Sugar in dog food: what does it actually do to your dog?

Reading time: about 7 min

A few years ago, I noticed sugar on the ingredient list of a veterinary dog food. Not a treat, but food a dog might eat every day. It raised two separate questions for me: why did the manufacturer add it, and what does that sugar actually do in a dog’s body? I’ve seen many ingredient lists, but this one made me read the packaging twice.

This article isn’t about a single supposedly “forbidden” bite. We’ll look at how the body uses sugars, when added sugar is a technical ingredient and when its amount or context matters. Our separate article “Does a dog need sugar?” discusses sweet treats more generally. Here the focus is on regular food, metabolism and how to judge an ingredient list.

Does a dog need glucose or added sugar?

These are different things. Glucose is important fuel for the brain and other tissues, and blood glucose levels are regulated by several hormones. But needing glucose does not mean a dog must eat a particular amount of table sugar every day.

A dog’s body can make glucose from other building blocks, including amino acids and glycerol. This is gluconeogenesis. FEDIAF’s nutritional guidelines specify recommended amounts for essential amino acids, fats, vitamins and minerals; they do not require a daily number of grams of added sugar. FEDIAF also notes that there is no minimum requirement for digestible carbohydrates in dog food, although they can provide energy.

There is therefore no evidence-based universal advice to give dogs a set number of grams of added sugar daily. This does not mean dogs cannot digest sugars or that all carbohydrates are bad. It means added sugar is not an essential nutrient in the same sense as certain amino acids.

Sugar, starch and carbohydrate are not interchangeable

Simple sugars and starch both belong to the carbohydrate family. Sucrose, or table sugar, comprises glucose and fructose. Starch consists of linked glucose units that must be broken down during digestion. Fibre is another carbohydrate, but acts differently in the digestive tract.

If a manufacturer lists “sugars”, that is not the same as listing corn starch or rice. And the word “carbohydrate” does not make all compounds in that family identical. Apples contain natural sugars alongside water and fibre. Honey also has natural sugars but a more concentrated energy content. Being “natural” does not mean the body excludes glucose or fructose from its energy balance.

Why do manufacturers add sugar to dog food?

Purina explains that small amounts of sugar may improve flavour, influence softness and texture or help with preservation. Those are genuine technical reasons, but not proof that the dog requires sugar for its health.

This brings me back to my original question: was the sugar added to supply something nutritionally important, or to make the product behave in a certain way and more likely to be eaten? There can be manufacturing reasons for both, but they are not equivalent. Purina says simple sugars typically provide a small share of the energy in its recipes. The actual amount in any particular food still needs to be checked instead of assuming a general company explanation applies to every bag.

Available evidence does not justify claiming that sugar causes the same clinically defined addiction in dogs as addictive substances do in people. Preferring a sweet treat is not an addiction diagnosis. But neither should added sugar be marketed as an indispensable nutrient.

What happens after a dog eats sugar?

Digestible carbohydrates are broken down to simpler sugars that are absorbed, affecting blood glucose and insulin. The response depends on the amount, the food’s composition and the individual dog’s metabolism. Healthy dogs fed diets containing different carbohydrate sources and formulations have shown different post-meal glucose and insulin responses. This does not establish that a small amount of added sugar automatically causes diabetes.

Canine diabetes is not simply a disease of “eating too much sugar”. Weight, hormonal disorders, pancreatic disease, inherited factors and other risks all deserve attention. A consistent surplus of energy from any source can promote weight gain. What matters is the whole diet: calories, protein, fat, carbohydrates, fibre and the dog’s activity.

Digestion, dental health and inflammation

Large amounts of readily available sugar may contribute to digestive upset in some dogs, particularly when they are unaccustomed to it. But diarrhoea, bloating or vomiting cannot always be blamed on sugar: fatty meals, abrupt food changes, infections and illness can cause the same signs. The dose and the entire food matrix matter.

In humans, frequent sugar intake has a well-established relationship with dental cavities. Cavities are much less common in dogs, whose major dental problem is periodontal disease. We should not copy the human cavity mechanism and claim that any sugary dog food automatically damages canine teeth. Oral bacteria and food debris still matter, and brushing and dental care remain important.

The inflammation claim also needs precision. Saying sugar “causes enormous inflammation” makes it sound as though the same clinical effect has been proven at every dose. It has not. Overfeeding, obesity and metabolic problems may be associated with inflammatory changes, but we cannot assign the whole effect to one ingredient without considering the dog’s overall diet and health.

What about corn starch and soy protein?

The food that prompted my original article also contained corn starch and soy protein. Corn starch is predominantly starch, not a synonym for fibre; with appropriate processing dogs can digest it. Soy protein can supply amino acids. But in a veterinary diet containing these ingredients I still want to know about the amino acid balance, digestibility, fatty acids, minerals and the specific clinical purpose of the formula.

A hydrolysed or selected-protein veterinary diet can have an important diagnostic purpose, for example during an elimination trial for adverse food reactions. That advantage does not mean it is necessarily my preferred long-term everyday food for every healthy dog. Nor does it mean elimination trials are only possible with veterinary prescription diets. Here I apply my white-bag test: remove the brand name and the word “veterinary”; can the formula still be justified for this particular dog’s situation?

Does sugar influence a dog’s food preferences?

A US study published in 2003 examined food choices in six adult beagles. Each was offered two experimental diets simultaneously, one containing protein and one protein-free. When both diets contained 6.4% sugar, the protein-free option made up about 16% of the food consumed. Increasing the sugar in the protein-free food to 25% increased its share to about 33%.

That does not mean a third of the dogs “chose sugar over protein”. Rather, changing palatability affected how much of one food they ate. Interestingly, although the dogs consumed more sweet protein-free food and total food intake increased, their absolute daily protein intake remained roughly unchanged.

To me, this raises an important question: if sugar is added to improve taste, does the dog eat more because the recipe better meets its nutritional requirements, or merely because it is more appealing? This was a small trial and cannot prove sugar addiction, but it illustrates why palatability and nutritional value should be assessed separately.

What should you look for on the label?

I don’t expect every treat to carry a “sugar-free” label. But when sugar appears in a complete food intended for daily feeding, I ask the manufacturer: why is it present; how much has been added; what proportion of energy does it provide; could the same texture or flavour be achieved without it; and is there a proven benefit for this dog’s health? “Because the dog likes it” is not enough for me.

In summary: evidence matters more than marketing

Years later, my original questions remain. If sugar is added to dog food, I want to know why. But it is also inaccurate to claim that every sugar crystal causes diabetes, heart disease or addiction. Science helps us ask a more useful question: why is it added, how much is there, what does it do in this dog’s total diet, and is it really necessary?

Dogs need energy and their bodies need glucose. That does not automatically create a need to add table sugar to their everyday food. For me, the point is straightforward: assess dog food by its composition, balance and intended purpose, not a confident label or manufacturer.

Sources

• FEDIAF: Nutritional needs of cats and dogs
• FEDIAF: Carbohydrates in dog and cat food
• FEDIAF: Nutritional Guidelines
• Purina: Sugar in pet food
• Postprandial glycemic and insulin responses in dogs (2023), PMID 37533455
• Palatability Affects the Percentage of Metabolizable Energy as Protein Selected by Adult Beagles (2003), PMID 14608067