Insulin resistance (IR) is an important factor in some horses with obesity and recurrent, unexplained laminitis. Dubbed “metabolic syndrome,” it was largely assumed that obesity caused IR, and many studies seemed to back up the theory.
However, Dr. J.A. Cartmill at Louisiana State University has thrown a whole new light on the problem. The culprit may actually be leptin resistance.
Leptin is a hormone produced by fat cells that’s normally a signal to stop eating. Its release is triggered by high cellular supplies of glucose, at which point leptin “tells” the brain to stop eating. Leptin also regulates the metabolic rate, increasing resting energy expenditure. With resistance to the effects of leptin, appetite increases and metabolism slows.
In Cartmill’s studies, there was a clear distinction between obese horses that were IR and those that were not, and they sorted out by their leptin levels. Those with high leptin, indicating leptin resistance, were the ones that were also insulin-resistant.
Anything that reduces body weight reduces leptin, simply because there isn’t as much fat there to produce it, but it doesn’t necessarily improve leptin resistance. Improvements in IR also improve leptin resistance, but the most effective way by far seems to be exercise.
More work needs to be done in this area, but Cartmill’s findings are significant. Differences in leptin may be the reason why not all fat horses become insulin resistant. If you’re struggling with trimming down a horse that has insulin resistance, it’s wise to remember that this type of diet is critically important and that exercise is one of your most powerful weapons. Avoid high-fat diets for your horse, as well as sugars and carbohydrates (see June 2004). In a future issue, we’ll discuss smart ways to take weight off your horse.
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