How to Eat Rice and Potatoes without Spiking Your Blood Sugar—Add Lentils

With D. Dan Ramdath, PhD, and Andrew Freeman, MD, FACC, FACP

When it comes to diet, not everything about keeping your blood sugar down (or decreasing your risk of diabetes) has to be difficult. Canadian researchers have come up with a clever diet swap that's both easy and gets great results in keeping down blood sugar.

Recognizing how much people want their rice and potatoes, these nutrition experts found a great way to help you enjoy your favorite carbohydrates, or more accurately starches—rice and potatoes—with a twist that avoids the usual glycemic spike that jeopardizes good blood glucose control.1

Swapping out half the rice or potatoes with cooked lentils improves blood glucose control.Good trick for people with diabetes, add lentils to rice or potatoes to skip the rise in blood glucose.

Advantages of Incorporating Lentils to Improve Blood Sugar Control

"When you eat potatoes or rice, you can replace half [of the amount you usually eat] with lentils and significantly reduce the negative effects on your blood sugar," says D. Dan Ramdath, PhD, a senior research scientist at the Guelph Research and Development Centre, and an adjunct professor of nutrition at the Universities of Guelph and Saskatchewan in Canada.

He and his colleagues conducted a study that looked at the effects of doing just that—blending in lentils to lessen the rise in blood sugar common with high glycemic foods like rice and potatoes.1 By replacing a portion of the potatoes and rice with lentils, Dr. Ramdath confirmed that they were able to reduce blood sugar spikes effectively, following these meals.1

The findings, published in the Journal of Nutrition, make total sense to Andrew Freeman, MD, director of cardiovascular prevention and wellness at National Jewish Health in Denver, Colorado, and co-chairman of the Nutrition and Lifestyle Working Group for the American College of Cardiology.  He reviewed the study findings for EndocrineWeb.

"Beans and legumes are inexpensive, readily available, tasty, and nutritionally beneficial," he says, being a great source of both plant protein and dietary fiber that moderate your blood cholesterol as well as your blood sugar while promoting a sense of fullness. In effect, lentils represent an all-around heart-healthy, anti-diabetes food choice, so you’d have to ask why not eat more? 

Studying the Favorable Impact of Lentils as a Starch Buddy

The investigators fed two groups of 24 healthy adults, whose average age was 27 years and at a healthy weight, white rice only, or half white rice with three different types of lentils (large green, small green, split red), potatoes alone, or half potatoes with one type of lentil.1

Blood samples were taken before and after the meals in order to analyze the participants’ glucose levels. In comparison to those eating rice alone, blood glucose was significantly lower in individuals who eat meals with rice mixed with any of the lentils. Blood sugar levels were also lower in meals in which the potato was combined with lentils instead of when the meal contained pure potatoes were eaten as is, although a little less so.1

As you likely know, blood glucose reflects the sugar level present in the blood during the process of digestion and changes in response to the types and amounts of carbohydrate contained in the foods (meals and snacks) as well as beverages consumed. Pulses, which are high in fiber, are lower in starch content than rice or potatoes, so are known to slow down the digestion and with it, reduces the release of the carbohydrates into the blood. The end result: lower blood sugar following a meal containing lentils.1

What Are Pulses and Where Do Lentils Fit in?

Lentils, classified as pulses, are defined as the dried seeds of legumes, also including chickpeas, dried peas, and beans.

More commonly known as the base for soup and Indian curry, Lentils—flattened, tiny disc-shaped edible seeds—come in five basic varieties: most often brown and green but red and yellow provide a more earthy flavor to soups and are great as a base for dips or spreads. They can be cooked to retain their wholeness for salads or go all the way to soft for a perfect thickener. You can imagine then, how substituting well-cooked lentils wouldn’t even be noticed in mashed potato, for example.

Then there are French lentils, which are more thick skinned, so they retain their shape when cooked and provide a more nutty, texture, especially for salads. Black (Beluga) lentils are by most accounts the most flavorful, and cook more like the French version but appear closer to the brown lentil. This would be a very pleasing and unobtrusive addition to brown or black rice.

