Understanding Insulin Resistance


insulin resistance

With so much concern over equine metabolic disorders, people are scrambling to cut down on sugar in their horses’ diets. But do sugars actually cause insulin resistance, and how much is too much?

It’s all over the news. High sugar intake and ingredients like high fructose corn syrup cause obesity and diabetes. As our awareness of equine metabolic syndrome spreads, so does our awareness of how much sugar our horses are consuming. A lot of people are trying to scale this sugar consumption back. But you can take things too far.

What is Insulin Resistance?

With insulin resistance (IR), the horse’s muscle and fat cells do not respond to normal levels of insulin. These tissues rely on insulin to signal cellular uptake of glucose. A rise in blood glucose triggers insulin release, which in turn signals the cells to take up more glucose. In the insulin resistant horse, much more insulin is needed to get the job done than in a normal horse.

The key to controlling IR, which can cause laminitis, is keeping blood glucose (aka blood sugar) steady and avoiding wide swings caused by diet. Glucose is the key word here. Both simple glucose, and sucrose (one glucose plus one fructose), are sugars in food items that can cause a blood glucose rise.

Sugars and Starches

Grains, alfalfa and grasses that thrive in warm weather also contain starch, a string of glucose molecules. Starch is the plant’s storage form of glucose. An enzyme called alpha-amylase, found in the horse’s intestinal tract, digests starch to glucose. Starch is therefore a very potent and concentrated source of glucose, which means blood glucose rises significantly after a grain meal. The 2% to 4% molasses in sweet feed is not the major source of blood glucose – the grain starch is.

While a horse with IR needs his intake of glucose sources (sugars and starches) limited, it is not true that grain feeding or pasture causes IR. Horses on high grain diets are less sensitive to insulin than horses on high fiber diets, but the difference is so small that it takes sophisticated intravenous testing to detect it. Their baseline insulin, which is clearly elevated in IR horses, is normal. Even obesity is not a reliable indicator of insulin resistance. The Virginia-Maryland Regional College of Veterinary Medicine completed a field study of 300 horses living on pasture. Of the horses classified as obese or very obese, only 35% were actually insulin resistant. This is higher than the 10% to 12% of horses in general estimated to be IR, but it also clearly shows that not all obese horses are IR.

What to Cut?

Should you cut out grain and pasture from your horse’s diet, just in case? No! Pasture is an excellent source of food and only needs to be avoided if the horse is known to be insulin resistant. If you suspect IR, get your horse tested. A blood glucose and insulin test should be done without fasting – but avoid all concentrates/bag feeds and allow free access to hay or pasture before the test.

It’s true that horses not in hard work rarely need grain, and that IR horses should never receive any. Overweight horses certainly don’t need it either, whether IR or not. However, hardworking horses and even some lightly worked or growing Thoroughbreds, Standardbreds and Quarter Horses often need grain to hold their weight. Each case should be evaluated individually; if your horse does better with some grain, don’t feel as if you are poisoning him or putting him at risk for IR by giving it to him. You’re not.

Taking Care of the IR Horse

If you do have a horse that is insulin resistant, strictly limiting glucose sources is absolutely critical since diet control and exercise are the only effective strategies. IR is not a disease per se – it’s a type of metabolism that does not tolerate high blood levels of glucose. If you knew someone with a strawberry allergy, you wouldn’t say she had a disease, but you certainly wouldn’t let her eat any strawberries! It’s the same general principle with IR.

The IR horse should have no grain. Most of the “safe” or “reduced carbohydrate” feeds out there still are not low enough. The target with an insulin resistant horse is to give him less than 10% starch and simple sugars combined. On an analysis, simple sugars are reported as ESC = ethanol soluble carbohydrates. That is the extraction method used to pull out the sugars so they can be measured.

Since sugar levels in grass vary tremendously depending on weather and growth stage, pasture should usually be avoided. Mature pastures that have gone to seed are the least likely to cause trouble, but once fall arrives and grass begins re-growing, it becomes risky again. Ironically, short/ overgrazed pastures can be more dangerous because the stress of overgrazing triggers sugar production, and sugars are concentrated in the lower portions of the plant.

Ideally, hays should be tested to confirm that ESC + starch is less than 10%. Alternatively, you can buy a bagged forage that is guaranteed to be 10% or lower. Ontario Dehy Balanced Timothy Cubes is a guaranteed low sugar/starch cube that also has all the necessary balanced minerals. They are available directly through some feed distributors and also at stores that sell the Triple Crown line.

In summary, controlling sugar and starch intake is very important for keeping insulin resistant horses healthy and sound. However, sugar and starch do not cause insulin resistance. If you are concerned, have your horse tested so you know for sure.


Dr. Eleanor Kellon is the co-owner of the almost 10,000 member Cushing’s and insulin resistance group on Yahoo. She is owner of Equine Nutritional Solutions, a nutritional consulting firm which also hosts 16 online courses on nutrition and horse care. Her work has led to unique nutraceutical approaches for horses with skin and respiratory allergies, degenerative as well as injury related tendon and ligament problems, chronic laminitis and performance issues. She is past veterinary and contributing editor to John Lyons Perfect Horse and Horse Journal magazines, and has written eight books and thousands of articles on equine nutrition, care and health issues. drkellon.com

 
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