Is grain-free bad for cats?

April 3, 2021

by Robyn Paterson

Picking the right cat food can be confusing and sometimes asking the vet makes it even more confusing.  If you were to go to a vet and ask, "Is grain-free bad for cats?" the answer you are likely to hear is, yes.  However, that is a simplified version of the correct answer.

Many of the top-name pet food companies use the term grain-free to appeal to pet buyers, but it is deceiving.  The ingredient cats need in their diet is meat, but grains are often added as a filler because meat is expensive.  Therefore, when pet-food companies saw public demand to remove grains from a cat's diet, they replaced those grains with vegetable proteins such as peas or soy.  This can have a double positive appearance to some buyers as not only is it grain-free, but it also shows a higher protein level.  The problem is that the type of protein - plant-based protein - is not one that cats can utilize.  Thus, some of these grain-free diets actually have less protein that is bio-available to a cat, even though the overall protein level is high.

People, unfortunately, tend to anthropomorphize and believe that a cat can utilize just as many nutrients from plant-based proteins as they can from meat-based proteins.  Given that cats do not have the same number of enzymes to break down plant material as humans do, this is unlikely to be the case, but as of yet, there have not been any in-depth studies to determine how much nutrition a cat can absorb from plant-based proteins. 

Why do Digestive Enzymes matter?

There are four types of digestive enzymes.

1. Protease breaks down proteins into amino acids. 
2. Amylase reduces carbohydrates into sucrose, lactose, and maltose. 
3. Lipase breaks down fats into beneficial fatty acids. 
4. Cellulase breaks down vegetables and fibers.

Most mammals produce amylase - the enzyme to break down carbohydrates - in their saliva, but cats do not.  A cat does produce this enzyme in its pancreas, but the fact that it is not in a cat's saliva suggests that nature did not intend for cats to extract nutrients from plants. In addition, cats do not have cellulase at all.  Typically this is an enzyme created in the gut of mammals to break down vegetables and fibers, but it does not exist in cats unless it is given to them through their food or supplementation. 

In sum, cats do not have the enzyme to break down vegetables, and their pancreas has to make the enzyme to extract nutrients from carbohydrates instead of it naturally being in their saliva as it is with most other mammals.  

Whether it be grains or the plant-based proteins that are used to replace grains, neither is good for cats.

Plant-based ingredients are not helpful, but are they harmful to a cat?

In addition to grains and plant-based proteins, some other common ingredients in cat food are plant-based starches such as potato, tapioca, sweet potato, and carrots. Too many carbohydrates in your cat's diet may have the following negative effects on your cat.

1. Decreasing protein utilization by slowing down the rate at which the food digests.
2. Reducing the fecal pH by altering the microbial fermentation, which increases the production of organic acids.  
3. Inhibiting normal intestinal flora's ability to survive in the intestinal tract.

When a cat is struggling with a diet high in carbohydrates, the initial signs are vomiting, diarrhea, and/or gas. Later in life, the effects of a high carbohydrate diet can manifest through food intolerance, diabetes, kidney disease, and inflammatory bowel disease. 

It is important to remember that these plant-based ingredients are cost-saving fillers. They do not provide a nutritional benefit to your cat and can, in the long term, be detrimental to its health. 

Why does my cat appear healthy on its plant-based diet?

In a study done on fruit flies, it has been discovered that young flies fare well on a diet they have not evolved to eat. However, in middle age, the health significantly declines at a rapid rate in comparison to flies that were fed on a diet they evolved to eat. 

How does this translate to cats?  Cats were not designed to eat plant-based foods.  However, as young animals, they can adapt and live healthy lives.  Once they hit middle age, however, the health problems begin to take effect, and cats who have eaten plant-based foods which they have not evolved to eat will decrease in their health more rapidly than cats who have been fed meat-based foods their entire life.

The good news coming out of this research study is that switching to an evolutionarily appropriate diet at any point in an animal's lifetime will benefit the health of the animal. It is never too late to switch to an evolutionarily appropriate diet. 

Is grain-free bad for cats?

Ultimately the answer is no; grain-free is not bad for cats when it is also vegetable and carbohydrate-free. If the food has replaced the grain with another plant-based ingredient, then grain-free may be the worse of two evils - depending on the grain it replaced and the vegetable used as the replacement. What you are looking for in cat food is one that is less than 10% carbohydrate. Most cat foods do not list the carbohydrate content because there is no minimum level of carbohydrates that are required in cat food, so you will have to do some math to figure it out. Add up the crude protein, crude fat, crude fiber, moisture, and ash.  Then deduct that total from 100%.  What you are left with is the percentage of carbohydrates. 

What should you feed your cat?

We recommend a premade, balanced raw diet that is composed of muscle meat, organs, bones, and supplements.  If you are going to make your own food, you have to be very exact with your ingredients to keep it balanced. Most people are not detail-oriented enough to do this successfully, which is why buying raw food that is already balanced is best for most.   If you cannot feed raw, the next best choice is canned food.  Some decent choices are as follows:

1. Ziwi Peak - at 2.5% carbohydrate  
2. Hounds and Gatos Pork - at 0% carbohydrate
3. Cats In the Kitchen Lamburger-ini  - at 2% carbohydrate
4. Tiki Cat After Dark Chicken and Duck - at 3.3% carbohydrate

It is not recommended that you feed your cat dry food.  As a treat, Vital Essential Mini Nibs fit the low-carbohydrate necessity, but because there is no moisture in the food, we recommend it is only used as a treat. 

Works Cited

Davidson, Seana K. “The Truth About Dog Digestive Enzyme Supplements.” AnimalBiome, AnimalBiome, 1 Mar. 2021,

“The Four Digestive Enzymes in Pets.” Thomas Labs, 2021,

Heinze, Cailin R. “Digestive Enzyme Supplements: Breaking Down the Evidence.” Clinical Nutrition Service at Cummings School, Cummings Veterinary Medical Center at Tufts University, 30 Oct. 2017,

Hofve, Jean, DVM. “Digestive Enzymes.” Innovative Veterinary Care, IVC Journal, 20 Feb. 2013,

Rutledge, Grant A., et al. “Evolutionary Biology of Diet, Aging, and Mismatch.” Journal of Evolution and Health: A Joint Publication of the Ancestral Health Society and the Society for Evolutionary Medicine and Health, Journal of Evolution and Health, 7 Nov. 2019,