Nutrient Richness Improves Insulin Regulation and Inflammatory Status

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Sometimes researchers set out to prove one thing, but end up proving another. That’s how we look at a fascinating new study by researchers in the Department of Nutritional Sciences at Pennsylvania State University who examined the role of legumes in healthy diets. In what they called the Legume Inflammation Feeding Experiment, the role of navy, pinto, kidney, and black beans in an overall healthy diet was studied for a period of 4 weeks. All 64 men participating in the study had previously been shown to be at risk for colon cancer, and the researchers wanted to determine how two different types of diets would affect several aspects of their colon cancer risk, including their ability to achieve healthy insulin balance and their ability to avoid unwanted inflammation.

Both diets provided 50% carbs, 18% protein, and 34% fat. (That’s a pretty healthy balance according to most research studies.) In addition, both diets met the Recommended Dietary Allowances (RDAs) for major vitamins and minerals. Both diets also provided at least 4 vegetable and 2 fruit servings per day. In other words, these diets were pretty healthy! One diet, however, focused on foods with low glycemic index (GI) values and provided an overall GI of 38. This diet also focused on intake of legumes and provided about 3 total cups per day of the specific beans listed above. The second diet did not include any beans, and it provided an overall GI of 69. This major difference in GI value also corresponded to a major difference in total fiber intake, with the low-GI diet providing about 40 grams per day and the higher-GI, legume-free diet providing about 18 grams.

Both diets resulted in better insulin regulation and inflammatory status for men participating in the study. And by improving these physiological factors, the researchers believed that the diets might also be helpful in reducing the men’s risk of colon cancer.

Yet, the study authors had expected to see additional benefits from the low-GI, legume-rich diet in comparison to the higher-GI, legume-free diet. Why did the 3 added cups of beans and the 20 additional grams of fiber and the focus on low-GI foods fail to provide extra help in blood sugar balance and insulin regulation? The authors speculated that the diets may have been too similar in overall high-quality nourishment to reveal special benefits from the beans. They also speculated that their approach to calories might have shifted the results. Instead of allowing participants to self-adjust their calorie intake based on appetite, they provided participants with whatever number of daily calories would maintain their current body weight. For example, if a study participant started losing weight on 2,000 calories of food, the daily calories for that participant were increased to 2,200 (or to whatever level would prevent weight loss). The researchers took this step to avoid having the study results confused by changes in weight. But in doing so, they may have prevented some of the special benefits of a higher-fiber, low-GI diet from shining through.

These overall results seem pretty astonishing! Here we have two nutrient-rich diets that provide RDAs for key vitamins and minerals, healthy amounts of protein, vegetables, and fruits, and at least twice the amount of dietary fiber as consumed by the average U.S. adult. This nutrient richness goes a long way in health benefits, and we see those benefits here in better insulin regulation and better inflammatory status. What we don’t see in this study-because the study methodology prevented us from seeing it-are the special benefits of fiber-rich, low-GI foods (including legumes of all kinds). As the authors themselves pointed out when discussing the results of their research, it might have been a mistake to require study participants to maintain their weight by increasing their calories whenever they started to lose weight during the study. For some of the participants, weight loss would have been a desirable health outcome, alongside of better insulin regulation and decreased risk of unwanted inflammation. If participants had been allowed to let their intake of high-fiber, low-GI legumes act as a natural regulator of appetite and satiety (their sense of fullness and satisfaction with food), we are confident that the legumes would have provided them with additional health benefits, including weight loss where weight loss would have proven beneficial. In addition, even better results might have been obtained in terms of insulin regulation and decreased risk of unwanted inflammation.

WHF Recommendations

Take advantage of the high-fiber, low-GI legumes (including all beans and lentils) and their ability to satisfy our appetite while providing us with a very moderate amount of calories. When part of an overall nutrient-rich diet, the value of this food group cannot be beat!

Beans are really easy to prepare. If you want to make them from scratch, all you need to do is soak them for 8-12 hours in fresh water and put them in the refrigerator. After rinsing them, place them in a pot of water (usually 3 parts water to 1 part beans will do), bring them to a boil and then down to a simmer. Most beans take about 1 to 1-1/2 hours to cook.

If you’re running low on time, you can also opt for canned beans. Look for ones that don’t include much other added ingredients (like salt) and try to find ones that come in BPA-free cans.

References

Hartman TJ, Albert PS, Zhang Z et al. Consumption of a Legume-Enriched, Low-Glycemic Index Diet Is Associated with Biomarkers of Insulin Resistance and Inflammation among Men at Risk for Colorectal Cancer. Journal of Nutrition January 2010, Vol. 140, No. 1, 60-67. 2010.