Friday, July 26, 2013

The Science Behind Everyday Foods that Could Poison Pets

Most pet owners have been told that feeding human food to pets is usually not a good idea, partly because the nutritional requirements for pets and people are different. Reputable dog and cat foods are designed to provide the proper nutrition that pets require. Most vets recommend that other food items like table scraps or treats should make up no more than 10% of your dog's or cat's daily food intake.

However, feeding certain human foods to pets can also be very dangerous. This is because there are many everyday foods and drugs that are very safe for us but are not safe for animals like dogs or cats. Most people know that chocolate is really bad for dogs and cats, but there are actually many more common foods that you may not know of that are also bad for your pets, especially if eaten in large amounts. When I first got a dog almost 2 years ago, I was confused by what "people foods" were really toxic to her.n For instance, someone would tell me that onions or garlic are toxic to dogs, but often they could not really explain why or where they learned this from. They also could not explain why garlic, despite being labeled as "toxic" for dogs, is often on the list of ingredients for dog treats and dog foods.

It was confusing, so I started reading about what is really known about toxicity of foods for pets.  I put this blog post together to create a list that may be useful and may help explain some of the science and reasoning behind why certain foods are "bad" for pets.
Read more about common foods that are safe for you but could be toxic or poisonous to your pets after the jump....

Obviously the best solution is to only feed your pet food that is made for them and which comes from a reputable company recommended by your vet. However, animals frequently get their paws on "people food" despite our best efforts. Little kids feed their own food to pets when adults aren't looking, and many people like to include table scraps along with their dogs dinner. In this post, we'll go through a list of "people foods" that could be toxic to pets, along with a little bit about the science behind the toxicity. Hopefully this serves to help a few pet owners who may be as confused as I initially was. A lot of foods on the list can cause mild symptoms such as short-term digestive upset, vomiting, or diarrhea; however, some of these foods, in high enough doses, can cause more severe symptoms that may result in death. Pet owners need to be aware of foods that are considered very safe for people that are not considered safe for animals.

There are two common reasons for the differential toxicity of some foods for pets despite their safety for humans. The first is that many dogs and cats are much smaller than people. The golden rule of toxicology is that dosage makes the poison. The 16th century physician Paracelsus wrote that all substances are poisons and it is only the right dosage that differentiates a remedy from a poison. For the most part, he was 100% correct. Lots of medications that people take everyday, including ibuprofen and tylenol, can be very toxic if taken in high enough dosages. At the indicated therapeutic dose, however, they are quite safe. Compared with people, bad effects can occur with much smaller amounts of toxic substances in dogs and cats due to their smaller body weights.

Because of the importance of body weight to toxicity, toxic doses of substances are usually reported as an amount per body weight. For example, an estimated toxic dose may be reported in milligrams (mg) per kilogram (kg) of body weight (1 kg is about 2.2 lbs). The toxic dose of a substance for a 20 kg dog (approximately 44 lbs) would be about twice as much as for a 10 kg dog (approximately 22 lbs) because the larger dog is about twice the size.  But, this is only a general guide; there will be a lot of variation between how different individual dogs or cats handle certain substances, just as there is individual variation in how certain drugs work for certain people.

The second common reason that some foods are safe for people but toxic for pets is that the metabolism and biochemistry of animals can be very different from people. Some substances like caffeine are easily handled by the liver and kidneys of a human and removed from the body; however, dogs and cats can't get the caffeine out of their bodies quickly, which makes the effects much stronger and longer lasting. Differences in metabolism like this can increase toxic effects of many compounds for pets.

Let's quickly discuss three important biological processes that can control the effects of a given "dosage" of a toxic substance. These are important concepts in toxicology, which is a branch of biology that studies toxic substances or poisons. The first process is the rate of absorption of a chemical. A chemical that is quickly absorbed out of the gastrointestinal tract (stomach and intestines) could reach a very high concentration within the animal very quickly, and thus may have more toxic effects than something that is absorbed more slowly. Second is the rate of metabolism of the toxic compound. If the liver of an animal can easily and quickly de-activate a toxic compound by breaking it down or turning it into something else (metabolizing it), the effects of that toxic compound may be minimal. Third is the elimination or exertion of the toxic compound. A toxic compound eaten by an animal that causes an animal to immediately vomit will likely have less toxic effects because it gets removed quickly. Likewise, chemicals that are absorbed but are quickly removed from the blood by the kidneys may also also have minimal toxic effects. Fast absorption, slow metabolism, and slow elimination/excretion are all bad when it comes to toxic or poisonous substances.

I think that most pet owners would agree that dogs typically have less "discriminating tastes than do cats. Dogs love to put things in their mouths. Because of this, dogs account for 3 times as many cases of potentially toxic exposures brought to vets. However, cat owners still need to be vigilant. There are many cases each year of cats being accidentally poisoned by foods meant for humans.

There's a large degree of variability of the responses of various individual animals to some of the below foods; some dogs or cats may be more or less sensitive to certain foods than others.
Dogs love to explore the world through their mouths.

