fish oil may reduce appetite [39], which could have led to the subjects consuming less total calories during the study. While a reduction in volitional food intake would explain the observed reduction in fat mass following fish oil treatment, it does not explain the increase in lean mass we observed. Although other studies have observed a significant [3, 5], or insignificant [21, 22], increase in lean mass following fish oil treatment, to date

no study has determined the mechanism by which dietary fish oil causes an increased accretion of lean mass. One possibility lies in the well-documented ability of dietary omega 3 fatty acids to reduce inflammatory cytokines [40], since inflammatory cytokines have the ability to increase Dimethyl sulfoxide protein degradation mainly by activating the ATP-ubiquitin-dependent pathway [41–45]. It is possible then, that dietary fish oil is simply decreasing the breakdown of protein tissue caused by inflammatory cytokines, and this results in an increased accretion of protein over time. An alternative possibility is that fish oil supplementation was able to increase lean mass by reducing cortisol levels since it is well established that cortisol increases protein catabolism [46–49]. The significant negative correlation (r = -0.504, p = 0.02) observed in the fish oil group between the change in lean mass and the change in salivary cortisol concentrations would support this hypothesis. Although other studies have observed a decrease in cortisol levels following fish oil consumption [20], the exact mechanism(s) responsible are currently unknown. However, it is possible that the reduction of IL-6 as a result of fish oil consumption [50] is causing a reduction in cortisol production since it has been shown that IL-6 induces increases in cortisol levels [51, 52].