Everything You Need to Know About Calories And Your Dog
Calories Don’t Mean Nutrition: Every Dog is Different
Why A Calorie Isn’t A Calorie In Your Dog Food: Calorie is a common term most often used to describe the energy density of human or animal food. Calories, which only come from food, provide the body with energy to carry out numerous metabolic functions. However, the science behind a calorie, and the energy they supply is not as simple as it may seem. This is because there are multiple factors that dictate how a body utilizes and expends these calories from different foods.
To put the importance of this discussion into context, obesity is an epidemic among pets and people. An alarming statistic shows us that 60% of cats and dogs are estimated to be overweight or obese in America today.(1) As a society we have been conditioned to believe the solution to this is to restrict calories in order to lose or control weight, but is this approach correct? Likely not, or at least it is just one piece of the puzzle. In fact, this dogma has led to some unintended nutrition and health consequences. The entire concept does not give credit to the complexity of nutrition, metabolism or individual differences among dogs. In other words, the concept of calories in, calories out for weight gain, maintenance or loss may not be something that can be extrapolated out for an entire population, human or animal. That’s why a calorie isn’t a calorie. As a general rule, it is individualized.
Let’s look at some of the reasons why:
What Exactly Is A Calorie?
The word calorie itself has a French origin, and was originally introduced between 1787 and 1824, and who exactly introduced it is still up for debate.(2) Regardless, the definition of calorie has evolved quite a bit over time and doesn’t just apply to food. Since a calorie is a unit of energy it can be used to describe anything that contains energy.
Today, the definition of a calorie is actually a bit technical and depends on the situation. A calorie, as a measure of energy, is classified under the metric system. A simple way to define a calorie is to equate it to 4.184 joules, which is a more common unit of energy used in the physical sciences. That said, calorie has two meanings when it comes to nutrition:
- The first is a small calorie or “gram calorie”, and is defined as the amount of heat energy required to increase the temperature of one gram of water by one degree Celsius.
- The second is a large calorie, or “kilo Calorie” (kcal), and is defined as the amount of heat needed to raise one kilogram of water by one degree Celsius. These are the calories we refer to when describing food and therefore what you see listed on food packaging. A large calorie is formally known as a kilo Calorie (kcal), and 1 kcal = 1,000 gram calories (small calories).
Calculating Calories is Not a Perfect Science
Calories come from 3 places: protein, fat and carbohydrates – these are known as macronutrients. You may have been told that protein carries 4 calories per gram, carbohydrates carry 4 calories per gram and fat is the most calorie dense at 9 calories per gram. If this is the case, then you’ve been given incorrect information – or at least incomplete information. The calories of a food are measured by complete combustion of food in a bomb calorimeter. This process shows that fat, proteins and carbohydrates, on average have a calorie content of 9.4, 5.7 and 4.1 calories per gram, respectively (3). So why don’t we use these calorie averages? Good question. There are two main answers:
- The Atwater System eventually simplified the bomb calorimetry values of macronutrients into the 4, 4 and 9 kcal of calories per gram of protein, carbohydrate and fat – which are known as today’s common values. These values were determined by correcting for losses in digestion, absorption and urinary energy excretion. From that, combined raw ingredients, or processed food products for human consumption are calculated by adding up the average digestibility of calories provided by the energy-containing macronutrients. This simply means that because this system simplified macronutrient calorie content into averages, the calorie content on food packaging is an estimate– not exact. Now you may start to see why there could be some significant margins of error.
- Even further complicating matters, the pet food industry operates on “Modified Atwater” which assumes the 3 values of macronutrients into 3.5, 3.5 and 8.5 calories per gram of protein, carbohydrate and fat. This is because the traditional Atwater equation has been found to overestimate the amount of calories available to dogs and cats in traditional commercial pet foods due to lower digestibility of these foods.(4,5) The problem is that several variables influence the availability, or digestibility of these calories including fiber content, food processing, health of the animal, age, breed and more. Regardless, this equation is what is used to determine the calorie content of commercialized pet food. This is the number you will see listed on the pet food packaging today.
