Carbohydrates act as a readily accessible energy source for the body and are available in various forms, ranging from simple sugars to complex starches, and fibers. These forms can be strategically integrated into nutrition plans to achieve specific goals related to such things as body composition, athletic performance, and overall health. Although carbohydrates are not an essential macronutrient for survival, when it comes to optimizing overall health, enjoyment of food, and athletic endeavors, carbohydrates become a necessary nutrient.

Essentially, carbohydrates function as an energy source for the body. When consumed, they are either rapidly utilized to support vital physiological processes and fuel physical activity, or stored for later use. Excessive glucose in the body is stored as glycogen, which has two forms: liver glycogen and muscle glycogen. Liver glycogen is used for regulating blood sugar when glucose is depleted, while muscle glycogen is utilized for higher intensity work.

If the body's glycogen storage capacity is exceeded, a process called lipogenesis occurs. This process converts excess glucose, which isn't immediately required for energy, into fat. With this in mind, we can understand the rationale behind the old saying of "earn your carbs." During lipogenesis, glucose is transformed into fatty acids and glycerol, which combine to form triglycerides — a type of fat. These triglycerides are stored in fat cells and can be accessed as an energy source when needed, ensuring a consistent energy supply for the body.

The Process of Lipogenesis

The process of sugar (glucose) being converted into fat (triglycerides) for storage in the body is known as lipogenesis. Here's an overview of the steps involved in this process: 

1. Blood glucose levels rise: When you consume carbohydrates, they are broken down into glucose during digestion. This glucose enters the bloodstream and causes blood glucose levels to rise. 

2. Insulin release: In response to elevated blood glucose levels, the pancreas releases insulin, a hormone that signals cells to take in glucose for energy or storage. 

3. Glucose uptake: Muscle and liver cells take up glucose from the blood. Some of this glucose is used for immediate energy needs, while the rest is stored as glycogen. 

4. Glycogen storage limit: The liver and muscles have a limited capacity for glycogen storage. Once these storage sites are full, the body needs to find another way to store excess glucose. 

5. Lipogenesis: When glycogen stores are at capacity, the liver converts excess glucose into fatty acids through a process called de novo lipogenesis. These fatty acids are then combined with glycerol to form triglycerides. 

6. Fat storage: Triglycerides are transported by lipoproteins in the blood and stored in adipose tissue (fat cells) for future energy needs. 

It is important to note that de novo lipogenesis occurs when there is a significant caloric surplus, and carbohydrate intake exceeds the body's energy needs. Balancing caloric intake with energy expenditure is crucial for maintaining a healthy body weight and preventing excessive fat storage.

Structure

Carbohydrates are made from chains of sugar molecules that vary in length and complexity. They are broadly classified as either a Simple carbohydrate, coming in the form of sugars such as glucose, fructose, lactose, and sucrose, or a Complex carbohydrate, in the form of starches or fibers. Simple carbohydrates consist of shorter chains of one or two sugar molecules, while complex carbohydrates consist of longer chains, which can contain hundreds or even thousands of sugar molecules. Overall, the composition and structure of carbohydrates determine how they are digested, absorbed, and ultimately metabolized by the body.

Simple carbohydrates, also known as simple sugars, are comprised of short chains of sugar molecules that provide a quick source of energy for the body. These carbohydrates can be categorized into two main groups: Monosaccharides and Disaccharides.

Monosaccharides are the simplest form of carbohydrates, consisting of single sugar units such as glucose, fructose and galactose. These sugars can be directly absorbed into the bloodstream without any further breakdown.

• Glucose is the primary sources of energy for cells and is found in various fruits, vegetables, and grains.
• Fructose, commonly referred to as fruit sugar, is found in fruits, some vegetables, and honey.
• Galactose, a component of lactose, is mainly found in milk and dairy products.

Once these monosaccharides are absorbed, they are metabolized differently. Glucose is transported to cells with the help of insulin to be used for energy if needed, while fructose and galactose must be metabolized by the liver before they can be utilized.

Disaccharides consist of two monosaccharides sugar units linked together, with the main types being sucrose, lactose, and maltose.

• Sucrose, or table sugar, is formed by combining a glucose molecule with a fructose molecule and is commonly found in sugar cane, sugar beets, and maple syrup.
• Lactose, also known as milk sugar, is composed of a glucose molecule and a galactose molecule, and is primarily found in milk and dairy products.
• Maltose, or malt sugar, is formed by the bonding of two glucose molecules and is commonly found in grains and malted beverages.

Disaccharides must be broken down into their constituent monosaccharides before they can be absorbed and utilized by the body. This process begins in the mouth with amylase, an enzyme produced to breakdown sugars, and continues in the small intestine, where more specialized enzymes break down the disaccharides into monosaccharides, which are then absorbed into the bloodstream and metabolized as described above.

