The term bioavailability covers several parameters, all of which are important to ensure that a nutrient actually benefits the body, from gastrointestinal digestion and absorption to metabolism, tissue distribution, and bioactivity. Functional food and drink products are often fortified with added nutrients but this does not necessarily mean those nutrients are benefiting the consumer’s health.
The bioavailability of a particular nutrient is highly dependent on its source – something that manufacturers should be aware of when formulating, for example, plant-based food and drink products. The calcium found in dairy is much more bioavailable than the calcium in leafy greens. In one small clinical study, researchers gave participants a meal of either dairy milk or spinach that both contained 200 mg of calcium. They found that the mean absorption from milk averaged at 27.6%, while from spinach it was 5.1%.
“You can’t just replace things and say, […] ‘If I convert to another source, it’s going to convert in the body in the same way. It doesn’t,” said Nora Khaldi, CEO of Irish startup Nuritas. “And why is this important? Because population-wise, these can impact hugely our health over time.”
Even when absorbed, not all nutrients will be processed by the body. “Let’s say you’re taking your protein, […] it’s getting into your blood as peptides or amino acids but your cells are not taking them up because maybe they are ageing,” Khaldi added. “That’s a different part of bioavailability but it’s a very important part: how actually your body processes those nutrients once they’re in.”
Testing if nutrients are absorbed
Conducting randomised controlled trials (RCTs) – the so-called gold standard in clinical research – can help a company determine if its ingredient is bioavailable and delivering on its claims. However, clinical trials represent a significant investment and it can be prudent to do other testing stages first.
Aelius Biotech is a contract research organisation (CRO) spun out from Newcastle University. It has developed an integrated gut model system that evaluates both the digestion and absorption of nutrients. It says its model can simulate digestion, mucus permeation, and epithelial absorption thanks to the addition of a patent-pending engineered mucus layer.
“The digestive tract – the stomach, small intestine, and large intestine – has a mucus layer,” explained Professor Jeffrey Pearson, professor of molecular physiology at Newcastle University and chief scientific officer of Aelius Biotech. “A lot of the models that test have a cell layer and they put digestive fluids on top of that. If you put mucus on top of that cell layer, it will kill the cells because it's not sterile.
“We engineer the mucus – and we've applied for a patent there – so that it doesn't kill the cells. We can model as in the in vivo situation, which is the cell, the mucus layer, and the digestive fluids on top.”
Using this model, Aelius Biotech can tell companies what happens to their products in the digestive tract and if the nutrients are absorbed. With this knowledge, companies can decide whether it is worth doing a clinical trial or if more product development work is needed.
Pearson told Vitafoods Insights that Aelius Biotech had advised one company its product was not being absorbed but the company in question decided to go ahead with a clinical trial – at a cost of around one million pounds – that subsequently failed.
“We've tested [probiotics] where the encapsulation is released in the stomach, so the acid kills the bacteria, and we also tested ones that are not released at all. In fact, they've encapsulated it so well that it just passes out in the faeces. Companies claim a lot of things that may not be right,” he added.
Using this mucus model, Aelius Biotech has done work with Japanese drinks giant Suntory to determine the health benefits of oolong tea by studying how it acts in the digestive tract.
The nutrient gap: What kind of fortification is actually needed?
There is sometimes a gap between the nutrients that consumers think they need and those that they actually need. Protein is an example. In Europe, the protein fortification trend has been growing steadily in recent years but, according to collated national food consumption surveys, the average protein intake of adults is often above recommended levels.
So, which nutrients are being underserved?
“Fibre is a big gap,” said Carole Bingley, technical specialist for food product development at contract research organisation RSSL. “There’s interest from a gut health perspective but the number of people that are actually meeting 30 g a day is pretty small. We all know that by increasing fibre intake, it has so many other health benefits on the entire body [and] the microbiome. It can also have a knock-on effect in improving absorption and utilisation of other nutrients within the body.”
Bingley noted that adding fibre into products can be difficult for food formulators as fibres absorb a lot of water and fat, making the texture dry and difficult to eat. Soluble fibres are easier to work with but product developers must strike the right balance when choosing types because people need a certain amount of insoluble fibre in the diet as well, she added.
Another nutrient that is currently missing in many people’s diets in the West is iodine. “Iodine deficiency is creeping back in as people move away from dairy products, which are an important source,” Bingley said.