Without diving too deep, a key concept to understand is that the amount of energy (heat) represented by a calorie can differ depending on the food. This means that a calorie listed on a food label is based on average of energy represented in different foods – and not necessarily representative of the number of calories in the given product. And this ‘average’ is used to estimate the calorie content of all food types, leaving significant room for inaccuracies. Said differently, the calories listed on the package may not be an accurate representation of the calories within that particular food. We’ll explain a bit more what factors can influence these variations.
So how do you determine your pet’s calorie requirement? Are there other variables that determine this amount? Can the calorie requirement of your pet change over time? And how do you know if they are obtaining all the necessary nutrients – both macronutrients and micronutrients (vitamins and minerals)? Glad you asked:
Estimated Energy (Calorie) Requirement
Estimated energy requirement (calorie requirement, or EER) is the number of calories needed to carry out all bodily functions of an individual/pet and maintain weight. The number of calories changes based on individual factors such as age, gender, height/weight, activity level and weight goals. Other factors that influence energy and therefore nutrient requirements include health status, stress, exercise, infection, inflammation, and digestive disorders among others.
EER shows us that individuality of the person/pet is highly variable. Said simply, one pet may have completely different energy requirement than another of a similar breed, age and size. Our pets’ bodies “burn” calories through the metabolic processes within the body requiring numerous enzymes. These enzymes break down the macronutrients into smaller products that the body can use. To release the energy, molecules from macronutrient break down must react with oxygen to release their energy. Much of the energy released by this reaction goes toward maintaining body temperature.
The EER can vary between individuals and change dramatically over time. Growing puppies, pregnant and lactating mothers for example have a substantially higher EER than a grown adult. Elderly pets typically will have a lower EER – although balance of the diet is still important because the protein requirement increases as much as 50% as pets age.(6) Therefore, it’s not quite as simple as adding additional protein to an already existing diet.
Pet Food Formulation & Balance
When we think about ‘complete and balanced’ foods we often assume this is just vitamins and minerals. However, ensuring complete and balanced ratios of macronutrients is just as important for ensuring proper metabolism at all life stages of our pets. For example, fiber or fat content of pet foods can greatly influence the digestibility, caloric and nutrient value of any given diet. Simply, just reducing calories also means you may potentially be reducing necessary levels of vitamins, minerals or amino acids (protein) – not just calories. These are just a few significant reasons why solely reducing or restricting calories for weight loss could lead to significant nutrient deficiencies. This is just one of the theories behind the current grain free and heart disease, or DCM Investigation.
Why You Should Focus on Digestibility – NOT Calories
Further complicating matters include the digestibility and state (raw, cooked or otherwise processed) of the food being consumed. Digestibility of foods can also vary from species to species, meaning that a human and dog may derive differing amounts of calories and nutrients from the same food. A food’s digestibility is the collective proportion of all nutrients in a food that is available to the dog/human for absorption from the intestines into the bloodstream. Some of this depends on the structure/function of the GI tract of the animal. For example, humans are much more efficient at digesting carbohydrates and fiber sources due to a longer GI tract, meaning there is more time to break down carbohydrates. In addition, humans have more of the enzymes needed for carbohydrate breakdown than dogs or cats do. For canines, high fiber can decrease overall digestibility since high levels of fiber in the diet can decrease the transit time through the gastrointestinal tract, which limits the time of contact between food and enzymes, and digestion products and absorptive surfaces.(7)
In short, pet food companies should be conducting digestibility studies on ALL foods they offer in the market. Digestibility studies involve feeding a predetermined amount of food to several dogs for 14 days, collecting the stool and analyzing it for the percentage of macronutrients and micronutrients compared to what was fed. Results tell us what the animal actually absorbed, and did not absorb. This process does not involve any invasive procedures, inhumane conditions or otherwise harm to the animal. It seems simple enough; however, the reality is that the vast majority of pet food companies don’t perform these studies and it ultimately means that they have no idea what the actual calorie content, or digestibility of their food is!
