Do You Know the Difference Between a Complete and a Complementary Cat Diet?

Dr. Amaya Espíndola, MRCVS is a holistic, cat and nutrition specialist, veterinarian based in Mallorca and the current president of the Raw Feeding Veterinary Society. She offers online consultations worldwide, focusing on nutrition as the first line of therapy. With a background in psychosomatic medicine, Amaya approaches each case by considering the deep connection between physical symptoms and emotional wellbeing, aiming to support feline health from a truly integrative perspective. You can find her at felvet.co.uk and on Instagram at @felvetforcats.  

For years we have seen the phrase “complete and balanced” printed on cat food labels, as if it were an absolute guarantee of nutritional adequacy. However, this concept, established by organisations such as FEDIAF, NRC, and AAFCO, is only a theoretical reference point, not a universal truth and certainly not a perfect formula for every cat.

What “complete” really means

A “complete” food is, by legal definition, one that contains all essential nutrients in sufficient quantity and proportion to meet the basic requirements for maintenance, growth or reproduction. So far, that sounds ideal. The issue lies in how this completeness is determined.

The nutrient values used to define a “complete” diet come from experimental studies carried out under laboratory conditions, with limited numbers of animals living in controlled environments. In other words, these are average estimates that do not take into account real-world factors such as ingredient digestibility, raw material quality, health status, or the individual cat’s lifestyle.

As a result, a product may meet every parameter “on paper”, yet fail to ensure that a particular cat, in a particular home, is truly receiving what they need.

What “complementary” means

By contrast, a complementary food is one that contributes to a cat’s overall diet but is not nutritionally complete on its own. It can be an excellent component of a feeding routine, for example fresh meat, organs, or a specific blend used to enrich variety, but it must be combined with other foods or supplements to ensure that all essential nutrients are covered.

Complementary foods are not inferior; they simply serve a different role. When chosen wisely, they allow greater flexibility and personalisation, helping you adapt the diet to the cat’s individual needs, preferences, and health status. In that sense, the distinction between “complete” and “complementary” is not about quality, but about context and balance.

What recent studies reveal

Several scientific papers have questioned the reliability of the “complete” label.
A study analysing commercial and prescription dry foods for cats found that several did not reach the minimum required levels for key minerals. Another investigation assessing commercial raw diets revealed nutritional imbalances in most of the products tested, including those marketed as complete.

A particularly revealing study from the University of Nottingham examined 177 pet foods labelled as “complete”, both wet and dry, and compared them with FEDIAF mineral standards. The researchers found that only a small percentage met all nutritional guidelines, and that many had significant calcium-to-phosphorus imbalances or exceeded safe levels for elements such as selenium and copper. Diets with high fish content also showed excessive arsenic concentrations. The authors concluded that, if fed exclusively and over long periods, many of these diets could compromise long-term health in cats and dogs.

Together, these findings underline that no food format is automatically reliable. Both processed and raw products can deviate from their declared nutritional targets. What truly determines adequacy is the combination of ingredient quality, formulation, and independent verification.

Why there is no perfect diet

The concept of “complete and balanced” began with a legitimate goal: to prevent nutritional deficiencies. But over time it has become a magical idea, a kind of promise of perfection that can easily mislead us. In reality, these standards are merely a starting point, not a destination, and certainly not a reflection of optimal nutrition for every animal.

The standards themselves can also be questioned, since they were developed under tightly controlled laboratory conditions that do not reflect the diversity of real feline lives. Separately, we must acknowledge that modern meats, eggs, and fish no longer have the same nutrient density they did decades ago; soils are poorer and production systems more intensive. This adds yet another layer of complexity when trying to meet nutritional targets through food alone.

On top of that, many industrial diets achieve their “balance” through synthetic premixes, whose actual absorption and bioavailability in the cat’s body may not be guaranteed. And rather than relying on functional ingredients, many foods are bulked up with cereals or carbohydrates that provide texture and calories, but little biological value for an obligate carnivore. Such fillers may lower production costs but contribute almost nothing nutritionally, and in some cases can displace or interfere with essential nutrients.

This is why, even when the label says “complete”, not all foods are created equal. A highly processed kibble, extruded at high temperatures and preserved with stabilisers, is not comparable to a raw or gently cooked meal made with fresh, bioavailable ingredients. Deep processing can denature amino acids, destroy heat-sensitive vitamins and deactivate natural enzymes that aid digestion. A cat, being a strict carnivore, needs foods that are biologically adapted to its physiology, not simply formulas that appear balanced on paper.

The value of variety and individualisation

For this reason, rather than obsessing over a label, we should focus on understanding what we are really feeding.
Knowing the ingredients, their origin, their digestibility, and how they interact with the specific cat in front of us is key.

A truly adequate diet is not defined only by meeting reference numbers, but by how well it fits the individual: their age, health, preferences, environment, and digestive response. And above all, by maintaining variety, rotating sources of protein and fat, and choosing foods from trustworthy origins that respect the cat’s carnivorous biology.

When we feed raw or lightly cooked foods made from quality meats, organs, and fats, we move much closer to providing a living, functional nutrition, one that nourishes through real ingredients rather than depending exclusively on additives and fortification.

Understanding nutrition as a living process

It is also worth remembering that we humans do not calculate our own calcium-to-phosphorus ratios or measure the precise mineral content of every meal. Instead, we rely on understanding the dynamics of nutrition, trusting variety, freshness, and balance over time.

The same perspective can be applied to our cats. What matters most is not perfection in every single bowl, but consistency, awareness, and responsiveness to the animal’s needs.

A sound feline diet is built from observation and adjustment, not blind faith in a label. Over time, the goal is not to achieve a fixed “perfect” balance, but to sustain a flexible, evolving equilibrium that supports each cat’s changing body and life.

Conclusion

Nutrition is dynamic, and there is no single perfect or permanent diet. Even so-called “complete” menus, whether raw, cooked, or commercial, have their limitations.

The key is to view them as a flexible base from which to build, combining variety, observation, and a critical eye. Rotating between menus, complementing with high-quality fresh foods, and, when necessary, consulting a qualified professional in feline nutrition are practical ways to ensure a more balanced outcome.

It does not mean you need to start cooking from scratch, nor to chase an impossible ideal of perfection. It simply means learning to adjust, accompany, and evolve your cat’s diet over time, acknowledging that true balance comes not from a label but from awareness, adaptability, and the quality of what you choose to feed.

References

• Bilgiç, B., Güzel, E., Akgül, Y., Karakaya, E., & Bayrakal, A. (2025). Investigation of Trace and Macro-Element Contents in Prescription and Non-Prescription Dry Cat Foods. Veterinary Medicine and Science.
• Vecchiato, C. G., Schwaiger, K., Biagi, G., & Dobenecker, B. (2022). From Nutritional Adequacy to Hygiene Quality: A Detailed Assessment of Commercial Raw Pet-Food for Dogs and Cats. Animals, 12(18), 2395.
• Davies, M., Jones, L., Alborough, R., Davis, C., Williams, C., & Gardner, D. S. (2017). Mineral analysis of complete dog and cat foods in the UK and compliance with European guidelines. University of Nottingham, bioRxiv preprint. https://doi.org/10.1101/172544
• FEDIAF (2023). Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs. European Pet Food Industry Federation.
• National Research Council (NRC) (2006). Nutrient Requirements of Dogs and Cats. Washington DC: National Academy Press.
• AAFCO (2015). Official Publication of the Association of American Feed Control Officials. Champaign, Illinois, USA.