Just as Ben Franklin wrote, "An ounce of prevention is worth a pound of cure. The items listed below are best kept away from your cats and dogs unless specifically told otherwise by a vet, which I am not. Thus, we need a disclaimer for this post: I am not a vet. I'm not telling you what you should feed your dog or cat. I'm only telling you that the foods and food products on the list below could be bad for your pet as they have been reported to be poisonous to some pets.

Alcohol (Ethanol)
Some people think it's funny give their dog some beer and watch him or her get drunk. This is a bad idea for your pets health. Ethanol is the major alcohol in wine, beer, and liquor. Ethanol is produced when yeast ferment sugar, as we discussed in a previous blog post.  Ethanol can be toxic to pets just like it can be toxic to people in high doses. The major difference is that pets are usually smaller, which makes ethanol all the more toxic to them. Pets can also get toxic doses of ethanol (the type of alcohol in beer and wine) from eating fermented fruits or fermented but uncooked bread doughs.    

When too much ethanol is ingested, pets can exhibit the same the depressant effects that are seen in people who drink too much. People die every year of alcohol poisoning, and so do pets. Due to their smaller size, alcoholic beverages intended for people can kill them more easily.

Alcohols like ethanol are absorbed through the lining of the gastrointestinal tract very quickly, in as little as 15 minutes, and symptoms usually appear within one hour of ingestion. Ethanol can act as an antagonist (a blocker) of N-methyl-D-aspartate (NMDA) receptors in the brain. Ethanol can also bind to and help activate isoforms of gama-aminobutyric acid (GABA) receptors and glycine receptors that are all important for inhibition of neural signals. Ethanol can also increase the levels in the dopamine in the body, potentially by inhibiting the enzymes that break dopamine down. We're only beginning to understand all of the pharmacological effects of ethanol, but the end result is typically a decrease in neural activity. Symptoms of alcohol poisoning include lethargy, depression, sedation, lack of coordination, and low body temperature (hypothermia). Alcohol can cause respiratory depression (slowing of breathing) that can even result in death.

Another reason to keep pets away from alcohol is that there are other compounds in alcoholic beverages in addition to ethanol that are safe for us but toxic to dogs or cats. For example, the hops in beer can potentially be toxic to some dogs. Ingestion of hops has been reported to cause fever (hyperthermia) in dogs, though this usually responds very well to treatment. However, the best strategy to keep your pet safe is to keep him/her away from alcohol and alcoholic beverages.

Avocado can be poisonous to some dogs and cats, though the exact mechanism or toxic dose is not known because the effects are very variable in different animals. Avocados have been reported to cause fluid accumulation in the lungs and chest of some dogs, leading to difficulty breathing and potentially death. The high fat content of avocados can also result in pancreatitis, a dangerous inflammation of the pancreas that small dogs are especially susceptible to. While some dogs appear to be just fine with eating avocados, pet owners should avoid feeding pets guacamole or other foods with avocados as an adverse reaction could be very bad. Symptoms of avocado ingestion can include gastrointestinal distress (diarrhea or vomitting) or respiratory distress and labored breathing.

Birds can be extremely sensitive to a chemical in avocados called persin, which is a fungicidal (fungus-killing) compound that the avocado plant makes to protect itself against fungal infection. In some birds, ingestion of avocado fruit or leaves can cause death within 12-24 hrs.         

Caffeine and Other Methylxanthines
Caffeine (1,3,7-trimethylxanthine) is found in tea, cola, and chocolate, as well as in diet pills, cold medications, and some herbal supplements.  In additional to caffeine, there are many other related methylxanthine compounds that similarly function as stimulants such as theobromine in chocolate (described below) and others in herbal supplements containing guarana, Hoodia gordonii, ephedrine, or 5-hydroxytryptophan).  Methylxanthine molecules like caffeine can have numerous toxic effects on dogs, cats, and other animals.    

Humans metabolize (break down) methylxanthines much more quickly than animals do, and thus the concentration of caffeine and other methylxanthines found in foods is not toxic to us, but it is to animals.  The minimum lethal dose of caffeine for dogs is estimated to be about 140-150 mg/kg of animal body weight.  Cats are slightly more sensitive and have a minimum lethal dose of about 100-150 mg/kg.  The average cup of drip coffee is about 80 mg caffeine per 5 oz cup, while cola has 40-60 mg per 8 oz cup.  Thus, a cup of coffee or a can of soda might not be enough to outright kill a dog or cat, but it could certainly make them very sick.  Solid sources of caffeine like coffee beans (280-570 mg caffeine per oz ) are much more dangerous.   Chocolate products contain anywhere from 2-40 mg/oz caffeine, but chocolate is even more toxic due to the presence of theobromine and theophylline, other methylxanthines that we'll talk about below.  Trace amounts of theophylline are also found in tea.   

