Researchers selected 10 randomized clinical trials that looked at the effect of eating legumes on lipids and lasted at least three weeks each. After analyzing the combined data in a meta-analysis, they found that of the 268 total participants (mostly middle-aged men), those eating a high-legume (non-soy) diet had total cholesterol levels that averaged nearly 12 points lower and LDL-cholesterol levels 8 points lower than those eating the fewest nonsoy beans and peas. HDL-cholesterol levels did not change significantly.
The researchers note that this is one of the first meta-analyses to document that a diet rich in non-soy legumes can reduce total and LDL-cholesterol blood levels as well as a highsoy diet. The researchers cite soluble fiber and plant nutrients like phytosterols in beans as contributors to the cholesterol-lowering effects.
This study demonstrates that beans other than soybeans benefit lipid levels in a way that helps prevent cardiovascular disease, one of the leading causes of death in the U.S. As a meta-analysis, it has the weight of many studies behind it. Because it focuses on a food, beans, that many Americans already eat, it offers a practical way to improve health. Current dietary guidelines recommend eating three cups of beans a week (about ½ cup per day).
This 10-country study of nearly 500,000 men and women (aged 25 to 70 years old) was conducted to determine the relationship between body fat and a Mediterranean way of eating. The researchers scored participants’ diets based on nine nutritional components characteristic of a traditional Mediterranean diet, one of which was legumes, such as beans. They found that a modified Mediterranean diet that included these traditional components, but was higher in meat and dairy intake than is typical, was not associated with body mass index (BMI). However, it was linked to a lower waist circumference, especially in people from northern European countries, even those with diverse eating patterns. The researchers conclude that even a modified Mediterranean way of eating may benefit body fat distribution.
Despite the fact that beans offer a diverse array of nutrients, including fiber, protein, and several vitamins and minerals, few Americans eat beans as part of their daily diets. American adults eat, on average, only 0.1 to 0.3 servings of legumes daily (¾ to 2 servings per week), with beans being most popular among Mexican-American, Hispanic-American, and other ethnic populations. This low intake is in sharp contrast to current recommendations.
The study’s authors compared the nutrient and food group intake of people who eat beans to those who do not eat them, using data from the 1999-2000 and 2001-2002 NHANES surveys. Only about 8 percent of Americans ate beans on any given day; pinto beans, refried beans, baked beans, chili, and Mexican and Hispanic dishes made with beans were the most popular. When they were eaten, beans appeared to have taken the place of other vegetables and often were eaten with grain foods, such as rice. The diets of bean eaters were more healthful, with more fiber, protein, carbohydrate, folate, magnesium, iron, and zinc. Moreover, the percentages of calories from fat and saturated fat were lower in bean eaters.
This study highlights that eating one-half cup of beans or peas can improve intake of key nutrients, particularly protein, fiber, folate, and important minerals like magnesium and zinc. The study suggests it’s best to eat beans in addition to other vegetables, not instead of them.
Metabolic syndrome (AKA syndrome X and insulin resistance syndrome) is now widely accepted as a distinct condition with agreed-upon criteria. While excess calories do not cause metabolic syndrome, inactivity and obesity are major contributors. This collection of symptoms puts people at much higher risk for heart disease, stroke, and diabetes. One theory is the syndrome may be caused by resistance to insulin or overall inflammation of body tissues.
What are the odds?
One in four American adults—47 million—now are considered to have metabolic syndrome (MetSyn). Mexican-Americans, especially women, appear to be most at risk, followed by African-American women, African-American men and Caucasians. Having a parent or a sibling with diabetes raises risk dramatically. Individuals with MetSyn are twice as likely to develop heart disease and five times more likely to develop diabetes. This is why it is crucial to treat the disparate symptoms (see box), which together signal more trouble than they might individually.
What Constitutes Metabolic Syndrome?
People who have at least three of the following five risk factors, meet the basic criteria for metabolic syndrome as generally accepted by most health and government organizations:
Fiber has been traditionally defined as either insoluble or soluble. But researchers have identified a third type that’s changed the traditional view of fiber. Resistant starch, like all fiber, resists digestion in the stomach and small intestine. However, resistant starch is broken down by bacteria in the large intestine.
Starch is comprised of two types of branched molecules, amylopectin and amylose. Cooking causes amylose to form a tight crystalline structure that is hard to digest, which is what creates resistant starch. Natural sources of resistant starch include beans and peas, as well as potatoes, vegetables, bananas, and grains (particularly after they’ve been cooked and cooled). Resistant starch also is present in a highamylose cornstarch sold as Hi-Maize, which can be used in cooking.
“Resistant starch has been shown to help boost feelings of fullness, to increase metabolism, and to protect digestive system health, all while balancing blood sugar levels,” explains David Feder, RD, author of The Skinny Carbs Diet (Rodale 2010), a cookbook of meals high in resistant starch. Because the starch is broken down in the large intestine, it also helps maintain bacterial balance by making the intestine more acidic, creating an environment that is unfriendly toward pathogenic bacteria. Additional benefits come from short-chain fatty acids produced by the intestinal bacteria, which stimulate blood flow, cell growth, and muscle tone in the colon.
“Beans have more resistant starch than any other food,” adds Feder. “Clearly we need to eat more beans. It is estimated that only about 9 percent of the resistant starch in our diet currently comes from beans and peas, while about 60 percent is from breads, cereals, pasta, and vegetables.”
Researchers studied the potential health benefits of a variety of beans, comparing their mineral availability, glycemic index (GI), and cholesterol-lowering effects. They found that lima beans rate the highest for iron availability, while kidney beans and pigeon peas ranked best for calcium and zinc. All the legumes studied were low-GI foods. Kidney beans stood out for their ability to significantly lower both total and LDL cholesterol. The researchers conclude that legumes have potential health benefits worth promoting, specifically lowering cholesterol blood levels and boosting mineral intake.
Many people are aware that beans are high in fiber and a good source of protein, but lesser known are beans’ benefits on blood sugar and blood cholesterol levels. The fact that they do not raise blood sugar levels much, despite being carbohydrates, is key to their ability to keep diabetes under better control, compared to sugary foods and refined carbohydrates that cause blood sugar to spike and then plummet. Beans are beneficial to treating and possibly preventing the onset of type 2 diabetes. Moreover, legumes like beans have shown the ability to lower cholesterol levels and thus reduce the risk of heart attack and stroke. Also, the minerals in beans can make a significant contribution to dietary intake.
In a meta-analysis that pooled the results of 41 studies, Canadian researchers found that beans had a positive effect on blood glucose levels. By itself, a high legume intake lowered both fasting blood glucose (by 80%) and insulin levels (by 50%). When combined with a low-glycemic index diet or a high-fiber diet, a high intake of legumes appeared to impart additional benefits consistent with better long-term glycemic control.
This comprehensive review drives home the importance of diet on control of blood glucose levels for treatment of those already diagnosed with diabetes, as well as for prevention for those who might be at risk for the disease. One of the food groups that is well-documented to benefit glucose levels is legumes. Analysis of these pooled studies confirms that simply eating more legumes, such as beans, can improve both glucose and insulin levels. But eating beans and other legumes as part of a high-fiber intake and keeping glycemic index low (by eating foods with less of an impact on blood sugar levels, such as whole grains, fruits, and vegetables) is more effective.