Tuesday, March 31, 2015

Legumes and Diet Quality

By Dr Alison Hill PhD, APD and Assoc Prof Alison Coates PhD, RNutr, University of South Australia

Pulses are part of the legume family, the most common varieties being dried peas, lentils, edible beans and chickpeas. Pulses have a unique nutrient composition: they are high in carbohydrate and protein and very low in total fat, which contributes to a low glycaemic index. They are rich in fibre and are a good source of vitamins and minerals, including, vitamin E, magnesium and iron. They also contain a complex mix of bioactives, such as oligosaccharides, lectins, enzyme inhibitors, phytates, and phenolic compounds that have, among other benefits, antioxidant properties. Observational studies have shown that frequent consumption of pulses (more than 4 times/week) is associated with a reduced risk of chronic diseases including 22% and 11% lower risk for coronary heart disease and cardiovascular disease, respectively compared to infrequent consumption (less than 1 time/week).1

Due to their nutritional profile, pulses can be included within the Australian Dietary Guidelines in the vegetables and legumes/beans group (which are rich in fibre, vitamins and minerals), or in the lean meat and poultry, fish, eggs, tofu, nuts and seeds, legumes/beans group (which are rich in protein, and trace minerals)2. When incorporated as a vegetable, 1 serve is ½ cup (75g) of cooked legumes while double the volume (150g) is needed for 1 serve as a meat alternative in order to provide sufficient protein. The inclusion of pulses in the diet therefore has the potential to improve diet quality.

Consuming a wide variety of nutrient-dense foods from within and across each food group may promote adherence to dietary patterns that have good diet quality3. The concept of diet quality allows for comparison of eating behaviours and linking of dietary patterns and health status. Typically, diet quality is assessed by comparing the intake of specific nutrients, or food groups, or a combination of both, against adequacy of nutrients or food-based dietary guidelines4. Diet quality scores have been developed that focus on legume consumption as a measure of adherence to a Mediterranean dietary pattern5 with legumes considered to be a beneficial component of the diet due to their nutrient profile. Better adherence to a Mediterranean dietary pattern containing legumes has been associated with greater longevity5

The relationship between pulse consumption and nutrient intakes and diet quality has been evaluated in 2 large observational studies, using data collected from the USA and Canada where pulse consumption is typically low (~8-13% of adults reported consuming pulses on any given day)6, 7.  These studies demonstrated that compared to non-consumers, pulse consumers had higher intakes of protein, fibre, zinc, iron, folate and magnesium.  Such differences, along with lower intakes of total and saturated fat, were observed with as little as ½ cup/day of pulses6.
In an Australian context, this is important because pulse consumption is extremely low. The most recent survey of Australians reported that only 4.6% of adults had consumed pulses on the day prior8. Increasing intake of pulses by ½ cup/day may therefore be an achievable dietary change for much of the population. Future studies should evaluate whether the provision of pulses can improve nutrient intake and therefore diet quality in the Australian population.
GLNC recommends Australians enjoy legumes at least 2 – 3 times per week.

1. Bazzano, L.A., et al., Legume consumption and risk of coronary heart disease in us men and women: Nhanes I epidemiologic follow-up study. Archives of Internal Medicine, 2001. 161(21): p. 2573-2578.
2. National Health and Medical Research Council, Australian Dietary Guidelines. 2013, National Health and Medical Research Council: Canberra.
3. Vandevijvere, S., et al., Overall and within-food group diversity are associated with dietary quality in Belgium. Public Health Nutr, 2010. 13(12): p. 1965-73.
4. Kant, A.K., Indexes of overall diet quality: a review. J Am Diet Assoc, 1996. 96(8): p. 785-91.
5. Trichopoulou, A., et al., Adherence to a Mediterranean Diet and Survival in a Greek Population. New England Journal of Medicine, 2003. 348(26): p. 2599-2608.
6. Mitchell, D.C., et al., Consumption of Dry Beans, Peas, and Lentils Could Improve Diet Quality in the US Population. J Am Diet Assoc, 2009. 109(5): p. 909-913.
7. Mudryj, A.N., et al., Pulse consumption in Canadian adults influences nutrient intakes. British Journal of Nutrition, 2012. 108(SupplementS1): p. S27-S36.
8. Australian Bureau of Statistics, Australian health survey: nutrition first results - foods and nutrients, 2011-12. 2014, ABS: Canberra.