The Health Benefits Of Therapeutic Fasting

Therapeutic fasting has shown results to increase well-being.

Fasting and the calorie restricted diet have both shown benefits for human and animal health as well as a lengthening of lifespan.1 Fasting consists of stopping food,  but there are a number of variations that allow the consumption of juice, supplements or other items.

Calorie-restricted diets usually aim to reduce the caloric intake to 70 percent of what is considered “normal,” either on a daily basis or by alternate day extreme restriction.

For humans, multiple nutrient-dense foods are consumed, with an emphasis on fruits and vegetables. For animals, calorie restriction research usually involves restricting the diet to 70 percent  of whatever the control animals are eating. Even without an increase in nutrient density, these animal studies show improved health, less degenerative disease and increased lifespan.

Calorie restriction induces a cellular response that results in decreased free radical production, increased resistance to free radical effects and production of other protective proteins.2

Oxidative stress resulting in clinical3 or subclinical chronic inflammation is considered to be the primary cause of aging and age-related degenerative disease.4,5 Ironically, as the benefits of fasting and a calorie-restricted diet gain increasing research support, both the human and the companion animal populations in the U.S. are suffering from increased incidences of obesity, and fasting has gone out of fashion.

What is Fasting?

Fasting is not the same as starvation. With therapeutic fasting, nutrient intake is enough to maintain vital tissues, like heart and muscle. Ideally, there will be an additional supply of co-factors for liver enzymes required to deal with the breakdown of fat and release of toxins that occurs. Starvation occurs when there are no reserves left in the body and insufficient intake of nutrients, so that vital tissues are broken down.

Complete or modified fasting is a natural part of a wild canine diet, and fasting or some form of reduced calories also benefits their health. The same is true for cats, but on a much more limited basis.

A few decades ago, fasting was all the rage. For humans, book titles such as “Fasting and Eating for Health”6 were common. Now, if you search for books on “fasting,” the predominant type is more commonly one such as “Fasting: Opening the Door to a Deeper, More Intimate, More Powerful Relationship with God.”7 Spirituality and mental, rather than physical, health are the prevailing themes.

A similar trend is seen in books and articles on holistic dog care. A search of the Whole Dog Journal online8 features one abstract from 2000 where “fasting” is included. (Nineteen other abstracts about feeding that came up on this search do not have the word “fasting” in the abstracts.) New editions of books originally written more than 20 years ago, such as “The Natural Cat”9 and Dr. Pitcairn’s “New Complete Guide to Natural Health for Dogs and Cats”10 discuss fasting in terms of health benefits, whereas more recent books, such as “Feeding Your Dog for Life: The Real Facts About Proper Nutrition,”11 discuss fasting mostly as a means to encourage acceptance of a new diet. “The Holistic Dog Book: Canine Care for the 21st Century”12 does not even mention fasting.

So fasting has become something of a lost art. This does not mean it has no value for small animals.

Looking Into the Past

Wolves, the dog’s closest living relative, are a window into normal dog physiology (before modification by kibbled dog food, dog sweaters and doggie beds). An ongoing study of wolves reintroduced to Yellowstone National Park confirms that they “are adapted to … feast-or-famine foraging.” When hunting is easy, packs make a kill every two to three days. An elk is consumed in this order: first, organ meats, then major muscle masses, and finally bone and hide. In this case, at the end of the two or three day period, lower caloric value is consumed, and bones are eaten at the same time as hide, including the fur. This mimics to a certain extent the alternate high calorie/low calorie day diet used in one type of CRD. In leaner times Yellowstone wolves have scavenged mostly bone and hide for several weeks at a time. This is more like a prolonged modified fast.13

Hepatic Lipidosis

We all know that prolonged fasting in cats, especially obese cats, can induce hepatic lipidosis. The feline liver does not down-regulate during fasting and so there is less protein-sparing effect. Hepatic lipidosis can occur with as little as two or three days of fasting in a susceptible cat. So fasting should not be continued for more than a single day, if that long.

On the other hand, restricting calories to 70 percent of a “standard” feline diet, the approach used in human CRDs, has been shown to favorably affect physical activity and a number of genes associated with lipid metablism, food intake, and insulin sensitivity.14  In addition, methionine, taurine, tryptophan and arginine are limiting amino acids for metabolic processes during fasting,15 and l-carnitine supplementation helps protect against hepatic lipid accumulation during dieting or fasting.16 These amino acids should be recommended to any clients who wish to impose a fast upon their cats.

