With today's trend of resorting to dietary modification and the addition of herbs and supplements into our meal-plan as a natural way of combating and preventing common human ailments, one should be very careful in how far the companion cat can be included in these recommendations. Many natural substances which aid human ailments may have an equally beneficial outcome on the cat, but equally many can also have a detrimental effects on the cat and her health.
The following is a summery of supplements often well meaningly added to cats' diet, under the misconception that their benefits for human wellbeing can also be applied to feline health.

Alfalfa powder, alfalfa sprouts
Alfalfa, known also as lucerne (legume), is widely used as a staple fodder plant for livestock, and has application in human health as tonic, antifungal, laxative, diuretic, detoxifier, digestive, nutritive, and anti-arthritic. However, when referencing veterinary literature it is listed as a toxic plant for cats. Alfalfa contains cyanide producing compounds (cyanogenic glycosides) which will only be destroyed by adequate cooking. In humans, these toxic substances are detoxified by the liver when ingested in small quantities, but in the much smaller cat alfalfa frequently cause vomiting, abdominal pain and/or diarrhea. Raw plant matter of any kind, including alfalfa sprouts and alfalfa powder, will lead to severe indigestion in the cat, who is not equipped to properly digest raw plant matter as a carnivore.

Alone the fact that alfalfa alkalizes the body makes it a dangerous substance to use in the cat's diet. Cats depend on a slightly acidic acid-base balance; a high body pH - as induced with the use of alfalfa - will put the cat at greater risk of developing urinary crystals.

Some years ago, before being aware of its toxicity, we mixed alfalfa powder in our cats' food, because it was so highly acclaimed as a mineral supplement. Shortly after ingestion of the food with the added alfalfa powder (1 tsp/1kg of food), 80% of our study group suffered of severe indigestion accompanied by burping and regurgitation of the food. We did not repeat this experiment.

Type of Illness: Lower Gastrointestinal	Common Plants:	Plant Toxin:
Intestinal irritation: nausea and vomiting, abdominal pain, and diarrhea immideatly after eating.	English ivy Alfalfa Beech Daphne Iris	Saponic glycosides Coumarin glycosides

"Lima and kidney beans are toxic uncooked. Both beans contain cyanide producing compounds (cyanogenic glycosides), which can be destroyed by adequate cooking. Small amounts of cyanogenic glycosides will be detoxified by the liver. Cyanogenic glycosides are also found in fruit pits millet, sprouts, yams, maize, chick peas, and cassava root."
Excerpt from: Food Chemistry: Chemical Stressors and Toxins in Plant Foods and Herbs.
Stephen Gislason, M.D. www.nutramed.com

"Alfalfa alkalizes and detoxifies the body. "
Adapted from Prescription for Nutritional Healing 2nd edition, James F. Balch, M.D., Phyllis A. Balch, C.N.C., page64

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Sprouts, other raw vegetables, and barley grass powder
It really makes no difference how fine raw vegetables are grated, pureed, made into juice, or freeze dried and powdered. The fact that cats lack the necessary enzymes to break down plant matter on a cellular level remains the same. Plant matter, especially vegetables and greens, represent dietary bulk - none of the nutrients are either bioavailable or essential to the cat - and it is usually simply passed through the digestive tract. Complications arrive, however, if this indigestible matter is blended with highly digestible matter, like meat, when it leads to indigestion in most cats. (see 'Home Made Diet Trouble Shooting')

But what about the cat's compulsion to eat grass?
Eating grass has a purely mechanical action for the cat. Ingested blades of grass will trigger regurgitation of indigestible or hard to digest matter, such as the cat's own hair swallowed during grooming or larger bones of her prey. Expelling this matter through regurgitation - in a very similar fashion to birds of prey - is safer than letting it pass through the digestive tract where it could potentially cause a blockage.

