Nutritional value of (wild) fruits and vegetables
Traditional fruits (also known as commercial fruits) are commonly fed to animals within zoos. However, in zoo literature, the feeding of such commercial fruits to herbivores, omnivores and especially primates is discouraged. This is because these fruits are cultivated to please the human palate, thereby referring to both the physical appearance as well as its nutritional composition. Often commercial fruits have a lot of pulp, few seeds and a sweet flavour. This flavour is due to the low fibre content and high concentrations of sugar in commercial fruits, which is also why we like to eat them. Contrastingly in the wild, frugivorous animals eat reproductive parts of plants that are present in their natural habitat, often referred to as ‘wild fruits’. Their appearance and nutritional composition largely differs from commercial fruits. For instance, they contain much less sugar and more fibre.
Therefore, the natural diet of many animals contains amounts of fibre that exceed the level in commercial fruits. Besides this, the combination of a high sugar and low fibre content in commercial fruits in comparison with wild fruits, makes them very rich in energy. This increases the risk of developing obesity, especially since many captive animals cannot display the same activity level as in nature. For this reason, it is thought that some vegetables might better suit the dietary requirements of frugivores than commercial fruits. Some vegetables are as rich in vitamins as commercial fruits while having lower sugar levels and higher fibre contents. Therefore, if we want to better mimic the nutrient composition of wild fruits, we need to (partially) replace commercial fruits with vegetables.
In support of this, we’ve established an overview of the nutritional compositions of several fruits and vegetables in order to compare them. With this data it is possible to better assess and evaluate the diets that are being fed to zoo animals. Next to this, it should encourage to critically think about the acceptance of diet components and potentially remove, add or replace them. Most macronutrients are shown, as well as the minerals iron, phosphorus and calcium. This is because some animals are prone to an iron overdosage and an unbalanced calcium/phosphorus ratio. Please be aware that both the sugar levels and starch contents are grouped under ‘available carbohydrates’ as available literature did not allow us to properly split these groups.
As can be seen from the graphs, generally vegetables better mimic the nutritional values (on dry matter basis) of wild fruits compared to commercial fruits. Although not perfectly resembling wild fruits, they are a more suitable alternative. However, it should be kept in mind that there are also differences between vegetables (read more here). Generally, fiber levels of both commercial fruits and vegetables are relatively low compared to wild fruits, however, this can be supplemented in the diet with other fiber sources (browse or roughages). On the other hand, the available carbohydrate fraction tends to be higher in commercial fruits, which is (partially) the result of higher sugar levels. The table also shows that generally vegetables have a better calcium/phosphorus ratio compared to commercial fruits. Lastly, it should be noted that vegetables do contain higher iron levels. Therefore, for iron sensitive species this should be adjusted to the maintenance levels of the animal in order to avoid iron-related diseases. Also fruits with high levels of vitamin C should be avoided with iron-rich vegetables as it enhances the absorption and increases health risks.
To conclude, it should be mentioned that the implementation of these changes in the diet are based on theory. In practice, animals might not always immediately tolerate dietary changes from fruits to vegetables. Regarding the used data, it can be seen that there was only few (usable and reliable) data available on the nutritional values of wild fruits. This was primarily due to the differences between methods of proximal analysis between studies, which resulted in unreliable comparisons. For this reason, we decided to only use the nutritional values for some wild fruits mentioned in Souci et al. (2008). In nature, other wild fruits may be consumed with different nutritional values.
Source: Souci, S. W., Fachmann, W. & Kraut, H. (2008). Food Composition and Nutrition Tables, 7th revised and completed edition. MedPharm.