During a fast, fat from the body is metabolized and any waste products stored in that fat are released. This includes breakdown products from substances produced naturally in the body which the liver was unable to process at the time, as well as items absorbed from the environment such as insecticides for flea control. (In addition, if no protein is provided in a modified fast, a pet will metabolize some of its own muscle for its daily protein requirement.)

Toxic Load Decreased

With little competition from substances absorbed after a large meal, the liver is able to fully process the released waste products and excrete them through bile, or release the processed products into the bloodstream for elimination through the kidneys, decreasing toxic load in the body.

Research on the favorable effects of intermittent fasting or long-term calorie restriction show that during fasting, mitochondria down-regulate, with fewer free radicals released from them.17

This process, known as hormesis, may be the reason that the CRD has been shown to decrease inflammatory molecules in so many different cell types. Inflammation underlies many degenerative diseases, and CRD has been shown to decrease the incidence of cancer,18,19,20decrease or reverse arthritis, cognitive decline,21 type II diabetes,2 hypertension, dermatitis23 and liver, kidney,24 and heart disease.25 One study showed its effect on improving age-related deafness.26  This effect has been seen in rats, mice, rhesus monkeys and in humans. All studies cited included subjects on some type of CRD, and do not include obesity studies. A 25-year ongoing study in rhesus monkeys also showed a slower rate of muscle loss with age, with no apparent loss of bone density.27

Favorable Effects

Lifetime studies involving calorie restriction to 70 percent of a “normal” diet in Labrador retrievers have shown a decrease in incidence and severity of osteoarthritis of the elbow,28 shoulder,29 stifle30 and coxofermoral31 joints compared to controls, as well as increasing their lifespans by two years. Interestingly, in one study the amount of gross and histopathologic damage in the shoulder joints was greater than radiographic changes,32 so similar studies based on radiographic changes alone are not necessarily as reliable.
In addition, fasting for 48 hours or longer has been shown to protect normal cells, but not cancer cells, from toxic effects of chemotherapy.33 This has been used in some human chemotherapy patients to mitigate the side effects of chemotherapy. It is worth pursuing for companion animal cancer patients.

And finally, an increased lifespan has been observed in yeast,34 fruit flies, rats, mice, rhesus monkeys35,36 and Labrador retrievers.37 I do not plan on helping any fruit flies in the near future, but what a simple way to keep our beloved pets with us a little longer. 


