Carbohydrates

Carbohydrates

The primary fuel source for muscle contraction.

Monosaccharides

Simple sugars consisting of single molecules, such as Glucose, Fructose, and Galactose. They supply energy, are absorbed into the bloodstream, and are converted to glucose in the liver.

Disaccharides

Carbohydrates formed from two monosaccharide molecules, such as Sucrose, Lactose, and Maltose.

Polysaccharides

Complex carbohydrates made up of many monosaccharide units, including Starch (digestible), Fiber (indigestible), and Glycogen (storage in animals).

Starch

A polysaccharide composed of glucose polymers, found in two main structures: Amylose (long, unbranched chains of glucose linked by alpha-1,4 glycosidic bonds) and Amylopectin (branched structure with alpha-1,4 and alpha-1,6 glycosidic bonds).

Fiber

A polysaccharide composed of glucose linked by beta-1,4 glycosidic bonds, making it resistant to digestion.

Recommended Dietary Allowance (RDA) for Fiber (Males)

38 \text{ g/day}

Recommended Dietary Allowance (RDA) for Fiber (Females)

25 \text{ g/day}

Carbohydrate Classification by Oxidation Rate (Faster)

Carbohydrates like Glucose, Maltose, and Amylopectin, with an approximate oxidation rate of 1.0 \text{ g/min } (60 \text{ g/h}), indicating fast digestion and quick energy utilization.

Carbohydrate Classification by Oxidation Rate (Slower)

Carbohydrates like Fructose, Galactose, and Amylose, with an approximate oxidation rate of 0.6 \text{ g/min } (35 \text{ g/h}), indicating slow digestion.

Glucose and Galactose in Exercise

These monosaccharides can be efficiently utilized during exercise due to their faster oxidation rates.

Fructose in Exercise

Can lead to gastrointestinal distress due to incomplete absorption when consumed during exercise, despite being a slower carbohydrate.

Digestion of Carbohydrates

Carbohydrates are broken down into monosaccharides (glucose, galactose, fructose) in the gastrointestinal (GI) tract by enzymes such as lactase, sucrase, and maltase.

Absorption of Glucose and Galactose

Absorbed in the small intestine via the Sodium-glucose transporter 1 (SGLT1).

Absorption of Fructose

Transported in the small intestine via GLUT5.

Glycogen

The storage form of glucose in the liver and muscle, playing a critical role in energy metabolism.

Glucose phosphorylation in muscle/liver

Glucose enters cells via facilitated transport and is phosphorylated by hexokinase to glucose-6-phosphate, preventing its exit, except in the liver/kidney where glucose-6-phosphatase can reverse this.

Muscle Glycogen in Athletes

Trained athletes maintain higher glycogen stores compared to untrained individuals, which helps maintain race pace in endurance events.

Insulin

A hormone responsible for maintaining blood glucose homeostasis by promoting glucose uptake and storage in cells.

Glucagon

A hormone responsible for maintaining blood glucose homeostasis by increasing glucose release into the blood.

Glycemic Index (GI)

A ranking system that indicates how carbohydrates affect blood glucose and insulin levels.

High GI Foods

Foods with a GI of 70 and above (e.g., white bread, rice) that rapidly increase blood glucose.

Medium GI Foods

Foods with a GI between 56 and 69 (e.g., sponge cake, whole wheat bread) that produce a moderate blood glucose response.

Low GI Foods

Foods with a GI of 55 and under (e.g., apples, beans) that produce a slow and sustained blood glucose response.

Carbohydrate Recommendation for Skill-based Training

3-5 \text{ g/kg/day}

Carbohydrate Recommendation for Moderate to High-Intensity Training

5-7 \text{ g/kg/day}

Carbohydrate Recommendation for High-Volume Endurance Training

6-10 \text{ g/kg/day}

Carbohydrate Recommendation for Extreme Endurance Training

8-12 \text{ g/kg/day}

Carbohydrate Recommendation for Low-Intensity Activities

3-5 \text{ g/kg} (e.g., Curling, Golf)

Carbohydrate Recommendation for High-Intensity Short-Duration Activities

5-7 \text{ g/kg} (e.g., Sprints, Weight Lifting)

Carbohydrate Recommendation for High-Intensity Long-Duration Activities

6-10 \text{ g/kg} (e.g., Marathon running, Triathlons)

Carbohydrate Loading

A strategy to super-saturate glycogen stores, enhancing endurance performance by approximately 20% in events over 90 minutes.

Post-exercise Carbohydrate Intake

Crucial for replenishing glycogen stores, with a recommended intake of 1.2 \text{ g/kg/hr} for up to 4 hours post-exercise.

Factors Enhancing Glycogen Synthesis

Timing of carbohydrate intake (maximized within 2 hours post-exercise), type of carbohydrate (high-glycemic index foods), ingestion of protein, and presence of caffeine.

Training in a Glycogen-Depleted State

Can elevate fat oxidation rates and mitochondrial function, but may impair exercise intensity.

FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols)

Certain carbohydrates that can induce gastrointestinal distress, found in high lactose products, apples, and some nuts.

Gluten-Free Diet for Athletes

Has no substantial benefits for non-Celiac athletes unless they have specific sensitivities.