Gene-Environment Interaction and Health

Copyright 2000, Adele C. Monroe, DVM, MSPH

On December 30, 1999, the news program 48 Hours interviewed a researcher studying longevity and aging at Mt. Sinai Hospital. The researcher stated that genetics accounts for only 30% of a person's longevity and that lifestyle is far more important than genetics in determining aging and lifespan in humans. Replace "lifestyle" with "management" and I believe the same principle applies to our animal companions.

When breeders of purebred animals start discussing the control and elimination of diseases that show a hereditary pattern, the influence of environmental factors on the expression of genes is often completely overlooked. I believe that the overwhelming majority of health problems in dogs and cats that are considered to be "genetic" result from the interaction of genes and environmental conditions and can be prevented by management.

A gene can be thought of as a region of a chromosome that is responsible for a discrete function or characteristic of the body. Chromosomes are present in every cell in the body and are composed of two strands of DNA each. All mammals (dogs, cats, horses, humans, etc.) have genes that are potentially harmful if they become active. Damage to the DNA of cells has been shown to activate genes associated with the aging process and with degenerative diseases including cancer. It has been estimated that each cell in the human body experiences 1,000 to 10,000 breaks in the DNA every day (Beating Cancer with Nutrition, Patrick Quillen PhD, RD, CNS; 1994: page 18). Normally, DNA repair mechanisms speedily repair these breaks as soon as they occur. Or, cells with DNA that is not repaired either die or are recognized and destroyed by surveillance cells of the immune system. Disease can result when DNA damage occurs faster than DNA repair, and when cells that have experienced DNA damage but have survived are not identified and destroyed by the immune system.

Two major factors causing DNA damage are environmental toxins and free radicals. You can reduce your animal's exposure to environmental toxins by eliminating the use of topical pesticides, by using only environmentally friendly pest control techniques and cleaning products, and by filtering drinking water. Free radicals are highly reactive molecules that are produced in the body during normal metabolic processes and when cells or tissues are damaged by injury or exposure to toxins. In turn, free radicals damage cells and tissues, and can damage DNA. Free radicals are neutralized by antioxidants, which are produced in the body and which can be supplied in the diet. Human studies have shown that eating a diet rich in antioxidants can reduce the risk of some degenerative diseases and some cancers.

I believe that nutrition truly is the foundation of health and that appropriate nutrition can control or eliminate many disorders currently considered to be hereditary. I started feeding a raw diet (raw chicken--backs, leg quarters, and whole birds, raw organ meats, pureed raw vegetables) plus supplements in August 1998. Although I had fed a premium naturally preserved commercial diet for years, I saw such a dramatic improvement in the overall vitality of my dogs that I cannot imagine ever again feeding commercial food as the basis of their diet. A properly designed raw diet is rich in a wide variety of natural antioxidants. (Details of the diet that I feed my dogs can be found in the whippet section of this web site under "Health Maintenance Program.")

In addition to the positive changes I have witnessed in my own dogs and in those of my clients who have adopted a raw diet, compelling evidence on the benefits of feeding raw foods comes from studies conducted by Francis Pottenger Jr., MD from 1932 to 1942. Dr. Pottenger's experiments involved 900 cats and several generations. One group of cats was fed exclusively raw foods (meat, bones, milk, and cod-liver oil). Another group was fed the same items either cooked or partially cooked. The cats eating raw foods remained healthy, produced healthy kittens without problems, and did not require veterinary attention. The cats eating cooked or partially cooked foods experienced behavior problems, allergies, skin problems, parasites, thyroid dysfunction, urinary tract disorders and other health problems remarkably similar to those experienced by modern cats. Severity of health problems was associated with the degree of cooking, with the worst health problems in the cats fed the most cooked foods. By the third generation, cats eating cooked food could not reproduce. When cats from the first and second generations of the cooked-food group were placed on a raw diet and bred, it took four generations of eating a raw diet for their descendants to attain the level of health enjoyed by the cats who had been eating raw foods exclusively.

