A 90-day adaptation to a high glycaemic diet alters postprandial lipid metabolism in non-obese horses without affecting peripheral insulin sensitivity.
Authors: Suagee J K, Corl B A, Swyers K L, Smith T L, Flinn C D, Geor R J
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary Concern about high-glycaemic feeds driving insulin resistance in horses is widespread among equine professionals, yet prior research often conflated dietary effects with concurrent weight gain or used horses across a wide body condition spectrum. Suagee and colleagues addressed this gap by feeding 18 lean horses one of three concentrates (10%, 20% or 60% non-structural carbohydrate) for 90 days, then assessing insulin sensitivity and metabolic responses. Whilst both the medium and high glycaemic diets provoked greater postprandial insulin spikes than the low-glycaemic control, formal glucose tolerance testing revealed no overt insulin resistance had developed—a surprising finding that challenges the assumption that high-glycaemic feeding automatically triggers this condition in lean animals. However, high-glycaemic-fed horses showed blunted suppression of plasma non-esterified fatty acids after feeding, suggesting that insulin's normal ability to switch off fat mobilisation was beginning to falter, potentially representing an early metabolic disturbance preceding full insulin resistance. The practical implication is that whilst high-glycaemic concentrates may not immediately destabilise glucose handling in lean horses over three months, their effects on lipid metabolism warrant longer-term investigation and may warrant caution in management protocols—particularly if feeding duration extends beyond 90 days.
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Practical Takeaways
- •Feeding high glycaemic concentrates to lean horses for 90 days does not necessarily cause insulin resistance but does alter their metabolic response to feeding
- •Changes in fat metabolism (NEFA suppression) may be an early warning sign of developing insulin resistance before traditional glucose tolerance tests become abnormal
- •Long-term studies are needed to determine if continued high glycaemic feeding beyond 90 days eventually leads to insulin resistance in lean horses
Key Findings
- •90 days of high glycaemic diet (60% NSC) increased insulinaemic responses to concentrate feeding compared to low glycaemic diet (10% NSC) but did not induce insulin resistance as measured by glucose tolerance test
- •High glycaemic diet feeding resulted in less pronounced post-feeding suppression of plasma non-esterified fatty acids (p=0.054), suggesting reduced insulin-induced suppression of adipose tissue lipolysis
- •Altered lipid metabolism may represent an early marker of insulin resistance development prior to measurable changes in peripheral insulin sensitivity
- •Study conducted in lean (non-obese) horses, distinguishing findings from previous research in horses with varied body conditions