PASSIONATE BREEDERS
ARE ALWAYS LEARNING.

Carbohydrates for Dogs

Archive document IAMS COMPANY

Iams is since 1999 a registered trademark of The Procter & Gamble Company. This is an archive document used historically by the Iams Pet Food company or for Iams Pet Food products. Any and all mentions included herein needs to be replaced in context of the time and geography of its initial use as circumstances and products may have changed since then. Products and relative data are for US only. No assertion or further use of these documents can be made without P&G's authorization.

CARBOHYDRATE PUZZLE: WHAT'S IN IT FOR MY DOG?

Sean M. Murray, PhD
Gregory D. Sunvold, PhD
Research and Development Division
The Iams Company, Lewisburg, Ohio USA
Presented at the Iams Breeder' Symposium, 2002 - 2003 Edition

INTRODUCTION

Carbohydrates are the largest class of organic compounds found in nature, mainly as components of plant material. Plants capture the sun's radiant energy and store it as carbohydrates. These plants and the grains they provide are then utilized as key components of dietary formulations for dogs. However, when ranked with other major ingredients that supply protein and fat, carbohydrates are generally considered the least important and are often regarded as the "filler ingredient". To the contrary, carbohydrates do not just provide "bulk" in the diet, instead they provide an excellent source of metabolizable energy for dogs. Thus, the puzzle surrounding the use of carbohydrates in dog diets centers on understanding how various carbohydrate sources impact blood sugar levels-to provide either quick or sustained energy-in addition to providing the most beneficial responses of the blood sugar levels for dogs in various life stages and lifestyles.

CLASSIFICATION OF CARBOHYDRATES

Carbohydrates are divided into two categories: simple and complex carbohydrates. Simple carbohydrates are often referred to as "simple sugars" due to being made up of one or two sugar molecules. These sugars require little or no digestive breakdown and are readily absorbed from the small intestine. Some examples include fructose (fruit sugar), sucrose (table sugar) and lactose (milk sugar). Complex carbohydrates are also made up of the simple sugars but are strung together to form much longer and more complex chains that do require additional breakdown by intestinal enzymes before they are absorbed and utilized by the dog. Some examples of complex carbohydrates include starches such as whole grains and potatoes.

WHAT IS STARCH?

Starch is simply the multiple linked chains of glucose that plants have effectively compacted together to store as energy for growth and production of seeds, such as cereal grains. For years, nutritionists have known that the starch, and more specifically, the glucose stored in these grains is a readily available source of energy for dogs. Records of dogs being fed carbohydrates date back to the late 1770's when they were typically fed vegetables as a dietary staple.¹ Today, canine diets contain starch, derived predominantly from cereal grains, which are incorporated through the use of extrusion technology.

Starch is abundant in the seeds of cereal grains and tubers (potatoes) and represents up to 70-80% of a grain's dry matter. It plays an important role (Figure 1) in the nutritive value of diets consumed by dogs since it is the primary source of energy for many body functions and is necessary for the synthesis and metabolism of other nutrients. Some examples include the use of glucose, derived from starch, as the only source of fuel used by the brain and red blood cells to maintain proper function. In addition, not only does starch provide an excellent source of metabolizable energy to the animal, but it also influences the way products are manufactured by providing for proper expansion and cohesion of dietary ingredients to form kibbled and different textured diets.

METABOLIZING STARCH TO GLUCOSE

On average, 30 to 60% of metabolic calories in a commercially available diet come from dietary starch. While several starch sources are available for use in developing canine diets, not all starch sources are alike. In general, all starches require further breakdown or degradation to their basic building block-glucose. However, some starch sources do contain more complex carbohydrates than others and, in essence, contain more potentially available glucose. Some starch sources may also require additional digestion time or require specific enzymes in the digestive process in order to make the glucose available. The ability to do this is achieved through a process by which digestive enzymes break apart the chemical bonds that once linked multiple glucose molecules together to form starch.

In dogs, the main enzymes that orchestrate the breakdown of starch are the alpha amylases. These enzymes are secreted in the saliva and from the pancreas, adhere to the large starch molecules, and continue to break up the starch into more simple sugars. Ultimately, the process results in the production of glucose that will be used as the major fuel source of all cells in the dog's body. Several other digestive enzymes exist that are important, as well as specific, to metabolizing a multitude of other carbohydrates in the dog. These enzymes will also be vital to the process of deriving glucose from many other simple and complex carbohydrates from the time your dog matures from a puppy to a beloved senior companion.

IMPORTANCE OF GLUCOSE

Metabolizing starch to glucose is important since glucose is the chief end product of starch digestion, as well as the primary metabolic fuel for cells in the body. Glucose is readily absorbed in the small intestine, is transported via blood vessels, and is found circulating in the bloodstream to provide tissues with needed fuel. The rate of starch digestion and absorption is directly responsible for the rise in blood glucose immediately following a meal. Thus, choosing the appropriate source of starch will have a substantial effect on a dog's blood sugar status.

