Sugars are carbohydrates, organic compounds made of carbon, hydrogen, and oxygen atoms. They serve as a primary energy source for living organisms. Carbohydrates range from simple units to complex chains, and understanding these forms helps clarify their biological functions.
Fundamental Sugar Categories
Sugars are classified by their molecular structure, based on the number of sugar units they contain. Monosaccharides are the simplest form, a single sugar molecule. Examples include glucose, the body’s main energy source, and fructose, often called “fruit sugar” due to its abundance in fruits, honey, and some vegetables. Galactose is another monosaccharide, found in milk as part of lactose.
Disaccharides form when two monosaccharide molecules link. Sucrose, or table sugar, is a disaccharide of glucose and fructose, found in sugarcane and sugar beets. Lactose, milk sugar, combines glucose and galactose. Maltose, or malt sugar, consists of two glucose units and is found in germinating barley grains.
Polysaccharides are complex carbohydrates with long chains of multiple sugar molecules. Starch is a polysaccharide used by plants for energy storage, found in foods like potatoes, grains, and legumes. Glycogen serves as the main energy reserve for animals, stored in muscles and the liver, and is composed of glucose chains. Cellulose is another polysaccharide, forming plant cell walls and providing structural support.
How Sugars Function in the Body
The body processes carbohydrates, including sugars, into usable energy. Digestion begins in the mouth with enzymes like salivary amylase, which starts breaking down starches. This continues in the stomach and small intestine, where carbohydrates are further broken down into simpler sugar units.
Once broken down, monosaccharides like glucose are absorbed into the bloodstream. Glucose is the body’s primary fuel source, utilized by cells throughout the body, including the brain, muscles, and organs, for immediate energy. Excess glucose can be stored in the liver and muscles as glycogen for later use.
The pancreas regulates blood sugar levels by producing insulin. When blood glucose levels rise after eating, insulin is released, signaling cells to absorb glucose from the bloodstream. This ensures cells receive a steady energy supply while maintaining balanced blood sugar levels.
Specialized Sugar Types and Their Effects
Sugar alcohols, such as xylitol and erythritol, are low-calorie sweeteners. Found naturally in small amounts in fruits and vegetables, they are often produced industrially for sugar-free products. These sweeteners provide sweetness with fewer calories than regular sugar and have a minimal impact on blood sugar levels because they are not fully absorbed by the small intestine. However, large quantities can lead to digestive discomfort like bloating, gas, or diarrhea, as they ferment in the large intestine.
Lactose intolerance occurs when individuals have insufficient lactase, an enzyme in the small intestine that breaks down lactose. Without enough lactase, undigested lactose moves into the colon, where bacteria ferment it. This leads to symptoms like abdominal cramps, bloating, gas, and diarrhea, appearing 30 minutes to two hours after consuming dairy. This condition is a digestive issue, distinct from a milk allergy, which involves an immune system response to milk proteins.
Dietary fiber, a non-digestible carbohydrate in plant-based foods, is a polysaccharide the human body cannot break down into sugar molecules. It passes through the digestive system largely intact, contributing to digestive health by promoting regular bowel movements and adding bulk to stool. Fiber also helps regulate blood sugar levels by slowing nutrient absorption and supports a healthy gut microbiome by acting as a prebiotic.