The food matrix and its impact on the fate of omega-3 fatty acids in our bodies

Why should we be interested in omega-3 fatty acids in our diet?

Omega-3 fatty acids are nutrients that are associated with numerous health effects in terms of preventing cardiovascular and inflammatory diseases, certain cancers and neurodegenerative diseases. However, the latest consumption studies show that the French population's intake of these fatty acids, and in particular alpha-linolenic acid (ALA), the precursor of omega-3s, is twice lower than the nutritional recommendations. Increasing our dietary intake of omega-3 is therefore of major nutritional interest. However, it is important to know that the quantity of omega-3 consumed (and more generally of any nutrient) does not correspond to the quantity that is biologically active in our body, which is known as bioavailability. In fact, before reaching a target tissue, the omega-3s provided by our diet are subjected to various physiological processes ranging from their digestion and intestinal absorption, through their transport in the body, to their accretion in the various tissues where they will be metabolised in order to be degraded, stored or used for physiological purposes. It is therefore important to take into account the factors likely to modulate their bioavailability. Certain parameters intrinsic to the food, which we call the food matrix, are the subject of various research projects currently underway to identify strategies for formulating foods to improve the bioavailability of ALA.

What are the food sources rich in ALA?

The main dietary sources of ALA that we are interested in are the so-called linolenic vegetable oils such as rapeseed oil, walnut oil, linseed oil, perilla oil and Sacha Inchi oil. Each oil has its own chemical signature, characterised in particular by its fatty acid composition and the structure of the triglycerides of which it is composed. Within these oils, ALA is therefore mixed with other fatty acids (which we call surrounding fatty acids), which can impact its bioavailability. This is why we also address this issue in the laboratory.

In preclinical approaches, we have combined flaxseed oil with other vegetable oils chosen according to their composition in major fatty acids: palm oil for its richness in saturated fatty acids, oleic sunflower oil for its richness in monounsaturated fatty acids or grape seed oil for its richness in omega-6 fatty acids. In our experimental conditions, we were able to observe that thecombination of flaxseed oil and oleic sunflower oil leads to an enrichment of ALA in the blood and liver compartments. These results show a positive impact of the association of ALA with oleic acid on the bioavailability of ALA, proof of the impact of the surrounding fatty acids of the food matrix.

What happens when plant sources of omega-3 are processed?

In the western food industry, lipids are often formulated and emulsification is one of the processes used by the food industry. Emulsification consists of the dispersion of lipids in the form of lipid droplets, which favours the action of enzymes involved in the digestion of lipids. The activity of these enzymes is dependent on the presence of surfactants. To date, there is little data on the impact of the nature of these agents on the bioavailability of ALA. ITERG therefore undertook to evaluate three surfactants used in the food industry, in collaboration with the CarMeN Laboratory in Lyon, the CBMN Laboratory in Bordeaux and the EIPL Laboratory in Marseille[1].

To this end, we developed an in vitro approach to gastrointestinal lipid digestion. By emulsifying linseed oil with each of the three surfactants, we observed an improved rate of lipolysis of linseed oil in the presence of soy lecithin and a decreased rate in the presence of the other two surfactants (caseinate, Tween). The impact of soy lecithin was confirmed in preclinical studies with an increased bioavailability of ALA, especially in terms of intestinal absorption.

We are currently exploring in more detail the impact of plant lecithins on the bioavailability of omega-3. A thesis in collaboration with the CarMeN laboratory (INSERM Unit U1060 / INRA UMR1397 / University-Lyon1 / INSA-Lyon) (DR Marie-Caroline Michalski) within the framework of the UMT ACTIA "Biodisponibilité Alimentation Lipides Intestin" (BALI) is currently in progress. Given the high ALA content of certain plant lecithins such as soy or rapeseed lecithins, the question arose as to the interest of adding these lecithins to a lipid formula to increase the bioavailability of ALA in the body. Currently, soy lecithins are the most widely used vegetable lecithins. However, in view of the socio-economic and environmental challenges, a specific health advantage of rapeseed lecithin would make it possible to use lecithins from the oilseed sector for the development of innovative lipid formulas aimed at the nutritional quality of food products or for applications in nutraceuticals such as food supplements

What other parameters are you interested in?

In vegetable oils, fatty acids such as ALA are distributed in three positions within the triglyceride molecules. Depending on the position on the triglycerides, ALA can be absorbed/carried differently in the body.

In order to study the impact of this position of ALA within triglycerides, we conducted a preclinical approach using synthetic structured triglycerides. Within these triglycerides, ALA occupies different positions, called internal or external. We observed that the position of ALA had no impact on its intestinal absorption. On the other hand, the position becomes significant at the time of distribution of ALA to the target tissues, once the intestinal compartment is passed. Our results underline theimportance for ALA to be carried internally in the ingested triglycerides, and this in a certain proportion, in order to guarantee its maintenance and to limit the oxidation phenomena of ALA (which we can assimilate to a degradation). Thus protected from oxidation, ALA can be bioconverted into EPA and DHA, omega-3s with multiple roles in our body.

What should we remember?

In conclusion, our studies confirm the importance of taking into account these different parameters specific to the food matrix in order to improve the bioavailability of ALA and more generally of omega-3s.

Further investigations are needed to 'weight' each of these parameters when combined and to identify those to be favoured when designing lipid formulas. Given the complexity of the food matrix, we also plan to evaluate the influence of other compounds co-ingested with lipids such as proteins and antioxidants, which may also have an impact on the bioavailability of omega-3s.
Finally, to better evaluate the impact of the food matrix on lipid bioavailability, we have integrated the intestinal microbiota as a factor that can modulate this bioavailability. This work is carried out within the framework of the UMT ACTIA "Biodisponibilité Alimentation Lipides Intestin" (BALI), in collaboration with our academic partners in Lyon (Laboratoire CarMeN) and Bordeaux (Laboratoire LMBA)[2].

[1 ] Laboratoire CarMeN, Inserm, INRAE, INSA Lyon, Université Claude Bernard Lyon 1(DR Marie-Caroline Michalski) ׀ Laboratoire CBMN, CNRS UMR 5248, Université de Bordeaux, Bordeaux INP (Pr Maud Cansell) ׀ Laboratoire EIPL UPR 9025 CNRS, Université de Marseille (DR Frédéric Carrière)
[2] https://www.actia-asso.eu/projets/bali/