Millet GI Score Influenced by Particle Size

By Robby Gardner, Associate Editor

Like all food items, cereal grains cause peaks in blood sugar. But each grain is different. The extent of a blood sugar rise is measured by a food item’s glycemic index, and it turns out that the glycemic index of finger millet is actually dependent on the way the ingredient is milled.

Finger millet is a staple grain in many parts of Asia and Africa, and it’s even picking up interest in United States in its whole bead-like form and as milled flour. The ingredient is rich in fiber, which makes it potentially appealing to type 2 diabetics, but “low glycemic index” is a strong selling point for this consumer group. Manufacturers would thus be keen to know how to lower the glycemic index of finger millet.

In a trial on roti and pittu variety millet, Sri Lankan researchers assigned 11 volunteers to eat 50 carbohydrates worth of each millet in crossover fashion, either as stone-ground flour or industrially milled flour. Blood glucose was monitored in volunteers up until two hours after millet consumption.

Roti millet yielded a glycemic index of 44±5 when stone ground and 59±7 when industrially milled. Pittu millet scored 67±5 when stone ground and 79±5 when industrially milled. The pattern indicates that a larger particle size, resulting from stone grinding, lowers the glycemic index of millet.

“The large particle size of flour makes the starch gelatinization relatively difficult and thus slows the enzyme attack, resulting in slow release of glucose from food, which prevents high peaks in post-prandial blood glucose levels,” explain the researchers. “This causes a significant decrease in the glycemic response, the peaking and glycemic indices of pittu and roti made using stone ground flour.”

Although finger millet is a whole grain that is high in fiber and various other nutrients, the researchers say previous studies have not shown low glycemic index values for finger millet. The processing method used in those studies now appears to be the reason why.