The major finding in the present pilot study on the fatty acid composition of structural lipids of skeletal muscle membrane in obese subjects during a weight stabilization period after a successful VLCD was that the important LCPUFAn-3 docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) increased. This improvement obtained in FA composition of structural lipids during the weight stabilizing period after a VLCD may have provided assistance to preserve insulin action and glycemic control in face of reversal of plasma lipids to pre-VLCD levels. The data also provide some evidence to suggest that the positive effect of a pancreas lipase inhibitor as Orlistat on body weight in the post-VLCD period may be associated with a beneficial effect on the FA composition of skeletal muscle structural lipids.
VLCD has proven to be effective in the short run, whereas the post-VLCD period has been a period of massive failure to simply just maintain the achieved weight loss . In this perspective close dietary advisory efforts may be of importance, but also anti-obesity medication may help in stabilizing body weight and may even facilitate further weight loss [1, 5]. The pancreas lipase inhibitor Orlistat has proven an effective tool to achieve a surplus of weight loss compared to placebo in studies where all obese subjects were undergoing dietary guidance concomitant with anti-obesity medication . Orlistat reduces the absorption of fat, including saturated fat from the intestinal with about 30%.
The present study aimed to obtain new knowledge about the changes in FA composition of phospholipids of skeletal muscle membrane during the setting of a post-VLCD period. Skeletal muscle is the major site of insulin action in terms of facilitating glucose metabolism. The FA composition of the skeletal muscle cell membrane is associated with insulin action such that a lower saturation and a higher concentration of LCPUFAn-3 facilitate insulin action [6, 8–10, 12, 13, 20–23]. The mechanism may involve changes in number of insulin receptors and facilitated insulin signal transduction in the skeletal muscle cell [7, 14, 24]. The phospholipid FA composition may be modified during moderate weight loss over 24 weeks as previously shown by us . Thus, changes in LCPUFAn-3 especially the DHA of this lipid entity may confer improved insulin sensitivity . As shown previously, the 8 weeks VLCD did not improve LCPUFAn-3 in skeletal muscle cell membrane . This was speculated to be caused by a longer retroconversion step of peroxisomal -oxidation in DHA formation  or increased usage of the muscle cell membrane DHA.
The present study suggests that adherence to a diet over 24 weeks, which is able to stabilize a fast obtained weight loss during a VLCD, may further improve the FA composition of phospholipids in skeletal muscle of obese subjects. Whereas the preceding 8 weeks VLCD was associated with a reduction in saturated FA and increased monounsaturated FA contents, only changes in the LCPUFAn-6 class (increase) and not the LCPUFAn-3 class were obtained during this preceding VLCD. During the subsequent 24 weeks on a weight stabilizing diet, the contents of the class of LCPUFAn-3 increased, which was primarily due to the fact that both DHA and EPA increased during this period. DHA and EPA in cell membrane phospholipids have been associated with improved insulin action [11, 13, 25]. The ratio of n-3/n-6 LCPUFA also increased during this period, which may further indicate a more "healthy" muscle membrane in terms of a FA composition likely to facilitate insulin action. The magnitude of improvement of LCPUFAn-3, especially the increase in DHA and the ratio of LCPUFA n-3 vs. n-6 may translate into a relative improvement in insulin sensitivity of approximately 25% given the results from other studies as discussed previously . Of note, no further improvement in saturated or monounsaturated FA was obtained during the 24 weeks of stable body weight after a VLCD, but throughout the total period of VLCD and weight maintenance the saturated FA of structural lipids decreased, which may also have aided in improving glucose metabolism . The mechanisms behind the improved skeletal muscle phospholipid FA profile in this setting could be several. It may be that the preceding VLCD did not reveal an increased concentration of DHA due to the complex and longer duration of DHA formation . A sustained dietary restriction program may increase level of LCPUFAn-3 as shown in the rat model . Indeed, the changes in dietary FA composition during the weight maintenance period may have conferred the observed changes in the structural lipids FA composition of these obese subjects [8, 9, 11, 28, 29]. The results also support that the dietary source of LCPUFAn-3 had been indirect through providing increased amount of dietary linolenic acid, which could be elongated and desaturated in situ to EPA and DHA. Thus, the study provides an example of dissociation between effects of diet restriction on skeletal muscle structural lipid composition and weight loss per se in obese humans.
In accordance with the known effects of Orlistat on weight reduction and maintenance, we observed a significant difference in changes in weight during the 24 weeks post-VLCD between those treated with Orlitat versus placebo in our relatively small study population [5, 19]. Accordingly, we cannot exclude the possibility that the trend towards a superior effect of Orlistat on the composition of the structural lipids to some extent may be due to a greater loss of body weight in the Orlistat arm. Nevertheless, this small pilot study obviously was not designed to address this aspect of Orlistat treatment, which needs to be addressed in a separate study.
A high amount of intramyocellular triglycerides in sedentary subjects has been associated with insulin resistance [30–34]. Taken together, the VLCD intervention followed by the 24 weeks weight maintenance period in the present study showed a trend for a 24% decline in intramyocellular triglycerides. Interestingly, the changes in the FA composition in intramyocellular triglyceride went opposite as compared to the changes in FA in phospholipids during the 24 weeks weight maintenance period. Thus the contents of LCPUFAn-3 and LCPUFAn-6 decreased in intramyocellular triglyceride. It should be acknowledged, however, that whereas the data to support an impact of the skeletal muscle FA composition on insulin action seems strong and consistent, the data to suggest an effect of the intramyocellular triglyceride FA composition playing some role for glucose metabolic parameters are scarce and contradicting [12, 35–38]. Nevertheless, the obviously opposite net effect on the FA composition of intramyocellular triglyceride versus skeletal muscle phospholipids suggest different metabolism of these lipid entities, at least when evaluated during a dynamic setting after a VLCD.