1. Effects of Diet on Canine Behavior;
Consumer Perceptions versus Scientific Research
Heather McEwan
The debate over the nutritional influence on dog behavior is an extensive topic.
As humans become more invested in the length and quality of life of their pets,
their interest in what their pet family members are eating and how they co-exist
with us becomes more important. The synergistic relationship between dogs and
humans has become more complex as the diseases affecting humans are more
commonly seen reflected in our canine partners. Obesity is now a pet epidemic in
North America. The Association for Pet Obesity Prevention reported 55% of dogs
in the United States were overweight or obese in 2010
1
. In Canada, Statistics
Canada estimates the number at 35%.
2
Canine Cognitive Dysfunction, a
condition similar to dementia in humans, is now commonly associated with the
aging pet population
3
. Studies on the behavioral effects of poor diet in young
children has led to a clearer understanding of the importance of diet on maternal
behavior and the implications to young animals.
4
By exploring the connection
between what we eat and how it affects our behavior, we can’t help but wonder if
there is a similar connection for our canine partners. Does our understanding of
human nutrition influence how we feed our pets and how does this
misinformation affect their behavior? It is a natural progression to connect “what
is good for us, is good for them” without regard to physiological differences or
consultation with the person most cognizant of these differences; the
veterinarian. But are our perceptions about what is healthy for our dogs
supported by scientific research?
1
Association For Pet Obesity Prevention, Feb 2011.
2
Statistics Canada 2010 Report
3
Landsberg G and Araujo JA. “Behavior Problems in Geriatric Pets.” The Veterinary Clinics Small Animal
Practice. 2005. Vol 35. p. 675 – 698.
4
Gallo PV et al. “Protein Restriction during Gestation and Lactation: Development of Attachment
Behavior in Cats.” Behavioral and Neural Biology. 1980. Vol 29, p. 216-223.

2. Pet food consumers have been trained since the 1980’s to read ingredient panels
and make their own judgments about the appropriateness of the ingredients for
their pets. Pet food companies attempting to break into the very competitive pet
food market, used ingredients as a marketing tool to differentiate their product
from the competition. It was cheaper and more convenient to ask the Pet
Professional at the pet food store their opinion on nutrition than to pay for an
appointment with the Veterinarian and “just get sold the food paying to line the
Vet’s pockets”. Consumers didn’t ask for educational credentials to justify these
opinions because the logical explanations offered by the Pet Professionals
appealed to our understanding of wholesome nutrition. Anecdotal reports of
changes in behavior replaced scientific research and experiments. Our pets are
our family, so if you wouldn’t feed it to your family why would you feed it to your
pet?
The problems with this approach to canine nutrition are as varied as the
differences to our behavior. Dogs are not humans. Although we are both
omnivores we have different dietary requirements. We are both social mammals
but our understanding of appropriate social communication is different. Behavior
is regulated by neurotransmitters and hormones. Changes in the availability of
these chemicals influence behavior. Unfortunately the effects of nutrients on
behavior are largely unknown. There are few nutritional behavior studies
available to us. In those studies we must determine what constitutes a behavioral
change and how we determine if the change was a direct result of a nutrient
deficiency or excess rather than an environmental factor? Consumers need to be
re-educated to look at the nutrients their pet’s food provides rather than the
ingredients, understand the importance of life stage nutrition and learn how
behavior can be affected by nutrients.
A pet food is the sum of its parts. Ingredients should be selected for nutrient
quality but no single ingredient makes a quality pet food. As ingredient quality

