FINAL UPDATE 12/27/22 The FDA has closed its investigation into this matter, saying there is “insufficient evidence” to establish a causal link between diet and DCM in dogs. They will not be providing any further updates.
NOTE: We now know that, as suspected all along, the purported link between grain-free pet foods and heart disease was entirely speculative. I can say with confidence that grain-free foods DO NOT cause heart disease in dogs or cats. There was and is no scientific evidence to support FDA’s original theory, much less its naming of brands involved. For a detailed history and analysis, see this article by Dr. Ryan Yamka.
I am leaving this information up to provide background, a little science, and a glimpse into the perhaps-too-cozy relationship between the FDA, pet food companies, and veterinary schools.
In July 2018, the FDA released a warning about grain-free dog foods and their possible connection to the development of a serious heart disease in dogs. Is this warning justified, based on science? Let’s take a look.
What is Taurine?
Taurine is an amino acid produced in the liver and almost exclusively found in meat. It is abundant in the brain, the eye (especially the retina), muscle tissue, and many organs. It is an essential component of bile acids, which are produced in the liver, stored in the gallbladder, and used to break down fats from food.
Most mammals produce their own taurine in the pancreas from amino acid precursors. (Notable exceptions are cats and weasels–including ferrets–who must consume taurine in their diet.) The first step involves the sulfur-containing essential amino acid methionine, which is used to make another amino acid, cysteine (also spelled “cystine”). Finally, taurine is made from cysteine. Taurine production naturally decreases with age.
Taurine plays many roles in the body. It is crucial for muscles, especially the heart muscle. Taurine is utilized in every area of the brain, as well as the retina of the eyes. It is essential for immune system function. Taurine acts as a potent antioxidant and anti-inflammatory agent. More specifically, it has been shown to improve periodontal disease in humans. It also helps regulate blood pressure, and is an extremely important cellular protector. It is used to treat hepatic lipidosis (fatty liver) in cats as well as people; and it may be helpful in kidney disease. Taurine has a profound effect on the development and course of both Type 1 and Type 2 diabetes.
Before WWII, more than 90% of commercial pet food came in cans, and contained mostly if not only meat. However, metal was needed for the military, and by the time the war ended, 85% of pet food was dry kibble. It still contained a large amount of meat, and this prevented taurine deficiencies from occurring.
The primary machinery for producing what we now know as dry food is called an extruder; it was introduced in the 1950s. To get the correct consistency of dough for the extruder, a minimum amount of starch is needed. This started the trend of ever-increasing quantities of cereal grain, such as corn, in dry foods. At the same time, meat processors were getting more proficient at getting more meat from livestock carcasses; so pet food makers substituted other leftover animal tissues or “by-products.” Over time, the result was a high-grain, low-meat dry food, for which the profit margin was—conveniently—much higher than for canned food.
In the late 1970s, cats started going blind or dying from congestive heart failure due to a condition called dilated cardiomyopathy (DCM). Many of those cats were eating the same food (Hill’s Science Diet); and this was noticed by researchers at UC Davis. In the mid-1980s, they published the results of their research showing that taurine deficiency was the issue. Pet food manufacturers hastened to supplement taurine in their feline diets. Since then, DCM (dilated cardiomyopathy) dramatically decreased in cats eating commercial, “balanced” cat food.
Taurine and Dogs
Dogs make their own taurine from sulfur-containing amino acids, primarily cysteine, but also methionine. It was thought that, because they could produce it themselves, dogs didn’t need supplemental taurine.
However, it is also known that that big dogs produce taurine at a slower rate than small dogs, putting them at risk for a deficiency. Genetics also play a significant role, with certain breeds and family lines being predisposed to developing DCM.
The existence of a link between taurine deficiency and DCM in dogs has been known at least since 1997—some dogs can’t supply their own taurine needs. Certain lines of spaniels, retrievers (notably Golden Retrievers), and Newfoundlands, are known to develop the same taurine-dependent form of DCM that killed tens of thousands of cats.
DCM is a common form of heart disease in dogs, especially in large and giant breeds. Diet is a likely factor in about 20-30% of dogs with DCM, for which supplementing taurine may reverse the disease. Symptoms of DCM include tiring easily, shortness of breath, and coughing.