Animals can absorb caffeine very rapidly, and caffeine can easily cross the blood brain barrier, which is one reason it functions so well as a stimulant in people.  Methylxanthines can stimulate an increase in heart rate and increase circulating levels of epinephrine (also known as adrenaline) and norepinephrine (also known as noradrenaline).  Methylxanthines also cause stimulation of the central nervous system by increasing production of an intracellular signaling compound called  cyclic-AMP (cAMP) and by interfering with receptors for a nerve transmitter called adenosine.  While that can be beneficial to a trucker drinking a cup of coffee to help him or her pay attention to the road, it can be dangerous to a dog or cat because of their inability to metabolize the methylxanthines the same way that a human can.   Symptoms of methylxanthine poisoning in animals can include cardiac arrhythmia (irregular heartbeat) or tachycardia, hypertension (high blood pressure), heart attack, neurological symptoms like siezures, convulsions, or tremors, fast breathing (tachypnea), weakness, or even coma.  Without proper and timely treatment, death can occur within hours.    

If you suspect that your dog or cat has eaten something containing caffeine, you should immediately contact your vet.  Effective treatment must start early.  The major vehicle for toxic caffeine exposure in pets is chocolate, but caffeinated beverages, espresso beans, tea bags, and other products containing caffeine are also dangerous. 

Chocolate contains caffeine, as well as two other  methylxanthines, theobromine (3,7-dimethylxanthine) and theophylline (1,3-dimethylxanthine).  Holidays like Valentine’s Day, Easter, Halloween, and Christmas are the most dangerous times for chocolate poisoning for pets because there often a lot of chocolate around.    The theobromine, theophylline, and caffeine come directly from the cocoa beans used to make chocolate.  Cocoa beans contain as much as 1-2% theobromine.  However, different types of processed chocolate have other additives and different amounts of cocoa.  The methylxanthine content of chocolate can vary from 14-28.5 mg per gram (400-800 mg/oz) for cocoa powder down to over 10-fold less (1.6-2.3 mg/g or 44-64 mg/oz) in milk chocolate.  Unsweetened baking chocolate (14-16 mg/g; 390-450 mg/oz) and semisweet dark chocolate (5-6 mg/g; 142-170 mg/oz) are particularly dangerous sources of methylxanthines for pets.  Darker and richer chocolates usually have a higher percentage of cocoa solids and thus a higher percentage of methylxanthines, making it more dangerous.   

White chocolate is not a significant source of methylxanthines (0.01 mg/g; 0.25 mg/oz) since it is only made from cocoa butter and not the dark part of the cocoa beans. Thus white chocolate is not nearly as poisonous to dogs and cats as regular chocolate.  Very large quantities of white chocolate must be consumed to poison most animals.  However, white chocolate is still a very high fat food that could cause problems such as GI upset or even pancreatitis and should not be given to pets.  

The effects of chocolate are dictated by variable factors such as cocoa composition, whether the animal ate the chocolate on a full or empty stomach, and the particular sensitivity of the individual animal.  In toxicology, the LD50 (or "lethal dose 50%") is a measure of the median lethal dose of a toxic substance; the LD50 is the dose at which half of the members of a population exposed to that dose would be expected to die.  This number is usually experimentally determined in the lab.  The LD50 for theobromine for pets is estimated to be around 200 mg/kg for cats to 250-500 mg/kg for dogs.  

Taking into account the amount of theobromine in various chocolates, it is estimated that less than 125 grams (4.4 oz) of baking chocolate or 60 grams (about 2.2 oz) of cocoa powder is enough to potentially kill a 10 kg (22 lb) dog, but serous symptoms may still occur with doses as little as 25 grams (0.8 oz) of baker’s chocolate in a 10 kg dog.  The smaller the dog, the less chocolate needed for a toxic reaction.  Because of the variability of the sensitivity of animals to chocolate as well as the variability of methylxanthines in different types and brands of chocolate, it is best to get in touch with your vet right away if you suspect your dog or cat has eaten chocolate.  

Cured Meats (Ham, Bacon, Salami, etc.)
First of all, cured meats are almost always very salty.  To much salt is bad for your dog or cat, especially if they don't have enough water to drink (for example, if you've left them home alone without refilling the water bowl--always give your pet plenty of water).  You can read more about this in the "Sodium" section below.     

However, cured meats also contain nitrates.  Sodium nitrate and potassium nitrate (also known as saltpeter) have been used to cure and preserve meats since the middle ages.  Nitrates and nitrites break down (decompose) into nitric oxide, which has anti-bacterial effects and prevents meat from spoiling.  In addition to being antibacterial, nitric oxide is also an important signaling molecule that causes blood vessels to dilate by stimulating the smooth muscle cells that surround them to relax.  Nitrites and nitrates in the blood can decompose to nitric oxide and decrease in blood pressure. This is a good thing when someone who is having a heart take nitroglycerine, which is rapidly absorbed and also decomposes to nitric oxide.  However, too much nitrate or nitrite in the blood of a small animal that has just eating an enormous piece of ham can also result in a large amount of nitric oxide in their body which can cause a dangerous drop in blood pressure (hypotension).  