More recently, researchers have documented that the effects of a deficiency of omega-3 fatty acids are cumulative over generations. The omega-3 fatty acid DHA (not to be confused with the hormone DHEA) is vitally important for proper function of the brain, normal behavior, stable emotional health, and the immune system. Also, DHA is highly concentrated in the retina, making it a critical nutrient for normal vision. Two studies cited in the book, Smart Fats: How Dietary Fats and Oils Affect Mental, Physical, and Emotional Intelligence, illustrate this cumulative effect. Study 1: Rats were fed a diet that was low in specific essential fatty acids over three generations. A decrease in the actual number of brain cells was observed in the third generation. Study 2: Rats were fed a diet deficient in omega-3 fatty acids from infancy through adulthood. By adulthood, there was a 50 percent drop in DHA levels in the brain. In the next generation fed the same diet, brain DHA levels decreased 90 percent in both infancy and adulthood. Omega-3 fatty acid deficiencies have been associated with emotional and behavior problems in humans and have been implicated in playing a role in allergic conditions and immune-mediated diseases. Although the studies have not yet been performed, I speculate that cumulative omega-3 fatty acid deficiency may be one factor contributing to PRA (progressive retinal atrophy), seizure disorders, and the increase of behavior problems that I have observed in over 15 years of involvement in dog sports. Numerous other associations between nutritional deficiencies and chronic disease have been documented in animals and in humans.

It is important to realize that nearly all modern commercial diets are processed at temperatures that destroy antioxidants, omega-3 fatty acids, vitamins, important food enzymes, and other nutrients, and that facilitate the formation of very harmful trans-fats. I believe that some bloodlines and even some breeds of dogs and cats have exceeded the maximum number of generations that can be raised exclusively on heat-processed grain-rich commercial food while maintaining a reasonable level of health and longevity. If Dr. Pottenger's cat studies are directly applicable to contemporary dogs and cats, these bloodlines and breeds may require at least four generations for health to be restored. On the other hand, there are breeds and bloodlines that are still maintained exclusively on commercial food and that experience relatively few "hereditary" health problems. I believe the clock is ticking for these breeds and bloodlines as well. Although they have not yet reached this limitation, I believe that they will eventually. I do believe that breeders who supplement commercial foods with vitamin/mineral supplements, fatty acid supplements, and/or raw foods extend the number of generations that commercial foods can be fed before encountering severe problems. I believe those breeders who have bloodlines and breeds in which a healthy animal "can't be found" have no choice but to switch to well-designed raw food diets, eliminate environmental toxins, and breed the healthiest stock they can find.

I am not saying that breeders should stop screening for hereditary diseases. However, if we do not feed our animals for optimum health and maximum longevity, we will not know how healthy they can be. If we do not feed breeding stock for optimum health, we cannot produce offspring with the potential to attain true health.

Recommended Reading:

  • The Nature of Animal Healing: The Path to Your Pet's Health, Happiness, and Longevity, by Martin Goldstein, DVM, 1999 (absolutely the best book I've seen yet on a more natural approach to health) 
  • Give Your Dog a Bone and Grow Your Pups with Bones, by Dr. Ian Billinghurst (Australian veterinarian; the BARF--Bones And Raw Foods--diet) 
  • Natural Nutrition for Dogs and Cats: The Ultimate Diet, by Kymythy R. Schultze, CCN (certified clinical nutritionist), AHI (licensed Animal Health Instructor, CA)--a good book to start with when implementing a raw diet 
  • Pottenger's Cats, A Study in Nutrition, Price-Pottenger Nutrition Foundation, 2667 Camino del Rio South, #109, San Diego, CA 92108-3767 (1-619-574-7763) 
  • Smart Fats: How Dietary Fats and Oils Affect Mental, Physical, and Emotional Intelligence, by Michael A. Schmidt

This article is a modification of a post sent by the author to the K9GENES email list on January 1, 2000.

Copyright 2000, by Adele C. Monroe, DVM, MSPH. Except for printing single copies for personal use, reproduction of this article, either electronically or in print, is strictly prohibited without prior written permission of the author.

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