Adding Lentils Offers Substantial Benefit to People with Diabetes

''We found that blood glucose levels decreased between 20 and 30%,'' Dr. Ramdath tells EndocrineWeb, in people who ate meals that incorporated lentils into their starches.1 "Compared with eating 100 grams (3.5 ounces) of rice, if you replace half that amount with lentils, the reduction in blood glucose is up to 1/3 lower,” he says, than for meals in which the person eat just rice or just potato.

Why didn't they have the participants give up all the starchy carbs and just eat lentils?  Dr. Ramdath says that the research team did that study first, and they did find that when lentils were served as the primary starch after-meal blood sugar levels were reduced by about 70%.2 Actually, this findings supported a diet incorporating any one of the pulses—be it dry beans (eg, black, pinto, kidney, red), peas, and chickpeas—which is of benefit to anyone looking to reduce their risk of diabetes, heart disease, or overweight.

Many find lentils more versatile and easier to cook than the dried beans, so were a good high fiber carbohydrate to examine. No matter which type of lentil was chosen, this pulse proved to have a beneficial effect on blood sugar, keeping it low, especially when eaten regularly, and as a replacement for starchy foods,1,2 according to Dr. Ramdath. The minimum amount to keep blood sugars from rising is ¼ cup dried pulses.

Recognizing that there are many people who still eat, and want to eat, rice and potatoes so he believed that conducting a study that is more ''real world," was a logical next step, he says. The message is that just a bit of effort pays off.1

And when people make even a small change like adding a little lentil to rice or potato, says Ramdath, over time ''this has the potential of affecting long-term glycemic control very favorably." Because high blood sugar and diabetes also raise heart disease risk, this cooking trick also has the potential for reducing the risk of heart disease in the long-term, he says.

People found the swap [of some lentils in place of half the preferred starch] pleasantly palatable, Dr. Ramdath says. No one dropped out, and "nobody said, 'Oh this is too much,''' he says.

The data will contribute to evidence supporting the legitimacy of a health claim in favor of blood sugar control for pulses, Dr. Ramdath says. Having such a health claim, he says, could make this very healthy food more top-of-mind and even boost its popularity in meal planning. Currently, only about 13% or fewer people in North America eat pulses regularly.1

Beans are Better than You Know, or Knew

Americans should find their bean mojo, some experts say.

"In America, bean consumption is low compared to the rest of the world," says Dr. Freeman. He hopes that will change as the nutritional benefits and health advantages become better known. And the fact that pulses “are cheap, and can replace many unhealthy choices,” should make them more appealing.  That and they have the potential to reduce serum cholesterol, blood glucose, and other cardiovascular risk factors, so what’s not to like!

He applauds the ''real world'' design of the study. "I would not get rid of the potato," he says. It has a lot of nutrients, he adds. It might be better to pick sweet potato over white. The same for the rice—but brown over white, he says.

From a nutritional standpoint
Lentils have a dual benefit: they provide an excellent source of plant-based protein (25% of a day’s needs), and dietary fiber (16 grams per cup). In addition to protein and fiber, lentils are nutrient dense, offering a good source of magnesium, calcium, potassium, zinc, iron, and phosphorus.

Since time is always an issue when planning a meal, of all the pulses, lentils Don’t need to be soaked overnight and cook more quickly than any of the other pulses.

A word of caution for anyone with gout or kidney problems: go easy on lentils since they contain purine, which breaks down to uric acid, which might aggravate these conditions. While you don’t have to avoid them entirely, just go easy and plan to have them in place of red meat, which is best avoided if you have gout or comprised kidney function.

Dr. Freeman agrees that long-term, such a swap [adding cooked lentils to rice or potatoes] will help promote heart health in addition to helping improve blood sugar control.

The study was supported by both the Canadian government and the pulse industry, with independent scientists conducting the research.

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