The potential benefit of fish oils for diabetes was noted in studies on Alaskan Inuit several decades ago.
In this population researchers observed a low prevalence of diabetes even when obese, but this changed when a non-traditional lifestyle was adopted.
Previous meta-analysis reported no benefit of fish oils on glycaemic control, but more recent animal studies revealed a threshold phospholipid enrichment needed before effects on glucose and protein metabolism were seen.
Other human studies used low doses and short timescales and the authors of this latest paper set out to address this.
They found whole body protein metabolism (WBPT) but not glucose metabolism was improved by fish oil.
This could mean fish oils hold potential for the maintenance of muscle mass.
Dr Gerald Lobley, who conducted the research with colleagues at Aberdeen University, told NutraIngredients: “Between the ages of about 35 and 70 most people lose about a third of their lean body mass most of which is muscle, it’s all part of the tendency to becoming frailer as you age.
“There is the possibility that fish oils might be beneficial in helping to maintain that muscle mass and thus creating less frailty which has both direct health implications and obviously improves quality of life.”
The study saw 33 subjects with impaired glucose regulation given either 6 g of fish oil or 6 g of maize oil daily for nine months.
The fish oil contained 3.9 g n-3 PUFA, falling between the safe upper limits of 3 g/day and 5 g/day for the US and Europe, respectively.
The primary outcome of the trial was the effect of oil type on insulin sensitivity related to glycaemic control.
The secondary outcome was the effect on whole body protein turnover (WBPT).
Three subjects completed an additional small pilot study using muscle biopsies to compare the erythrocyte and skeletal muscle phospholipid enrichment.
The researchers found long-term supplementation with fish oil at doses around current safety limits did not affect glycaemic control but did alter whole body protein kinetics in an insulin-stimulated but not fasting state.
The results on WBPT reflected previous studies on animals and elderly humans whose protein synthesis increased following fish oil supplementation.
However the authors observed this did not necessarily translate into improved net protein anabolism as growth rates didn’t improve in these previous animal studies and no changes in lean body mass were seen in their latest nine-month study.
Yet in catabolic states such as age-related sarcopenia, future studies may reveal a health benefit.
Asked about further research, Dr Lobley said colleagues at the University of Aberdeen were currently conducting a study on the impact of fish oil plus exercise on muscle mass and strength.
“This would be extending the observations we made and those that were made in the USA to see if they can detect a true increase. There might be an additive or synergistic effect.”
While Lobley is now retired, he said future research should focus on improving elderly wellbeing with fish oils rather than prevention of type 2 diabetes.
The control of glucose metabolism may require a different type of n-3 PUFA than that found in conventional fish oils, Lobley said.
The Inuit consume mammalian fatty acid sources such as seals and those differences may be important, he said.
Doses in the study equate to two portions of fish a day compared to two portions per week which are the current recommendations.
“What somebody needs to do is give the equivalent of two portions of fish in terms of capsules a week to see whether they can show the same responses in protein metabolism,” Dr Lobley said.
Source: British Journal of Nutrition
Published online ahead of print, doi: 10.1017/S0007114515004274
“Fish oil supplemented for 9 months does not improve glycaemic control or insulin sensitivity in subjects with impaired glucose regulation: a parallel randomised controlled trial”
Authors: L.F. Clark et al.