Tuesday, April 5, 2011

We 'heart' legumes

Sound science supports legumes and cholesterol lowering for a healthier heart

There is consistent evidence from epidemiological studies showing that eating legumes can play a role in preventing some of our most serious chronic diseases, including cardiovascular disease, diabetes, as well as improving gut health and assisting with weight management. Despite this, Australians are not eating enough legumes. A consumption survey conducted by Go Grains Health & Nutrition in 2009 (which is currently in field again for 2011) found that not even a quarter of the 1700 Australians surveyed consumed legumes over the 2 day period food intake data was collected.

The research in support of legumes and health is not as extensive as that for cereal grains, mainly because there is generally a low intake of legumes in most free-living populations. Much of the legume research has focused on soy beans due to higher intakes of soy products such as tofu, soymilk, tempeh and textured soy protein; however, a meta-analysis just published has focused on non-soy legumes in relation to blood lipids. This is the second meta-analysis of this topic, is more vigorous in its methodology and includes four new studies since the 2002 review.

A total of 140 papers were retrieved from a search through MEDLINE, EMBASE and Cochrane databases through to July 2009. Ten randomised controlled trials were selected for analysis that compared a non-soy legume diet to a control diet. Each of the 10 studies lasted a minimum of 3 weeks duration, and reported blood lipid changes (in cholesterol, hypercholesterolemia or hypertriglyceridemia and/or cardiovascular disease) in intervention and control diets. The research included a total of 286 participants (70% males) from 5 countries with a mix of high, borderline high and normal baseline cholesterol levels.

The legume intake in the 10 studies ranged from 80-440g/day of peas, lentils, baked beans, pinto beans, lima beans or black eyed peas with a study length of 21 to 56 days. All studies reported net decreases in total cholesterol with a mean reduction of 11.76mg/dL (translating to around a 5% reduction). The combined results showed a significant decrease in unhealthy LDL cholesterol and triglycerides, however little effect on HDL cholesterol.

Although the number of participants was relatively small and majority were middle aged hypercholesterolemic men, the meta-analysis appears to be carried out very carefully. There was no publication bias or significant differences in the way the protocols were performed, and sensitivity analysis found no effect of study type, length or type of control on the results. The levels of legume intake in the studies are considerably above average legume consumption in Australia today, limiting the potential applicability in the findings, but also highlighting the potential health benefits if legume consumption can be increased amongst Australians, especially in those at higher risk of raised cholesterol and cardiovascular disease.

Non-soy legumes have a similar effect as soy-based supplementation on cholesterol lowering. The authors concluded this meta-analysis of randomised controlled trials provides the strongest evidence to date that non-soy legume consumption lowers serum total and LDL cholesterol and therefore may lower the risk of cardiovascular disease. This provides added weight to the body of scientific evidence supporting the role of legumes in the diets of Australians.

Bazzano et al 2011 Non-soy legume consumption lowers cholesterol levels: A meta-analysis of randomised controlled trials. Nutrition, Metabolism and Cardiovascular Disease (21) 94-103.