My pet got fat eating kibble because it’s so high in carbohydrates!
How often have you heard the above statement? Let’s discuss carbohydrates and how it relates to weight gain and obesity in our pets.
Carbohydrates are a macronutrient, meaning they are needed in fairly large amounts in your diet. Carbohydrates are an energy supplying nutrient, but depending on the type of carbohydrate, varying amounts of energy will be provided. Types of dietary carbohydrates include monosaccharides, disaccharides, polysaccharides and dietary fibres.
Dietary fibres are not ‘digested’ and generally don’t provide energy in the same levels as digestible carbohydrates such as starch and sugars. Complex carbohydrates are broken down into digestible and indigestible components; indigestible components like dietary fibre will pass through the gut without being digested or absorbed, not providing any energy to the host whereas digestible components are types of simple sugars that provide energy in the form of glucose.
So, why does this matter?
The sugar and starch components of the diet are what contribute to caloric intake, not fibre. The way in which carbohydrates are reported on pet foods is only the crude fibre component – not Nitrogen Free Extract (NFE) which is a calculated amount of total carbohydrates that includes all types of carbohydrates (the digestible and indigestible components) which again isn’t perfect but it’s something.
So when we make a claim that “kibble contains high levels of carbohydrates”, what are we referring to?
What is “high in carbohydrates” anyway?
In the case of your standard kibble diet, crude fibre is the only measure of carbohydrates used, so for a diet to be considered “high fibre”, this is typically referring to a diet with more than 7% crude fibre – most standard pet foods will contain up to 5% crude fibre.
But this doesn’t really tell us the information we are looking for – we want to know total carbohydrates, so we are looking for NFE. Critics of kibble often claim some ridiculous values of carbohydrates, quoting anywhere from 50% carbohydrates, all the way up to a whopping 80%!!!
Now, before I address those wild claims, let’s use some logic here – remember that fibre is indigestible, so would not be providing energy or nutrients to the system (food for the microbiome maybe, but that’s a different conversation), so we would still need a complete and balanced diet – other macronutrients have certain requirements under AAFCO lifestage profiles, so if we had a minimum of 25% Protein and 8.5% Fat, then accounting for vitamins, minerals (around 5%) and Moisture (15% or less in a dry food), let’s do the math; this makes up 53.5% of the diet composition. Subtracting from 100%, this leaves us with only 46.5% left to possibly be carbohydrates. This is why it’s simply impossible to have a complete and balanced kibble diet with more than 45% carbohydrates – and based on the composition of high fibre diets (used for weight loss and gastrointestinal diseases), they do not exceed 45% carbohydrates (NFE).
So what about digestible carbohydrates? Would a high proportion of digestible carbohydrates lead to weight gain?
Well, how much are we talking about here? Ingesting 1g of digestible carbohydrates provides 3.5 kcal – this is the same amount of energy provided by protein. Fat is more energy dense, providing 8.5 kcal/g. So in layman’s terms, you’d need to consume nearly 2.5 times the amount of carbohydrates to obtain the same amount of energy in fat.
Why is that important? It means while your pet might ingest more digestible carbohydrates in their diet than fat, it does not mean they are getting the same amount of calories by consuming more carbohydrates. And as we discussed before, some components of carbohydrates (such as fibre) do not provide energy at all – and this is why they use them in weight loss diets!
So, to simply equate carbohydrate consumption with obesity is not only untrue, but doesn’t even make sense when you look at it in terms of calories.
Why then, is there an obesity epidemic amongst pets?
Overfeeding. As we discussed above, it’s the amount of calories consumed not the amount of a particular nutrient that results in weight gain, in conjunction with a net energy imbalance ie. too many calories in and not enough calories out. 95% of obesity cases are the result of excessive caloric intake and an inactive lifestyle – the other 5% of cases are related to endocrine disorders that affect the body’s normal metabolism.
To simply blame kibble doesn’t actually look at the big picture – many pet owners are adding toppers, including treats, providing table scraps and human foods (which are arguably more calorie dense than most pet foods), on top of their pet’s daily intake of food, alongside many supplements and oils that also contribute substantially to caloric intake.
So, not only is it possible that pet owners are overestimating how much kibble to feed their pets – as kibble is actually very energy dense typically due to the inclusion of fats and oils – they aren’t necessarily thinking about what else they are adding on top; which has been shown time and time again through pet owner surveys and studies.
Why can’t we use protein or fat as an energy source in pet food?
We absolutely can, and do, use fat and protein as an energy source in pet food – but carbohydrates actually serve a quite unique purpose.
Beyond the gut health benefits of indigestible prebiotic fibres that feed the organisms in the gut microbiome, digestible carbohydrates actually have a protein-sparing effect. When protein is low (14% ME) and carbohydrates are high (as high as 47% ME), protein oxidation is reduced and it is spared to be used more effectively for protein synthesis and amino acids.
Protein provides a number of valuable resources to the body; filling amino acid requirements for important metabolic processes, providing the building blocks for the development of muscle mass and growth, and last but not least, keeping the hair and skin in top condition – in fact, 30% of the protein consumed by the pet is used purely for this purpose! This is why most pet foods will have a slight excess in protein to ensure they aren’t just meeting bare minimum levels required by AAFCO, but go slightly beyond it so that the pet is looking and feeling their best, and at the same time including a decent balance of carbohydrates to provide energy, so the protein is being used effectively.
Similarly with fat, this is extremely energy dense, so we need to balance the level of fat in the diet with the essential fatty acid content (linoleic acid, DHA, EPA, etc), so again we can use it for energy but really the fatty acids are what we need fat for. Some dogs also can’t tolerate high levels of fat, so using carbohydrates as an energy source helps to reduce the amount of fat used in the diet where needed.
What about weight loss?
The nutritional management of obesity actually uses carbohydrates to help induce weight loss; by increasing the level of fibre (insoluble carbohydrates), selecting lower glycemic index carbohydrates and decreasing the level of digestible carbohydrates. Studies have actually shown cats fed high carbohydrate, low fat diets have obesity protective-effects while high fat (greater than 25% ME), low carb diets increased risk of obesity by 2.5 times! Cats fed low fat/high carb diets also had less body fat.
In summary, carbohydrates don’t cause obesity – overfeeding your pet does. So, instead of overthinking your pet food labels and manually calculating how many carbs is in their diet – take the time instead to calculate how much they are eating, and cut back on the treats. You’ll be well on your way to better quality of life for your furry friend.
References
Images and tables sourced from Small Animal Clinical Nutrition Textbook
https://www.petobesityprevention.org/2023
https://www.petobesityprevention.org/pet-caloric-needs
Rankovic, A., Adolphe, J. L., & Verbrugghe, A. (2019). Role of carbohydrates in the health of dogs. Journal of the American Veterinary Medical Association, 255(5), 546-554. Retrieved May 19, 2024, from https://doi.org/10.2460/javma.255.5.546
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