Introduction

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From sugary candy bars to whole grain cereals, carbohydrates can be seen in many of the food products we consume. With this being said their influence in the body differs which is determined by glycemic index (GI). Glycemic index is the rate at which ingested carbohydrates raises blood sugar and its accompanying effect on insulin release. The GI for a food is determined when the particular food is consumed by itself on an empty stomach. As seen in Table 2, foods lower on the glycemic index are good sources of complex carbohydrates, fiber and overall nutritional value. In comparison, simple carbohydrates are on the higher end of the glycemic index and contain sugars causing a spike in blood glucose levels.

Through the processes of digestion and absorption, all disaccharides and polysaccharides are ultimately converted into simple sugars such as glucose or fructose. However, fructose must be converted to glucose in the liver before it can be used for energy. Simple carbohydrates are able to convert to glucose faster than complex carbohydrates causing higher levels of blood glucose. Some of the glucose (or blood sugar) is used as fuel by tissues of the brain, nervous system, and muscles. Because humans are periodic eaters, a small portion of the glucose is converted to glycogen after a meal and stored within the liver and muscles. Any excess is converted to fat and stored throughout the body as a reserve source of energy. When total caloric intake exceeds output, any excess carbohydrate, dietary fat, or protein may be stored as body fat until energy expenditure once again exceeds energy input.

Role of Fiber in Health

One of the greatest contributions made by dietary complex (lower GI) carbohydrate is fiber. Higher intakes of dietary fiber are associated with lower incidence of heart disease and certain types of cancer (2,3). Fiber is an indigestible carbohydrate. There are two types of dietary fiber, soluble and insoluble. Soluble fiber is dissolved by water and forms a gel-like substance in the digestive tract. Soluble fiber has many benefits, including moderating blood glucose levels and lowering cholesterol. Good sources of soluble fiber include oats and oatmeal, legumes (peas, beans, lentils), barley, and many uncooked fruits and vegetables (especially oranges, apples, and carrots).

Insoluble fiber does not absorb or dissolve in water. It passes through the digestive tract close to its original form. Insoluble fiber offers many benefits to intestinal health, including a reduction in the risk and occurrence of colorectal cancer, hemorrhoids, and constipation. Most of insoluble fibers come from the bran layers of cereal grains. The recommended intake of fiber is set at 38 grams/day and 25 grams/day for young men and women, respectively (4). Additionally, fiber provides bulk and delays stomach emptying in diet thus increasing the feeling fullness (3-9). The feeling of fullness can result in fewer calories consumed aiding in weight loss or the prevention of excessive weight gain.

Using the Glycemic Index

The Glycemic index can be a useful tool when tracking blood sugar. It can aid in making healthful choices to lower GI foods in those concerned about elevated blood sugar levels. Diets emphasizing lower glycemic index foods decrease the risk of type II diabetes, heart disease and colorectal cancer (10). This practical tool answers many of the questions regarding carbohydrate intake.

Carbohydrate-Intake Recommendations

A diet containing between 6 and 10 g/kg per day of carbohydrate (2.7 to 4.5 g/lb), is recommended (11). According to the Institute of Medicine, the Acceptable Macronutrient Distribution Range for carbohydrate intake for an adult is 45% to 65% of total caloric intake (12). Complex carbohydrates (such as whole grains and fresh fruits and vegetables) should constitute the majority of calories because of their nutrient-dense (providing B vitamins, iron, and fiber) nature.

Carbohydrate and Weight Gain: The Facts

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A significant amount of time, energy, and resources is spent investigating the link between carbohydrate intake and the increased prevalence of obesity in Americans. The accusations are familiar: “carbohydrates make you fat,” and “Americans are getting fatter, despite lower fat intakes.” Data available from the Third National Health and Nutrition Examination Survey (NHANES III), which summarizes Americans’ nutrition patterns for the years 1988 through 1991, show that percentage of calories consumed from fat has dropped, from 36% (NHANES II 1976–1980) to 34% of total energy intake (13). However, when total fat intake (grams per person per day) is measured, and not simply the percentage contributed, the data shows that fat intake has remained quite constant for the past several years (14). Additionally, this data may not accurately reflect fat consumption in America, as many people underreport fat consumption owing to its negative health connotations. The data from NHANES III also shows an increase in total energy intake supporting the relationship of excessive energy intake leading to increased fat stores. When reviewing the data on Americans’ food intake, it is interesting to note that in the early 1900s, the percentage of carbohydrates consumed as energy intake was higher and consumption of fat was lower than it is today, without the prevalence of obesity. Only during the last two decades has there been a significant increase in obesity. The data supports two primary variables responsible for this dramatic rise in obesity: an increased energy intake and a reduction in energy expenditure. It is estimated that more than 75% of the American adult population do not partake, in a daily basis of 30 minutes of low-to-moderate physical activity. Currently, total fat intake is higher, carbohydrate is lower, and obesity has reached epidemic proportions. In addition, energy intake has increased and energy expenditure has decreased. The facts are very clear: America’s increasing problem of obesity is not a direct result of carbohydrate intake, but rather of energy imbalance.

Conclusion

Carbohydrates play an important role in providing us with energy for our daily routines and picking the right carbohydrate sources can be significant in one’s health. The glycemic index provides rationale in an easy and understandable method but it can’t be used as a sole determinant when making carbohydrate choices. Understanding intake recommendations and choosing carbohydrate sources rich with nutrients can make a substantial difference in one’s health. Simply neglecting carbohydrates from dieting isn’t the most pragmatic approach towards weight loss like thought in our culture. Basic knowledge of energy balance within the body will help towards knowing the importance of a balanced diet and that weight gain is correlated with greater food intake and a decrease in exercise. It is with these fundamentals that individuals will be able to make the right food choices and know how important of a role activity plays in achieving a healthier lifestyle.