3. increases, so does the bioavailability of the nutrients. Feathers contain protein
but they are not the most bioavailable source of protein. There are six essential
nutrients for optimal health; proteins, carbohydrates, fats, vitamins, minerals and
water. Nutrient needs vary according to an animal’s age, activity level,
environment, health and reproductive status.
5
Isn’t it logical for nutrients to affect
behavior if they affect every other part of life?
According to a commissioned survey by Iams in October of 2010 only 11% of pet
owners consider age to be the most important factor when determining what pet
food to buy their pets.
6
The nutrition a puppy receives during its first year of life
helps establish a foundation for the rest of their life. However, many owners
neglect the importance of nutrition during pregnancy and lactation. Malnutrition
can occur either directly to the puppy or thru a malnourished mother. In a
recently published study (Kumon et al 2010), a deficiency in calories was
demonstrated to impact behavior in lactating mice.
7
Restricted mothers were fed
70% of the daily ration of the control mothers for 21 days after parturition. The
resulting offspring were not only smaller in body weight and brain weight but
showed reduced locomotor activity and anxiety behavior leading to the
researchers concluding the effect of maternal malnutrition on lactation was more
significant than the effect on pregnancy.
8
Although all nutrients are essential for development, only protein restriction has
been studied in association with behavior and development. In a study published
by Gallo in 1980 on the development of attachment behaviors in kittens and
protein restricted mothers, cats were fed a diet gradually decreasing from 30%
5
Roudebush, P. et al Small Animal Clinical Nutrition 4th
Edition. Missouri. Walsworth Publishing
Company. 2000.
6
Ipsos Reid Poll commissioned October 2010 of U.S. households of 1006 randomly selected adults over
age 18.
7
Kumon M, Yamamoto K et al. “Maternal Dietary Restriciton during lactation influences postnatal growth
and behavior in the offspring of mice.” Neurochemistry International. 2010. Vol 57. p. 43 – 50
8
Kumon M, Yamamoto K et al. “Maternal Dietary Restriciton during lactation influences postnatal growth
and behavior in the offspring of mice.” Neurochemistry International. 2010. Vol 57. p. 43 – 50

4. protein on Day 43 of gestation, to 24% on Day 50, and finally to 18% on Day 57.
The cats were not started at 18% protein because previous studies had found
this resulted in a large number of abortions. Litters were culled to 2 – 3 kittens
with the lowest birth weight kittens removed in an attempt to keep the size
constant. Researchers found kittens born to restricted mothers cried more
regardless of mother proximity. This difference continued after the kitten
matured. Researchers concluded these kittens were more emotionally
responsive in stressful situations because they had not received comfort during
an important developmental period.
9
Food is a source of comfort for many
species, not just humans.
The restricted kittens also gained less weight after birth. The lack of weight gain
was significant because it was believed prior to this that a mother fed a diet
deficient in a specific nutrient would produce less milk but the quality of the milk
would remain the same. This study indicates both quantity and quality of milk are
affected.
10
Another interesting finding from this study was the response to the kittens by the
protein restricted mothers. Researchers noticed protein restricted mothers often
walked past their kittens when they were returned and crouched in a corner
alone. The restricted mothers also remained upright when a kitten did navigate
their way to them rather than lying on their side to expose the mammary area. If
nipple attachment did occur, it was brief because the mother repositioned herself.
This behavior by the mother increased the kittens’ emotional reactivity and
vocalizations.
11
Nutritional deficiencies affect the socialization process of
developing mammals by increasing the stress levels of both the mother and her
offspring. Not only do animals deprived of the proper nutrients for growth and
development become delayed in physical milestones such as walking, climbing
and body size but they have many behavioral problems. They are more vocal,
9
Gallo PV et al. “Protein Restriction during Gestation and Lactation: Development of Attachment Behavior
in Cats.” Behavioral and Neural Biology. 1980. Vol 29, p. 216-223.
10
Gallo PV et al. “Protein Restriction during Gestation and Lactation: Development of Attachment
Behavior in Cats.” Behavioral and Neural Biology. 1980. Vol 29, p. 216-223.
11
Ibid Gallo et al.

