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Gros plan de gousse de pois protéagineux.. © INRA, WEBER Jean

Legumes to appease

Legumes a day keep the doctor away

Recent studies have underscored the nutritional value of legume crops, identifying new properties in legume fibre and bioactive peptides. These findings encourage research on fractionation processes to develop healthy, enriched foods targeted to different groups of people.

By Pascale Mollier, translated by Daniel McKinnon
Updated on 02/21/2014
Published on 01/17/2014

Market Vegetable Stall. © Jean Weber. © INRA, WEBER Jean
Market Vegetable Stall. © Jean Weber © INRA, WEBER Jean

Starch and fibre

Legumes crops are high in starch and fibre. This means they have a low glycaemic index (1) of around 40, whereas the glycaemic index of white bread is 100, of rice is 90, and of potatoes is 110.
Fibre also has other benefits. Soluble fibre lowers cholesterol. The cholesterol-lowering effect of legumes has been clearly proven through a meta-analysis of findings in published literature (Bazzano et al., 2011). Recently, this effect has also been proven through a study which gave elderly patients two portions of legumes per day (150g/day) for two months (Abeysekara et al., 2012). Insoluble fibre produces butyrate when it ferments, which can reduce the incidence of colorectal cancers. A recent study highlighted the positive effects on bowel functions of the insoluble fibre in lupins (Fechner et al., 2013).

Micronutrients

Legumes contain iron, potassium, calcium, selenium, magnesium, polyphenols, and vitamins B1, B3, and B6.

Protein for the future

The world’s growing population, combined with the rising standard of living in developing countries, will increase the global demand for protein, and for animal protein in particular. Foresight studies have demonstrated that it will not be possible to fully meet this demand. Among other possible protein sources, including insects and seaweed, legume crops are, at the moment, the most realistic alternative because they are already readily available.

Legume proteins digested quickly and easily

Legume flours and isolates have very high digestibility (2). Antinutrients such as protease inhibitors, tannins, and lectins, which could adversely affect digestibility, are effectively destroyed by cooking. The rate of digestion is a new criterion to consider when determining the nutritional quality of proteins. Proteins that are quickly digested are beneficial to the growing population of older people who need a higher intake of amino acids to activate protein synthesis and fight muscle loss and sarcopenia (Dardevet et al., 2013). However, differences in the rates of digestion of legume proteins have yet to be measured, particularly in comparison to the rates of digestion of animal proteins.

Complementary relationships among different plant proteins

Legumes are high in arginine and fairly high in lysine, but are low in methionine and cysteine. Consequently, legumes can be associated with other protein sources – grains in particular, which are low in lysine but well-balanced in other amino acids – in combinations such as chickpea/durum wheat, or kidney bean/maize. To this end, research is being carried out at INRA to develop formulas for pasta that combine durum wheat and legumes (3), for example a pasta made with beans. This research has demonstrated the technological feasibility of producing pasta with a high legume content (35%) while maintaining standard production methods.

Amino acids and bioactive peptides

New research findings have also shown that certain amino acids and peptides derived from dietary protein digestion have a number of special properties influencing the vascular and central nervous systems.

It is now well-known that certain amino acids act as signals, stimulating protein synthesis in the case of leucine, or synthesising nitrogen oxide (NO) in the case of arginine, which produces beneficial peripheral vasodilation in cases of hypertension. Legume proteins are rich in these two amino acids.

A number of research project are currently underway to study the antihypertensive effect of legume protein hydrolysates (lentils, soy, peas, lupin) by inhibiting angiotensin-converting enzymes (Boscin et al., 2014).

The overall nutritional benefits of legume proteins warrant additional research in this area, as well as research into extraction and fractionation processes to develop specially enriched foods targeted to different groups of people such as the elderly or the physically active.

(1) Glycaemic index: a measure of how quickly or slowly blood glucose levels rise after eating a particular food. It allows people with diabetes to monitor their eating habits by choosing foods with a low glycaemic index (International table: Foster-Powell et al., Am J Clin Nutr 2002, 76, 5–56).
(2) Joint Research Unit for Nutritional Physiology and Feeding Behaviour (PNCA) with AgroParisTech, led by Daniel Tomé.
(3) Pastaleg Programme (in French)

Contact(s)
Scientific contact(s):

Associated Division(s):
Nutrition, Chemical Food Safety and Consumer Behaviour
Associated Centre(s):
Auvergne-Rhône-Alpes