Kibble marketed as “complete and balanced” is formulated to meet every nutrient requirement a dog or cat needs for a given life stage, and in the United States that claim is backed by regulatory nutrient profiles or feeding trials overseen by the Association of American Feed Control Officials (AAFCO). But “balanced on paper” and “balanced in the bowl” are not always the same thing. Extrusion processing, ingredient sourcing, mineral absorption rates, and species-specific metabolism all introduce gaps between what the label promises and what a pet’s body actually gets.
What “Complete and Balanced” Actually Means
When a bag of kibble carries the phrase “complete and balanced,” it means the manufacturer has substantiated that claim through one of two routes. The first is formulation: the food’s nutrient levels fall within the ranges set by the AAFCO Dog or Cat Food Nutrient Profiles, which replaced older National Research Council recommendations as the recognized authority in the United States. These profiles set minimum and, for some nutrients, maximum levels, with separate tiers for adult maintenance versus growth and reproduction. The second route is a feeding trial conducted under AAFCO protocols, where the food is actually fed to animals and health markers are tracked over a defined period.1PubMed. The Association of American Feed Control Officials Dog and Cat Food Nutrient Profiles: substantiation of nutritional adequacy of complete and balanced pet foods in the United States
The distinction matters more than most pet owners realize. Formulation-based claims are essentially a recipe check: the manufacturer confirms that the ingredient list, on paper, meets the targets. A feeding trial, by contrast, puts the food through a biological test. The formulation method is far more common because it is cheaper and faster, but it does not account for how well the animal actually absorbs each nutrient from the specific ingredient matrix in that food. A kibble could meet every profile number and still deliver less bioavailable zinc or calcium than the label implies.
What Extrusion Does to Vitamins
Kibble is made through extrusion, a process that pushes a dough of ground ingredients through a heated barrel under high pressure. The heat and moisture are what give kibble its characteristic puffed shape, but they also degrade certain nutrients. A review of the research on vitamin retention during extrusion found that fat-soluble vitamins A, D, E, and K, along with vitamin C and folic acid, were the least stable. Temperatures above 100°C were the most damaging factor, and for vitamins E and C specifically, increasing moisture was just as destructive as increasing heat. B-group vitamins, including thiamin, held up much better through the process.2The Journal of Nutrition. A literature review on vitamin retention during the extrusion of dry pet food
Manufacturers compensate by adding vitamin premixes after extrusion, often sprayed on with the fat coating that finishes each kibble piece. This works reasonably well for getting the nutrient content back up to target levels at the time of packaging, but it means the vitamins present in the final product are largely synthetic additions rather than nutrients that survived intact from the original ingredients. Whether that distinction matters nutritionally is debatable, but it does mean the “whole food” character of the ingredient list can be somewhat misleading.
Extrusion has an upside, too. Raw grains and legumes contain compounds like trypsin inhibitors, phytates, and polyphenols that can interfere with protein digestion and nutrient absorption. Many of these are heat-sensitive, and under the right conditions, extrusion effectively destroys them, improving the overall quality of plant-based ingredients in the finished diet.3PubMed Central. Special topic: The association between pulse ingredients and canine dilated cardiomyopathy: addressing the knowledge gaps before establishing causation
Protein Sources and How Well They Are Digested
Pet food labels list protein sources prominently, and owners often assume that animal-derived protein is inherently superior to plant-derived protein. The digestibility data paints a more nuanced picture. When researchers compared dogs fed diets based on soybean meal, poultry meal, poultry by-product meal, and beef and bone meal, the protein was well-utilized from all four sources. Total tract protein digestibility was highest for the poultry meal diet, while soybean meal, poultry by-product meal, and beef and bone meal were similar to each other. Dogs on the soybean meal diet produced more feces on a dry-matter basis, largely because of the higher fiber content in that ingredient, but ileal digestibility of protein was not significantly different across treatments.4PubMed. Selected animal and plant protein sources affect nutrient digestibility and fecal characteristics of ileally cannulated dogs
Cats tell a slightly different story. When plant protein levels increase in cat food, cats actually show improved protein digestibility compared to dogs eating the same formulations. Plant proteins, when properly processed through extrusion, proved to be a satisfactory complement to animal protein ingredients for meeting the amino acid needs of both species.5PubMed Central. Cats Have Increased Protein Digestibility as Compared to Dogs and Improve Their Ability to Absorb Protein as Dietary Protein Intake Shifts from Animal to Plant Sources That said, digestibility of protein overall does not guarantee that every individual amino acid arrives in adequate amounts, and this is where the grain-free controversy enters the picture.
