So much of what heart disease is about for people concerns the arteries becoming clogged with “gunk” because of a diet that’s high in saturated fat and cholesterol. The unhealthful diet translates to high amounts of cholesterol in the blood (and sometimes triglycerides), and this means arteries filling with plaques and narrowing over time until one of them becomes too narrow to allow blood to flow, resulting in a heart attack. The process leading up to the heart attack is called atherosclerosis.
It’s possible for dogs to get heart disease in this way, but it’s very rare. Unlike humans, dogs naturally have very little of the “bad” cholesterol in their blood and almost all “good” cholesterol, so they have an advantage from the start to have a lower risk for atherosclerosis than we do. Instead, four out of five cases of heart disease in dogs are about the deterioration of the valves that control the flow of blood between the heart’s four chambers. When a valve deteriorates, it no longer closes as tightly as it should after each heartbeat, so some blood ends up flowing backward instead of going forward and out from the heart to all the body’s tissues, like it’s supposed to. Through a stethoscope, the backward flow is heard as a murmur — a blowing or swooshing sound. It should be noted that this process can take a long time to develop; your dog may have a murmur for many years without any clinical problems.
It has nothing to do with what you feed your pet. Rather, the cause of the valve deterioration (what your veterinarian may refer to as chronic valvular disease) is genetic and tends to strike small- and medium-size dogs, including dachshunds, poodles, Maltese terriers, cocker spaniels, miniature schnauzers, Chihuahuas, and Cavalier King Charles spaniels.
The rest of the cases of heart disease in dogs are caused by problems with the heart muscle itself, resulting in progressive enlargement of the heart chambers and a reduced ability of the heart to contract vigorously enough with each beat. This kind of heart disease (called dilated cardiomyopathy) mostly affects large breeds: Dobermans, Great Danes, Irish wolfhounds, boxers, and Newfoundlands.
So are fat and cholesterol ever a concern for dogs?
What a Dog’s High Blood Cholesterol Means
There are in fact diseases that may cause a dog’s level of cholesterol or triglycerides in the blood to be too high. But they have nothing to do with the heart. Much of the time, elevated cholesterol or triglycerides are a marker for a disease of the endocrine system, that is, a disease involving the body’s hormones. For instance, hypothyroidism, which is too little production of thyroid hormone, can decrease the level of an enzyme responsible for dissolving fats and therefore lead to high blood fats. In fact, hypothyroidism is the most common cause of high blood cholesterol in dogs.
Diabetes, a deficiency of the hormone insulin, can also decrease critical levels of that fat-dissolving enzyme. Cushing’s disease, which results in too much production of the hormone cortisol, can result in high blood cholesterol, too, as can certain types of kidney disease. Yet another disease that can cause high blood cholesterol is a disease of the liver called nephrotic syndrome. That condition causes the liver to produce too much cholesterol, which then makes its way to the bloodstream.
In all of these cases, once you treat the disorder, the dog’s blood cholesterol and blood triglyceride levels return to normal. In other words, high blood fats are more the collateral damage of those illnesses than anything else. They do not cause those conditions.
That said, sometimes a veterinarian will treat the disease that results in high blood levels of cholesterol and triglycerides, and those fatty substances will remain elevated. Certain drugs, like cortisone, can also keep fatty substances in the blood elevated. And breeds like miniature schnauzers are simply prone to high blood fat levels; it’s in their genetics. Whatever the cause, you don’t want to leave things that way. Excess fat in the blood can cause our canine friends to suffer various symptoms, including everything from vomiting and diarrhea to abdominal pain, a swollen abdomen, and even seizures.
In those cases where treating an underlying disorder does not correct overly high blood levels of cholesterol and/or triglycerides or the dog must remain on a drug that leads to increased fats, or lipids, in the blood or has a genetic predisposition to high cholesterol, a veterinarian will prescribe a reduced-fat diet. That ratchets down the fat load the dog’s body must handle. A couple of months later, the veterinarian will draw some of the dog’s blood after a 12-hour fast. If the level of fat in the blood remains too high, an even lower-fat diet will be prescribed — something on the order of 2 to 3 grams of fat for every 1,000 calories consumed. It represents a drastic change in a dog’s typical high-fat diet but may be the only way to keep blood fat levels down. In some cases, even cholesterol-reducing drugs are called for.
Rest assured that very few dogs have to go on reduced-fat or very low-fat diets or take medication to reduce their blood cholesterol. Most of the time, when your vet treats the disease that leads to high levels of fatty substances in the blood, the levels return to normal. However, because high-fat diets are also high in calories, it’s best for healthful dog diets to provide moderate amounts of fat in general, along with moderate amounts of protein and carbohydrates that result in a low- or moderate-calorie food — the key phrase is “everything in moderation.”
Sodium’s Role in Canine Heart Health
While eating a lot of fat will not cause or exacerbate a dog’s heart disease, sodium plays a role in controlling that condition, just as it does for people. In people, sodium, a component of salt, is an issue for those with high blood pressure. To understand high blood pressure, think of your blood vessels as so many garden hoses. The pressure of the water tunneling through the hoses will rise if they are narrowed and pinched or if the spigot is turned up and forces more water through. Either way, that’s more wear and tear on the walls of the hoses, or blood vessels, which eventually will lead to their not working as they should and potentially result in a heart attack or stroke.
“Gunk” collecting along the walls of the “hoses” is what causes them to narrow, forcing the same amount of fluid to barrel through a tighter spot. The “spigot” is turned up if the volume of the fluid increases. That happens in many people with excess salt intake; salt holds water, so the blood becomes greater in volume and more fluid gets forced through in the same amount of time. That’s why cardiologists always recommend that people keep down their salt intake; the blood vessels do not need to be handling larger amounts of blood volume than necessary.
In dogs with heart disease, reducing sodium intake is about controlling blood pressure but also about reducing fluid build-up with congestive heart failure. Congestive heart failure is what occurs in dogs instead of heart attacks when their heart valves don’t work right or their heart muscle malfunctions. It doesn’t mean the heart completely fails to operate all at once and the dog dies immediately. It means that over time, fluid collects around the lungs or the chest, making it harder and harder to breathe until there’s no medical treatment left to control the problem.
It’s for that reason that a veterinarian treating a dog for heart disease will often limit the pet’s salt intake — to reduce fluid build-up. This is especially the case in advanced cases. Research at Tufts has shown that sodium-restricted diets leading to less fluid retention even reduces the size of the heart in a dog with heart failure — the heart doesn’t need to pump as hard because the blood volume is reduced, so the amount of heart muscle actually decreases. At the other end of the feeding spectrum, many dogs with heart failure develop more severe signs of fluid congestion after holidays or family gatherings during which they receive salt-laden table scraps.
Whether to restrict dietary sodium after a dog’s heart valve starts causing a murmur but before congestive heart failure actually begins to have effects is controversial, with equivocal evidence. Excessive sodium restriction at that stage may actually result in more harm than good by leading to water retention. The body will detect reduced blood volume and will activate mechanisms to restore it. Your vet will guide you through the complexities of picking a time to begin limiting sodium in your dog’s diet.
Of course, at any stage in heart disease, or even in healthy pets, there is no harm in avoiding very high-salt diets. High-salt foods usually come in the form of treats, or in the ways we give medicine to our pets: wrapped in cheese, deli meats, or bread. Just as with fat, moderation is key in healthy pets.