Rover and Fido on low-carb diets?
This last year I have been living what people call a "low-carb lifestyle." I quit dieting about 25 years ago, but I have recently found that curtailing my consumption of things like bread, pasta, sugar, and other high-carb victuals, has resulted in positive changes. I've lost weight, have more energy, and no longer have chronic heartburn. But I was concerned about how my new menu, with the increased portions of eggs, cheese, and meat, might affect my cholesterol. So before my last visit to the doctor, I skipped breakfast. I knew that if we wanted to accurately assess my cholesterol levels, I needed to fast for 12 hours before the blood draw. Most of you probably are careful about the fat content in your diet and have heard of LDLs and HDLs, the "good" and the "bad" cholesterol, but what about Schnitzel the Schnauzer? Should we be testing his cholesterol? His HDLs and LDLs? After all, he does eat a lot of meat. If you really want to understand, let's start at the beginning and define our terms.
Lipids. Lipids are fat molecules that are necessary for our bodies to function. They are insoluble in water. Oil and water don't mix, right? Triglycerides are one type of lipid. Cholesterol is another. In order for our water-based blood to move these water-insoluble lipids around to where they need to be, we form lipo-protein complexes. There is a bunch of different type of lipoproteins including chylomicrons, very-low-density (VLDL), low-density (LDL), and high-density (HDL.) Have I lost you yet? All you really need to know is that each of these lipo-proteins has a specific function. The doctors want us humans to have low levels of LDL and high levels of HDL because, in people, it is thought that LDLs are more likely to build up and clog the arteries that lead to the heart and brain while HDLs may actually remove excess cholesterol from the arteries, reducing the risk of heart attack and stroke.
Feed or fast?
Next big word: hyperlipidemia. Hyper is from the Greek meaning "over, above, exceedingly." Lipid, which we already covered, includes cholesterol and triglycerides. Emia is from the Greek haima meaning blood, hence "hyperlipidemia," which may include hypertriglyceridemia, hypercholesterolemia, or both. The most common cause of hyperlipidemia in dogs is lunch... or dinner, or breakfast. It can take as long as 12 to 16 hours for postprandial lipid elevations to clear. If I have drawn blood on Schnitzel for some other reason at a routine appointment, say to check his kidney function, and I happen to see a high cholesterol, I remember that he probably wasn't fasted. Then I consider a few factors including his age, breed, weight, and other medical conditions. Then, if I am still concerned, I'll advise we recheck the cholesterol and triglycerides after withholding food for 12 hours. If he is still hyperlipemic, we continue our search.
The majority of cases of fasting hyperlipidemia in dogs are secondary to other metabolic disturbances. Diabetes. Hypothyroidism. Cushing's disease. Protein-losing nephropathy. Your vet can tell you about any of these that seem likely for your particular pet, and discuss the next diagnostic steps. If there is no evidence of any underlying disease, there is a small chance your dog may have primary hyperlipidemia. What's that? You know how those commercials for Lipitor and other such drugs tell us that it's not just what we eat that affects our cholesterol levels, because that we can have an inherited tendency to high cholesterol? Well, although it is rare, there does appear to be an inheritable, familial form of hyperlipidemia in animals, primarily in miniature schnauzers, although it has also been reported in Doberman pinschers and rottweilers. In cats, an inherited form of hyperchylomicronemia is reported, especially in Himalayans.
So what are the medical implications of hyperlipidemia in dogs and cats? Dogs with persistent fasting hypertriglyceridemia are predisposed to pancreatitis and other gastrointestinal problems including intermittent episodes of tummy aches, poor appetite, and vomiting. Both cats and dogs may develop abnormalities in their eyes, and are prone to benign fatty tumors in the skin and abdominal organs. Cats may develop neurological problems in their limbs. Miniature schnauzers may seizure. But all these syndromes are fairly rare. The main concern when we see fasting hyperlipidemia is to ferret out and address underlying illnesses. If Honey the Hound has diabetes, once we get her insulin going and her blood sugar regulated, the hyperlipidemia may resolve. If Pokey the Poodle has hypothyroidism, a little thyroid supplementation should do the trick. But if the hyperlipidemia persists, or is primarily familial in origin, then it may make sense to introduce some changes to try and lower the lipid levels.
Fish oil benefits
The first step is simple, and the same as you or I would do for ourselves - a low-fat, high-fiber diet. There are many commercial dog foods available that fit the bill, but if these don't do the trick, there are special recipes for home-cooking. Many specialists advise supplementing dogs who have hyperlipidemia with fish oils. I know that may seem counterintuitive, but apparently our grandmothers were right when they touted the benefits of a regular dose of cod liver oil (though I recommend using a more refined and scientifically formulated fish oil product nowadays). Finally, the use of lipid-lowering medications may be recommended, although there are far fewer scientific studies on the safety and efficacy of these drugs in pets than in humans.
Do dogs with hyperlipidemia get atherosclerosis like people do? Probably a lot less often than we do. Do we check HDLs and LDLs? Not at this point in the state of the art. Dog and cat metabolisms are different than human and the usefulness of monitoring these parameters is in question. Bottom line is that for Schnitzel, Honey, Pokey, and all the other pets, common sense is paramount. Keep them at a healthy weight and on a regular exercise program. Get annual checkups with your veterinarian. If indicated, switch to a low-fat diet. Remember that, for pets, high cholesterol levels usually don't pose an immediate health risk. Their main usefulness is to send up a little red flag now and then, giving us a hint to look for underlying endocrine or metabolic disease. My levels were fine, by the way. Two eggs over easy, please. Hold the toast.