The differences in metabolism between monosaccharides and disaccharides can affect how quickly they raise blood sugar levels. Monosaccharides, particularly, glucose, can cause rapid increases in blood sugar, while the breakdown of disaccharides takes longer, resulting in a more gradual rise in blood sugar. However, it is safe to assume that both types of simple carbohydrates can lead to blood sugar spikes, especially for individuals with conditions of metabolic dysfunction such as diabetes or insulin resistance.

Complex carbohydrates, made of a large number of sugar molecules (monosaccharides) strung together in long chains, are also known as polysaccharides ("poly" meaning many). Due to their length and complexity, polysaccharides take longer to digest compared to simple carbohydrates, which are quickly broken down and absorbed. As a result, complex carbohydrates provide a more sustained source of energy for the body and are generally referred to as either Starches or Fibers.

Starches, which are predominantly found in plants, consist of long chains of sugar molecules. The intricacy and composition of these chains hinge on the balance of their two primary components: Amylose and Amylopectin.

• Amylose is a straight chain of sugar molecules, causing it to have more surface area overall, making it harder for the body to break down and digest. This mean it releases energy more slowly, which has a beneficial impact on blood sugar and satiety levels.
• Amylopectin, on the other hand, has a branched structure — like a tree — with many sugar molecules connected in a more complex way. It is easier for the body to break down and digest, meaning it releases energy more quickly, causing faster increases in blood sugar than that of amylose.

Typically, starch is made up of 20–30% amylose and 70–80% amylopectin, and it is this combination that determines the overall structure and complexity. The ratio of amylose to amylopectin can affect the physical properties of starch, such as its texture and digestibility. For example, amylose is less soluble in water and is more resistant to digestion than amylopectin, which can impact the glycemic response of the food.

Fiber, a plant-based compound, varies in structure and composition depending on its type and source. It is primarily composed of long chains of non-starch polysaccharides and other indigestible carbohydrates such as cellulose, hemicellulose, pectin, and lignin. These components are linked together in a way that makes them resistant to human digestive enzymes, allowing fiber to pass through the digestive system largely undigested. Fiber can be classified into two main categories: Soluble and Insoluble.

• Soluble Fiber, composed of glucose molecules like pectin, absorbs water to form a viscous, gel-like substance in the gut, which slows the movement of materials through the digestive system. As bacteria in the colon ferment soluble fiber, it produces beneficial fats called Short-Chain Fatty Acids (SCFAs). These SCFAs offer numerous health benefits, such as supporting gut and brain health, regulating blood sugar and cholesterol levels, reducing inflammation, and promoting weight management and immune system balance.
  • Sources include: Oatmeal, Oat Cereal, Lentils, Apples, Oranges, Pears, Oat Bran, Strawberries, Nuts, Flaxseeds, Beans, Dried Peas, Blueberries, Psyllium, Cucumbers, and Carrots 
• Insoluble Fiber consists of non-glucose polysaccharides like cellulose, which do not absorb water and remain undigested—picture the stringy parts in celery. This type of fiber works to accelerate the movement of material through the digestive system, while also adding bulk to our stool. These properties are helpful for promoting regular bowel movements and managing constipation.
  • Sources include: Whole Wheat, Whole Grains, Wheat Bran, Corn Bran, Seeds, Nuts, Barley, Couscous, Brown Rice, Bulgur, Zucchini, Celery, Broccoli, Cabbage, Onions, Tomatoes, Carrots, Cucumbers, Green Beans, Dark Leafy Vegetables, Fruit and Root Vegetables Skins 

What is the best type of fiber to recommend for overall health and body composition?

When considering the optimal type of fiber for overall health and body recomposition, it appears that a balanced intake of both soluble and insoluble fiber is most beneficial.

In a study from the book Nondigestible Carbohydrates and Digestive Health, it was observed that a long-term intake of insoluble fiber resulted in lower liver fat levels and improved fat metabolism. However, soluble fiber displayed benefits in promoting healthy gut bacteria, a marker of efficient metabolism. Furthermore, in a meta-analysis led by Jovanovski and colleagues, supplementation with soluble fiber within an unrestricted diet showed a reduction in body weight and waist circumference.

Soluble fiber is known to feed gut bacteria and assist in lowering cholesterol, while insoluble fiber helps suppress hunger post-meal, supports healthy digestion of fats, and aids in the absorption of essential fatty acids and fat-soluble vitamins. Regardless of the fiber type, higher fiber intake overall, from both soluble and insoluble sources, has been associated with greater weight loss and dietary adherence, independent of overall macronutrient and caloric intake. Thus, incorporating both soluble and insoluble fiber into your diet appears to be the optimal strategy for health and body recomposition.