However, it may not be a specific taurine deficiency in the food that is a contributing factor in DCM. Some research suggests it may be insufficient cysteine that limits the dog’s ability to produce taurine. Remember that dogs make cysteine from methionine, and taurine from cysteine. Any weak link in the chain of methionine, cysteine or taurine could be problematic.
Because of this dependency, only methionine has a minimum level in dog food according to current AAFCO standards; there is also a minimum for the combination of methionine + cysteine. There is no requirement for taurine in any dog food.
L-carnitine, another amino acid found primarily in meat, may also play a role in the development of DCM in a small percentage of dogs. L-carnitine becomes unavailable in pet food through processing, and is generally not added back due to its high cost.
In early studies, most of the dogs with DCM were eating lamb and rice dog foods. Lamb has a relatively low level of sulfur-containing amino acids compared to chicken and other poultry. Another study found that dogs eating foods containing beet pulp had lower blood taurine levels.
Possible reasons for low blood taurine levels in dogs fed an otherwise “complete and balanced food” that have been suggested include:
- Differences in protein digestibility and bioavailability may limit available precursors
- Interference with reabsorption of taurine-containing bile acids in the gut so that more taurine is excreted
- Interaction of food and/or food form (canned vs. dry) with gut bacteria
- Type of processing that limits taurine bioavailability
The FDA’s No Good Very Bad Theory
The FDA reported a link between DCM and “grain-free” dog foods that rely heavily on potatoes, legumes, and exotic proteins. Vegan and homemade diets were also reportedly involved. This caught FDA’s attention because some of the dogs were not the breeds that are known to develop DCM due to taurine deficiency; these dogs included Labrador Retrievers, Whippets, Miniature Schnauzers, one Shih Tzu, one Bulldog, an unspecified number of mixed-breed dogs–and at least 20 cats.
Specifically, the FDA stated that “potatoes or multiple legumes such as peas, lentils, other “pulses” (seeds of legumes), and their protein, starch and fiber” were main ingredients of the food in several cases of DCM reported to the agency. Note the careful language used in its statement: potatoes are singled out, but with regard to legumes, multiple legumes and their isolated components were main ingredients in implicated diets. The term “BEG” (boutique companies, exotic ingredients, or grain-free diets) was quickly coined by a group of researchers at Tufts University. The lead veterinarian has often expressed strong opinions against homemade pet food, raw pet food, and pretty much any pet food that isn’t made by the biggest U.S. pet food makers. As we’ll see, both FDA and the Tufts professor were flat out wrong.
FDA did say that people should “not tak[e] intuitive leaps beyond what is explicitly stated in our public notice.” That is, don’t assume that all legumes are problematic, and their information should not be taken as advice to switch pet foods.
The majority of implicated diets were dry foods (not a great logical leap since that is what the vast majority of dogs are fed in the US). It may be worth noting that, in the case of cats, canned foods need supplemental taurine at a much higher level than dry foods, because cats’ gut bacteria interact differently with those food forms.
Based on FDA’s statement and previous research, ingredients that may be correlated with DCM in dogs and are (more or less commonly) used in dog foods include:
|Animal Products||Plant Products|
* While it was not named by FDA in this situation, beet pulp is known to decrease taurine status in dogs under some conditions.
** Previous studies found taurine deficiency in dogs (and cats) eating diets containing rice or rice bran.
Along with Tufts, FDA also suggested that food made by small “boutique” manufacturers were more likely to be problematic. Indeed, some foods that appear to be overloading plant proteins were from smaller manufacturers. However, FDA definitely did not exclude products from big manufacturers; many of the so-called “boutique” brands are in fact owned and produced by the world’s biggest pet food companies. I personally reviewed a set of 19 cases where DCM was tied to a particular dog food. Of those 19 foods, 15 (80%) were from major manufacturers.
In July 2019, FDA named 16 dog food brands associated with 10 or more cases of DCM. Of those, only 2 were made by small, independent manufacturers. The rest were owned and/or manufactured by large multinational companies or co-packers for a wide variety of private-label pet foods.