A cat craving a "stomach cleanse" with no available grass may start to nibble on all sorts of things - especially house plants. Therefore, provide indoor cats with potted grass at all times, but discourage your cat from eating grass right after meal time, as otherwise dinner may come right back out.

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Garlic
The use of garlic and other members of the Lily family such as onions, shallots, and chives in the cat's diet is not advised. Ingestion of these plants in a raw, cooked, or dried form can lead to damage of the red blood cells, which are rejected by the body from the bloodstream, and a continued use of garlic or onions can eventually result in hemolytic anemia. If the anemia is not controlled by discontinuing the use of the plants, it can potentially lead to death. Less significant but important is that raw garlic and onions irritate the mouth, esophagus, and stomach and can cause or exacerbate ulcers.

"An alkaloid, N-propyl disulphide, present in both cultivated and wild onions, chives, and garlic, affects the enzyme, glucose-6-phosphate dehydrogenase, in red blood cells that interferes with the hexose monophosphate pathway. Oxidation of hemoglobin results because there is either insufficient phosphate dehydrogenase or glutathione to protect the red blood cells from oxidative injury. The resulting formation of Heinz bodies within erythrocytes is characteristic of onion poisoning. (...)"
Marielle Gomez-Kaifer, PhD, Department of Chemistry, University of Miami

"Onion poisoning has been described in the cat by Kobayaschi (1981) who reported a hemolytic anemia and increase in Heinz bodies in cats that had consumed onion soup. (...)"
Excerpt from Nutrient Requirements of Cats, Revised edition by the National Research Council.
Ref.: Kobayaschi, K. 1981. Onion poisoning in the cat. Feline Pract. 11:22.

"Some people may have difficulty with eating raw garlic as it can be irritating to the intestinal linings."
Benjamin Lau, M.D., Ph.D. is a leading authority on garlic and health, professor of microbiology and immunology at the School of Medicine at Loma Linda University

"Allicin, which gives garlic its odor, is a strong oxidant, that is, a chemical that creates free radicals, which in excess, can be dangerous. Allicin can cause stomach irritation and, in rare cases, hemolytic anemia, destruction of red blood cells. If placed directly on the skin, allicin can cause blistering."
"Cats or Dogs should never be given raw, un-aged garlic because it is very irritating to the mouth, esophagus, and stomach and can cause or exacerbate ulcers."
The Garlic Information Center hotline, 1-800-330-5922 at Cornell University Medical College.

What are Heinz bodies?>
"Heinz bodies are pieces of oxidized hemoglobin; on a Romanowsky-stained blood smear, they appear as pale, circular structures that often protrude from the side of the RBC."
The Merck Veterinary Manual 8th edition, page 1208

What is Hemolythic anemia?
"The immune response can become directed against the body's own blood cells, including red blood cells, neutrophils, and platelets. In some instances, the cause of this is unknown, and the body is truly reacting against itself (an autoimmune disease). However, this is fairly uncommon, and usually the reaction against the body's own cells is initiated by exposure of the cat to a foreign antigen (...)"
The Cornell Book of Cats 2nd edition, page 276

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Yeast - brewers yeast, baker's yeast, nutritional yeast
Ones ingested, yeast will start to ferment in the warm, moist, nutrient rich environment of the stomach, and cats frequently suffer of bloating when given yeast. In the health-compromised domestic cat population it can also cause severe allergies in individuals. All the nutrients, which make yeast acclaimed as a nutritional supplement, are readily available in meats, organs, and eggs of a normal feline diet.

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Vitamin C (Ascorbic Acid)
Cats synthesize sufficient vitamin C (ascorbic acid) from glucose in their small intestine, and the cat's natural prey diet is devoid of a pure source of this vitamin. Additional supplementation can be harmful, because excessive ascorbic acid is excreted in the urine as oxalates. A high concentration of oxalate in the urine can contribute to the formation of calcium oxalate stones in the urinary tract, including the kidneys. A controlled study has also shown that large doses of injectable ascorbic acid has no beneficial effects for preventing or reducing the severity of feline respiratory disease. In addition, an overdose on vitamin C can enhance iron absorption and cause a resulting overdose of this mineral. The cat's resistance to disease is much less dependant on vitamin C, as is the case for humans. Instead, it is much more vital that sufficient amounts of vitamin A are available to the cat through her diet, which promotes disease resistance and proper immune function.