Excess nitric oxide can also react with proteins including hemoglobin, the protein in red blood cells that is responsible for carrying oxygen throughout the body.  Nitric oxide is very reactive, as it is a free radical.  Free radicals are highly reactive toward other molecules because they possess unpaired electrons that want to form covalent bonds.  Nitric oxide can react with the iron-containing heme group in hemoglobin to form S-nitrosylated hemoglobin, which is pinkish red.  This is why almost all cured meats have a particularly reddish-pink hue, as in the above picture showing ham and pepperoni.  Nitric oxide can be damaging to tissues in high doses, and over time it could also be carcinogenic.

There are many anecdotal stories of dogs getting sick from eating ham.  Other dogs may do fine with ham in small amounts.  Pet owners must understand that large amounts of any cured meat could potentially have bad effects on your pet, and thus cured meats should be kept where pets can't get to them.         

The idea that garlic is toxic to pets can seem puzzling to some people (including me at first) when they see that the ingredients of many dog foods contain garlic.  However, garlic can be quite safe when used in moderation (moderation is the key).  Dogs love the taste of garlic, but achieving a level of garlic they can taste only requires small amounts.  Higher doses of garlic are indeed toxic to dogs and cats.  Garlic contains two compounds, allicin and ajoene, that are smooth muscle relaxants and can dilate blood vessels and cause low blood pressure (hypotension).  Large amounts of garlic may also  cause destruction of red blood cells (hemolysis) and anemia.  The bottom line is that the amounts of garlic used in pet foods are very low and thus safe, but pet owners should never feed pets human foods with garlic, which may contain much more garlic than they can handle.  Also, garlic cloves should be kept where pets cannot get to them. 

Grapes, Raisins, and Currants
Grapes contain a yet unknown toxin that can be potentially dangerous to dogs and cats.  Because raisins are just dehydrated (dried) grapes, they are an even more dense source of these pet-toxic compounds than grapes are.  This means that eating an equal weight of raisins is more dangerous than an equal weight of grapes.  Grape/raisin toxicity is more of a concern in dogs due to their greater preference for sweet foods compared with cats.  Grapes and raisins have been reported as the causes of dog poisonings since the mid 1990's.  However, the evidence that grapes or raisins can cause poisoning in cats is still considered by some to be anecdotal and unconfirmed.  However, the best thing to do is keep both dogs and cats away from grapes and raisins, and this seems to be what is recommended by most vets. 

The reason the identity of the toxic compound is still unknown is because the toxicity appears to be quite variable, possibly due to different sensitivities of different dogs and cats or variability of the concentration of the toxin in grapes from different plants.  It is also possible that the toxicity comes from some other yet-unknown contaminant; for example, it may be a fungal or bacterial toxin that contaminates some batches of grapes and not others.  For this reason, it is recommended that any exposure to grapes or raisins be treated a potential toxic exposure. It is estimated that as little as 32 g/kg grapes or 11-30 g/kg raisins is enough to cause potentially severe kidney (renal) injury in dogs.  That equals to about 11 oz of grapes or 4-10 oz of raisins for a 10 kg (22 lb) dog.  In even smaller dogs, eating just a few grapes or raisins has been reported to be toxic.  However, other case reports have described other dogs that are completely fine after eating a pound of raisins or more.  Because of the extreme variability and unknown nature of the toxic chemical(s) that mediate the response, any exposure to grapes or raisins is a potential cause for concern for the health of your pet.      

The toxic compound is grapes/raisins appears to primarily be toxic to the kidney (nephrotoxic). Symptoms of grape/raisin poisoning can be seen as little as 6 hours after ingestion, and can include vomiting, diarrhea, lethargy (extreme tiredness) or weakness, tremors, or excessive urination (polydipsia).  Renal (kidney) failure can develop within 1-3 days.  Because animals digest fruits somewhat more slowly than some other foods, immediate treatments (for example, inducing vomiting) to remove the ingested grapes from the gastrointestinal tract  (called “decontamination”) can be very successful in treating the dogs by getting the toxic material out of their body.  If grape or raisin poisoning gets to the point of renal failure, the prognosis (the likely or expected outcome of treatment) is usually not good.  If you suspect that your dog or cat has eaten grapes or raisins, contact your vet right away.  Treatment requires aggressive therapy like fluid replacement and monitoring of serum chemistry and blood pressure that only your vet can perform.                 

Green Raw Tomatoes, Tomato Plant Stems and Leaves, and Green Potatoes
The green parts of tomato plants and/or unripened tomatoes can contain solanine, a glycoalkaloid that can be poisonous.  Solanine production in potatoes is stimulated by exposure to light; potatoes exposed to light will begin to turn green (due to chlorophyll production) and also produce solanine as a natural defense to prevent the uncovered potato from being eaten by insects or other predators.  The US National Institutes of Health recommends that potatoes which are green below the skin should not be eaten.    

