There are many mental illnesses and disease that are related to the consumption of meat. Take Alzheimer for example. According to the American Alzheimer Association, between 6 and 8% of the population over 60 has Alzheimer's disease, and the rate has been increasing steadily. Several scientific literatures have affirmed that Alzheimer correlates with the consumption of meat and dairy. A review of studies published in Preventive Magazine two years ago sheds important light on a central risk factor in Alzheimers -- high levels of a blood substance called homocysteine.
Homocysteine is an amino acid. Amino acids are the building blocks of proteins. The only source of homocysteine for use in our bodies is that which the liver forms after the ingestion of another amino acid, methionine. Methionine is found in protein foods. Animal protein contains two to three times the amount of methionine as does plant protein. Homocysteine levels can be lowered very effectively by avoiding meat and dairy consumption. In fact, a recent study performed at Harvard Medical School showed that subjects who adopted a vegan diet had their homocysteine levels drop between 13% and 20% in just one week.
A 1993 study found that subjects, who ate meat, including poultry and fish, were more than twice as likely to become demented as their vegetarian counterparts. [Neuroepidemiology, 12:28-36, 1993]
Depression, anxiety, and schizophrenia can be connected to meat consumption. The amount of tryptophan (An amino acid necessary for normal growth in infants and for nitrogen balance in adults.) in the foods that are eaten has only a small influence upon the amount of tryptophan that enters the brain. The most important factor determining the total amount of tryptophan that does enter the brain is the concentration of other large-molecule amino acids concurrently present in the blood. Large-molecule amino acids, among them tryptophan, compete with each other to enter "gates" between the circulating blood stream and the relatively confined brain fluids. A high-protein meal (full of meats, dairy foods, and eggs) provides many other amino acids that compete with tryptophan for entry into the brain; the end result is less tryptophan passing into the brain and a decrease in the synthesis of serotonin (a phenolic amine neurotransmitter that is a powerful vasoconstrictor and is found especially in the brain, blood serum, and gastric mucosa of mammals). Conversely, a low-protein, carbohydrate-rich diet (full of starches, vegetables, and fruits) results in the highest levels of serotonin in the brain, because fewer large-molecule amino acids are competing with tryptophan to enter the brain. For most this means less hyperactivity, anxiety, depression, and insomnia-provided they eat a vegetarian diet.
In some people anxiety, depression, and fatigue are caused by allergic reactions to foods. The most common causes of food allergies are dairy products, followed by eggs. These reactions are often subtle and difficult to recognize until the offending food has been eliminated, either by accident or by intention, and then, later, when the body is challenged with the suspect food, a recognizably adverse reaction occurs.
A serious psychological disease caused by foods in some people is schizophrenia. In hospital-based studies, some patients have been identified who react with dramatic behavioral changes to milk products and animal products. Some people with schizophrenia have actually been cured of their disease by changing their diet, (eliminating meat and dairy) and including more natural foods like fruits, vegetables, and whole grains.
I recall an Herbalist saying, “Tell me what a person eats and I shall tell you what sort of person he or she is and what type of character and behavior they hold.” No doubt, there are other factors also that determine a person's personality and behavior, but food also has a great effect on one's mind. Experience tells me that one's diet is closely connected with one's thoughts and conduct. So anyone who wishes to purify their thoughts and to elevate their character must partake in a vegetarian diet. If we eat live food, we will be helping our mind and emotions to remain in a state of peace and self-control. Pure food enables one to feel light and fresh and the mind opens out to the pure life and beauty of the world. The mind becomes undisciplined, wild, agitated or fickle when the diet is exciting, intoxicating or inebriating (intoxicant), the character constantly declines and the result is tension, depression, sorrow and disquiet.
Finally, the subject of meat consumption linked to brain disease has firmly come to the front of my research with the issue of “mad cow” disease. While scientist debate whether it is due to a mysterious prion or a virus, health-conscious advocates and nutritionist are using the scandal to point out numerous disadvantages of the typical animal-based Western diet as well as the corrupt manner in which the meat-producing industry is manufacturing its products. Specifically, it is imagined that ‘mad cow’ disease results from contaminated animal feed which has been fortified with ground up intestines, brains, spinal cords, bones, and other parts from cows, chickens and sheep – in effect turning herbivores into cannibalistic carnivores. Four with “mad cow” disease (also known as bovine spongiform encephalopathy – BSE), which is being linked to a correspondingly similar brain disorder in humans known as Creutzfeldt-Jakob disease, the symptoms are attributed to microscopic holes in the brain. So how did cows get mad cow disease, known by its medical name as "bovine spongiform encephalopathy," or "BSE"? For several decades, cattle feed had included a cheap protein supplement made from the carcasses of other animals, including sheep and cows. BSE probably arose when sheep infected with scrapie or cows with BSE were turned into feed. The feed then infected other cows that ate it, and when those animals died, they were fed back to more cows, creating a rapidly escalating epidemic. It was a kind of cattle cannibalism. And for two years after BSE was known, infected cattle were still allowed into England's food supply, raising fears that people might get BSE. To assess that risk, the British government called upon the scientific community. The scientific community noticed several behaviors, which has been related to the effects of people who ate beef from cows with “mad cows” disease. Some of those behaviors were hallucination, disorderly conduct, hyperactivity rudeness, agitation, and neglectfulness. With all this information, I see why Oprah stated to millions of Americans that she will never eat another hamburger again.
A vegetarian diet produces higher levels of behavior than a diet containing meat when all types of caloric intake are equal. Vegetarians were shown in one university study to score higher on examinations than meat eaters. Vegetarians also showed less frustration and lower levels of irascibility than meat eaters. (Bulletin of the Psychosomatic Society 10:35-36, July 1977)
Vegetarianism is a cause that addresses several key major social issues: ethics, the environment, and health – mental, spiritual and emotional as well as physical. As Albert Einstein wrote: "Nothing will benefit human health or increase the chances for survival of life on earth as the evolution to a vegetarian diet. It is my view that the vegetarian manner of living, by its purely physical effect on the human temperament, would most beneficially influence the lot of mankind."