Tomato Is Poisonous To Pets

One of the most common home garden plants and a widely used ingredient in everything from a pizza to a hamburger, tomatoes are everywhere. As such it is highly likely that your pet will come into contact with them at some point during its life. The word "tomato" may refer to the plant (Solanum lycopersicum) or the edible, typically red, fruit that it bears. In the case of the fruit, tomatoes have received a somewhat undeserved reputation for being a pet killer. Tomatoes contain a substance called alpha-tomatine that can be toxic to the heart. Tomatine is one of the tomatoes natural defenses against being eaten. Found throughout the plant, it is much more concentrated in the leaves and stem. The level of alpha-tomatine present in the green unripened tomato is slightly higher than the amount contained in the ripened red tomato. The tomato fruit is most vulnerable when it’s green, so the green tomatoes produce more tomatine to discourage insects. Whereas it's not needed by red tomatoes as once the fruit is ripe, it’s done its job of producing seeds. The amount of tomatine in either the ripe or unripened tomato is very small. Additionally, tomatine is very poorly absorbed by the intestinal tract. As such, it means that a dog would have to eat a massive amount of tomato before the heart would be affected. So much so, that the sheer volume of the attempt would make them nauseous forcing them to vomit prior to absorbing the potentially harmful toxin.

By weight fresh green tomatoes contain 48 ppm (4.8mg/100g) of tomatine (Tomato Glycoalkaloids: Role in the Plant and in the Diet, by Mendel Friedman). The generally accepted LD50 (lethal dose at which 50% of subjects will die) for tomatine in a human is .5g per kg of body weight. It is also commonly accepted that tomatine is more toxic to a dog than it is a human. In tests done on mice weighing 25g, the LD50 was 500mg/kg or 50mg/100g or 12.5mg per mouse. Figuring your average tomato weighs 120g, the tiny mouse would need to eat just over 2 whole green tomatoes (2.18 to be exact) or 10.46 times its bodyweight in green tomatoes to have a 50% chance of dying. Let's assume dogs are 5 times more susceptible to the toxin than both mice or humans and apply an LD50 of .1g per kg of body weight. This means a 60lb (27.21 kg) dog would need to ingest 2721mg (2.7g) of tomatine or 472 tomatoes to have a 50% chance of dying. 2721mg/4.8mg (tomatine per 100g) = 566 (100 gram units or 56,687.5 grams of tomato); 566 / 1.2 (120g average tomato)= 472 tomatoes or 124.96lbs (56.68kg) of tomato. If the toxicity is the same regardless of size a 30lb dog would need to eat 236 tomatoes and a 10lb dog would need to eat 78.6 tomatoes. That's a heck of a lot of tomatoes. Ripened tomatoes contain even less, .04mg/100g or 120 times less tomatine than green tomatoes; meaning your 60lb dog would need to eat a measly 56,640 ripe tomatoes to get 2700mg of toxin.

Research is also conflicting as to how negative tomatine really is. In 2000, Dr. Mendel Friedman of the federal Department of Agriculture and his colleagues issued a report stating that lab animals failed to absorb the majority of ingested tomatine, or that essentially all of it passes through the animal unabsorbed. This is due to the fact that tomatine apparently binds to cholesterol in the digestive system, and the combination is naturally excreted, removing both tomatine and cholesterol. In fact this finding left them with the positive conclusion that tomatine may be beneficial in lowering undesirable levels of LDL cholesterol in animals. Dr. Friedman also noted that a purified extract of green tomato lowered the incidence of cancer in animals. This led to another report touting the benefit of tomatine in inhibiting the growth of various human cancer cells.

Tomato plants also contain solanine but like tomatine, the amount is extremely low (5 mg/100g tomato). So like tomatine it would take at the very least, a couple hundred tomatoes for a dog to ingest enough solanine to have a 50% chance of dying.

The publicity of tomato poisoning as it relates to pets seems to have originated with grazing animals like cattle or goats and possibly horses, that have reportedly suffered fatal consequences after gaining access to tomato patches and subsequently made a meal out of rows and rows of entire plants; leaves, stems, unripe fruit and all. The leaves and stems are known to contain considerably more toxin than the fruit. Thus it is conceivable that a grazing animal could die if it ate a significant poundage of fresh whole tomato plants. It is also possible that a dog or cat could suffer ill consequences if they chose to eat whole leaves or stems off the plant. Although unsubstantiated there have been reports of both dogs and cats falling ill and dying from ingesting a large quantity of tomato leaves and stems. Regardless the risk of death or serious illness to a pet from ingesting tomato is low.