5. more easily stressed, less exploratory, and more anxious when separated from
their social group. In an unpublished study by Purina in 1979, researchers
studied the effects of malnutrition on maternal behavior and lactation. Kittens
whose mothers were fed 45g of Purina Cat Chow per day (half of the daily
required amount) during pregnancy were fostered to mothers that were not
deprived. Although the kittens eventually reached the same body weight as
control kittens they were significantly delayed in many “normal“cat behaviors
such as washing, lapping and using the litter pan. They also exhibited many
antisocial behaviors such as abnormal posturing and alternating dominant or
submissive behaviors.
12
The effect of DHA on the trainability of puppies has been well documented.
(Hoffman, et al. 2008). High DHA nourished puppies were significantly more
trainable than low DHA nourished puppies. They were also less destructive,
more sociable in the family environment and quicker to grasp obedience
challenges.
13
DHA, an omega-3 fatty acid, is an important component of the
nervous system. It is transferred across the placental barrier, present in milk and
accumulates in the brain and retina during fetal and perinatal development. In
adult animals, DHA can be synthesized by the liver but in young animals
synthesis is often insufficient.
14
Common sources of DHA in pet foods are eggs,
organ meat and fish. Recent studies have shown DHA levels in puppies are
highly dependent on the mother and her levels during the last third of her
pregnancy and initial postnatal period so bitches should be supplemented during
pregnancy also.
15
When we think of nutritional behavior problems and our pets we don’t usually
think of obesity and yet it is the number one health issue in veterinary clinics.
12
Worden, AN. “Nutritional Factors and Abnormal Behaviors” Ralston Purina, St Louis, MO. 1979.
13
Hoffman L., Kelley R. Waltz D. “For Smarter More Trainable Puppies: Effect of Docosahexaenoic Acid
on Puppy Trainability.” Iams Symposium. 2008.
14
de la Presa Owens S. Innis SM. “Docosahexaenoic and arachadonic acid reverse changes in
dopaminergic and serotoninergic neurotransmitters in piglets frontal cortex caused by linoleic and alpha
linolenic acid deficient diet.” Journal of Nutriion. 1999. vol 129. p. 2088- 2093.
15
Hoffman L., Kelley R. Waltz D. “For Smarter More Trainable Puppies: Effect of Docosahexaenoic Acid
on Puppy Trainability.” Iams Symposium. 2008.

6. Food and love are very closely linked in human society. We use food as a form
of communication with our pets. We communicate our acceptance, guilt and love
through food rewards. We share our table food as a way to socialize with our
pets. When you ask a pet owner what their pet’s worst behavior problem is, not
many say overeating! Yet the health problems associated with pet obesity are
multiple; arthritis, breathing difficulties, diarrhea, congestive heart failure,
diabetes, high blood pressure, liver disease, mammary tumors, skin disease and
urinary incontinence.
1617
There are also many behavior problems that can be
attributed to obesity; food stealing, elimination problems, begging and many
other attention seeking behaviors.
18
We need to educate pet owners not only to
modify the pet’s diet by increasing the fiber thus improving satiety
19
but to keep
track of calories provided from sources such as treats and table scraps.
Every person who has ever wanted to lose weight has been told “Just eat fewer
calories!” In a study on the effect of caloric restriction on the behavior of dogs,
39 dogs were split into four groups for weight loss. The dogs were mixed
according to breed, sex and initial body condition scores. The groups were
restricted from 0, 25, 40 or 50% of the total caloric energy requirements for their
size. Dogs were removed from the restricted diet when they reached their target
weight or at the completion of a 16 week period, whichever came first. Eighteen
dogs did not reach their target weight. All of the dogs were videotaped for
behavioral responses. Some of the results were to be expected. Severely
restricted dogs also severely restricted their activities. Dogs on milder restriction
remained more active. This suggests severe caloric restriction to be counter
productive to weight loss. Barking increased at the beginning of the study but
16
Small Animal Clinical Nutrition 4th
ed., Topeka, KS, Mark Morris Instititute, p. 402- 403. 2004
17
German AJ. “The Growing Problem of Obesity in Dogs and Cats.” The Journal of Nutrition. 2006. Vol
136. p. 1940 -1946.
18
Kealy RD, Lawler DF, Ballam JM et al. “Effects of Diet Restriction on Lifespan and Age-Related
Changes in Dogs.” Journal of American Veterinary Medical Association. 2002. Vol 220. p. 1315 - 1320.
19
Crowell-Davis SL, Barry K et al. “The Effect of Caloric Restriction on the Behavior of Pen Housed
Dogs: Transition from Unrestricted to Restricted Diet.” Applied Animal Behavior Science. 1995. Vol 43. p.
27 – 41.