The Grain-Free Question and Heart Disease
One of the most consequential nutritional-balance failures in recent kibble history involves certain grain-free formulas and their possible link to dilated cardiomyopathy in dogs. The concern centers partly on taurine, an amino acid dogs can synthesize from methionine and cysteine but may not produce in sufficient quantities depending on what raw materials are available in the diet. Some novel protein sources now common in grain-free kibble are unexpectedly low in taurine itself or in its sulfur-containing amino acid precursors. Rabbit, for instance, is low in taurine, while lamb meal is low in methionine and cysteine. Because these ingredients were not historically common in dog food, there is limited data on the bioavailability of taurine and its precursors from many of them.6PLOS ONE. Taurine deficiency and dilated cardiomyopathy in golden retrievers fed commercial diets
The legume side of this equation has also drawn scrutiny. In a 28-day feeding trial comparing grain-containing and pulse-based diets, dogs fed a wrinkled-pea-based diet showed impaired stroke volume, reduced cardiac output, and increased levels of a heart-stress biomarker called NT-ProBNP, though these changes were subclinical. Digestibility of sulfur-containing amino acids also dropped on the pulse-based diets, likely due to higher fiber levels. Plasma methionine was significantly lower after feeding all test diets compared to the baseline commercial diet. A lentil-based diet did not produce the same heart-related changes, suggesting that not all legumes carry equal risk.7PubMed Central. Effects of a 28-day feeding trial of grain-containing versus pulse-based diets on cardiac function, taurine levels and digestibility in domestic dogs
The picture remains incomplete. Researchers have cautioned against declaring a definitive cause before the knowledge gaps are filled, and the FDA’s investigation into a possible link has not resulted in a conclusive regulatory finding. What is clear is that a kibble can meet every AAFCO profile number for protein and amino acids and still deliver a functionally imbalanced amino acid supply if the specific ingredient sources have poor bioavailability for key compounds. It is a reminder that “balanced” as a regulatory designation is not the same as “optimized.”
Minerals That Do Not Absorb the Way You Would Expect
Mineral content on a kibble label reflects what was added to the mix, not what a dog or cat will absorb. A study using stable isotopes to measure actual mineral absorption from a standard dry dog food found that dogs absorbed only about 10% of the calcium, about 9% of the iron, roughly 23% of the copper, and about 12% of the zinc present in the food.8The Journal of Nutrition. Mineral and Trace Element Absorption from Dry Dog Food by Dogs, Determined Using Stable Isotopes Those are strikingly low numbers, and they explain why formulations often include minerals at levels well above the minimum requirement: the excess accounts for expected losses during digestion.
The form a mineral takes also matters. Earlier research had shown that zinc bound to amino acid chelates could be absorbed at rates around 88%, roughly double the rate for zinc oxide. The much lower absorption seen in the stable-isotope study, where zinc came from inorganic sources in the kibble matrix, was likely due to both the mineral form and the higher total zinc intake, which tends to reduce fractional absorption. For pet owners, this means that two kibbles with identical zinc levels on their guaranteed analysis could deliver very different amounts of usable zinc depending on the mineral source listed in the ingredient panel.