It seems odd that this problem should occur now, even though potatoes have been used in dog food—particularly “hypoallergenic” formulas—for decades. Many such foods also included, and continue to include, lamb or other above-listed animal ingredients as the primary or sole animal protein.
For example, Hill’s Science Diet d/d lists potatoes, potato starch, [venison, salmon, or duck], and potato protein as its first four ingredients. One would think such a would be particularly dangerous, except that Hill’s adds taurine to these foods. Most vegetarian and vegan dog foods also include both taurine and carnitine. Evidently, this issue was not hard to anticipate in low- or zero-meat diets.
Of course, correlation does not equal causation, and there are no doubt other factors involved. Unfortunately, some media reports have focused on legumes, even though potatoes are a far more common pet food ingredient. Legumes are very nutritious, and used properly, can be a very healthy ingredient.
Many grain-free diets contain two or more of the ingredients noted by FDA and other researchers. For example, several salmon-based foods also contain potatoes and/or beet pulp. Some foods list up to five legumes/derivatives, sometimes in addition to potatoes or a listed lower-taurine meat like venison or lamb, as major ingredients.
As with many cat products, some dog foods are inordinately high in plant-based products with not so much meat. Certainly, plant proteins are often used to increase total protein and decrease cost in many dog foods.
Ingredients are listed by weight on the label; using multiple legumes, potatoes, or fractions thereof (a practice referred to as “splitting”) allows a company to include far more plant protein than meat protein, while allowing the named meat to remain at the top of the ingredient panel. So, it may not be potatoes or legumes that are the problem; rather, it may be an overwhelming amount of potatoes or legumes.
Most small-manufacturer and grain-free diets are relatively high in protein, but the proportion of plant to animal sources may be a crucial factor for those foods implicated by the FDA.
There are several other factors that could affect dogs’ blood taurine levels that have not been considered:
- Perhaps there is some intrinsic factor in legumes and potatoes that is acting as an “anti-nutrient” and binding or otherwise interfering with taurine metabolism.
- Something is happening during processing that is causing taurine in these foods to become unavailable. (We know, for instance, that taurine from fish is diminished by heat processing; the loss is about 30%.)
- Disruption of the microbiome (gut bacteria population) alters taurine bioavailability in cats through the action of gut bacteria; perhaps this is true for certain dogs as well.
- Affected dogs may have altered pancreatic function, such as subclinical pancreatitis, that prevents nutrient absorption and/or adequate taurine synthesis.
To my knowledge, these possibilities have not been explored at all.
At this time, FDA is not recommending a diet change for any dog, as their investigation is in the very early stages. They have found DCM in dogs eating all kinds of foods, from those with a simple ingredient list to very complex foods. And while all the above ingredients have at some time been associated with DCM in dogs, at this time FDA is only correlating potatoes and legumes.
FDA further clarified to me that “foods containing multiple pulses that appear near the top of the product’s ingredient list have appeared more frequently in the reports we have received thus far.” (Emphasis added.)
It’s important to note that not all dogs with DCM—and not even all dogs who also had very low blood levels of taurine—responded to taurine supplementation (whether via diet change or separate supplement). This implies that it may not be taurine itself that’s the problem (at least in those cases); but as noted, it certainly could be lack of methionine and/or cysteine. Conversely, many of the sick dogs had perfectly normal blood taurine levels. An earlier study concluded that “there was no clear relationship between low [whole blood taurine] and presence of DCM.”
The association between diet and DCM is far more complicated than simply blaming the problem on one or two ingredients. It seems clear that the interplay between genetics and one or several of ingredients, and perhaps the food’s overall content of methionine, cysteine, l-carnitine, and taurine, that is at the root of DCM in these cases. But as of FDA’s latest update (June 2019), no one really knows which factors are actually problematic, or in what amounts or combinations.
It still seems most likely that in a product containing sufficient animal protein, taurine levels will be adequate. BUT… if a food has an animal protein at the top of the ingredient list, but also:
- Contains four or five plant proteins and fractions of plant proteins that—in reality—constitute the majority of total protein, or
- Consists primarily of a meat ingredient known to be relatively low in taurine (ruminants like lamb, beef, venison and bison, as well as kangaroo) plus plant proteins
Then there may not be enough taurine or its precursors to support adequate synthesis in the dog.