Function

Carbohydrates play several important roles in the body, including:

• Energy Production: Carbohydrates serve as the most readily accessible fuel source for anaerobic metabolism, providing quick energy during high-intensity activities that require short bursts of power. This is particularly important for athletes and individuals engaging in rigorous exercise.
• Blood Sugar Regulation: Consuming carbohydrates helps to maintain blood sugar levels within a healthy range, as they are broken down into glucose and absorbed into the bloodstream. Complex carbohydrates, such as those found in whole grains and vegetables, are absorbed more slowly, providing a steady supply of energy and preventing large fluctuations in blood sugar levels.
• Prebiotic "food" for Gastrointestinal (GI) Bacteria: Some types of carbohydrates, particularly certain fibers, act as prebiotics, providing nourishment for the beneficial bacteria residing in the gut. This helps to maintain a healthy balance of gut bacteria, which can support overall digestive health and immune function.
• Substrate for GI Mucosa Lining: Carbohydrates, particularly short-chain fatty acids produced during the fermentation of dietary fiber, serve as an essential energy source for the cells lining the gastrointestinal tract. This helps to maintain the integrity of the GI lining, protecting it from damage and supporting its function in nutrient absorption.
• Backbone of ATP & RNA: Carbohydrates, specifically ribose, a sugar molecule, form the backbone of adenosine triphosphate (ATP), the primary energy carrier in cells, and ribonucleic acid (RNA), which plays a crucial role in protein synthesis and various cellular processes.
• Facilitating Cell-to-Cell Communication: Carbohydrates are linked to proteins and lipids to form glycoproteins and glycolipids, respectively. These molecules are important for allowing cells to communicate with each other, recognize one another, and help control the body's immune system.
• Supporting GI Motility and Toxin Conjugation: Dietary fiber helps to promote gastrointestinal motility by adding bulk to stool and promoting regular bowel movements. Fiber also assists in toxin elimination, binding to potentially harmful substances and facilitating their removal from the body.
• Anticatabolic: Carbohydrates play a crucial role in preventing muscle breakdown, also known as their protein-sparing effect. When consumed in sufficient amounts throughout the day, carbohydrates provide the body with an easily accessible energy source in the form of glucose. This ensures that the body has enough fuel to perform various activities and functions without needing to break down muscle tissue for energy.

Role in Muscle Building: Carbohydrates primarily support muscle growth by providing energy for high-intensity efforts, such as resistance training. They are broken down into glucose to fuel muscle contractions and help maintain blood sugar levels. Carbohydrate intake influences glycogen — the storage form of glucose — levels in muscles, with the body converting them into glucose for energy during physical activity. Replenishing glycogen stores also contributes to increased muscle volume through a mechanism called sarcoplasmic hypertrophy. Each gram of glycogen stored in muscle draws in approximately 3-4 grams of water, enhancing muscle volume and creating a fuller appearance. Ultimately, carbohydrate intake influences the body's ability to perform, or store energy for physical activity.

Resistance training, especially at moderate to high intensities, relies heavily on carbohydrate availability in the form of glucose to fuel the working muscles. Bodybuilders and athletes who engage in high-volume, high-effort workouts can experience muscle glycogen depletion by as much as 24-40 percent. This significant reduction emphasizes the importance of consuming adequate carbohydrates to support optimal performance and recovery in those who wish to perform at a high level of effort. It further emphasizes the need to maintain adequate carbohydrate intake in order to sustain desired training performance or volume, reinforcing the concept of "earn your carbs."

Conversely, for the general population, typical resistance training sessions will likely not deplete glycogen stores to anywhere near the same extent as in bodybuilders or athletes. Nonetheless, when aiming for muscle gain, it's essential to maintain a minimum carbohydrate intake to provide sufficient energy for intense workouts, preventing the body from resorting to gluconeogenesis.

Pre / Intra Workout

Carbohydrate intake immediately prior to resistance training has the potential to enhance work output, but research in this area has yielded mixed results. Performance-enhancing effects were observed only in training sessions lasting 50 minutes or longer, while most studies found no impact on performance in sessions lasting 40 minutes or less. This highlights the complexity of determining the ideal carbohydrate intake strategy for different training scenarios.

The optimal amount of carbohydrates to consume pre-workout for maximizing resistance training performance varies based on individual circumstances, and can range from being a non-issue to a significant consideration, depending on total daily carbohydrate intake and the intensity and duration of the training session. For those seeking a cautious approach, training within two hours after a moderate mixed-macronutrient meal containing 0.23-0.45 g/lbs of carbohydrates is a range suitable for most individuals.