In fact, you’d be surprised on how low the bar is for pet foods to enter the marketplace – but that is an entirely different topic for another day.
So, Proof is NOT in the Poop!
After reading the previous section this may seem contradictory. However, if you visit a few pet food company websites they will lead you to believe that measuring the volume of stool, not analyzing it for nutrients, can tell you the digestibility of the food. Some well-known blogs will even tell you that smaller stools mean better digestion.(8) However, the visual cues from poop actually tell us very little at all from a nutrition perspective. So, don’t be fooled: the digestibility of any given food, fresh or processed, can only be determined via proper digestibility studies as mentioned above.
Summary: Calorie ≠ Calorie: Why?
In this discussion we uncovered several factors that influence the caloric density of various foods. We also know that individuals can utilize the energy supplied in these foods at differing amounts. We also discussed how the age and health status of the animal can greatly impact calorie needs, and how those calories are utilized. Further, malabsorptive and maldigestive disorders as a result of disease can also complicate calorie utilization.
From this information, we now understand why just counting calories by what is listed on a label to in order to feed our pets may not be the best approach. We need to take into account the type of food, the digestibility and nutrient status of that food and individual factors that contribute to digestion and other metabolic processes. When making decisions on your pets’ food, be sure to ask questions and consider the above points to determine if the option you chose is actually right for your pet.
ABOUT THE AUTHOR: Nicole Cammack
Nicci’s undergraduate and graduate education includes biology, chemistry, business and nutrition. She has worked in the pharmaceutical industry on projects including cancer research, diabetes, schizophrenia, Alzheimer’s Disease, and hepatitis. She’s had the privilege to learn from leading international figures in the human and pet health industry, and regularly lectures at local and national conferences and organizations, including federal, state, and municipal K9, guide, and therapy dog teams on proper preventative nutrition and supplementation.
The reality is that much of the information about pet food and nutrition is incomplete, biased, or misleading. Nicci helps to break through many of the marketing claims, presenting data for what it is to help retailers and consumers better understand the industry and make better decisions. Her interests include fresh diets, metabolic disease and complementary diets for cancer treatment. Her current research involves examining pathogenic risk factors and transmission among raw fed dogs and cats through a comprehensive worldwide survey of raw feeders.
For more from Nicole, visit her blog here.
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- Association for Pet Obesity Prevention. Association for Pet Obesity Prevention. Accessed July 2, 2020. https://petobesityprevention.org
- Hargrove JL. History of the Calorie in Nutrition. J Nutr. 2006;136(12):2957-2961. doi:10.1093/jn/136.12.2957
- Castrillo C, Hervera M, Baucells MD. Methods for predicting the energy value of pet foods. Rev Bras Zootec. 2009;38(SPE):1-14. doi:10.1590/S1516-35982009001300001
- Asaro NJ, Guevara MA, Berendt K, Zijlstra R, Shoveller AK. Digestibility Is Similar between Commercial Diets That Provide Ingredients with Different Perceived Glycemic Responses and the Inaccuracy of Using the Modified Atwater Calculation to Calculate Metabolizable Energy. Vet Sci. 2017;4(4). doi:10.3390/vetsci4040054
- Kendall PT, Holme DW, Smith PM. Comparative evaluation of net digestive and absorptive efficiency in dogs and cats fed a variety of contrasting diet types. J Small Anim Pract. 1982;23(9):577-587. doi:10.1111/j.1748-5827.1982.tb02518.x
- Laflamme DP. Pet Food Safety: Dietary Protein. Top Companion Anim Med. 2008;23(3):154-157. doi:10.1053/j.tcam.2008.04.009
- Brambillasca S, Purtscher F, Britos A, Repetto JL, Cajarville C. Digestibility, fecal characteristics, and plasma glucose and urea in dogs fed a commercial dog food once or three times daily. Can Vet J. 2010;51(2):190-194.
- The Poop On Dog Diet And Digestion. Dogs Naturally. Published March 7, 2013. Accessed July 13, 2020. https://www.dogsnaturallymagazine.com/the-poop-on-dog-diet-digestion/