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2. Mattson MP. Gene-diet interactions in brain aging and neurodegenerative disorders. Ann Intern Med. 2003 Sep 2;139(5 Pt 2):441-4.
3. Sarkar D, Fisher PB. Molecular mechanisms of aging-associated inflammation.Cancer Lett. 2006 May 8;236(1):13-23. Epub 2005 Jun 22.
4. Kim HJ, Jung KJ, Yu BP, Cho CG, Choi JS, Chung HY. Modulation of redox-sensitive transcription factors by calorie restriction during aging.Mech Ageing Dev. 2002 Nov;123(12):1589-95.
5. Chung HY, Cesari M, Anton S, Marzetti E, Giovannini S, Seo AY, Carter C, Yu BP, Leeuwenburgh C. Molecular inflammation: underpinnings of aging and age-related diseases. Ageing Res Rev. 2009 Jan;8(1):18-30. Epub 2008 Jul 18.
6. Fuhrman, J and Barnard ND, Fasting and Eating for Health. St. Martin's Griffin 1995.
7. Franklin J and James L Fasting: Opening the Door to a Deeper, More Intimate, More Powerful Relationship With God  Christianaudio Seed 2009
8. Kern, Nancy Whole Dog Journal Accessed April 24, 2011.
9. Frazier A and Eckroate N The Natural Cat: The Comprehensive Guide to Optimum Care ,2008 Plume
10. Pitcairn, R and Pitcairn S. Dr. Pitcairn's New Complete Guide to Natural Health for Dogs and Cats 3d edition 2005 Rodale.
1. Morgan, D Feeding Your Dog for Life: The Real Facts About Proper Nutrition Doral Publishing 2002
12. Flaim D The Holistic Dog Book: Canine Care for the 21st Century Howell Book House 2003
13. Stahler DR, Smith DW, Guernsey DS. Foraging and feeding ecology of the gray wolf (Canis lupus): lessons from Yellowstone National Park, Wyoming, USA. J Nutr. 2006 Jul;136(7 Suppl):1923S-1926S.
14. Belsito KR, Vester BM, Keel T, Graves TK, Swanson KS. Impact of ovariohysterectomy and food intake on body composition, physical activity, and adipose gene expression in cats. J Anim Sci. 2009 Feb;87(2):594-602. Epub 2008 Nov 7.
15. Biourge V, Groff JM, Fisher C, Bee D, Morris JG, Rogers QR. Nitrogen balance, plasma free amino acid concentrations and urinary orotic acid excretion during long-term fasting in cats. J Nutr. 1994 Jul;124(7):1094-103.
16. Blanchard G, Paragon BM, Milliat F, Lutton C. Dietary L-carnitine supplementation in obese cats alters carnitine metabolism and decreases ketosis during fasting and induced hepatic lipidosis. J Nutr. 2002 Feb;132(2):204-10.
17. Ristow M, Zarse K. How increased oxidative stress promotes longevity and metabolic health: The concept of mitochondrial hormesis (mitohormesis).Exp Gerontol. 2010 Jun;45(6):410-8. Epub 2010 Mar 27.
18. Dogan S, Johannsen AC, Grande JP, Cleary MP. Effects of Intermittent and Chronic Calorie Restriction on Mammalian Target of Rapamycin (mTOR) and IGF-I Signaling Pathways in Mammary Fat Pad Tissues and Mammary Tumors. Nutr Cancer. 2011 Apr;63(3):389-401.
19. Seyfried TN, Kiebish MA, Marsh J, Shelton LM, Huysentruyt LC, Mukherjee P. Metabolic management of brain cancer. Biochim Biophys Acta. 2010 Sep 8. [Epub ahead of print]
20. Omodei D, Fontana L. Calorie restriction and prevention of age-associated chronic disease. FEBS Lett. 2011 Mar 26. [Epub ahead of print]
21. Mattson MP. The impact of dietary energy intake on cognitive aging. Front Aging Neurosci. 2010 Mar 8;2:5.
2. Rains JL, Jain SK. Oxidative stress, insulin signaling, and diabetes. Free Radic Biol Med. 2011 Mar 1;50(5):567-75. Epub 2010 Dec 13.
23. Perkins SN, Hursting SD, Phang JM, Haines DC. Calorie restriction reduces ulcerative dermatitis and infection-related mortality in p53-deficient and wild-type mice. J Invest Dermatol. 1998 Aug;111(2):292-6.
24. Wielinga PY, Yakala GK, Heeringa P, Kleemann R, Kooistra T. Beneficial effects of alternate dietary regimen on liver inflammation, atherosclerosis and renal activation. PLoS One. 2011 Mar 31;6(3):e18432.
25. Johnson op cit.
26. Sebastian C, Mostoslavsky R. SIRT3 in calorie restriction: can you hear me now? Cell. 2010 Nov 24;143(5):667-8.
27. Kemnitz JW. Calorie restriction and aging in nonhuman primates. ILAR J. 2011 Feb 8;52(1):66-77.
28. Huck JL, Biery DN, Lawler DF, Gregor TP, Runge JJ, Evans RH, Kealy RD, Smith GK. A longitudinal study of the influence of lifetime food restriction on development of osteoarthritis in the canine elbow. Vet Surg. 2009 Feb;38(2):192-8.
29. Runge JJ, Biery DN, Lawler DF, Gregor TP, Evans RH, Kealy RD, Szabo SD, Smith GK. The effects of lifetime food restriction on the development of osteoarthritis in the canine shoulder. Vet Surg. 2008 Jan;37(1):102-7.
30. Kealy RD, Lawler DF, Ballam JM, Lust G, Biery DN, Smith GK, Mantz SL. Evaluation of the effect of limited food consumption on radiographic evidence of osteoarthritis in dogs.Am Vet Med Assoc. 2000 Dec 1;217(11):1678-80br /> 31. Kealy RD, Lawler DF, Ballam JM, Lust G, Smith GK, Biery DN, Olsson SE. Five-year longitudinal study on limited food consumption and development of osteoarthritis in coxofemoral joints of dogs. J Am Vet Med Assoc. 1997 Jan 15;210(2):222-5.
32. Runge, op cit.
3.   Raffaghello L, Safdie F, Bianchi G, Dorff T, Fontana L, Longo VD. Cell Cycle. 2010 Nov 15;9(22):4474-6. Epub 2010 Nov 15. Fasting and differential chemotherapy protection in patients.
34. Balázsi G. Network reconstruction reveals new links between aging and calorie restriction in yeast. HFSP J. 2010 Jun;4(3-4):94-9. Epub 2010 Apr 6.
35. Ristow, op cit
36. Kenmitz op cit
37. Huck op cit


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