7. there was a subsequent decrease after the dogs received no reward for their
barking.
20
Pet owners should be cautioned to prepare for an increase in barking
when putting their dog on a diet.
Some of the results offered further insight into dog behavior. There was an
increase in mouthing and object manipulation, indicating a need for objects to
chew on. Aggression did not increase in most dogs even though they were
severely restricted. Most interestingly, there was no increase in coprophagia.
Although many breeds and sizes of dogs were represented in this study, the
differences in gastric emptying time were not taken into account. Large breed
dogs have a longer large intestinal transit time.
21
Future research could look at
the breed differences in behavior and satiety in relation to dietary fiber.
Often pet owners think the solution to an obese pet is to increase the vegetables
in their diet and supplement the dog’s food with carrots. Pet owners should be
discouraged from this practice as the sugar in carrots increases the dog’s
hunger. If the owner feels the need to supplement the dog with a “natural” fiber,
suggest canned pumpkin. It is a natural form of cellulose and adds to the feeling
of satiety by absorbing moisture in the intestines like a sponge and helping to
slow intestinal transit time.
22
Studies are also being conducted on Carnitine as a
supplement for weight control. Carnitine is a water soluble vitamin that plays a
key role in burning fat and maintaining muscle by helping to convert fatty acids
into energy. It has been shown to improve heart function in dogs, help maintain a
healthy liver and lose weight while maintaining lean muscle mass
23
. Pet owners
should be encouraged to engage in non-food related bonding activities with their
dogs such as leash walks, swimming in a lake or pool, fetch or other interactive
20
Crowell-Davis SL, Barry K et al. “The Effect of Caloric Restriction on the Behavior of Pen Housed Dogs:
Transition from Unrestricted to Restricted Diet.” Applied Animal Behavior Science. 1995. Vol 43. p. 27 –
41.
21
Weber MP, Hernot D, Nguyen PG, et al. “Effect of size on Electrolyte Absorption Rates and
Fermentative activity in dogs.” Journal of Animal Physiology Anim Nutr. 2004. Vol 88. p. 356 – 365.
22
Hills Veterinary Consult line. www.hillsvet.com
23
Gross, KL., Wedekind, KJ, Kirk CA. et al. “Effect of dietary carnitine and chromium on weight loss and
composition of obese dogs” Journal of Animal Science. 1998. Vol 76. Hills Science and Technology
Centre, Topeka, KS.

8. games.
24
Owners could also be encouraged to provide their pets with puzzle
toys, such as a Kong or Tug a Jug to encourage the dog to problem solve to get
his food or use a portion pacer or specialty food bowl to slow down their eating.
Canine aggression is the most common behavior problem seen by
veterinarians.
25
There are two studies hypothesizing a direct link between protein
and aggression in dogs. Dodman et al. (1996) studied the effect of protein levels
on aggressive behavior and found a reduction in protein reduced territorial
behavior associated with fear but did not affect other types of aggression.
26
DeNapoli et al (2000) studied the effect of high and low protein diets with or
without tryptophan supplementation on dominance aggression, territorial
aggression and hyperactivity. They felt a low protein diet and tryptophan might
reduce aggression because tryptophan is a precursor to serotonin, the
neurotransmitter associated with resting and digesting. Tryptophan is found in
low concentrations in most protein sources. Increasing dietary tryptophan
increases serotonin levels. The results demonstrated dominant dogs fed high
protein (30%) diets without tryptophan were more aggressive than the dogs fed
the other three diets. Dogs fed the low protein (18%) diet with tryptophan were
the least territorially aggressive. There were no dietary effects on dogs with
hyperactivity or fearfulness.
27
Raw food proponents provide anecdotal support of their diets despite the lack of
scientific research supporting them. Claims of less aggression, a cure for
24
LaFlamme DP. “Understanding and managing Obesity in Dogs and Cats.” The Veterinary Clinics Small
Animal Practice. 2006. Vol 36. p. 1283- 1295.
25
Bamberger, M, Houpt, KA. “Signalment factors, comorbidity and trends in behavior diagnoses in
Dogs:1644 cases (1991-2001). Journal of the American Veterinary Medical Association. 2006. Vol 229. p.
1591- 1601.
26
Dodman NH, Reisner I, Shuster L et al. “Effect of Dietary Protein Content on Behavior in Dogs.”
JAVMA. 1996. Vol 208. p. 376 – 379.
27
DeNapoli JS, Dodman NH, Shuster L et al. “Effect of Dietary Protein Content and Tryptophan
Supplementation on Dominance Aggression, Territorrial Aggression and Hyperactivity in Dogs.” JAVMA.
2000. Vol 217. p. 504- 508.