However, solanine poisoning in dogs and cats is rare as raw green potatoes often have a bitter taste that can makes them unpalatable to animals.  Solanine poisoning is usually more often seen in cattle that are chronically exposed to it from grazing on tomato plants or some other feed contamination with green potatoes.  However, it is still best to keep your dog from eating the leaves of your tomato plants or unripened tomatoes.  Throw away all potatoes that have green skin or are green under the skin.  Solanine poisoning can cause gastrointestinal upset (vomiting, diarrhea, etc.) both in people and in humans.  Neurological symptoms can also be seen with higher doses.  A famous case of solanine poisoning involved over 70 school children in Britain in the 1970s, though no fatalities occurred in this case.  

Interestingly, tomatoes and potatoes both belong to the nightshade (solanaceae) family of plants, which produce various alkaloid chemicals such as solanine that can be both beneficial and poisonous.  Various species of tobacco plants (Nicotiana genus) are also included in this family.  Nicotiana plants produce the alkaloid nicotine, which activates certain types of receptors for acetylcholine (a neurotransmitter).  Other more toxic members of the nightshade family include the deadly nightshade (Atropa belladonna), Mandrake (Mandragora officinarum), Jimson weed (Datura stramonium), and henbane (Hyoscyamus niger), which produce alkaloids such as atropine and scopolamine that are among the most potent acetylcholine receptor blockers.  

Macadamia Nuts
Macadamia nuts are eaten as a snack food and are a popular addition to cookies.  Most of the macadamia nuts sold in the US originate in California or Hawaii.  The two species of macadamia nut trees (Macadamia integrifolia and Macadamia tetraphylla) were introduced to the US from Australia in the late 1800s.  While macadamia nuts are generally fine for humans with the exception of those who have nut allergies, as little as 1-5 g/kg of macadamia nuts (raw or roasted) can make dogs sick.  A single roasted macadamia nut is about 2-3 g.  That means as little as 1 nut/kg of dog body weight, or 10 nuts for a 10kg (22lb) dog, can make a dog sick.
The identity of the chemical in macadamia nuts that is toxic to dogs is not yet known.  Symptoms can include weakness, vomiting, fever (hyperthermia), or tremors.  While not usually fatal with appropriate veterinary treatment, macadamia nuts can significantly add to adverse symptoms if they are ingested along with other poisons such as chocolate.    

Moldy Foods
Dogs are not garbage disposals.  Feeding a pet contaminated (moldy, spoiled, etc.) food is never a good idea.  In particularly, various types of fungi like molds can produce several toxins that can make animals sick.  Fungi from the genus Aspergillus can make a chemical called aflatoxin that can severely affect liver function and cause weakness or lethargy, gastrointestinal problems, or abdominal pain.  Dogs are especially sensitive to the liver-toxic effects of aflatoxin.  Aflatoxin is very potent, and can be very dangerous, particularly in cases where dog food in made with grains contaminated with aflatoxin.  Moldy bread or rotten corn should never be fed to animals because of the risk of aflatoxin contamination.  
Moldy foods could also contain vomitoxin (deoxynivalenol), which is made by fungi of the Fusarium genus.  Vomtoxin can make dogs vomit and/or cause gastrointestinal lesions.  Animals will often refuse food that is contaminated with vomitoxin because it makes them sick.  Other fungal toxins that can be found in moldy cheese, bread, or nuts include penitrem A and roquefortine, produced by various species of Penicillium fungi.  Symptoms of these compounds can vary from excessive salivation or panting to tremors or seizures.  While the symptoms can usually be treated by a vet, the best solution is not to knowingly feed pets moldy or contaminated foods and to keep them out of compost piles, which can also be another source of toxin-producing fungi.

Milk and Milk-Based Products
Lactose, the sugar in milk, may cause digestive upset or diarrhea in animals that are lactose intolerant.  Many animals (and many people, too) lose the ability to digest lactose after they are weaned off of their mothers milk.  Lactase is the enzyme necessary to break down lactose; most mammals stop producing lactase after weaning, which leads to an inability to break down the lactose.  The "lactase persistance" seen in many humans who can continue to digest lactose throughout their lives is relatively unique to our species.  Most other animals are lactose intolerant after childhood.  Because they can't digest the lactose, it passes through the stomach and intestine where it is metabolized by bacteria in the colon.  The bacteria start to ferment the lactose, which creates copious amounts of gasses, including carbon dioxide, hydrogen, and methane.  This can lead to uncomfortable bloating and cramping.  Additionally, the excess sugar in the colon can draw water into the colon through osmosis, which can lead to diarrhea.  It is best to avoid giving pets, especially dogs, products like milk or ice cream.
Common onions (and related species like leeks, scallions, and chives) are full of flavonoids and alk(en)yl cysteine sulphoxides that have been suggested to be beneficial to human health.  Various compounds in onions have been suggested to have anticarcinogenic, antidiabetic, antiasthmatic, or antibiotic properties.  However, onions also contain compounds that can be toxic to animals if eaten in high enough doses.  These compounds can damage red blood cells and cause them to burst (called hemolysis).  This can lead to anemia, an abnormal decrease in the amount of functional red blood cells.  Red blood cells are filled with hemoglobin, which is the iron-containing protein that transports oxygen in your blood.  Inhaled oxygen crosses the alveoli of the lungs and is picked up by the hemoglobin in red blood cells, which transport that oxygen throughout the body to other tissues that need it.  A lack of enough functioning red blood cells in anemia can lead to hypoxia (a lack of oxygen) in the body, which can result in poor concentration, weakness and fatigue, or even death depending on the severity of the anemia.   

