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Digestion System

Digestion, Exercise and Bodybuilding

I wondered how I ate so much without exploding when I was younger. I mean, my stomach expanded when I ate, but it was back to its regular size after a while. I thought my stomach was a magic store, but it made no sense why it kept asking for more food no matter how much I put in.

I’ve since learned that the food I eat undergoes a process known as digestion to produce energy. However, digestion is complex and involves many steps to provide several benefits and ensure that the human body stays alive. Keep reading to learn all about the complexities and benefits of digestion. 

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What is digestion?

Digestion refers to the breakdown of large food molecules into smaller absorbable forms. Food contains all of the major nutrients needed for healthy living, including glucose, amino acids, fatty acid and glycerol, fibers and essential vitamins and minerals. However, all of these nutrients are locked within a complex matrix of food items like carbohydrates, proteins and fats.

Without these macromolecules breaking down, you will not get the desired nutrients locked within the food. Digestion is the process that breaks down these complexes to release the needed micromolecular nutrients that are easily absorbed into the bloodstream, taken up by cells and used for several cellular processes.

Digestion System

The Digestive System

The digestive system consists of the gastrointestinal tract (GIT), aided by the liver, pancreas and gall bladder. The GIT consists of interconnected hollow organs, including the mouth, esophagus, stomach, small intestine, large intestine, rectum and anus, which form a tube-like tract.

Every component organ of the digestive system works together to ensure that;

  • consumed food is properly broken down to release nutrients;
  • released nutrients are absorbed to be used by the body; and
  • Waste products are excreted.

Digestion begins in the mouth. Chewing food is the first step in digestion, breaking down large food particles into smaller, easily digestible ones. Saliva also mixes with food in the mouth and breaks down the particles into smaller ones. From the mouth, chewed food moves through the esophagus to the stomach via a process known as peristalsis.

In the stomach, food gets mixed with digestive enzymes that continue to break it down. From the stomach, food gets sent to the small intestine. The small intestine comprises three segments – duodenum, jejunum and ileum. Food moves along the small intestine segments via peristalsis and is broken down using digestive juices from the pancreas and liver. While the duodenum is mainly responsible for breaking down food, the ileum and jejunum are responsible for absorbing nutrients into the bloodstream.

The colon connects the small intestine to the rectum and is responsible for processing waste products. Stool leftover from digestion is transported through the colon to the rectum. The rectum has nerve connections that signal the brain whenever stool or gas reaches it. When the brain decides that the rectum can release its contents, the rectum contracts to release stool into the anus, the last part of the digestive tract responsible for excreting stool.

The pancreas, liver, and gall bladder are also important digestive system components. The pancreas secretes digestive enzymes and insulin, responsible for glucose metabolism. The liver functions as a processing factory that converts absorbed nutrients into the chemicals required by the body. The liver also acts as a store for excess carbohydrates and fats and releases bile into the small intestine to aid in fat digestion. The gall bladder is a storage unit for bile produced in the liver.

Carbohydrate digestion

Dietary carbohydrates, including starches, sugars and fiber found in grains, vegetables and fruit, milk products, nuts, seeds, and legumes, are the major sources of glucose, which is the primary energy source in the body:

Digestion of starches into glucose molecules starts in the mouth. An enzyme called amylase, found in saliva, breaks down starchy foods into simpler absorbable sugars. However, starch digestion is primarily in the small intestine via enzymes like α-amylase and α-glucosidase, secreted by the pancreas. Similarly, specific enzymes also break down the disaccharides sucrose, lactose, and maltose.

The end products of all carbohydrate digestion are the monosaccharides glucose,  fructose and galactose. These units are absorbed across the intestinal membrane and transported to the liver. In the liver, these monosaccharides are either processed and stored as glycogen or distributed to the rest of the body. Insulin acts on glucose to transport it into cells, where they are burned for cellular energy. Excess glucose is then stored in the muscles, adipose tissues or liver.

Benefits of Carbohydrate digestion

All organs in the body rely on glucose as their major energy source.

  • The brain uses up more glucose than any other organ in the body. Nerves cannot effectively transmit signals without glucose. Thus, a lack of glucose from carbohydrate digestion can lead to nerve degeneration and eventual brain damage.
  • Muscles use glucose for energy, especially during high-intensity exercise.
  • Excess glucose is stored in adipose tissues, liver and skeletal muscles and released as a fuel source during fasting periods.
Protein Digestion

Protein Digestion

The body needs 20 amino acids for optimal functioning. However, it only produces 11 of these, requiring that the other 9, known as essential amino acids, be obtained from the diet. Proteins are the macromolecules that break down into amino acids. Protein-rich diets like meat, egg and dairy are rich sources of these essential amino acids.

As with other foods, protein digestion starts in the mouth as chewing action breaks down large food molecules into smaller, more absorbable ones. In the stomach, proteins undergo further mechanical digestion via peristalsis and chemical digestion via the action of hydrochloric acid and the enzyme pepsin. First, hydrochloric acid causes protein denaturation, i.e., exposure of its polypeptide chain. Pepsin then acts on the peptide bonds to break the protein molecule into shorter peptides.

Proteins are larger and more complex than carbohydrates. Thus, their digestion takes more time than carbohydrates but less time than fats. Thus, you will feel fuller for longer after eating a protein-rich meal.

In the small intestine, peptides are acted upon by two pancreas-secreted enzymes – chymotrypsin and trypsin. These enzymes further break down the peptides into tripeptides and dipeptides and then into individual amino acids, the end product of protein digestion. The amino acids are absorbed across the membranes f the small intestine and transported via various transport systems to different parts of the body where they are used.