9. arthritis, no doggy odor, smaller stools, a decreased or non existent vet bill, no
allergies, and a longer life for your dog can be found all over the internet. . To
date there has been no scientific studies to back up any of these claims. Most of
the diets contain excessive protein because of the perception a dog is a
carnivore. Many of the diets do not utilize organ meat and advocate large
portions of bones and rice. Consequently many of the diets have inverse calcium
to phosphorous ratios as high as 1:10.
28
The only study on raw food not related
to contamination was a survey related to the owner’s source of the recipe for
their diet. Fifty four owners were surveyed. Sixteen owners reported using a
recipe specifically designed for dogs. Of these recipes, eight were from a
Veterinarian, three were from the Internet and five were from other sources.
29
Raw food diets are claimed to mirror a more natural wild diet. This is one area
where the owners recognize the dog as a separate species but lack the scientific
understanding to make healthy choices for their pet. Human nutritionists advise
us to eat a variety of foods from a variety of food groups. Carbohydrates are an
essential energy source but many raw food websites claim “Grains will kill your
dog!” Homemade diets are rarely balanced for minerals (iron, copper, zinc,
iodine) or vitamins because owners feeding these diets often think over the
counter pet vitamin-mineral supplements are complete and use these instead.
OTC supplement products were designed as treats and not meant to replace the
recommended daily allotment provided in nutritionally balanced commercial
foods. They are not regulated by AAFCO because they fall under the treat
category and do not have regulated standards. The only supplements specifically
designed to balance homemade diets must be sold only by veterinarians
(BalanceIT supplements) because they do not come with dosing instructions and
are meant to be calculated by vets for the animal’s body weight. However the
majority of owners using these diets do not consult a vet to determine if the diet
28
Streiff EL, Zwischenberger B. et al. “A Comparison of the Nutritional Adequacy of home-prepared and
commercial diets for dogs.” J Nutr. 2002. Vol 132. p. 1698 – 1700.
29
LaFlamme DP, Abood, SK, Fascetti AJ et al. “Pet feeding practices of dog and cat owners in the United
States and Australia.” Journal of the American Veterinary Medical Association. 2008. Vol 232(5) p. 687 –
694.

