What are carbohydrates?
Carbohydrates are an essential part of a pets’ diet and one of three categories of macronutrients alongside protein and fat in the diets of animals. Sugars, starches and dietary fibres are different types of carbohydrates which play different roles in the pets’ body. Below is an image taken from Pet Food Manufacturing Association (PFMA) that is a classification and illustration of carbohydrates.
Carbohydrates are molecules made from just three elements: carbon, hydrogen and oxygen. As shown in Image 1 the smallest and simplest form of carbohydrates are sugars which can be divided into monosaccharides (e.g. glucose) and disaccharides (e.g. sucrose). Other carbohydrate molecules are much larger (complex) and include polysaccharides such as starch and dietary fibre.
Starch
Starch is often produced in plant cells as a way of storing energy. Cats and dogs have the enzymes to break them down into smaller molecules (glucose), which can then produce energy for their cells. It is important to note that most plant-based foods will have a combination of different carbohydrates (sugar, starch and dietary fibre) in different amounts (PFMA, 2015).
Table 1. Starch and Sugar content of some typical ingredients used to provide carbohydrate in pet foods. McCance and Widdowson, (2002) & Frida (2019).
| Carbohydrate Source | Starch Content (g/100g) | Total Sugar Content (g/100g) |
| Brown Wheat Flour | 66.8 | 1.7 |
| White Wheat Flour | 76.2 | 1.5 |
| Oats | 36.2 | 1.1 |
| Brown Rice | 75.9 | 1.3 |
| White Rice | 79.8 | 0 |
| Sweet Potato | 15.6 | 4.18 |
| Potato | 16.7 | 1.24 |
| Barley | 62.2 | 0 |
The major form of carbohydrate in these typical ingredients is starch. Starch is broken down to provide glucose for energy, but is also essential for the internal structure of the kibble too. During the extrusion process, gelatinisation occurs where the starch becomes soluble and has ability to absorb water. After the kibble has passed through the die plate where the shape is formed the hot mixture expands or ‘pops’. Vaporisation of the water occurs from the hot material and the kibble is left with a porous structure (Moscicki et al, 2013).
The sugar content of the carbohydrate ingredients listed in Table 1 is generally low, with the exception of sweet potato where the presence of endogenous sugars is slightly higher. Sucrose (disaccharide of glucose and fructose) is the main sugar found in these ingredients.
