What actually are glucose disposal agents (GDA’s)
Several supplements exist on the market which is collectively known as glucose disposal agents (GDA’s). These are typically a combination of a number of different ingredients that are proposed to do a number of different things. Firstly, they have been associated with improved insulin sensitivity, which as we have discussed in Part 1, which is important for cellular uptake of muscle building nutrients helping us replenish depleted energy stores after training.
Some GDA’s also claim to have other positive effects on glucose metabolism, helping to control blood glucose levels and promoting lean muscle gain as a result of increased glycogen synthesis in the muscles with less conversion to stored body fat. Several supplements have shown promise at improving insulin sensitivity and are summarised below. These are commonly found in GDA supplements:
Inositol is a part of the b-vitamin family. 2-4g daily has shown to improve insulin sensitivity in some studies on women with polycystic ovary syndrome (PCOS). Unfortunately, studies in other populations are scarce.
Gynostemma pentaphyllum is a form of the herb ginseng. A very limited amount of studies has been performed, focusing on diabetics and those with fatty liver disease, but insulin and glucose metabolism appears to be improved with the equivalent of 6g per day of southern ginseng in the form of a tea.
Tauroursodeoxycholic Acid (TUDCA)
Tauroursodeoxycholic Acid (TUDCA) is a naturally occurring bile acid. Again, studies are limited, but around 2g per day has shown improvements in insulin sensitivity in obese populations.
Curcumin is an active ingredient in the spice turmeric. A study using 750mg per day split over three 250mg doses showed some benefits on insulin sensitivity in overweight but non-diabetic individuals.
Resveratrol is a molecule found in wine. Dosages as small as 10mg and up to 1g daily (higher doses appeared to have no further effects) have shown benefits in overweight individuals and those with impaired glucose tolerance.
Fenugreek is a herb containing the compound 4-hydroxyisoleucine which has glucose metabolism regulating effects, alongside several other compounds that have potentially beneficial effects on blood glucose control. 1g of fenugreek daily showed an improvement in insulin sensitivity in those with type two diabetes.
L-Carnitine is synthesised from the amino acids lysine and methionine in the body, but is also available in various forms as a supplement and is primarily used for its support of fatty acid metabolism. 2-3g of Carnitine a day has shown beneficial effects on insulin sensitivity in those with impaired glucose tolerance, such as diabetics.
Unfortunately, many of these supplements have only been tested in obese participants, or those with other medical conditions that effect insulin sensitivity (diabetes, polycystic ovary syndrome etc.). Of all these supplements, it appears L-Carnitine is the only supplement that has been researched in healthy individuals that has shown positive effects.
Drawing meaningful conclusions from the available evidence is challenging and I am still firmly sat on the fence when it comes to suggesting whether these should be included in your supplement armoury, but I would say that they might have a more beneficial effect on those who already have impaired insulin sensitivity associated with higher levels of body fat.
Anecdotally, GDA’s get good reviews from those who use them as a supplement for lean muscle gain and ‘carbing up’ but unfortunately the measurable effects of these supplements in leaner or more active populations is largely under-researched (so far). That is not to say they would have no beneficial effect, however, the positive effects of some of the common ingredients outlined above on insulin sensitivity can only be inferred from the available science, and unfortunately, much of that science does not focus on athletic or highly active populations.
Whether or not you get any benefit from GDA’s, or any of the insulin-sensitising supplements outlined above is really at this stage a case of trying them and see… Not very scientific, I know, but it’s the best advice I can give at present.