Physiology, Carbohydrates

Issues of Concern

Carbohydrates are associated with dental caries. Eating large amounts of sugary foods is known to lead to plaque formation, tooth decay, and cavities. The worst carbohydrate for dental decay is sucrose. On the other hand, fructose serves as an energy source for oral cavity bacteria.[4][5][6]

Many people falsely believe that diets high in carbohydrates lead to the development of type 2 diabetes when, in fact, the opposite is true. Data show that the risk of developing type 2 diabetes is lowered as the amount of calories from carbohydrates is increased. Diets that are high in carbohydrates tend to increase the sensitivity of insulin. Thus, today, healthcare providers usually recommend that type 2 diabetics eat a high carbohydrate diet. An additional benefit of a high carbohydrate diet for type  2 diabetics is that it lowers the risk of heart disease.

Individuals who eat high fiber diets also tend to have low serum cholesterol and high HDL levels than people who consume a low fiber diet; the lowering of cholesterol also decreases the risk of heart disease. In many parts of Africa, people who eat high fiber diets tend to have a very low risk of intestinal cancer. But the exact amount of fiber to eat to prevent colon cancer remains unknown. Anecdotal reports maintain that eating fiber may lower blood pressure, lower the incidence of gallstones, and decrease blood sugar.

Cellular Level

Metabolism

Carbohydrate digestion begins in the mouth, where salivary amylase starts the breakdown. After breaking down throughout the digestive system, monosaccharides are absorbed into the bloodstream. As carbohydrates are consumed, the blood sugar levels increase, stimulating the pancreas to secrete insulin. Insulin signals the body’s cells to absorb glucose for energy or storage. If blood glucose falls, the pancreas makes glucagon, stimulating the liver to release stored glucose.

The body is not able to digest fiber, and therefore fiber does not provide calories or energy. It has a variety of health benefits, including bulking stool for easier excretion preventing constipation, prebiotic properties, satiety, and intestinal issues.

Function

Nutrition

Carbohydrates are an important part of a nutritional diet. The healthiest sources include complex carbohydrates because of their blunted effects on blood glucose. These options include unprocessed whole grains, vegetables, fruits, and legumes. While simple carbohydrates are acceptable in small amounts, white bread, sodas, pastries, and other highly processed foods are less nutritious and cause a sharp increase in blood glucose. Healthy adult diets should include 45% to 65% carbohydrates as part of the daily intake, equaling about 200 g to 300 g per day. Carbohydrates contain about 4 kcal/ gram (17 kJ/g). Fiber is an important carbohydrate as well. Healthy adults should consume about 30 g per day of fiber, as it is found to reduce the risk of coronary heart disease, strokes, and digestive issues.

A glycemic index is a tool used to track carbohydrates and their individual effects on blood sugar. This scale ranks carbohydrates from 0 to 100 based on how rapidly the rise in blood glucose occurs upon consumption. Low glycemic foods (55 or less) produce a gradual increase in blood sugar. These foods include steel-cut oatmeal, oat bran, muesli, sweet potatoes, peas, legumes, most fruits, and non-starchy vegetables. Medium glycemic foods (56 to 69) include quick oats, brown rice, and whole-wheat bread. High glycemic foods (70 to 100) increase the risk of type 2 diabetes, heart disease, obesity, and ovulatory infertility. These foods include white bread, cornflakes, white potatoes, pretzels, rice cakes, and popcorn.[7]

Clinical Significance

Two things that constantly affect the body include physical activity and diet. A diet needs to be nutritionally balanced, including the proper type and amount of carbohydrates. An increase or decrease in carbohydrates beyond the desired amount can affect both physiological and metabolic processes. An increase in simple carbohydrates may contribute to obesity, a disease that puts individuals at an even greater risk for further disorders such as cardiovascular disease. Carbohydrate intake also contributes to non-insulin-dependent diabetes (type 2 diabetes), a growing epidemic. However, foods rich in non-starch polysaccharides and low-glycemic foods protect against diabetes. Increased sugar consumption also contributes to the development of dental caries.[8][9]

Carbohydrate malabsorption can present with symptoms of constipation, diarrhea, flatulence, and abdominal pain. It may occur as a result of congenital or acquired defects in enzyme metabolism or intestinal mucosa. Celiac and Crohn's disease are examples of secondary malabsorption. Small intestinal bacterial overgrowth (SIBO) can occur as a result of gastric bypass or gastric dysmotility disorders (chronic diabetes, scleroderma), resulting in a compromise of the absorptive interface and severe malabsorption. On the other hand, lactose intolerance is a primary lactase deficiency. Lactase is the enzyme that breaks down lactose, a disaccharide, into monosaccharides glucose and galactose in the brush border of enterocytes. Lactase deficiency is the most common enzyme deficiency in the world.[10] The most frequently used method for diagnosing carbohydrate malabsorption is the hydrogen exhalation test. In incomplete absorption, undigested carbohydrates enter the colon, where hydrogen-gas-producing bacteria reside. The hydrogen gas (H2) level is measured on the first exhalation. Non-metabolized carbohydrates act as osmotic agents in the gastrointestinal tract, contributing to the symptoms of diarrhea and flatulence. Treatment of most carbohydrate malabsorption disorders includes avoidance of the associated mono- or disaccharide.[11][12]