10. is balanced. To date there is no evidence for any of the claims made by the raw
food advocates and both the FDA and CVM advise against feeding raw meat or
seafood to pets.
30
,
31
Perhaps the most important research on the effects of diet on behavior was in
the area of aging pets and dietary enrichment. The aging process affects every
part of the body. Canine cognitive dysfunction was initially thought to be just a
natural side effect of aging. Pet owners’ anecdotal evidence was attributed to
other disease functions and old age. Researchers at the University of Toronto
(Milgram et al. 2001) saw the anecdotal evidence from owners and found four
common complaints; disorientation and confusion (not recognizing family
members or familiar surroundings), interaction changes, sleep or activity changes
(including pacing) and housetraining accidents.
32
,
33
They incorporated these
complaints into a study on the effect of diet on aging behaviors. Diets were
enriched with the antioxidants vitamin E, vitamin C, selenium, and beta carotene,
fatty acids DHA and EPA, lipoic acid, and carnitine. Only dogs 7 years of age or
older with at least two of the clinical signs participated in the study. Dogs were
excluded if they had any other disease conditions that could impact the clinical
signs. Many different breeds and both sexes of dogs were included. A total of
125 dogs completed the double blind trial, 61 fed the antioxidant enriched diet
b/d and 64 fed the control diet. Dogs were tested using a Landmark
discrimination test
34
for problem solving abilities and an Oddity Discrimination test
(sort of like Sesame Street for dogs, one of these things is not like the other
30
FDA. Guidance for Industry. Manufacturer and Labeling of Raw Meat Foods for Companion and Captive
Noncompanion Carnivores and Omnivores.
31
CVM Update. Tips for preventing food-borne illness associated with pet food and pet treats. July 2007
32
Landsberg G and Araujo JA. “Behavior Problems in Geriatric Pets.” The Veterinary Clinics Small
Animal Practice. 2005. Vol 35. p. 675 – 698.
33
Neilson JC, Hart BL, Cliff KD, and Ruehl WW. “Prevalence of Behavioral Changes Associated with
Age-related Cognitive Impairment in Dogs.” JAVMA. 2001. Vol 218. No. 11. p. 1787 – 1791.
34
Milgram NW, Head EA, Muggenburg B et al. “Landmark discrimination learning in the dog; Effects of
age, an antioxidant fortified food and cognitive strategy”. Neuroscience Biobehavior Review. 2002. Vol
26(6). P. 679 – 695.

11. using 3 items). The dogs were given food rewards for correct responses. The
results were significant. Dogs fed the antioxidant enriched diet showed significant
improvement in 13 of the 15 individual behavioral categories. Dogs fed the
control diet only showed significant improvement in 4 out 15 of the same
categories. Even more significantly, dogs in the antioxidant enriched group
continued to improve after the 60 day trial period indicating the benefits are long
term.
35
The humanization of the pet food market has resulted in misconceptions about
the influence of diet on dog behavior. Pet owners are bombarded with opinions
masquerading as fact on the internet, in the pet food store and in the media
about what is good for their dog. Misinformation about nutrition and normal dog
behavior clouds our perception of what is healthy for our dogs. Anecdotal reports
have replaced clinical research in the minds of dog owners. Pet owners need to
be educated by veterinarians about the importance of life stage nutrition and how
good nutrition affects behavior. Pet owners need to trust the veterinarian as a
source of good information not a money grabbing pet industry. There is a lot of
room for research on diet and behavior. Specific breed research could be
conducted in the areas of obesity and satiety. Do smaller dog breeds become
obese because of inactivity or less satiety due to faster intestinal transit time? Is
there a difference between breeds and the effects of fiber on satiety? What are
the optimum levels of nutrients in milk replacer for less anxious orphan puppies?
Does diet have an effect on separation anxiety? What is the optimum level of fat
and antioxidants to reduce stress and improve performance in working dogs? I
know many police officers would love a study on how to decrease stress related
disorders in police dogs through diet. Raw food supporters would love a study to
prove or disprove the benefits and disadvantages of raw food diets on behavior.
Do raw food diets actually decrease aggression? Are pica and coprophagia
related to nutrient deficiency or is it strictly a behavioral issue? What is the effect
of obesity on aggression; Are obese dogs less aggressive because their
35
Milgram NW, Zicker SC, Head EA et al. “Dietary Enrichment counteracts age associated cognitive
dysfunction in Canines. Neurobiology of Aging. 2002. Vol 23. p. 737 – 745.

12. neurotransmitters are hyper stimulated? The questions are endless. Until we
have a better understanding of the link between diet and behavior the questions
and misconceptions will continue.