Classifications of Carbohydrates

Classification of Carbohydrates

• Monosaccharides: single sugar molecules, including glucose, fructose, and galactose
• Disaccharides: sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (2 glucose)
• Oligosaccharides: raffinose and stachyose
• Polysaccharides: starch (plant-based), glycogen (stored energy in muscles and liver), and cellulose (plant-based)

Carbohydrate Digestion and Absorption

• Amylase in saliva breaks down carbohydrates
• Lactase, maltase, and sucrase break down their respective disaccharides into monosaccharides
• Carbohydrates are broken down into monosaccharides before being absorbed into the bloodstream

Metabolism of Carbohydrates

• Excess glucose is converted to glycogen via glycogenesis, which requires energy and occurs in the liver or muscles
• When energy is needed, glycogen is broken down into glucose via glycogenolysis, producing lots of ATP

Blood Glucose Regulation

• High blood sugar promotes insulin to stimulate glucose uptake
• Low blood sugar promotes glucagon to stimulate glycogen breakdown to form glucose for energy

Choosing a Carbohydrate Source

• Nutrient density: the amount of nutrients per amount of food
• Glycemic index: measures how quickly a food raises blood sugar levels
• Glycemic load: takes into account the amount of carbohydrates consumed
• Fructose content: high fructose intake is associated with negative effects
• Fibre content: foods high in fibre are lower in GI and reduce the risk of negative effects

Glycemic Index Studies

• Low and high GI foods have similar outcomes when caloric intake is controlled
• Fibre is a significant confounder
• Baseline characteristics and variability in findings affect outcomes
• GI studies have limitations, including assessment on an empty stomach and variability in preparation and lifestyle

Fructose Metabolism

• Fructose has a different metabolic fate than glucose
• Fructose goes straight to the liver to be transformed to glucose via fructolysis
• Fructose has no negative feedback loop and can deplete energy stores
• Fructose is associated with increased blood pressure, type 2 diabetes, and obesity

Fructose Animal Studies

• High fructose intake leads to increased body weight, food intake, blood glucose, and decreased insulin
• Fructose intake is associated with increased uric acid and triglycerides

Fructose Survival Hypothesis

• Fructose turns on a survival switch to prepare for periods of starvation
• Increased fructose intake leads to increased blood pressure, eating, fat storage, insulin resistance, and low-grade inflammation

Fructose Human Studies

• High fructose intake increases visceral adiposity and leads to weight gain
• Fructose intake is associated with negative health effects, including increased blood pressure, type 2 diabetes, and obesity