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Are Starches and Sugars Really Detrimental to Horses?By Kentucky Equine Research Staff · January 23, 2015

Starch and water-soluble sugars are getting a bad rap in the equine community lately. This is partly due to the fact that feeds high in starch and water-soluble carbohydrates (sugars) are not recommended for certain horses, such as those that are overweight, have insulin resistance/equine metabolic syndrome, or suffer chronic laminitis.

How do diets high in starch and sugars contribute to insulin resistance? One theory propounds that these diets promote the production of inflammatory molecules. In other words, horses with a chronic, low-level state of inflammation are at risk of developing insulin resistance, and therefore laminitis.

Several studies supporting that theory have been published, but most of those studies involved overfeeding starch to horses. To study inflammation in horses fed more moderate amounts of sugars and starches, a group of researchers*, including Ray Geor, B.V.Sc., Ph.D., professor and chairperson of Large Animal Clinical Sciences at the College of Veterinary Medicine at Michigan State University, who specializes in endocrine/metabolic disease and clinical nutrition, took a different approach. They fed 12 mature, idle, nonpregnant Thoroughbred mares either a total diet (including the forage) that was either low-starch (10% nonstructural carbohydrates) or high-starch diet (20% nonstructural carbohydrates) to see if routine consumption of diet higher in starch and sugar, but not overfeeding, generated a state of chronic inflammation.

The study authors found that after 90 days there were some changes in interleukin-1β (a proinflammatory molecule). Interleukin-1β could play a role in insulin resistance, and more research is needed.

“The negative effects of high-starch and high-sugar diets have been discussed widely but one must keep in mind that many horses tolerate nonstructural carbohydrates just fine. Performance horses are one example, but research also shows that even ‘normal’ nonperformance horses do not suffer ill effects from a total diet with 20% nonstructural carbohydrates**,” says Kathleen Crandell, Ph.D., equine nutritionist at Kentucky Equine Research.

*Saugee, J.K., R.K. Splan, K.L.Swyers, et al. Effects of high sugar and starch diets on postprandial inflammatory protein concentrations in horses. Journal of Equine Veterinary Science. In press.

**Note: Less than 10% nonstructural carbohydrates is recommended for horses with insulin dysregulation.