Also, vitamin C supplements are not very palatable to the cat. When mixed into the regular diet vitamin C supplements can discourage a cat from eating. Continuous force feeding of this vitamin is rather cruel, especially since there are no known benefits of vitamin C for cats.

The cats of Feline Future's study group have never received supplemental vitamin C in any form in their diet. We are continuously breeding very healthy litters of kittens who grow up to be very healthy adult cats. Since 1995 we have had only two short episodes of upper respiratory disease in our colony, each time only affecting the immature individuals of the population.

"Repeated trials have failed to demonstrate a need for dietary ascorbic acid in cats. Successful growth and reproduction are routinely obtained with commercial and purified (Kane, Morris, and Roger, personal communication, 1985) diets containing no supplemental ascorbic acid."
Nutritional Requirements of the Cat revised edition, National Research Council, page 28
Ref.: Carvalho da Silva, A. 1950. The domestic cat as a laboratory animal for experimental nutritional studies. II. Comparative growth and hematology on stock and purified rations. Acta Physiol. Lat. Am. 1:26.

"Cats normally synthesize vitamin C (ascorbic acid) from glucose, so there is no need to supplement the diet unless there is a high metabolic need or inadequate synthesis. Excessive supplementation may actually be harmful, because excessive ascorbic acid is excreted in the urine as oxalate. A high concentration of oxalate in the urine has the potential to contribute to the formation of calcium oxalate stones in the urinary tract."
The Cornell Book of Cats, 2nd. edition, page 82

" A controlled study showed that large doses of injectable ascorbic acid had no beneficial effects for preventing or reducing the severity of FVR [Feline Viral Rhinotracheitis]"
The Cornell Book of Cats, 2nd. edition, page 242

"Too much of the vitamin [vitamin C] may enhance the absorption of iron, resulting in an overdose of this mineral."
Nutritional Almanac 4th edition, Kirschmann, Gayla J. and John D., Nutrition Search, Inc.

"[In humans] When tissues are saturated, additional intake is excreted in the urine. (...) Even with large doses, the blood levels of vitamin C do not rise above 1.5 to 2mg/100ml because of reduced absorption from the intestines and increased excretion through the kidneys.
In children, large doses of vitamin C can cause nausea, diarrhoea, increased susceptibility of red blood cells to hemolysis, and reduced leukocyte bacterial activity. Patients with kidney disease should avoid high vitamin C intake, since this vitamin might aggravate the formation of kidney stones in these people. Megadoses of vitamin C can result in false positive results on diabetes tests and can interfere with hemoglobin testing."
The Nutrition Desk Reference, Robert Garrison, Jr.,M.A.,R.Ph. and Elizabeth Somer, M.A.,R.D. page136

"There are many molecular substances in foods that offer no nutritional benefit, and must be processed and excreted. Oxalic acid, for example, is excreted in the urine, and its crystals are commonly found in microscopic urinalysis. Too much oxalic acid in the urine will result in kidney or bladder stones. Calcium combines with oxalic acid to form the less soluble salt, calcium oxalate, which is also found in kidney stones. Plant leaves, especially rhubarb, cabbage, spinach, and beet tops, contain oxalic acid. Oxalic acid is also found in potatoes and peas. Vitamin C is metabolized to oxalic acid; it contributes to over-saturation of the urine with crystals and possibly to stone formation."
Excerpt from: Food Chemistry: Chemical Stressors and Toxins in Plant Foods and Herbs.
Stephen Gislason, M.D. www.nutramed.com