You are what you eat

Good food boosts your immunity and helps function on every level, especially when it comes to sports and other forms of physical activity. When we refer to “healthy” foods more often than not we focus on the nutrient content of a food. Other components present in food that may influence “nutrient bioavailability”, however, we frequently ignore. Nutrient bioavailability refers to the amount of a nutrient that is absorbed and actually becomes available for utilization by the body.

This process is particularly relevant for vegetarians and/or vegans. This process is based on the fact that some components in food enhance nutrient absorption and bioavailability and others have a negative impact. Three important minerals – calcium, zinc and iron – have numerous components in foods that will act either as inhibitors or promoters of these nutrients. It is also important to keep the effects of inhibitors and promoters of nutrients in perspective, as some will have a significant effect on human nutrition. If there is an excess of one mineral, for example, due to supplementation, the absorption of other minerals may be compromised.

CALCIUM

Calcium is a vital mineral, but it can also be one of the most difficult for some humans to absorb due to a variety of conditions, including lactose intolerance. For this reason and several others, we will use this mineral as our chief example:

Factors that will negatively affect calcium balance include: sodium, phytates, fibre, caffeine, oxalates and alcohol. Sodium or salt intake can have a profound effect on calcium balance because sodium increases the amount of calcium that is excreted from the body. Some research has shown that if we decreased our sodium intake to the recommended levels, then the amount of calcium we would need to consume to ensure calcium balance would be reduced by a third. This is significant amount given most individuals find it difficult to consume the recommended amount of calcium. Caffeine also increases calcium excretion, although the effect is quite minor when compared to sodium.

Protein can increase calcium excretion, but this only tends to be a problem if calcium intakes are low. Some have suggested that an increased intake of fruit and vegetables may buffer the acid load and therefore reduce the protein-induced effect on calcium loss. Other minerals can compete with calcium for intestinal adsorption. This means that if there is an excess of one mineral, for example due to supplementation, the absorption of other minerals may be compromised. There are also various components that enhance calcium absorption, vitamin D being one of the most important ones. Lactose, the sugar in dairy products, is also thought to increase calcium absorption. It’s therefore important when considering which foods provide rich sources of nutrients such as calcium, to consider the amount of nutrient present and the amounts that will be absorbed.

Milk, broccoli and sesame seeds are touted as excellent sources of calcium. But how much of the calcium in these foods are actually calculated? With milk, the amount of calcium per cup is around 380mg. But the percentage of calcium absorbed from milk is around 32 percent, which means that the quantity of “absorbable” calcium in a cup of milk is around 122mg. The absorption of calcium from broccoli, mean time, is nearly twice that of milk at around 61 percent. Sesame seeds have been touted as the best source of calcium. And yes, they do contain significant amounts of calcium when in the whole form which includes a coloured hull. In this form they contain around an impressive 1g-per-100g, which appears extremely high. But most of the calcium in the sesame seed is found in the hull, which is full of oxalate (calcium oxalate) and, as discussed, oxalates reduce the absorption of calcium. So for sesame seeds with the hulls removed, the amount per calcium present is about 120mg per 100g.

IRON

Iron in foods is present in two forms: haeme and non-haeme. Haeme iron is found only in animal foods, whereas non-haeme iron is found in plant and animal products. Non-haeme iron is susceptible to various inhibitors and promoters. Probably one of the largest effects on iron absorption is your actual iron status i.e. The body will absorb more iron if iron stores are low, and less iron stores are adequate. Inhibitors of iron absorption include polyphenols such as tannin derivatives which are found in tea, coffee and wine. Enhancers of iron adsorption include vitamin C, which acts as a reducing agent and forms a chelate (complex) with non-haeme iron at an acid pH. This chelate remains soluble in the small intestine and thus improves intestinal absorption of iron. Meat, fish and poultry factors (commonly referred to as the MFP factor) enhance non-haeme iron. There are various food components that may inhibit or enhance nutrient bioavailability, however the body has important mechanisms for optimizing nutrient availability. The body has homeostatic mechanisms whereby we will absorb more nutrients if our status is low.

Also, those who take supplements of individual nutrients may run the risk of reducing the bioavailability of other nutrients as they compete for absorption. This is the reason why many nutritional scientists would recommend a low–dose, multi-mineral supplements ahead of larger doses of individual nutrients.