Delivering Iron: How Beans Can Provide a Critical Nutrient

Ray Glahn is a research physiologist at the Robert W. Holley Center for Agriculture & Health in Ithaca, NY. His work focuses on iron nutrition from staple food crops and food products. 

Welcome to Under the Microscope Dr. Glahn

UM: Why have you focused on iron in your research? Why is it important?

RG: Iron is an essential micronutrient. It is a necessary component of hemoglobin and myoglobin, two blood proteins that transfer oxygen from the lungs to tissues. It is also necessary for physical growth, neurological development, cellular function, and is a critical element for synthesis of some hormones. It plays a central role in human metabolism and growth, and thus is extremely important, particularly for women of child-bearing age and children.

Approximately 1/3 of the global population is iron-deficient. It is one of the leading global nutritional deficiencies. In the U.S., iron deficiency is on the rise, with 14-15% of adults diagnosed as iron-deficient. Rates can be much higher in women and children. Obese individuals are also at greater risk of iron deficiency, primarily due to the inflammation associated with obesity. Because it reduces oxygen carrying capacity, iron deficiency can have a profound impact on worker productivity, making workers less productive. It’s also a huge problem in developing countries, where anemia rates can reach 60-70% in certain populations. 

UM: What’s the difference between iron content and iron bioavailability in food? Why does bioavailability matter?

RG: Iron content is simply the amount of iron in a given amount of food. Iron bioavailability is the portion of the iron content that may be absorbed and utilized in normal iron metabolism. It’s an important – even critical – distinction: just because iron is present in food, even in high amounts, that doesn’t automatically translate into a person being able to access and use that iron. That depends on the bioavailability.

UM: Why did you decide to focus on beans as a way to increase dietary iron content?

RG: Beans are eaten worldwide and are a common and integral part of many food systems. They are a relatively nutrient-dense food for protein, complex carbohydrates, fiber, vitamins and minerals. Beans are also rich in iron content relative to other crops like corn, wheat, and rice, so they have more potential to alleviate iron deficiency.  Overall, beans are an affordable, easy way to increase the nutritional quality of a diet.

We are also  learning how to enhance the iron bioavailability in beans, and we can determine  the bean varieties that are delivering highly bioavailable iron. Given all of the above , there is now great  potential to alleviate iron deficiency via bean breeding and consumer education.

Bean plants grow in a greenhouse as part of research to identify those with the most promising traits (Photo courtesy of Ray Glahn).

UM: How do beans compare with other foods in terms of nutritional benefits?

RG: It depends on the variety of bean, and the variety within a given color or market class. One benefit of beans is that they offer a kind of “time release capsule” for carbohydrates, staggering the rate at which they are absorbed into the bloodstream. That kind of steady, gradual processing has a number of health and metabolic benefits, including keeping blood sugar levels relatively stable, as well as keeping people feeling full for long periods, without sudden spikes in hunger, or cravings.

UM: How have you explored the issue of bioavailability in your research?

RG: In order to measure bioavailability, we have developed a way to capture the delivery of iron from food, using high throughput technology: the Caco-2 cell bioassay. Others have tried to develop techniques to measure bioavailability, but my lab is unique in that we run this bioassay all year long, with highly trained and experienced technicians.  A government lab such as ours is ideally suited to provide the consistent resources and expertise for this type of work.

UM: How can consumers tell which beans to choose to get the nutrients they want, like iron?

RG: Consider the market (color) class of bean you plan to consume.  For improved iron nutrition, right now we can say that white beans in general are a great source of bioavailable iron. Our newest yellow bean varieties are in production at our research plots to increase the amount of seed available to growers. These new yellow bean varieties are high in bioavailable iron, higher than white beans, and also fast cooking, another trait that consumers find highly desirable.

Processing matters in determining how nutrients persist as the beans pass from the field to the consumer. We are currently working with a large industry partner to identify food products and processing methods that have enhanced bioavailable iron. In flours and pastas made from beans, we can boost nutrition based on bean variety, how they’re ground – for instance, sonic grinding processes for bean-based flours can improve the release of iron. Bean flours made from white beans and certain yellow beans can actually be quite high in bioavailable iron, depending on the market class (color class) of beans used for the flour.

One other important thing to note is that the bean seed coat contains flavonoids, also known as polyphenols, which are collectively the primary factor influencing iron bioavailability from beans.  Most of these flavonoids inhibit iron bioavailability; however, our lab has identified flavonoids that actually promote iron bioavailability.  Although the polyphenols can inhibit iron absorption, the flip side is that these compounds are great antioxidants. Thus, I recommend eating a variety of bean color classes in one’s diet.

Yellow beans can be ground into flour that can produce pasta that is both high in nutrients and cooks very quickly (Photo by Stephen Ausmus, D5156-3).

UM: What’s the role of genetics in your work? Are there certain traits you’re looking at in particular?

RG: Genetics play a major role in our work. We collaborate extensively with bean breeders all over the world. We are looking at several traits in our research. Most notably, we are focused on the genetics of seed coat color. It is controlled by several well-known genes, a few of which we now know to be key to iron bioavailability. We can identify how the color genes of bean seed coats interact to promote or inhibit iron absorption from beans or other foods eaten with them. 

We’re also looking at traits related to cooking time. Our research has shown that shorter cooking times can be linked to high iron bioavailability, creating opportunities to identify and develop bean varieties that are highly desirable to both growers and consumers.

UM: What are the ultimate goals of your research?

RG: We want to identify bean varieties with the best iron bioavailability, while still maintaining all of the other traits important to growers and consumers. We certainly want to identify varieties that are already present in the food system, and available to farmers and consumers right now. In addition, we apply our research tools and approach to develop new varieties with enhanced iron nutrition and monitor varieties to make sure the nutritional benefit is maintained. To my knowledge, no other group in the world has this mission and these capabilities.

The research tools that I have developed and apply in my work are widely accepted. They have been validated for many years and are now in the “payoff” mode as applications of the models are having an impact. The innovations and increased understanding of the factors that enhance iron nutrition from beans represent advances that can have a global impact on improving the nutritional quality of beans, and as a result, the nutrition and wellbeing of people.