The essential fatty acids α-linolenic acid (ALA, C18:3 (n-3)) and linoleic acid (LA, C18:2 (n-6)) and their metabolites play an important role in human health. Metabolism of ALA and LA produces a range of pro- and anti-inflammatory eicosanoids, and the dietary ratio of the parent fatty acids is known to affect the downstream cellular inflammatory response. Gamma linolenic acid (GLA, 18:3 (n-6)) is a metabolite of LA, which possesses potent anti-inflammatory effects in vivo. It achieves this by increasing production of the series 1 prostaglandin PGE1, via the intermediate dihomo-γ-linolenic acid (DGLA, C20:3 (n-6)). Research has shown a link between essential fatty acids and insulin sensitivity, adipocyte differentiation and lipogenesis. Obesity is increasingly being seen as an inflammatory condition, and so the anti-inflammatory effects of GLA may be beneficial in weight control.
Researchers1 have investigated the effects of GLA on weight regain in 50 formerly obese individuals who demonstrated weight loss of 12 kg on a very low energy diet and maintained their weight for 6 months. The treatment group received 890 mg/d of GLA in the form of 5g of borage oil, and the control group received a similar quantity of olive oil. The body weight and the adiposity of the individuals was assessed at baseline and at follow up points to assess changes. After 12 months, 12 subjects in each group were assessed and the results showed that the weight regained in the GLA group was 1.78 kg, whereas the weight regained in the placebo group was 2.78 kg. The remaining subjects were assessed over the next 6 months and comparison of the groups revealed a 1.8kg and 7.6kg regain of weight in the treatment and control groups, respectively.
A follow up study by the same team of researchers used a cross over design and found a significant effects of GLA against weight regain when compared to an olive oil placebo. From these result it could be concluded therefore that GLA is beneficial in preventing weight regain following a calorie restricted diet in obese individuals. It is not fully clear why GLA might be beneficial, but the authors presented evidence that suggest that GLA (and perhaps other fatty acids) are able to improve the compartmentalisation of fuel into tissue other than adipose tissue. One possible scenario is an improvement in peripheral glucose disposal in skeletal muscle due to increased insulin sensitivity. This supports previous studies that have shown beneficial effects of other long chain fatty acid and their metabolites on insulin sensitivity, perhaps due to an anti-inflammatory effect.
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