15 Sep Is Glycemic Index a Major Player in Cardiovascular Disease?
Written by: Ibani Kapur
Medically reviewed by: Rob Philibert MD PhD
WHAT ARE CARBS?
Recently, you may have come across the term “macro” being used by people who wish to lose weight or eat well. But what exactly is a “macro”? The term “macro” is an abbreviation for the term “macronutrients.” There are three types of macros: Proteins, Carbohydrates (Carbs), and fats. Each of these macros is an essential part of the diet and is required in large amounts by our bodies. Macronutrients, whose energy content is often measured using “calories”, are the main sources of energy and mass for our bodies. In contrast, micronutrients, such as vitamins and minerals, are also required by the body. But the amount of micronutrients that are required is much smaller.
In casual conversation, the topic of carbs often evokes ambivalent comments. Given social pressures to maintain ideal body weight, questions like “Should I be consuming less carbs?”, “What kind of carbs are good for me?”, “Are carbs even healthy?” are commonly asked. When considering responses to these questions, it is important to remember that in moderation, the vast majority of carbs are actually helpful and supply the energy for the cells in your body. However, supplying glucose for energy is not the sole function of carbs. Carbs may be used in the synthesis of amino acids-the key constituents of proteins.
The effect of carbs on your body is often dependent on their composition. Carbs can be classified as complex or simple based on the number and organization of the sugar subunits in the structure of the carb. Simple carbs have only one or two sugar subunits. These simpler carbs are absorbed and metabolized quickly resulting in rapid blood sugar level spikes. In contrast, complex carbs are composed of a larger number of sugar units. These more complex carbs take longer amounts of time for the gut to digest and absorb. As a consequence, the resulting rise in blood sugar levels is much more gradual. Finally, the family of complex carbs also includes plant fibers that help maintain a healthy digestive system and cholesterol levels. Therefore, when it comes down to the choice of carbohydrates, the type of carb often matters more than quantity of carb.
GLYCEMIC INDEX (GI)
As noted above, secondary to differences in their chemical composition, the speed of absorption of each type of carbs in the small intestine varies. These differing rates of absorption can have a strong impact on the resulting sugar level and insulin response. In part, the Glycemic Index (GI) is a measure of the rate at which carbs are converted into glucose by the body. The GI can help predict the postprandial (or after eating) metabolic response. Initially, the GI was introduced as a tool for patients with Diabetes Mellitus to allow them to make food choices that would help control postprandial hyperglycemia. Foods with a GI above 70 are considered High-GI whereas those with a GI below 55 are considered Low-GI. However, other factors, such as the amount of food, also can influence the metabolic response which ultimately predicts serum glucose levels. Therefore, the Glycemic Load (GL) was introduced which is obtained by multiplying the GI of the food by the weight of carb (in grams). Both the GI/GL are useful in predicting cardiovascular and other health-related outcomes. Grains low in glycemic index, such as millets, are beneficial in controlling blood sugar and may reduce the incidence of cardiovascular disease. Lignan and fiber intake have also been reported to have a beneficial effect on heart health.
GLYCEMIC INDEX’S IMPACT ON MORTALITY AND HEART DISEASE RISK
Most of the prior literature on the relationship between the GI and cardiovascular risk have focused on subjects from Western countries with high incomes. But in a recent study by Jenkins and colleagues, examined the relationship between GI and cardiovascular outcomes using data from 137,851 participants between the ages of 35 and 70 years from different 4 high income, 11 middle income, and 5 low income countries. They found that a positive correlation was inferred between Glycemic Index and risk of cardiovascular disease and death. Similarly, other recently published studies of subjects with diabetes have demonstrated the effects of a low GI diet on Low Density Lipoprotein (LDL) cholesterol, body weight, and blood insulin levels.
The GI and GL are helpful concepts for understanding the relationship between carbs and our health. By being aware of the type of carbs that we consume, we can better control postprandial glucose levels. The goal should be to eat balanced meals which will help moderate variation in blood sugar levels and avoid the serum glucose spikes that are associated with adverse cardiovascular outcomes.