Calcium-to-Phosphorus Ratio in Growing Dogs
Getting the overall mineral levels right is one challenge; getting the ratios right is another. The calcium-to-phosphorus ratio is one of the most critical nutritional parameters for growing puppies, and kibble formulations aim for a range generally cited around 1.3-to-1 up to 2-to-1. When researchers fed growing puppies of two different breeds a diet with low phosphorus while calcium remained unchanged, the resulting calcium-to-phosphorus ratio climbed above the recommended range. Several puppies from both breeds developed poor appetite, stunted growth, and degraded skin and coat quality. A few showed clinically relevant musculoskeletal problems, including rapid loss of muscle strength with severe deviation of the limb axis and hyperflexion of the joints, though radiographs did not show bone abnormalities.9PubMed. Effects of low phosphorus supply on the availability of calcium and phosphorus, and musculoskeletal development of growing dogs of two different breeds
The takeaway for puppy owners is that supplementing calcium on top of a kibble already formulated as complete and balanced can push the ratio out of range just as effectively as a deficiency can. Large-breed puppy formulas exist specifically because these breeds are more vulnerable to skeletal problems from mineral imbalances during their longer growth phase. Adding calcium powder or bone meal to an already balanced large-breed puppy diet is one of the more common well-intentioned mistakes owners make.
Fat Quality and Oxidation
Polyunsaturated fatty acids, particularly omega-3s, are a genuinely beneficial component of kibble. They help reduce inflammation, support energy metabolism, and facilitate absorption of fat-soluble vitamins. But the same chemical structure that makes them useful also makes them vulnerable to oxidation by free radicals, especially at higher concentrations.10Journal of the Brazilian Chemical Society. Lipid Quality and Oxidative Stability in Industrial Foods for Dogs and Cats Kibble is typically coated in fat after extrusion to improve palatability and deliver these fatty acids, and that surface fat is exposed to air every time the bag is opened.
A study on the palatability effects of coating kibble with chicken fat enriched with free fatty acids found that adding 5 to 20% oleic acid to premium chicken fat did not negatively affect digestibility or palatability in Labrador retrievers. Free fatty acids alone did not appear to influence how eagerly dogs ate the food.11Translational Animal Science. Effects of coating kibble with chicken fat enriched with free fatty acids on digestibility and palatability in Labrador retrievers This is relevant because free fatty acids increase as fat oxidizes, and it suggests that mild oxidation does not immediately change how the food tastes to a dog. The practical implication is that your dog may happily eat kibble whose fat has started to go rancid before you notice a problem. Storing kibble in a cool, dry place and keeping bags sealed tightly is more than a freshness preference.
Fiber and the Gut Microbiome
Fiber in kibble serves structural and digestive functions. It helps bind the dough during extrusion and, once eaten, feeds beneficial bacteria in the gut. In a study of senior dogs, adding a prebiotic fiber blend to kibble significantly reduced the incidence of poor-quality feces from 1.5% to 0.3% of stools, produced firmer feces overall, and lowered fecal pH, which is associated with greater resistance to pathogenic bacteria colonizing the gut.12PubMed Central. A Novel Prebiotic Fibre Blend Supports the Gastrointestinal Health of Senior Dogs
For older pets, fiber balance becomes especially important because gut microbiome diversity tends to decline with age. But more fiber is not always better. The soybean-meal protein trial mentioned earlier showed that high fiber from plant protein sources increased fecal output, and the pulse-based diet trial found that higher fiber reduced digestibility of sulfur-containing amino acids. Getting fiber right means choosing sources that promote fermentation in the hindgut without impairing absorption of other nutrients upstream, and that balance depends heavily on the specific fiber type. Beet pulp, for example, behaves very differently in the gut than cellulose or pea fiber.
Why Cats Need a Different Kibble Than Dogs
Dogs and cats do not choose the same macronutrient balance when given the option. In a controlled study where both species had access to foods of similar palatability, cats chose to consume most of their calories from carbohydrate (about 43%) and protein (about 30%), while dogs gravitated toward fat (about 41%) and carbohydrate (about 36%). Cats also showed a wider spread in individual protein preferences than dogs did.13Journal of Experimental Biology. When fed foods with similar palatability, healthy adult dogs and cats choose different macronutrient compositions
These different preferences reflect genuinely different metabolic machinery. Cats are obligate carnivores with limited ability to synthesize certain amino acids and fatty acids that dogs can produce on their own. The carbohydrate content of cat kibble is a longstanding point of debate. Many dry cat foods contain 30% or more carbohydrate because starch is structurally necessary for extrusion. In a clinical trial comparing diabetic cats fed a low-carbohydrate, low-fiber canned diet versus a moderate-carbohydrate, high-fiber diet, 68% of cats on the low-carbohydrate diet reverted to a non-insulin-dependent state by week 16, compared to 41% on the moderate-carbohydrate diet.14PubMed Central. Comparison of a low carbohydrate-low fiber diet and a moderate carbohydrate-high fiber diet in the management of feline diabetes mellitus That study used canned food rather than kibble, which is part of the point: achieving a truly low-carbohydrate diet is structurally difficult in an extruded kibble format.
