Table of Contents

NUTRIDATE

Volume 31, Issue 1, March 2020

NUTRIDATE

Volume 31, Issue 1, March 2020

LOVE YOUR LEGUMES

Dr Tim Crowe, Nutrition researcher and educator

Looking for a food that is packed with nutrients, offers a host of health benefits and is good for the environment? Then it is time to rediscover a love for legumes. These powerhouse foods are staples in cultures the world over making them rightly deserving of a place in any diet.

Figure 1: Legumes have been enjoyed by multiple cultures for thousands of years.

What is a legume?

A legume is a plant belonging to the botanical family of Fabaceae (also called the Leguminosae family). A legume can also refer to the part of any plant from the Fabaceae family and that includes its leaves, stems, and pods. Just to confuse things a little, you may see the term ‘pulses’ used interchangeably with legume. While the two words mean similar things, a pulse is strictly the edible seed from a legume. Examples of pulses include kidney beans, lentils and peas.

History

For thousands of years, legumes have been right up there with grains in their importance to humans. Evidence of the cultivation of lentils has been found in Egyptian pyramids. And there have even been recipes for their use written in cuneiform (one of the earliest systems of writing). Legumes were also among the first cultivated plants in the Mediterranean. The large seeds of many species of legumes are easy to gather and store for extended periods of time. This makes them a valuable source of nutrition in times of food scarcity.

Diversity

The legume family is a diverse and hardy one. Found on all continents except Antarctica, they are the third-largest family of flowering plants on the planet with almost 20,000 different species. Some well-known examples include: 

  • Lentils

  • Split peas

  • Cannellini beans

  • Kidney beans

  • Navy beans (baked beans)

  • Broad beans

  • Mung beans

  • Soybeans

  • Chickpeas

  • Lupin

  • Lima beans.

Figure 2: When mixed together, legumes make a vibrant and colourful display.

Heath benefits

Legumes are one of the few foods deserving of the title ‘superfood’. A list of their nutritional and health benefits makes for a long read. For starters, they are a good source of B-group vitamins like folate. Then there is the iron, phosphorus, zinc, calcium and magnesium they contain. They are also low in fat, rich in carbohydrates and a superior source of protein than most other plant foods. Not to mention the antioxidants that make legumes a true superstar with some of the highest levels of any food. In fact, red kidney beans top the list with even more antioxidants than blueberries.

Figure 3. Antioxidant capacity of a range of different foods

Legumes, when eaten as part of a healthy balanced diet, may help prevent the development of numerous chronic diseases. The type of fibre in these nutritional gems can help to lower cholesterol and reduce spikes in blood glucose after a meal. High cholesterol and blood glucose increase the risk of heart disease. Accordingly, a review of research studies in this area found that people who eat legumes four times each week had a 14 percent lower chance of developing heart disease.

Legumes can also be an important food to help control body weight which is valuable considering the high rates of overweight and obesity in a country like Australia. A combination of their protein and fibre content can help increase feelings of fullness after a meal which helps curb the desire to overeat. One study involving over 8,000 adults found that people who ate beans regularly had on average lower body weights and smaller waist circumferences compared to people who did not eat beans. The regular bean eaters also had more dietary fibre, potassium, magnesium, iron and copper in their diet.

The potassium, magnesium, and fibre found abundantly in legumes are all nutrients with a positive influence on blood pressure. A recent review of eight clinical trials found that regularly eating legumes could lower blood pressure. And the benefit was seen both in people with high blood pressure and those with normal blood pressure to begin with.

Figure 4: Legumes are packed with nutrients, fibre and antioxidants – putting them in excellent company with fruit and vegetables.

Gut bacteria also profit from a meal of legumes. The fibre diversity found in legumes provides a great fuel source for the growth of beneficial bacteria like Bifidobacteria and Lactobacillus. This can translate into improvements in gut barrier function which provides a defence against harmful invaders. A healthy gut means improved immunity and greater regularity of bowel movements. With more beneficial probiotic bacteria in the gut, they turn up the production of fibre fermentation by-products called short-chain fatty acids (SCFAs). These SCFAs are linked to a range of health benefits including lowering the pH in the bowel, improving the bioavailability of calcium and magnesium, and inhibiting the growth of potentially harmful bacteria.

Environmental impact

Food choices are more than just about health. Food sustainability and the environment are now important considerations in the food choices many people make. Legumes rank highly in any environmental assessment of their merits.Greenhouse gases released from the growing of legumes are up to seven times less than for a similar area of land compared to crops such as wheat. Because of their hardiness in many different environments, legumes can be grown in more arid environments when other crops would fail.

Figure 5: Legumes are a sustainable food crop that replenish soil with nitrogen.

The environmental benefits don’t stop there. Legumes can use nitrogen from the atmosphere through a process called nitrogen fixation. This means less nitrogen-based fertilisers need to be used in the farming process.It also leaves nitrogen in the soil after harvesting, which can benefit the next crop that is planted in the soil.