Thiosulfate compounds in onions can cause hemoglobin inside the red blood cells of dogs and cats to denature (unfold) and aggregate, forming clumps of hemoglobin called Heinz bodies.  Heinz bodies can be seen under the microscope and can help diagnose onion poisoning in dogs and cats, though other animal poisons can also cause Heinz body formation.  Tylenol (acetaminophen or paracetamol, discussed below) can also cause Heinz body formation and anemia when ingested by cats while zinc poisoning causes Heinz body anemia in dogs.  Damaged red blood cells containing Heinz bodies are cleared (removed from the blood) by macrophages in the spleen, and rapid clearance of the damaged red blood cells before they can be replaced can cause anemia.    

Beware of feeding baby food to pets; baby food can sometimes contain onion powder that is also toxic to pets.  

Peach and Plum Pits
If your dog gets a hold of a whole peach or plum, he or she doesn't know not to try to eat the pit.  These can cause intestinal obstruction and serious health problems requiring surgery.  

Raw Eggs
Raw eggs can contain bacteria like E. coli or Salmonella that can cause mild to severe gastrointestinal problems.  People generally don't eat raw eggs (unless you are crazy like Rocky Balboa), so you shouldn't give raw eggs to pets, either.    

Salt (Sodium Chloride)
All animals, including dogs, cats, and people, need salt to live.  Salt cannot really be considered a poison because it is an essential component to life.  However, until we learned how to mine salt and/or evaporate sea water to get it, salt was relatively rare in human history, even being used as a currency in various cultures.  Our bodies are not necessarily optimized to handle the enormous amounts of salt that are available to us in processed and otherwise seasoned foods.  Thus, excessive consumption of salt has been linked to a wide range of health problems over time, including high blood pressure (hypertension). 

Water is passively distributed throughout your body, as it flows easily through biological membranes.  Osmosis is the diffusion or movement of water from one compartment (or cell or tissue) with a lower solute (dissolved substances) concentration to a compartment with a higher solute concentration.  Sodium is the predominant cation (positively charged ion) in your serum (the non-cellular part of blood).  Excess sodium in serum (hypernatremia) increases the solute content of blood and can draw water into the blood and increase the fluid volume of blood and thus increase blood pressure.  Normally this is OK in an acute (short-term) setting, as the kidneys can excrete (get rid of) the excess sodium; some water is lost in the process, but that can usually be replaced by drinking.  However, over months or years, the hypertension caused by excess sodium consumption can cause health problems.  In cases where there is some kind of kidney damage and the excess sodium can't be excreted, or if the rate of sodium intake just exceeds the rate of the kidney's ability to get rid of it, short term hypernatremia can be a major problem.  Hypernatremia can also be caused in animals during a lack of access to water and extreme dehydration, when water content of the blood can decrease and cause sodium concentration to increase.

Hypernatremia is dangerous because the excess sodium in the blood draws water out of the cells of various tissues in the body, including nerve cells (neurons) of the central nervous system.  Neurological symptoms are common with hypernatremia, but the symptoms can vary from gastrointestinal distress (vomiting and diarrhea), lethargy, muscular rigidity, tremors, seizures, or coma.  

Sodium from food is not usually a source of acute poisoning, but sodium poisoning can occur in pets after water deprivation, or consumption of nonfood items that have a lot of salt, such as play dough, rock salt or other kinds of ice melt, sea water, or water softener chemicals.  Paintballs contain chemicals that draw water into the intestine and thus out of the blood, and ingestion of paintballs can thus cause severe dehydration and cause hypernatremia as sodium concentration increases.  All of these items should be kept away from pets.        

Uncooked Yeast Bread Dough
Uncooked bread dough contains fermenting yeast that produce alcohol.  In addition to possible alcohol poisoning, the yeast can ferment and create gas in the stomach of the animal, creating discomfort and bloating.    

Xylitol and Similar Artificial Sweeteners
Xylitol and related artificial sweeteners like sorbitol are called "sugar alcohols" or "polyols."  They are used in a variety of products from sugar-free gum, toothpastes, mouthwashes, sugar-free candies, and cold medications like cough syrups.  In humans, xylitol is relatively inert and easily metabolized by the liver.  In dogs, though, xylitol stimulates insulin secretion from the pancrease, which leads to low blood glucose concentrations (hypoglycemia), which can cause weakness, lethargy, or even coma.  Xylitol also causes liver toxicity.  Please keep all products containing xylitol away from your dog and contact your vet right away if you suspect he or she ate a product containing xylitol.  

