Sweet potato in pet food: what the research says about sweet potato starch

Why pet food manufacturers use sweet potato

Every dry extruded pet food needs a starch source. Starch gelatinises during extrusion and holds the kibble together; it also supplies energy. For decades the default choices were cereals: corn, wheat and rice.

Sweet potato entered pet food through the grain-free and limited-ingredient segments. Industry commentary points to three drivers [5]:

• Consumer perception. Sweet potato is widely seen, in human food, as a more nutritious alternative to standard potato, particularly as a source of dietary fibre.
• Recipe flexibility. It fits limited-ingredient and hypoallergenic-style formulas, because potatoes are not considered a common allergen in dogs and cats.
• Label appeal. It is a single, recognisable ingredient that works in both kibble and treats.

Perception is not evidence, though. The more useful question for a formulator is what controlled feeding studies actually measured.

What the studies measured

Dogs: glycaemic response and fermentation

Kaelle et al. (2023) compared seven starch sources in diets for 14 adult Beagle dogs: corn, brown rice, sorghum, potato starch, sweet potato flour, chickpea and pea flour [2]. Key findings for sweet potato:

• Glycaemic response: dogs fed the sweet potato diet did not show the higher blood-glucose peaks seen with corn and potato.
• Gut fermentation: faecal short-chain fatty acids — products of fibre fermentation by gut bacteria — were higher with sweet potato than with the potato and brown rice diets.
• Digestibility: the sweet potato diet had the lowest coefficient of total tract apparent digestibility of nutrients among the sources tested.

The authors concluded that sweet potato and pulses improved indicators of gastrointestinal function and helped control the post-meal glycaemic response.

Vastolo et al. (2023) fed healthy dogs three diets: a grain-free diet with sweet potato, a grain-free diet with pea starch, and a cereal-based diet with spelt and oats [3]. The sweet potato diet produced the smallest area under the curve for both glucose and insulin after a meal; the cereal-based diet produced the highest.

Cats: glucose, lipids and microbiome

Zhang et al. (2023) fed 30 young cats, for 28 days, diets based on five carbohydrate sources — potato, cassava, sweet potato, rice and wheat [1]. The sweet potato diet measured the highest degree of starch gelatinisation (90.2%) and had the numerically highest overall gut microbial diversity. On post-meal glucose it was the cassava group, not the sweet potato group, that had the numerically lowest mean and peak values and the lowest serum lipids; the sweet potato group’s mean glucose was not the lowest (the wheat group’s was lower). The important caveat is that glucose, insulin, serum lipids and overall microbiome diversity did not differ significantly between diets (P > 0.05); some individual bacterial groups did differ. The authors nevertheless concluded that cassava and sweet potato diets were worth developing for cat food, and noted that inclusion levels and mechanisms need further study. Read this as a trend in a small, short trial, not as an established effect, and note that it concerns complete diets, not any single ingredient.

The trade-offs formulators should know

1. Digestibility. In dogs, the smaller glucose response and more fermentation in the gut went together with the lowest digestibility of the seven sources in the same trial [2]. Depending on the product — a weight-management formula versus a high-energy performance diet — this can be an advantage or a cost.

2. The DCM question. The FDA has investigated reports of dilated cardiomyopathy (DCM) in dogs eating certain diets, many of them labelled grain-free [4, 6]. In the case reports it analysed (received between 2014 and April 2019), potatoes or sweet potatoes appeared in 42% of the diets, compared with 93% for peas and/or lentils [4]. The FDA has stated that the case reports it has received are not sufficient to establish a causal relationship, describes the issue as complex and possibly multifactorial, and in December 2022 said it would not publish further updates until there is meaningful new scientific information [4]. The percentages describe the reported diets, not the relative risk of any ingredient. For formulators, the practical point is that a grain-free label alone says little; the full recipe and its nutritional balance matter.

3. Inclusion level and balance. None of the studies above set an optimal inclusion rate for sweet potato. Sweet potato is also naturally rich in beta-carotene, and some nutritionists caution against treating any single ingredient as a nutritional shortcut [5]. As with any carbohydrate source, the finished diet must be formulated to meet the complete nutrient requirements of the target species.

4. Evidence base. These are small, controlled studies in healthy animals, typically lasting weeks rather than years. They are useful for comparing ingredients, but they are not proof of long-term health outcomes, and claims on a finished pet food label are the manufacturer’s responsibility under the rules of the market where it is sold.

What this means when sourcing sweet potato ingredients

For R&D and purchasing teams evaluating sweet potato as a starch source, the research suggests several practical checks:

• Form. Sweet potato is supplied as flour or powder, as pellets, and as dried chips. Powder blends directly into a mix; pellets and chips are usually milled before use. Choose the form that fits your milling and dosing set-up.
• Consistency between lots. Starch, fibre and moisture drive both extrusion behaviour and digestibility. Ask for a signed specification with test methods, and a certificate of analysis for every lot.
• Food safety documentation. Check the manufacturing site’s food safety certification, contaminant limits (heavy metals, mycotoxins, pesticide residues) against the rules of your market, and lot traceability back to the raw material.
• Single-ingredient status. Confirm whether the material is 100% sweet potato or a blend, and whether any processing aids or additives are used.