Barley for Food and Health: Science, Technology, and Products

184 HEALTH BENEFITS OF BARLEY FOODS
GLYCEMIC RESPONSE TO CARBOHYDRATE CONSUMPTION
The worldwide incidence of diabetes is increasing rapidly, as well as a related
condition called the metabolic syndrome (CDC 2007). Both of these conditions
are related to carbohydrate metabolism, in which food carbohydrates are digested
into glucose and absorbed as such into the bloodstream. This action stimulates
the release of insulin from the pancreas into the blood, facilitating the entry of
glucose into body cells. In diabetes, there is either an absence of insulin (type 1)
or inefficient use of insulin (type 2) by the cells, causing glucose to build up in
the blood, thereby creating serious complications if treatment is not provided. In
the condition known as the metabolic syndrome, the body cells do not respond
normally to insulin, resulting in elevated insulin as well as elevated glucose in
the blood. This relative insulin resistance initiates further complications, such as
abdominal obesity, hypertension, and elevated blood triglycerides.
Carbohydrate foods differ in their rate of digestion and absorption into the
blood, and these differences were the basis of establishing the glycemic index (GI)
(Brand-Miller 1994). Food carbohydrates, especially starch, that have slower rates
of digestion, are sometimes termed “lente” or slowly digested and absorbed carbohydrates.
In general, foods with a high GI value are processed rapidly in the digestive
tract, causing a steep high peak in blood glucose, and in normal individuals are followed
by a corresponding rapid release of insulin. Low-GI foods, on the other hand,
have slower absorption with a blunted, lower, and more prolonged glucose peak.
The AACC addressed the need for consistent information about glycemic response
by developing standard definitions of terms (Jones 2007) that could enable food
manufacturers to communicate the glycemic effect of foods to consumers.
The stomach-emptying rate is a major factor in the delivery of glucose into
the small intestine for absorption (Horowitz et al. 1993). Fat and protein tend
to delay gastric emptying, and some studies have concluded that the GI of individual
foods may not accurately predict the glycemic and insulinemic effect of
mixed-nutrient meals as foods are normally eaten. Wolever et al. (2006) demonstrated
that when foods were tested in meal-type settings, the GI can reliably
predict the glycemic effect of mixed meals, regardless of protein or fat content.
In their study, the carbohydrate content and GI determined 90% of the variation
observed in mean glycemic response to the mixed meals. Other food functional
properties affecting the digestion and absorption of carbohydrates include the
amount and type of fiber, food structure, physical texture, hydration of starch,
and starch type (Björck et al. 1994; Björck and Elmståhl 2003; Huth et al. 2000).
Foods being tested for glycemic responses are conducted on subjects in the fasting
state. Measured quantities of test foods are consumed, after which blood
samples are measured for glucose and insulin concentrations at timed intervals
after eating. The glucose and insulin blood concentration plots over time are
calculated into areas under the curve (AUC) and the time to reach peak concentrations.
Graphs with superimposed curves of different products are often an
effective visual comparison of responses to the foods.
The method of measuring the GI is time consuming and expensive, with unaccountable
variability in repeated testing and between individuals. Some critics