Not the full amount of nutrients ingested is absorbed and utilised by the human body. To describe this, we use the term bioavailability. Bioavailability is that proportion of a nutrient that can be digested, absorbed and used by the body (FAO). The bioavailability of a nutrient depends on many factors and differs for each nutrient. However, it is important to realise that not the full proportion of the nutrient from the food will be available for use in the human body, and that this can be influenced in the pathway from growing to consumption.
The bioavailability of carbohydrates, protein and fat, the so-called macronutrients, is usually very high at more than 90% of the amount consumed. Micronutrients, i.e. vitamins and minerals, and bioactive phytochemicals (e.g. flavonoids, carotenoids) can however vary widely in the extent they are utilised and absorbed (EUFIC).
In Figure 2.2 the pathway that micronutrients follow from the soil through the crop and food into the human body is shown. Several critical factors determine the success of cultivation practices to improve micronutrient status among humans. These factors depend on nutrient bioavailability at different stages: the presence and bioavailability of soil nutrients for plant uptake, nutrient allocation within the plant, re-translocation into the harvested food and availability of nutrients in prepared food for uptake in the human body (de Valença and Bake 2016).
Figure 2.2. Schematic overview of micronutrient (MN) pathway from soil to humans and the factors that influence MN bioavailability to the next level (de Valença and Bake 2016)
Bioavailability from soil to crop is influenced by both many soil factors and the crop variety (genotype), while the bioavailability from crop to food is influenced by the crop variety (which, amongst others, defines the allocation and re-localization of nutrients into the edible parts of the crop) as well as the processing of the harvested part (i.e. milling and dehusking of rice). Storage additionally influences micronutrient content. These two forms of bioavailability will be further explained in Chapter 5 and §5.3 specifically.
Bioavailability from the food for the human body is influenced by both food preparation (e.g. cooking), dietary intake such as the amount of food consumed, food composition, and individual health status (de Valença and Bake 2016). As for example genetical differences and diseases may impact the uptake of nutrients. Also, the microbiome composition in the human gut can significantly influence the amount of nutrients that is taken up (Kau et al. 2011). It is, moreover, important to realize that the methods of preparation of the food can strongly influence the content of (micro)nutrients in the food. For example, water-soluble vitamins can leach out into the cooking water, be broken down due to oxidation or heat, etc. Researchers document the content of nutrients in foods in different forms (raw, uncooked) in Food Composition Tables, the Dutch example is the NEVO table: https://nevo-online.rivm.nl/ProductenZoeken.aspx.
de Valença AW, Bake A. 2016. Micronutrient management for improving harvests, human nutrition, and the environment. : 21.
European Food Information Council. (n.d.). Nutrient bioavailability: Getting the most out of food: (EUFIC). Retrieved from https://www.eufic.org/en/food-today/article/nutrient-bioavailability-getting-the-most-out-of-food
Food and Agriculture Organization of the United Nations. (n.d.). FAO TERM PORTAL. Retrieved from http://www.fao.org/faoterm/en/
Kau AL, Ahern PP, Griffin NW, Goodman AL, Gordon JI. 2011. Human nutrition, the gut microbiome and the immune system. Nature 474: 327–336. DOI: 10.1038/nature10213.