This includes “[d]iets in cases reported to the FDA frequently listed potatoes or multiple legumes such as peas, lentils, other pulses (seeds of legumes), and their protein, starch and fiber derivatives early in the ingredient list, indicating that they are main ingredients.” (Emphasis added)
One thing that is clear from all this is that AAFCO needs to revisit its Nutrient Profiles (which are based on research published prior to 2003) and either (1) increase the minimum for methionine, (2) increase the minimum for methionine-cystine (sic), and/or (3) add a notation that cysteine and taurine are at least conditionally essential amino acids for dogs. Taurine minimums for cat food also need re-examining, as cats have also been affected. (See 8/10/18 Update below.)
Most importantly, of the tens or perhaps hundreds of thousands of dogs eating “boutique” and grain-free foods, only a handful have been linked to the problem. It is not yet time to press the panic button, despite the ongoing media storm.
However, it would be helpful if pet food manufacturers would test for the four key amino acids to ensure that levels are sufficient for all dogs, or perhaps simply supplement taurine in food for dogs, as they already do for cats. Several companies have already taken that step.
If you’ve been feeding a potentially taurine-deficient food, you may want to give your dog supplemental taurine, about 250 mg per day for every 40 pounds of the dog’s body weight. Fortunately, taurine is very safe, even at extremely high doses.
UPDATE 6/29/19: Top pet food brands associated with DCM cases
- Acana – 67
- Zignature – 64
- Taste of the Wild – 53
- 4Health – 32
- Earthborn Holistic – 32
- Blue Buffalo – 31
- Nature’s Domain – 29
- Fromm – 24
- Merrick -16
- California Natural -15
- Natural Balance -15
- Orijen -12
- Nature’s Variety – 11
- [N]utriSource – 10
- Nutro – 10
- Rachael Ray Nutrish – 10
UPDATE 8/5/18: NBC did a report (1:53 minutes long and somewhat misleading). The veterinarian they filmed specifically said dogs need a GRAIN-based dog food. Sadly, people are being scared off ALL grain-free foods and back to GMO, pesticide-soaked, corn-based foods.
We’ve never advocated grain-free food, since most of it simply replaces grains with high-carb starchy vegetables, like potatoes, peas, sweet potatoes, and legumes–and carbs are the worst problem. Make sure your dog’s food contains mostly meat and not half a dozen vegetables or fractions (potato starch, pea fiber, etc.) that add up to the largest proportion of the food.
UPDATE 8/8/18: The FDA’s characterization of “boutique” foods is apparently way off the mark. Major pet food companies (including but not limited to Champion, Mars, and Purina) are involved: they either make grain-free diets themselves, or they’ve bought out small manufacturers (and not changed the brand name –most consumers are unaware of these acquisitions). Specific brands that have been implicated include (in alphabetical order): Acana (made by Champion), California Natural (owned but discontinued by Mars), Merrick (owned by Purina), Nutrisource (owned by co-packer Tuffy). (Sources: American College of Veterinary Internal Medicine, Veterinary Information Network)
UPDATE 8/10/18 The FDA has released a “Questions and Answers” post for consumers. They revealed that their initial report involved 30 dogs and 7 cats. They never mentioned cats before. They now have 150 confirmed reports of affected dogs, and an unknown number that are being examined. With growing public awareness, there are undoubtedly hundreds of reports pending, but not all will be confirmed as taurine-deficiency DCM. It is possible for a dog to have DCM with completely normal taurine levels, and some dogs with low taurine levels will not develop DCM.
UPDATE 8/10/18 More brands involved–to find out which ones, join the Facebook group “Taurine-Deficient Dilated Cardiomyopathy.” The data is confidential and may not be shared outside the group, but it’s extremely valuable information!!
If your veterinarian wants to to do a blood test for taurine, the lab at UC Davis is doing the tests. Normally their turnaround time is 48 hours, but as you might expect, they are swamped, and processing time is now at least a week. Please be patient!
UPDATE 6/27/19 FDA releases an update on the steps it is taking to investigate this issue.
UPDATE 12/27/22 The FDA announces that there is “insufficient evidence” to establish a causal link between diet and DCM in dogs. They will not be providing any further updates.
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