The ability of legumes to fix nitrogen from the atmosphere is shared by no other cultivated plant. The plant can’t take all the credit here though as it is done as part of a symbiotic relationship with a soil-borne bacterium known as rhizobia. Nitrogen fixation is one of the key reasons why legumes became such a successful family of plants.It also explains why legumes are such a great source of protein. Because of their nutrient, fibre and protein content, legumes appear in the Australian Guide to Healthy Eating twice: once in the vegetable group and a second time in the protein group along with meat, fish, eggs and nuts.

Tips to enjoy them

With so many different legumes to choose from, there is no shortage of ways to enjoy them.Legumes have a unique texture that gives them a mouth feeling similar to meat.Combine that with being an excellent source of protein all makes for legumes being great plant-based substitutes for meat, chicken and fish.

Soups and stews are tailor-made for legumes as they get plenty of time to cook.Classic bean soups can include split peas, lentils, black beans and navy beans.Use your favourite combination of legumes and vegetables, simmer them together for 30 to 40 minutes, add in a few herbs and some lemon juice, and you will have a delicious and healthy Mediterranean soup.

Figure 6: Legumes make a hearty, nutritious addition to an array of tasty soups.

A basic legume salad can be made from a combination of any kind of cooked legumes, together with chopped herbs, lemon juice, olive oil, salt, and pepper. Then add chopped vegetables or fruit, cheese cubes, or even slices of chicken breast.

A traditional Indian dhal with either green, red or brown lentils makes for the quintessential legume curry. Hummus made from chickpeas makes for a great healthy snack that you can buy pre-made or make from scratch. Don’t just save legumes for lunch and dinner, legumes make a great breakfast addition and go well with many egg dishes such as frittatas and omelettes.

Many people think dried legumes are hard to prepare and need hours of soaking and boiling before you can use them. It is true that soaking dried legumes can make them easier to digest and absorb, but it is not essential in every case. Split peas and lentils never need soaking and cook quickly. Although it takes some time, soaking and cooking legumes does not take much planning or effort. You can also prepare slow-cooking legumes in advance and store them in the freezer. For added convenience, canned legumes are a handy alternative to dried legumes as they’re ready to consume almost straight out of the can.

Figure 7: Hummus, made from chickpeas, is a staple of Middle Eastern diets.

Figure 8: Legumes can be eaten for snacks, lunch, dinner or even breakfast, like this popular “Shakshouka” dish with tomatoes, cannelini beans and poached eggs.

Gas can sometimes be a problem for someone adding more legumes in their diet. This is actually a good sign as shows that your gut bacteria are doing their job fermenting the fibre for the benefit of your health. To help ease any gut discomfort, introduce legumes gradually over several days to weeks. Soaking dried beans for at least three hours before cooking them may help reduce this side effect. Changing the water several times during soaking and discarding the final soaking water also will help.

In summary

Legumes make a tasty addition to any diet. They are an environmentally sustainable and inexpensive source of food that is high in protein and fibre and a host of other nutrients. They’re also great for your health.

Student activities

1. Name as many legumes commonly eaten in Australian diets as you can

2. Research some legumes you’ve never heard of and list them with some traditional recipes

3. What are some of the defining nutritional benefits of legumes?

4. Describe several of the health benefits linked to regularly consuming legumes

5. For people with high cholesterol, how much of a benefit could consuming legumes have in reducing their cholesterol?

6. Name two types of beneficial gut bacteria that the fibre in legumes may help to feed

7. What can you do if legumes make you a bit windy?

8. What does it mean when legumes are described as ‘nitrogen fixing’? What is the unique symbiotic relationship that helps achieve this?

9. Do all legumes need to be soaked for several hours before cooking them?

10. Find a recipe on the Internet that makes use of legumes and try making it at home

References

Afshin, A.et al.2014, ‘Consumption of nuts and legumes and risk of incident ischemic heart disease, stroke, and diabetes: a systematic review and meta-analysis’, American Journal of Clinical Nutrition, vol.100, no.1, Jul., pp.278-88.

Australian Guideline to Healthy Eating: https://www.eatforhealth.gov.au/guidelines/australian-guide-healthy-eating

Jayalath, V.H.et al.2014, ‘Effect of dietary pulses on blood pressure: a systematic review and meta-analysis of controlled feeding trials’, American Journal of Hypertension, vol.27, no.1, Jan., pp.56-64.

Jeuffroy, M.H.et al.2013, ‘Nitrous oxide emissions from crop rotations including wheat, oilseed rape and dry peas’, Biogeosciences, vol.10, Mar., pp.1787-97.

Papanikolaou, Y and Fulgoni, V.L.2008, ‘Bean consumption is associated with greater nutrient intake, reduced systolic blood pressure, lower body weight, and a smaller waist circumference in adults: results from the National Health and Nutrition Examination Survey 1999- 2002’, Journal of the American College of Nutrition, vol.27, no.5, Oct., pp.569-76.

Wu, X.et al.2004, ‘Lipophilic and hydrophilic antioxidant capacities of common foods in the United States’, Journal of Agricultural and Food Chemistry, vol.52, no.12, Jun., pp.4026-37.