Black beans might improve insulin sensitivity, mouse study suggests

Dear Doctors: I just heard black beans are considered some kind of miracle food. What makes them so special?

Dear Reader: Headlines about benefits of black beans are tied to the results of an animal study by the federal Agricultural Research Service.

According to the research, conducted in obese mice, the animals’ sensitivity to insulin improved dramatically when cooked black beans were added to their high-fat diet. The mice that were fed the human equivalent of one half cup of cooked black beans a day saw an 87% drop in insulin resistance.

Insulin is the hormone the pancreas releases into the bloodstream in response to the presence of glucose after eating. It helps move glucose into the cells of the muscles, fat and liver, where it’s used for energy.

When the body’s sensitivity to insulin in the blood diminishes, it’s known as insulin resistance. That means cells have become less efficient at accepting glucose from the blood.

The glucose that remains in the blood then prompts the pancreas to release even more insulin. The danger is that the insulin-producing cells of the pancreas will become unable to keep pace with the increasing need. Then, glucose created through digestion is left in the blood. This can lead to prediabetes, a risk factor for type 2 diabetes.

This research echoes findings of previous studies linking the addition of cooked black beans to the diet with improved blood-glucose management.

Only the mice fed whole, cooked black beans showed these improvements. Mice fed components from cooked black beans didn’t see the same benefits.

The researchers also found the mice whose high-fat diet was supplemented with cooked black beans experienced a 28% drop in low-density lipoprotein, or LDL — the “bad cholesterol” that can cause fatty deposits called plaque in blood vessels. This can lead to heart disease, heart attack and stroke.

Levels of triglycerides, another lipid linked to heart disease, dropped 37% in the bean-eating mice. Certain biomarkers of inflammation in the blood decreased as well.

The researchers also saw improvements to the balance of the gut bacteria in the bean-eating mice. The ratio of two types of bacteria linked to obesity dropped by 64%. Bacteria associated with inflammation also decreased. The mice whose high-fat diet lacked black beans didn’t show similar improvements.

The researchers suspect black beans interfere with a metabolic pathway tied to inflammation, which has been linked to insulin resistance.

Mouse studies don’t necessarily translate to humans.

But cooked black beans — never eat raw beans, as many varieties can be toxic — are low in fat, high in fiber and can be a healthful component of a varied diet.

Dr. Eve Glazier and Dr. Elizabeth Ko are internists at UCLA Health.