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Food, Health, and Eco-news
Beans Seen to Discourage Weight Gain and Diabetes

So-called “resistant” starches in beans, whole grains, and quick-chilled pastas or potatoes can actively aid weight control and anti-diabetes efforts.

by Craig Weatherby

Glycemic index:
Resistant starch looks good
under new food-ranking system

Resistant starch is great in part because it reduces the impact a starchy food has on blood sugar levels: the less the better to prevent diabetes and inflammation.

Beans and other foods high in have a low “glycemic index” or GI: a measure that ranks individual foods according to their impact on blood sugar levels. But another measure called “glycemic load”—which is calculated by multiplying the glycemic index by the grams of carbohydrates in a serving is more helpful.

This description by blood sugar guru David Mendosa ( explains the difference well:

“The glycemic load (GL) is a relatively new way to assess the impact of carbohydrate consumption that takes the glycemic index into account, but gives a fuller picture than does glycemic index alone.

“A GI value tells you only how rapidly a particular carbohydrate turns into sugar. It doesn't tell you how much of that carbohydrate is in a serving of a particular food. You need to know both things to understand a food's effect on blood sugar. That is where glycemic load comes in.

“The carbohydrate in watermelon, for example, has a high GI. But there isn't a lot of it, so watermelon's glycemic load is relatively low. A GL of 20 or more is high, a GL of 11 to 19 inclusive is medium, and a GL of 10 or less is low.”

Ever since Dr. Atkins took up his cudgel against dietary carbohydrates (sugars and starches), people have tended to perceive this major food group as fattening fare.

To be sure, Atkins was right about the potent glycemic (blood-sugar-raising) effects of sugars and the rapidly absorbed starches in refined flour products like pastries, white bread, and pasta.

But there are important distinctions between starchy foods: ignorance of which leads many to shun high-starch foods that do no harm and can even help control weight and discourage diabetes.

Regular vs. “resistant” starch: the basics

Dietary carbohydrates consist of simple carbohydrates, or sugars, and complex carbohydrates, or starches.

Starches are chains of sugar molecules, whose individual conformations make them distinctly different with regard to digestion, absorption, and blood-sugar control.

Most starches are digested and absorbed into the body in the small intestine.

But some starches resist digestion and pass through to the large intestine where they behave like dietary fibers: the even longer and less digestible chains of sugar molecules from which plants build their physical structures.

Nutrition scientists named these special kinds of carbs “resistant starch.”

Legumes (beans, lentils, split peas, string beans) and whole, unprocessed grains contain the highest percentages of resistant starch. See table, below, for the resistant starch content of common beans and grains.

Resistant starch limits the sharp spikes in insulin and glucose levels that normally follow consumption of foods high in easily digestible starches (sugars, fruit juice, soda, white bread, potatoes, and pastries)… even when the source of resistant starch is consumed many hours beforehand.

Research indicates that resistant starches can really help control people's weight and reduce their risks of cardiovascular disease and diabetes:

Weight Control:
  • People who eat resistant starches increase fat-burning (thermogenesis) in their bodies. The authors of an Australian study found that when participants enjoyed a meal in which only 5.4 percent of its starch was the resistant kind, the rate at which their bodies burned (oxidized) body fat increased by 23 percent for a full day afterwards. Adding more resistant starch did not increase the rate of fat burning or its duration. It seems that a little goes a long way in this regard.
  • Rodents given resistant starches along with digestible starches maintain smaller fat cells (adipocytes) than companions fed only foods high in digestible starches.
  • When present in carbohydrate foods, resistant starch beneficially lowers the “glycemic response” to foods by releasing glucose into the bloodstream at a low, slow, steady rate.
  • People and animals who consume foods high in resistant starches along with foods high in regular starches maintain higher (i.e., healthier) levels of insulin sensitivity, compared with people and rodents who consume only foods high in regular starches.

Heart Health:
Compared with people who consume only regular, digestible starches, people who also consume foods high in resistant starches enjoy lower cholesterol and triglyceride levels.

When resistant starch reaches the colon, bacteria feed on it, just as they do on dietary fiber, producing a short-chained fatty acid called butyrate that's known for its ability to curb the risk of colon cancers.

