Grainless foods are popular these days. And sometimes rightfully so – I know many have seen a difference when they switch an ailing dog or cat from a standard grain-based food to one that is lower in "carbohydrates" (presumably starch). It’s wrong to blame the grains, though, in many cases (I’ve talked about this here before).
Quick tutorial: Carbohydrates are essentially fibers, sugars and starches. Some (starches and sugars, mostly) are digestible, and are degraded from large molecules on ingestion to small molecules that are absorbed in the small intestine for energy. Grains like barley, wheat, corn, and oats contain digestible and indigestible carbohydrates in addition to fatty acids and proteins – they are more complex than a simple carbohydrate such as starch. Digestible carbohydrates are also contained in root vegetables like potatoes and yams, yuca (or tapioca), taro root, etc.
My biggest quibble with companies that tout a ‘grainless’ label on a dry food is that they are not carbohydrate-less, which is in reality what most pet owners think they are getting when they search for a Paleolithic, low carb (i.e. low starch) diet. I’m just saying, pet owner beware, because you cannot make a dry food without some carbohydrate, and these companies will simply substitute a starch from potato, sweet potato, tapioca or the like to do it. That’s not necessairly a 'low carb’ food.
But I want to talk about today is why some animals do better when switched from a high starch, or even moderate starch food, to a low starch food.
Many people go looking for alternative pet foods because they are forced to – they have a chronically ill animal (“chronically ill” pretty much defining a condition not amenable to conventional therapy). You would almost have to live under a rock to avoid the advice you’d get from fellow pet owners, pet store employees and websites that grain-free diets fix everything from skin disease to GI disorders to cancer.
In the case of animals with chronic conditions of many types, the central problem may be a sick gut. We used to (and still do) call this a leaky gut, but more recently gastroenterologists have come to agree that the condition exists, and call it a hyperpermeable gut. Chronic inflammation of the gut may appear due to food allergy or less well understood inflammatory processes like inflammatory bowel disease. Even a transient gastroenteritis or antibiotic therapy can lead to inflammation of the gut lining.
There are probably many arthritic dogs on long term therapy with nonsteroidal anti-inflammatory agents such as Metacam®, Previcox®, Deramax®, and Rimadyl® walking around with leaky guts, as well. The syndrome even has a name – NSAID enteropathy. For your edification, a review from the Journal of Pharmacy and Pharmaceutical Science in 1999 stated unequivocally that in people, “NSAIDs produce inflammation of the small intestine in 40 to 70% in long-term users” (Davies 2000). And if you’re really interested, “Exposure of the small bowel mucosa to NSAIDs is thought to lead to the loss of intracellular integrity and increased permeability because the NSAIDs damage surface membrane phospholipids and cause an uncoupling of oxidative phosphorylation” (Feagins 2010). Interestingly, NSAID use is also associated with lower numbers of Lactobacillus in the bowel (the good bacteria) which are known to improve gut mucosal integrity. (Mäkivuokko, 2009)
So chronic inflammation in the gut begins to erode the most superficial layers of the mucosal lining. The microstructure of the gut consists of tiny folds called villi, and the villi themselves have surfaces composed of enterocytes (cells of the gut mucosa) that have microvilli on the end that is exposed to the gut lumen. These cells actively secrete enzymes and other products that aid in normal digestion, absorption, and even immunity, and these products become more active as they mature, moving from the deeper layers of the gut to the tips of the microvilli. So what happens when the most superficial layer of the gut is eroded away due to inflammation?
One of the earliest theories from holistic medicine writers was that the gut immune system is exposed to abnormally intact molecules of food, and the animal (or person) subsequently develops food allergy or gluten enteropathy. Since the immune system can potentially become sensitized to any protein ingested, the poor patient experiences signs of food allergy constantly, including skin inflammation and diarrhea, and if you read the more esoteric literature, arthritis and a wide variety of autoimmune diseases.
But another circumstance suggests a simpler explanation for the inconsistent stool we see in some of these animals that eventually improve on a ‘grain free’ or low carb diet. In the ‘stressed’ enterocyte, mature digestive enzymes – disaccharidases that digest starches and sugars – are lost because of erosion of the luminal end – the part that is exposed to the GI contents, NSAIDs, etc. Examples of disaccharidases include lactase, maltase, sucrase, trehalase, isomaltase, and others.
So, disaccharides that result from digestion of more complex carbohydrates in the stomach and upper intestine flow down into the small intestine where disaccharidase enzymes would further digest them into a form that is easily absorbed. If they remain in disaccharide form, they are not absorbed and in fact pull water into the intestine. The result is loose stool, or diarrhea.
The problem is compounded the longer it exists. Carbohydrate malabsorption will lead to increased bacterial fermentation, which will cause gas and discomfort. Bacterial overgrowth (due to a surfeit of nutrition for them) can itself lead diarrhea.
So the neighbor comes along and recommends a grain-free diet, and the dog or cat gets better, and once again, the grains get the blame, when in actuality, the *starch* should get the blame. While allergy may or may not be a component of the reaction seen when grains are fed to these animals, the carbohydrate overload seems to be a bigger problem. And as I said before, carbohydrates are certainly common in ‘grain free’ diets - grain free does not mean low starch.
The good news is this – and I can verify that clinically this is extremely common – these ‘allergies’ aren’t permanent, unless the patient has a genetic disaccharidase deficiency (which is vanishingly uncommon in dogs and cats). In general, balancing the bacterial populations with probiotics, changing the diet so that it contains lower carbohydrate levels and sometimes different proteins, and addressing the cause of the initial bowel inflammation is all that is needed. Whether or not the owner wants to go back to feeding a diet higher in carbohydrates depends on other factors, like owner philosophy, financial capacity to buy the more expensive meat products, and whether the dog or cat has a weight problem (carbohydrates are used in weight loss diets to ‘cut’ the fat while still giving some bulk to the diet).
I just had to get this out there. Temporary carbohydrate intolerance is different from real food allergies. It's a much better diagnosis for your pet though, as there are no permanent food restrictions.
Davies NM, Saleh JY. Detection and Prevention of NSAID-Induced Enteropathy.J Pharm Pharmaceut Sci 3(1):137-155, 2000
Feagins LA, Cryer BL. Do Non-steroidal Anti-inflammatory Drugs Cause Exacerbations of Inflammatory Bowel Disease? Digestive Diseases and Sciences 2010;55(2):226
Mäkivuokko H, Tiihonen K, Tynkkynen S, Paulin L, Rautonen N. The effect of age and non-steroidal anti-inflammatory drugs on human intestinal microbiota composition. Br J Nutr. 2010 Jan;103(2):227-34. Epub 2009 Aug 25.