For years, conversations about weight issues and feline diabetes have centered on carbohydrates. This is not wrong; cats are obligate carnivores that are poorly equipped to manage large glucose loads. High‑starch diets (kibble, some canned diets, and even many raw diets that are too high in carbs) absolutely stress the pancreas and disrupt insulin metabolism. This alone can cause weight gain, insulin resistance, and an increased risk of type 2 diabetes.
But it turns out that carbs are not the whole story.
There is another factor that receives far less attention: fat. Not just fat per se, but the type of fat in the diet, its source, and what happens to it inside the body, especially over time.
Fat is not just energy. It is structural, and it actively participates in hormonal and inflammatory signaling. Insulin resistance that leads to obesity and diabetes begins at the level of cellular signaling, long before blood sugar abnormalities appear.
Contrary to popular opinion, eating fat does not make your cat fat. Fat is fuel, and cats have a relatively high requirement for it. Carbohydrates are turned into fat (triglycerides) for storage; these and other fats are primarily stored. Some fats are converted into ketones and burned for energy. Others are structural. They get incorporated into cell and mitochondrial membranes, where they influence their stiffness or suppleness. One of the reasons Omega-3s are so important is their role in maintaining healthy membrane fluidity.
The cell membrane is the interface between the cell and the environment. It has sensors (receptors) and channels that regulate what goes in and out. The membrane is made of a phospholipid bilayer with embedded proteins. These proteins are where hormones like insulin deliver their instructions. That structural role makes fat quality a long‑term metabolic issue.
Linoleic Acid (LA)
LA is an omega‑6 polyunsaturated fatty acid (PUFA). It is not a bad guy itself. The AAFCO standards require a minimum level in pet food. In a cat’s natural prey‑based diet, LA is present in modest, balanced quantities.
LA is also found in plants. It is the primary fat in seed oils like corn, safflower, and soybean oils.
The problem is not LA itself, but how much of it modern diets now contain, especially when fats come from highly processed sources. Poultry fat, beef fat, pork fat, seed oils, and blended rendered fats are all rich in LA. Pet food often contains levels of LA far beyond what feline physiology can appropriately handle.
When LA intake is excessive, more of it is stored in fat tissue and incorporated into cell membranes.
Membranes Are Crucial to Function
Cell membranes are not passive wrappers. They are essential working surfaces that control how signals are received and transmitted by cells. Insulin receptors sit within these membranes. Their ability to function depends on the physical properties of the surrounding lipids. A very stiff or very soft membrane cannot function properly.
When membranes contain excessive amounts of PUFAs like LA, they can become too fluid. The insulin receptor is still present, but signaling becomes less efficient. Cells need more insulin to achieve the same effect.
This is one way insulin resistance begins—quietly, gradually, and long before blood glucose rises.
As insulin signaling weakens, the pancreas compensates by producing more insulin. Elevated insulin then promotes more fat storage and firmly locks LA into stored fat, reinforcing the cycle. By the time diabetes develops, this process has been happening behind the scenes for years.
Normal Fats vs LA
When the body manufactures its own fat internally, it primarily makes palmitic acid and oleic acid. These fats are good, stable long‑term fuel and storage forms. They are far less disruptive to cell membranes than large amounts of dietary LA.
A wild mouse has an Omega-6 to Omega-3 ratio of around 3.5:1. It contains largely saturated palmitic acid and monounsaturated oleic acid, is relatively low in LA, and high in the Omega-3 DHA. Pet food, both dry and canned, has a much higher 3:6 ratio, as much as 30:1. The LA content may be up to 10 times what cats need. Plant-heavy pet foods also contain more LA.
Modern processed diets override this natural prioritization by delivering LA in huge quantities. Much of it is already damaged (rancid, or oxidized) before it even gets to the pet food plant.
Fats in Pet Food
Rendered fat is a major ingredient in pet food. Rendering combines fats from many sources: slaughterhouse waste, expired supermarket meat, and other discarded animal materials. In addition to these sources, used restaurant grease is commonly collected and added to rendering vats.
Outside countless restaurants sit large drums filled with fryer oil that has been used until it is no longer fit for cooking. Every fast‑food outlet—in fact, every restaurant that serves anything fried—contributes to this stream. That grease is picked up by rendering trucks and processed along with all the other animal waste.
Rendering is simply cooking, much like soup. Raw materials are cooked in big vats to break them down, kill bacteria, and separate out the fat. Just like chicken soup, when the fat cools it rises to the top and solidifies. Then it can be skimmed off and sold separately for not only pet food but biofuel and other uses in the cosmetic, pharmaceutical, agrochemical and other industries. (My renderer friends assure me that plastics and packaging materials do not enter the final products.) Even so, these fats have already been heated repeatedly, oxidized, and degraded before they ever reach a pet food plant. Further high‑temperature processing during extrusion or canning further oxidizes and degrades them.
These highly oxidized, LA‑rich fats place a very different metabolic burden on the body than fresh, biologically appropriate fats.
Cats Are Vulnerable
Cats are efficiently designed to make the most of their expected diet of prey animals. They have limited metabolic flexibility; they’re unable to compensate when that efficiency declines. This helps explain why diabetes can appear to develop “suddenly” in cats, even though the groundwork was laid much earlier.
This is also why some cats do not fully recover insulin sensitivity on low‑carbohydrate diets alone (although about 70% will, especially with early intervention). Reducing dietary carbohydrate lowers insulin demand, but it may not be able to correct years of altered membrane composition.
What You Can Do
Choosing diets with healthy fat sources (animal fats, Omega-3s), minimizing processed and oxidized fats, and keeping insulin low all support a well-functioning metabolism over time—especially for cats.
In addition to choosing diets with appropriate fat sources, certain nutrients may support cellular health. Phospholipids like lecithin provide building blocks for normal membrane repair and may support liver and metabolic function. (Sunflower lecithin is preferable over soy to avoid GMOs). Long-chain marine-source omega-3s contribute to balanced membrane composition and signaling, which may be especially helpful in animals under metabolic stress. These are adjuncts, not cures, and work best alongside an already- healthy, cat-appropriate diet. That is, low-carbohydrate, high moisture food like raw, canned, or homemade. (See this article for a brief overview of the ideal feline diet).