Resistant starch and fiber content of beans and grains

The table at right, based on research by Dr. George C. Fahey and his team at the University of Illinois at Urbana-Champaign, shows how much of the starch in each food is resistant. (The two other forms of starch (rapidly digesting and slowly digesting) are broken down in earlier stages of digestion, and are not shown here.)

Note the differences between the whole and refined versions of grains: for example, brown rice vs. white rice flour, whole wheat vs. white (refined) wheat flour or corn kernels vs. corn meal and hominy grits. It is interesting to see that there is little difference between brown and white rice, with both being pretty rich in resistant starch.

The percent of resistant starch reaching the colon is important because that is the portion available to be fermented, with beneficial anti-cancer and appetite-suppressing effects.

*Note: We are not sure how the researchers define "potato starch," which their figures suggest has a very high proportion of resistant starch (66.9 percent). Given the generally medium-to-high glycemic indices and glycemic loads of baked and boiled potatoes, we cannot assume that this figure means that cooked, un-chilled potatoes are as high in resistant starch (To see the GIs and GLs of many foods, go to

Resistant starches: Any repast's healthful pièce de résistance

Pièce de résistance means the best part, highlight, or feature of something, such as a meal.

Beans, whole grains, and other foods rich in resistant starch meet the definition, as they add a healthful highlight to any a meal. In fact they make the perfect anti-aging complement to colorful, antioxidant-rich fruits and vegetables and to oily, omega-3-rich fish such as wild salmon.

The richest food sources of resistant starch--beans, lentils and other legumes--are also high in protein, fiber, and antioxidants.

Beans top the resistance charts

What starchy food satisfies energy and protein needs, delivers anti-inflammatory, antioxidant polyphenols, burns body fat, and moderates blood levels of both blood sugar and insulin?

The answer is “legumes”: that is, beans, lentils, and string beans. Beans contain the highest percentages of resistant starch, followed, at some distance, by whole, unrefined grains.

Prized by traditional cultures--and contemporary fans of ethnic cuisines--beans also serve double-duty as ace weight control allies.

The high levels of resistant starch in beans and whole grains could explain why, in population studies, people who get more of their protein from these complementary plant foods than from meats enjoy healthier body mass indices (height-weight ratios).

A meal featuring legumes raises blood sugar very slowly and moderately, and even moderates the blood-sugar (i.e., glycemic) response to relatively high-glycemic foods (sugars, refined flour products) consumed in the same or next meal you eat.

Aside from resistant starches, beans owe some of their weight-control and anti-diabetes benefits to three other factors:

  • The non-digestible starches we call fiber—in which beans are especially rich—are satiating and stabilize blood sugar: two key factors in weight-control.
  • Many studies show that higher fiber intake is associated with lower body weight, body fat, and body mass index (weight-to-height ratio). Results from clinical trials are more mixed, although in most cases, higher fiber intake cuts peoples' food consumption and drops their body weight.
Starch blockers (amylase inhibitors):
  • Beans contain compounds called amylase inhibitors, which block the action of the enzyme (amylase) needed to digest starches.  Hypothetically, this effect should help prevent digestion of some of the starch in beans themselves, and of the starch in other foods eaten with beans.
  • It is not clear exactly how effective the amylase inhibitors in whole beans are compared with taking purified phaseamolin: a supplemental amylase inhibitor extracted from white kidney beans.
Antioxidant pigments: 
Most of the pigments that color beans are anthocyanins: the same kinds of antioxidant polyphenol pigments that color berries. Anthocyanins help control blood sugar modestly and blunt the inflammatoryhence, pro-diabetic, blood-thickening, and artery-damagingimpact of dietary sugars and standard starches.

Beans offer pound-shedding protein in a tasty package

Beans and other legumes are ample, weight-controlling sources of protein.

While beans can't replace the unique benefits of omega-3-rich fish or match its protein content, they and other legumes can replace almost all need for animal protein when combined with a little bit of whole grain to boost the level of nutritionally complete protein in both.

Beans and lentils also come in a wide variety of flavors, shapes, sizes and textures, lending themselves to a broad range of uses, and making it easy to choose one compatible with most any meal.