IMPORTANCE OF INSULIN

Insulin is a hormone secreted by the pancreas in response to elevated blood levels of glucose. The magnitude of the insulin response is directly proportional to the level of glucose present in the bloodstream. Hence, the more glucose present in the blood will result in greater levels of insulin being released. Insulin promotes the efficient storage and use of glucose molecules by controlling their transport across cell membranes. Insulin acts as the key that unlocks the cell and permits glucose to enter and be metabolized (Figure 2). Therefore, just as in the case of glucose, a dog's post-meal insulin level is strongly influenced by digestion and absorption of the starch contained in its diet.

AFTER MEAL GLUCOSE AND INSULIN RESPONSE

The nutritional importance of the "after meal" glucose and insulin response to different sources of carbohydrates is gaining greater awareness. In dogs, the body's ability to control glucose may be impaired in a number of life stages or conditions. Diabetes, obesity, gestation, and aging are examples of such life stages or conditions.

One of the primary concerns with overweight pets is abnormal glucose metabolism, since obesity and poor glucose metabolism are highly correlated. Animals with impaired glucose control have difficulty storing blood glucose, and glucose levels remain higher for longer periods of time than in normal individuals. Therefore, to reestablish a state of normalcy more quickly in these individuals, diets that minimize the glucose response after a meal should be sought.

It was originally believed that complex carbohydrates (starches) would result in lower glucose surges because their digestion rate is slower than simple carbohydrates.² However, a number of studies evaluating the after meal glucose and insulin responses to both simple and complex carbohydrate foods have contradicted this assumption.^2-6 For instance, in some cases complex carbohydrates result in comparable blood sugar and insulin responses to simple carbohydrates.^3,4,6 After a meal, blood glucose surges appear to be regulated by several factors in the diet such as the chemical nature of carbohydrates,^7,8 protein, fat,⁹ dietary fiber,¹⁰ and the type of food processing.¹¹

In humans, the different sources of starch have been ranked comparatively based on blood sugar response.^12,13 The resulting "glycemic index" utilized white bread as the standard and all other foods were ranked accordingly.¹⁴ These efforts have resulted in the publication of an international table of the glycemic index summarizing hundreds of separate entries. The glycemic index and dietary levels of carbohydrates have been used to explain approximately 90% of the reason for differences in glucose and insulin responses to a meal.¹⁵ This evaluation of a starch's influence on blood glucose and insulin is important to determine its influence on glucose response. No such glycemic index has been developed for animals.

DOES STARCH SOURCE MATTER?

The source of starch affects the blood sugar response in a clinically relevant manner. For instance, the consumption of a diet using whole sorghum significantly reduces plasma glucose peak levels and percent of glycemic response in diabetics when compared to consumption of dehulled sorghum, wheat, and rice recipes.¹⁶ In humans, barley had the lowest glycemic index when compared to other starch sources such as corn, wheat, rice, and millet.¹² These findings suggest that the source of starch influences the glucose and insulin response to food in simple-stomached animals and humans.

STUDYING STARCH SOURCE IN CANINE DIETS

Recognizing that carbohydrates are a significant portion of the daily diet of dogs, The Iams Company designed a study to evaluate the blood sugar response of diets containing corn, wheat, barley, rice, or sorghum as a chief source of energy in 30 weight stable, clinically normal, adult dogs. The dogs were housed individually according to approved Animal Welfare Act standards. All procedures were reviewed and approved by the Institutional Animal Care and Use Committee and the dogs were treated humanely and ethically during the entire study period.

Each testing period lasted a minimum of 2 weeks and a blood sugar response test was performed at the end of each testing period. During the first study, the dogs were randomized into 1 of 5 dietary treatment groups of 6 animals each. The dogs were re-randomized and assigned to a different experimental diet for the second period. Immediately following the collection of 2 baseline blood samples approximately 10 minutes apart, the dogs were fed an amount of food based on their body weight and allowed a maximum of 15 minutes to eat the experimental diets. Time 0 corresponded to the end of the food intake. The blood samples were collected at 10, 20, 30, 45, 60, 120, 180, and 240 minutes after the food was consumed. The extracted plasma was assayed for glucose and insulin.

During the stabilization period, dogs were fed their respective maintenance diet. The daily food intake was adjusted for each animal during this period to stabilize body weights. The five experimental diets were formulated to contain a similar starch content so that blood sugar response was not influenced by differences in carbohydrate intake. Evaluation of the carbohydrate sources in a complete diet matrix was also a consideration. To achieve this, protein levels needed to vary considerably while fat levels were at similar levels. The concentrations of the following nutrients were consistent across all diets: 32% protein, 10% fat, and 30% starch.