Other toxic home substances for pets (I know these aren't really "foods" per se, but they really deserve mentioning here):

Acetaminophen (Tylenol)
Acetaminophen (also called paracetamol) poisoning often comes from a well-meaning ownder trying to treat a dog or cat who appears to be in some sort of pain or have a fever.  Don't give your dog or cat acetaminophen unless directed to do so by a vet.  Acetaminophen can cause liver injury or failure in dogs and anemia in cats.  The differences in toxicity between these two animals comes from two different cell types that are more susceptible to acetaminophen toxicity.  In dogs, the liver cells (hepatocytes) are more sensitive to acetaminophen while in cats, red blood cells (erythrocytes) are more sensitive to acetaminophen.  Acetaminophen can deplete cells of a chemical called glutathione, which is important for protecting them from oxidative damage.  The end result of acetaminophen-induced glutathione q can be altered metabolism, damage to cell membranes, and cell death (necrosis).  Acetominophen is also found in cold remedies like NyQuil.  All acetominophen-containing products should be kept away from pets.         

Cold Packs or Freezer Packs
Cold packs containing various gels are used to refrigerate food in coolers or reduce swelling from injuries.  Cold packs can contain chemicals like ethylene glycol, silica gels, or ammonium nitrate (common in "instant" cold packs that don't require freezing).  The contents of cold packs can be highly toxic to dogs, and dogs have been reported to become ill and die after ingesting cold packs.  Cold packs should be kept out of reach of dogs and cats.         

Cough Drops with Menthol
We discussed the use of menthol in cough drops and other products in a previous blog post.  Menthol cough drops are great when used as directed.  However, ingestion of large amounts of cough drops by pets can cause gastrointestinal distress.  In some cases, an overdose of menthol could cause sedation, or even heart, lung, or kidney problems.  Also keep products like vaporubs and mouthwashes away from pets. 
Citrus Oil Extracts
Citrus oil extracts are found in many products marketed to fight against fleas, ticks or mosquitoes.  Citronella candles, bug sprays, and some pet flea products can contain citrus oil extracts.  While people may think these are safe because they come from a "natural" source, they can be quite dangerous to pets if ingested or otherwise used improperly.  Two of the major active ingredients in citrus oils are D-limonene and linalool, both of which are thought to be toxic to fleas and mosquitoes and help repel them.  Limonene and linalool can be found in high concentrations in some citrus oil extracts.  Pets can absorb these compounds through the skin as well as orally, and they may promote vasodilation (dilation of blood vessels) and cause a drop in blood pressure in both dogs and cats.  Other symptoms may include an increase in salivation (hypersalivation), tremors, or skin reactions.  Dogs and cats have died after improper use or exposure to products containing citrus oils.  If you are going to use a product containing citrus oil or citrus oil extract for your pet, consult with your vet first and only use it according to the instructions of the manufacturer or your vet.  Keep pets away from citronella candles and bug sprays intended for human use.             

Keep your pets away from cigarettes and cigarette butts, nicotine gums and patches, cigars, and chewing tobacco.  Chewing tobacco with flavoring agents such as honey or other types of sugars can be especially tasty to dogs. The LD50 (median lethal dose) for oral nicotine in animals is about 9mg/kg.  Cigarettes have anywhere from 9-30 mg of nicotine, so eating one cigarette can be enough to make a 10 kg (22 lb) dog very sick or potentially kill a smaller dog.  Nicotine is absorbed very quickly from the gastrointestinal tract and can even be absorbed through the skin, as in the nicotine patches that people use to quit smoking smoking.  Nicotine activates particular types of acetylcholine receptors, called nicotinic acetylcholine receptors, that are found in nerve and muscle cells.  Nicotine can act as a stimulant and cause excitement, vomiting, cardia arrhythmia, increased drooling (hypersalivation), or tremors.  At higher doses, though, the stimulatory effects of nicotine actually get canceled out as these receptors are blocked, and this can result in opposite effects such as lethargy, paralysis of muscles.  Death can occur due to paralysis of the diaphragm, the muscle that controls breathing.  Always keep your cigarettes and cigarette butts away from your pet.    

Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofin
All human medications should be kept away from pets.  Commonly used NSAIDs like ibuprofen (Advil) and aspirin can be potently toxic to pets.  NSAIDs are only OK if prescribed by your vet in the appropriate dosage for the appropriate reason; human doses of NSAIDs, particularly ibuprofen, can severely harm or kill pets.  A common poisoning scenario is the accidental ingestion of chewable ibuprofen by a dog or cat.  Ibuprofen was reported as the number one cause of dog poisonings and number seven cause of cat poisonings from 2001 to 2005.  Cats may be twice as sensitive as dogs to the toxic effects of ibuprofen, which can include gastric ulceration or perforation as well as renal or liver failure, seizures, or coma.  If your pet is on other medications, interactions of these meds with accidentally ingested NSAIDs can increase NSAID toxicity.  Aspirin is generally safer than ibuprofen for dogs and cats and is often prescribed by vets for pain or inflammation relief, but aspirin should only be used as indicated by your vet.  