Of the 29 food and feed ingredients studied by a team at the University of Illinois at Urbana-Champaign (see table, below), the seven legumes tested offered substantially higher percentages of dietary fiber and resistant starch.

Black beans contain the highest amount of total dietary fiber (43 percent), and 63 percent of their total starch content is resistant starch that makes it to the colon to ferment, with beneficial results.

But in terms of making the least impact on blood sugar, an uncommon—but obtainable—legume from the Indian subcontinent may be the best bean of all.

This lentil, called chana gram dal, comes from a distinct variety of the same plant that gives us plump yellow chickpeas (Cicer arietinum). However, the chana dal variety of chickpea is much smaller and darker, and also higher in fiber and phytoceuticals.

Indian grocers call these two types of chickpea desi (chana dal) and kabuli (standard yellow chickpeas).

While standard chickpeas rank very low on the glycemic index, chana dal ranks even lower, making it a superstar among the many blood-sugar-stabilizing stars in the legume family.

Grains and resistant starch: Making a good thing better

Cereal grains, especially barley and corn, are second only to beans in their percentages of resistant starch.

Whole grains contain much more resistant starch than the heavily processed flours made from them.

But even whole grains are second best to legumes (beans, lentils). In addition to a lower percentage of resistant starch, grains have less fiber than beans, making them less beneficial with regard to the overlapping benefits of both kinds of indigestible carbohydrates.

And you can actually increase the percentage of resistant starch in fresh-baked bread or in cooked pasta and potatoes just by cooling them quickly: a process called “retrogradation”.

When you heat a starchy food like bread or pasta the digestible starchy adopts a gel-like form, and when you cool it quickly, it morphs into digestion-resistant forms.

This is what happens to bread when it cools after cooking: a process you can promote and accelerate by putting fresh-cooked bread in the refrigerator.

And ever wondered why, despite the Atkins Diet's critical stance toward spaghetti, the traditional, pasta-centered rural Italian dietone of the “Mediterranean” approaches to eating considered preventive-health paragonsdoesn't produce many overweight people?

To be sure, the small portions of pasta, fishy diets, and manual labors of rural Italians explained some of the health benefits found among them and their Cretan counterparts by the famed Seven Countries Study, which began in the 1960's and led to lionization of both populations' classic Mediterranean diets.

But the tradition of rinsing cooked pasta in cold water, while done to reduce stickiness, had the side benefit of literally making this unfairly maligned white-flour food considerably less glycemic and caloric.

Likewise, you can raise the resistant starch content of potatoes considerably by chilling them immediately after cooking: a trick that makes potato salad healthier than a hot potato, especially if you leave in the fiber- and antioxidant-rich skins.

Corn comes in from nutritional cold

Conventional wisdom holds that corn is full of rapidly absorbed, blood-sugar-spiking starches and sugars and low in nutrients.

But let's not be so hasty to abandon as unhealthful the staple food of most indigenous Americans, which served them very well over millenia.

In addition to the fact that whole corn is quite high in antioxidants, research released this year by scientists at the the Louisiana State University Agricultural Center show that fermentation of natural resistant starch from one corn has considerable positive impact on cellular metabolism and accumulation of body fat.

Drs. Michael Keenan, Jun Zhou and Roy Martin of the LSU Agricultural Center also conducted a series of studies to pinpoint the sources of the overlapping anti-obesity effects of dietary fiber and resistant starch.

As they reported at the 2006 Annual Meeting of the North American Association for the Study of Obesity, “By comparing diets matched for different variables, we were able to show that the fermentation was the mechanism with the greatest impact of the three mechanisms tested.” As we've seen, both fiber and resistant starches offer bacteria fertile fare to ferment.

Earlier animal research by the same team showed that the dietary consumption of a corn-derived resistant starch raised levels of key satiety hormones (PYY, proglucagon, GLP-1) and significantly and reduced abdominal fat in the experimental rodents.

Dr. Keenan said this at the time: “We believe the fermentation of resistant starch may be an effective natural approach to the treatment of obesity. The advantage of the resistant starch is that it can be added to foods more readily than non-fermentable fiber.”

So when you're planning meals, don't overlook beans--alone or with a little whole grain or “retrograded” pasta or potatoas your carbohydrate component. Your waistline--and healthier future selfwill thank you. 


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