The different cereal sources were corn, wheat, barley, rice, and sorghum. The experimental diets were processed similarly with each starch source consisting of whole grain without the hull. Supplementation of micronutrients was held constant among diets since certain vitamins^17,18 and minerals^19,20 have been shown to alter signs of glycemic status. Individual daily feed allowances were based on the stabilization period intake. Glucose and insulin levels were analyzed using standard laboratory methods accepted by nutritionists.²¹ The results of glucose and insulin assays from the two baseline samples were averaged and reported as one baseline value (also called the area under the curve, or AUC).

STUDY RESULTS

Results of the study are summarized in Table 1. The rice diet resulted in higher glucose levels from 20 to 180 minutes after eating and also the greatest average glucose and after meal peak (Figure 3). The sorghum diet had consistently lower after meal plasma glucose levels than the other diets between 20 and 60 minutes and the glucose levels gradually increased for the remainder of the time points. The sorghum diet also resulted in the lowest average glucose levels (Figure 3). The glucose response to corn, wheat, and barley were intermediate to sorghum and rice with corn tending to yield the lowest glucose response of the three diets. The rice diet had a significant increase in blood insulin levels at 45- and 60-minute time points over all other experimental diets. The rice diet also resulted in a higher average insulin level, and insulin peak (Figure 4).

Rice

• Higher glucose levels
• Greatest average glucose
• Greatest after meal peak
• Increase in blood insulin levels
• Higher average insulin level
• Higher insulin peak

• Rice-based diets increase the blood sugar response after a meal and result in significantly higher post-meal glucose and insulin responses
• Used judiciously, rice may be effective in diets specifically formulated to provide a combination of quick and sustained energy for performance dogs
• Rice should not be used as the main carbohydrate source in a diet formulated for animals with poor glucose control, such as diabetes and obesity

Sorghum

• Lower after meal plasma glucose levels
• Gradually increased glucose levels
• Lowest average glucose level
• Intermediate insulin response

• Sorghum diets result in the lowest post-meal glucose response
• Dietary recommendations for improving glucose control in dogs should include sorghum

Corn

• Intermediate glucose response vs rice
• Intermediate insulin response vs rice
• Lower glucose response vs wheat and barley

• Corn when used with sorghum, barley or both will help to achieve a more even glycerin response

Wheat

• Intermediate glucose response vs rice
• Intermediate insulin response vs rice

• Wheat is not as effective as corn in leveling glucose
• May be used as secondary starch source along with appropriate levels of sorghum and barley

Barley

• Intermediate glucose response
• Lowest plasma insulin levels
• Lowest insulin response

• Barley resulted in the lowest post-meal insulin response
• Dietary recommendations for improving glycerin (glucose and insulin) control in dogs should include barley

Combined carbohydrate sources

• Corn
• Rice
• Sorghum

In the case of extreme energy needs, a combination of corn, rice and grain sorghum can provide highly active/very athletic dogs with rapidly available energy for exertion, while helping them maintain adequate body weight and condition in adverse environments

Conversely, the barley diet resulted in the lowest plasma insulin levels from 20 minutes to 240 minutes and the lowest insulin response. The corn, wheat, and sorghum diets were generally intermediate for most insulin response criteria.

STUDY CONCLUSIONS

This study showed that the rice-based diet increased the blood sugar response after a meal and resulted in significantly higher post-meal glucose and insulin responses. Sorghum generally resulted in the lowest post-meal glucose response while barley resulted in the lowest post-meal insulin response. These findings suggest that the source of starch influences the glucose and insulin response in dogs after a meal.

DIETARY RECOMMENDATIONS

So what exactly is in it for your dogs? It's simple- Eukanuba® and Iams® diets contain the appropriate types of carbohydrates that help your dog achieve optimum blood sugar and insulin levels. Iams carbohydrate research has shown that some products are best formulated using a combination of carbohydrate sources to fit the special nutritional requirements of your dog during specific life stages and life-styles. Iams uses carbohydrate sources such as grain sorghum, corn, and barley that are all highly digestible, which means your dog's body will metabolize a high percentage of each for energy. What's unique about the carbohydrate sources used in Eukanuba® and Iams® dog foods is the slow breakdown that results in moderate, stable blood glucose and insulin levels after a meal. By minimizing blood glucose, diets containing such a blend supply sustained energy.

Therefore, dietary recommendations for improving glucose control in your dog should include feeding diets that contain grain sorghum, corn and barley. It should be noted that in the case of extreme energy needs a combination of highly available carbohydrate sources (corn, rice, grain sorghum) can provide highly active/very athletic dogs with more rapidly available energy for exertion and can help them maintain adequate body weight and condition in adverse environments. However, rice as the main source of carbohydrate in a canine diet is not recommended for those animals with poor glucose control, such as dogs that suffer from diabetes or obesity.

Finally, you as dog owners can now solve the carbohydrate puzzle by completing the last piece-Help enhance the health and well being of your dog by providing them with Eukanuba® and Iams® diets that contain the appropriate carbohydrate sources to achieve optimal glucose control.

Eukanuba and Iams are registered trademarks of The Iams Company.

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