Vitamin D-containing supplements
There are two natural forms of active vitamin D.  Vitamin D2 is derived from plants, while vitamin D3 (also called cholecalciferol) is made by the skin of animals during stimulation with UV light from the sun.  Both forms of vitamin D are steroid hormones that have important functions in the body.  Vitamin D2 and D3 as well as analogues of these compounds (usually metabolic products or other similar chemicals) are often used in supplements and medications.  Vitamin D poisoning can occur in animals from accidental ingestion of large amounts of vitamin D supplements or medication.  Because D3 (colecalciferol) is about 10 times more potent than D2, supplements or medications containing D3 or D3 analogues are the most dangerous.  

Vitamin D is an important regulator of calcium homeostasis, and vitamin D poisoning can result in elevated serum calcium levels (hypercalcemia) that also stimulate hyperphosphatemia (elevated serum phosphate levels).  This can impact the nervous system as well as muscles and the gastrointestinal, renal, or circulatory systems.  Symptoms can include lethargy or weakness, GI upset (vomiting, constipation, lack of interest in eating), or excess urination and/or dehydration.  Gastric ulceration resulting in gastric bleeding can be a particularly dangerous symptom.  Effective treatment requires getting your dog or cat to the vet as soon as possible so that he or she can perform the appropriate diagnostic lab tests to treat the animal appropriately. 

Because of the variability of various forms of vitamin D and its analogues, a lethal or toxic dose of vitamin D is hard to establish.  It is also thought that puppies are more sensitive than dogs to vitamin D; cats of all ages are thought to be even more sensitive than puppies or dogs.  Because pet foods contain appropriate amounts of vitamin D for your pets optimum health, the simple solution to prevent vitamin D poisoning is to keep all vitamin D supplements away from pets and never give pets any herbal or pharmaceutical remedies containing vitamin D.  

Wild mushrooms
It is very difficult for anyone but an expert to tell a poisonous mushroom from a safe mushroom.  The only safe mushrooms to eat are those that you purchase in a grocery store specifically for eating.  It is never advisable to let your pet eat any wild mushroom.  Poisonous mushrooms can have toxins that affect the gastrointestinal tract, kidney, or nervous system, and potentially could even be deadly.

This has been a long post, but I hope it serves its role as a mini-reference guide.  If you made it through, I hope that you now have a somewhat better knowledge of which important everyday foods should be kept away from your pets.  

© 2013 TheMadScienceBlog

Sources and further reading:
  • K. Bischoff and M. Mukai.  "Toxicity of Over-the-Counter Drugs."  Chapter 28 in Veterinary Toxicology.  Ed. R.C. Gupta.  Elsevier: St. Louis, MO USA.  2012.  
  • L.P. Case, L. Daristotle, M.G. Hayek, M.F. Raasch.  "Common Nutritional Myths and Feeding Practices."  Chapter 26 in Canine and Feline Nutrition, 3rd Edition.  Mosby Elsevier: Maryland Heights, MO.  2011.    
  • LK Dolder.  "Methylanthines: Caffeine, Theobromine, Theophylline."  Chapter 60 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • A.S. Flood, K.T. Fitzgerald.  "The Poison-Proof Practice."  Clinical Techniques in Small Animal Practice.  2006.  21:164-173.  
  • S.M. Gwaltney-Brant.  "Macadamia Nuts."  Chapter 56 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • S.M. Gwaltney-Brant.  "Miscellaneous Indoor Toxicants."  Chapter 24 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • N. Kovalkovicova, I. Sutiakova, J. Pistil, V. Sutiak.  “Some food toxic for pets.”  Interdisciplinary Toxicology.  2009.  2:169-176.  Available here.  
  • M. McMillan and J.C. Thompson.  "An outbreak of suspected solanine poisoning in schoolboys: examinations of criteria in solanine poisoning."  Quarterly Journal of Medicine. 1979. 48:227-243.  
  • M.S. Mostrom.  "Grapes and Raisins."  Chapter 48 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • K.H. Plumlee.  "Nicotine."  Chapter 64 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • K.H. Plumlee.  "Citrus Oils."  Chapter 40 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • J.A. Richardson.  "Ethanol."  Chapter 46 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • W.K. Rumbeiha.  "Cholecalciferol."  Chapter 38 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • N.M. Sutton, N. Bates, and A. Campbell.  "Factors influencing outcome of Vitis vinifera (grapes, raisins, currants, and sultanas) intoxication in dogs."  Veterinary Record.  2009.  164:430-431.   
  • P.A. Talcott and S.M. Gwaltney-Brant.  "Nonsteroidal Antiinflammatories."  Chapter 65 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • P.A. Talcott.  Mycotoxins.  Chapter 63 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.
  • J.H. Tegzes.  "Sodium."  Chapter 77 in Small Animal Toxicology, Third Edition.  Eds. M.E. Peterson and P.A. Talcott.  Elsevier: St. Louis, MO USA.  2013.


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