Urinary Health and Dietary Acidification in Cats
Cat kibble formulations must also account for urinary tract health, particularly the risk of struvite and calcium oxalate crystals forming in the bladder. Nutritional interventions target three main factors in stone formation: urinary pH, the concentration of mineral solutes in urine, and overall crystallization potential. Controlled dietary acidification is the primary tool for struvite prevention, and many cat kibbles include urinary acidifiers such as DL-methionine, sodium bisulfate, or phosphoric acid.15PubMed Central. Revisiting feline urinary tract health: the role of diet and acidifying agents in urolith prevention and long-term cat health
Adding DL-methionine or ammonium chloride to dry cat food has been shown to decrease urinary pH and reduce struvite crystal formation in clinically normal cats.16Journal of Veterinary Medical Science. Effect of Supplementation of Dry Cat Food with D,L-Methionine and Ammonium Chloride on Struvite Activity Product and Sediment in Urine But pushing urine pH too far in the acidic direction can create a different problem. Foods with the lowest urine pH values have tended to show the highest calcium oxalate supersaturation, although the relationship is not entirely consistent, and factors beyond pH also play a role in both struvite and calcium oxalate crystal risk.17The Journal of Nutrition. Urinary Relative Supersaturations of Calcium Oxalate and Struvite in Cats Are Influenced by Diet Formulating cat kibble for urinary health is therefore a balancing act: acidify enough to prevent struvite, but not so much that you promote calcium oxalate. This is one area where veterinary-prescribed diets genuinely differ from over-the-counter kibble, because the therapeutic versions are formulated to target a narrow urinary pH window that general-market products are not required to hit.
Dry Kibble Versus Wet Food and Oral Health
One of the oldest claims in pet nutrition is that dry kibble helps clean teeth through the mechanical action of chewing. The evidence offers partial support. In a study comparing adult dogs consuming either dry extruded food or wet canned food, plaque coverage tended to be higher in dogs fed wet food, though the difference only approached statistical significance. More clearly, dogs on dry food had higher salivary pH, lower breath sulfur concentrations, and an oral bacterial community more closely associated with oral health: higher levels of beneficial genera and lower levels of bacteria linked to periodontal disease.18PubMed Central. Oral microbiota populations of adult dogs consuming wet or dry foods
That said, kibble is not a substitute for dental care. The mechanical scraping effect applies mainly to the tips of the teeth that contact the kibble, and many dogs swallow pieces with minimal chewing. Breeds with crowded teeth or misaligned bites get almost no cleaning benefit. The microbiome differences are interesting and suggest a real oral-environment effect beyond simple abrasion, but they do not eliminate the need for professional cleanings or daily brushing. Thinking of dry food as mildly supportive of oral health rather than actively protective is the more honest framing.
When Kibble Alone Might Not Be Enough
For the majority of healthy adult dogs and cats, a well-formulated kibble from a manufacturer that conducts feeding trials provides a nutritionally adequate diet. But “adequate” and “optimal” are not interchangeable, and several populations may benefit from adjustments. Senior pets with declining gut function may absorb minerals and amino acids less efficiently than the animals used to validate the food’s formulation. Large-breed puppies need tightly controlled calcium-to-phosphorus ratios that generic “all life stages” kibbles do not always deliver. Diabetic cats may do better on lower-carbohydrate wet food than on any dry diet. Dogs with breeds or lineages historically fed grain-free legume-heavy diets may warrant taurine monitoring, especially if echocardiographic screening reveals early cardiac changes. None of this means kibble is broken as a food category, but it does mean that the phrase “complete and balanced” should be read as a regulatory floor, not a ceiling.