The benefit of carbohydrate intake during exercise largely depends on glycogen availability throughout the training session. A hypothetical resistance training scenario that would benefit from intra-workout carbohydrate ingestion is a lengthy, high-volume session performed immediately after an overnight fast, without a pre-workout meal containing carbohydrates. In this case, carbohydrates ingested during training would provide fuel for muscle contractions throughout the workout. However, this applies to a limited segment of the training population. As a result, carbohydrate intake during resistance training, following a meal with carbohydrates, offers minimal to no benefits for maximizing muscle growth. This suggests that for most individuals, focusing on overall nutrition and training strategies may be more beneficial than emphasizing carbohydrate timing.

Post Workout

Post-exercise carbohydrate intake is often promoted for its anti-catabolic effects, as it raises insulin levels. However, evidence suggests that muscle protein synthesis (MPS) plays a more significant role in muscle growth than the suppression of muscle protein breakdown (MPB). Morton and colleagues found that in healthy individuals, changes in MPS are 4-5 times greater than MPB in response to exercise and feeding, meaning that the effect of carbohydrate intake pales in comparison to stimulating the muscle through resistance training along with consumption of adequate protein. Supporting this notion, Glynn and colleagues compared the post-exercise anabolic response using 20 grams of essential amino acids (EAAs) plus 30 grams of carbohydrates, versus 20 grams of EAAs plus 90 grams of carbohydrates. The study observed only minor changes in MPB, indicating that MPS is the primary driver of anabolism, independent of carbohydrate dose or insulin load.

Reinforcing these findings, Hulmi and colleagues conducted a study that found no difference in muscle size and strength gains between subjects consuming 30 grams of protein post-exercise and those co-ingesting protein with 34.5 grams of maltodextrin, a polysaccharide, while participating in a progressive resistance training program. This evidence underscores the importance of MPS in muscle growth and suggests that post-exercise carbohydrate intake may not be as crucial as previously thought.

Intake

Carbohydrates are a consistently newsworthy topic, often singled out as the prime culprit for weight gain. However, a one-size-fits all approach to dieting, such as universally prescribing a low-carb diet, may not serve the best interests of every individual on their weight loss journey.  Contrary to popular belief, there is no magic threshold of carbohydrate intake below which body composition is optimized. The International Society of Sports Nutrition underscores this in their position statement: "No controlled, inpatient isocaloric diet comparison, where protein is matched between groups, has reported a clinically meaningful fat loss or thermic advantage to the lower carb or ketogenic diet."

In fact, a wide array of dietary approaches, ranging from low-carb/high-fat to high-carb/low-fat, and everything in between, can be similarly effective for improving body composition. This diversity provides ample flexibility when designing personalized nutritional programs and meal plans.

The primary factor determining the level of carbohydrate intake is an individual's ability to adhere to the diet plan. In a meta-analysis conducted by Huntriss and colleagues, it was discovered that a very-low carbohydrate diet (less than 50 grams per day) was more challenging to maintain compared to a moderately low-carbohydrate diet (less than 130 grams per day). A similar conclusion was reached in another meta-analysis by Goldenberg and colleagues. They found that low-carbohydrate diets (less than 130 grams per day) outperformed very-low-carbohydrate/ketogenic diets (less than 10 percent of total calories from carbohydrates) in terms of weight loss at the six-month mark. However, this difference disappeared among subjects who strictly adhered to the ketogenic diet. This suggests that while ketogenic diets may not be as sustainable in the long-term compared to less restrictive low-carbohydrate diets, achieving weight loss goals is heavily influenced by individual preferences and adherence levels.

Fat loss can be achieved at any level of carbohydrate intake, so long as a net caloric deficit is consistently maintained over time. While carbohydrate restriction can indeed be a potent catalyst for weight loss in certain individuals, it is crucial to understand the potential and detrimental effects of excessive restriction on muscle gain. Inadequate carbohydrate consumption can jeopardize both muscle gain and maintenance. Consequently, the optimal level of carbohydrate restriction is one that an individual can adhere to over the long-term, which is dependent largely on by personal preferences, tolerances, and goals.

And, let's not forget about fiber as it has been associated with promoting weight loss and improved dietary adherence, independent of overall macronutrient and caloric intake. The general dietary guidelines suggest an intake of 14 grams per 1000 calories for both children and adults. This aligns well with current scientific research showing that at least 25 to 29 grams can help reduce various health issues, including heart disease, stroke, type 2 diabetes, and colorectal cancer.

Carbohydrate Dosing Cheatsheet

• Low Carbohydrate: 0.25 to 0.5 g/lbs per day
• Moderate Carbohydrate: 0.50 to 0.75 g/lbs per day
• High Carbohydrate: 0.75 to 1 g/lbs per day