Benefits of Protein Digestion

Amino acids may be;

  • Used for protein synthesis in cells around the body
  • Used to make nonessential amino acids needed for protein synthesis
  • Used to make other nitrogen-containing compounds
  • Rearranged and stored as fat. There is no storage form of proteins.

However, if there is a glucose deficit in the body, amino acids may be;

  • Rearranged into glucose
  • Metabolized for an immediate source of energy

Muscles, hair, eyes, organs, and many hormones and enzymes are primarily made of protein. Amino acids also help to repair and maintain body tissues.

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Fat Digestion

Mechanical and chemical digestion of fats begins in the mouth. First, the enzyme lingual lipase in saliva acts on fats to turn them into small drops. Then gastric lipase in the stomach acts on fat to yield diglycerides and fatty acids. However, this process is very slow, with only 30% of fats converted in three hours. Finally, unprocessed fats, diglycerides and fatty acids move to the small intestine, containing bile secreted from the liver.

Bile contains lecithin, bile salts and emulsifiers that help break down fats. Then, with the help of lipase from the pancreas, fats are broken down into monoglu=ucerides and fatty acids. The fatty acids are then absorbed across the small intestine and taken up by cells.

Benefits of Fat Digestion

Fats are vital for health. They provide energy, cushion the organs, help cells grow and reproduce, and keep the body warm.


Exercise and Digestion

Effect of Exercise on the Digestive System

Exercise being great for fitness and emotional well-being is no secret. However, exercise is also important for the digestive system. Several factors affect digestive health, including weight, lifestyle, stress, smoking, etc. Exercising helps relieve stress and reduce weight, which greatly benefits digestive health.

An inactive lifestyle, unhealthy diets, and stress can cause several digestive problems, including constipation, bloating, and flatulence. Regular physical activity stimulates the gut and increases intestinal activity. This aids in preventing or relieving these digestive disorders. Exercising improves blood flow to skeletal and smooth muscles, including the stomach. Increased blood flow to the stomach enhances the gastric activity and shortens gastric transit time, i.e., the time required for food to move from the stomach to the small intestine.

Exercising after a meal

Although it is often recommended to eat before exercising to boost energy supply to aid activity, eating too close to exercise time may cause problems. Allowing sufficient time for the food to digest avoids these problems, but the time required varies based on the type of exercise.

It takes 2-4 hours for food to reach the small intestine after a meal. Waiting for the food to settle in the stomach at least ensures that you get the best benefits and avoid problems with digestion. Waiting about 2 hours after a moderate meal or 30 minutes after a snack is recommended. Heavy meals before workouts are not recommended. When performing high-intensity tasks, eating snack bars during activity is allowed to ensure that depleted glucose keeps getting replenished. 

Eating too close to exercise time may affect digestive health, causing bloating, flatulence,  cramping or reflux. This will also affect performance and reduce efficiency.

Carb Loading and Exercise

Carb loading is a nutrition strategy aimed at improving exercise performance. Carb loading involves adjustments in diet and physical activity to boost carbohydrate stores in the body. Carbohydrate is stored as glycogen in the muscles and liver. This glycogen can be called upon for energy production during workouts. Carb loading ensures that the glycogen stores are above normal levels.

Carb loading involves eating more carbs than usual while decreasing physical activity for several days. The increased glycogen stores act as an efficient fuel source during activity; thus, athletes commonly use this strategy before events. However, carb-loading may not be effective for all activity types. It is specifically appropriate for workouts that decrease the amount of glycogen in muscles, e.g., prolonged cycling, marathon races etc.

There are several carb-loading programs, including the classic 6-day, 6-day, classic 3-day, modified 3-day and 1-day programs. The difference in these programs is their duration, the number of carbs consumed and the level of exercise limitation. Before carb loading, ensure that your workout will benefit from it. Carb loading for programs that won’t benefit is useless. Also, ensure that you know the program you’re sticking to, know the required foods to eat and how much to change your diet.

Carb Loading Meals

The following meals are required in your carb-loading program

  • Low-fiber cereals
  • Fruit juices
  • White bread
  • White rice
  • Fruit smoothies
  • Skinned white potatoes
  • Fruit, including bananas, oranges and watermelon
  • White flour, used in cooking
  • Sports drinks
  • Low-fat energy bars
  • Proteins

Try to eat more lean proteins such as fish, lean meat, poultry or fat-free dairy. Ensure that you eat foods that you are used to and enjoy. Also, avoid high carb diets that are high-fat too. These compromise carb-loading programs.

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Healthy Eating and Muscle Building

The nutrients obtained from food are essential in building muscles. Muscles are primarily made of proteins. Thus, adequate protein intake is necessary to achieve muscle gains. However, protein intake while ignoring other essential nutrients is detrimental and counterproductive. Absorbed amino acids in the absence of glucose are converted to glucose rather than channeled towards protein synthesis and muscle growth. Thus, you must maintain a healthy balanced diet to ensure that amino acids are properly channeled.

When it comes to taking proteins, the recommendation is to take 1 gram of protein per pound of body weight per day. Thus, a 200-pound athlete only requires 200 grams of protein per day. But, ironically, the higher the protein intake, the lesser its utilization. Thus, if the same 200-pound athlete were to take 300 grams of protein per day, his body would only utilize 50% of it. In contrast, his body utilizes 90% of the proteins when he takes 200 grams a day.

Foods to eat to grow muscle

When attempting to build muscles, the goal is to optimize protein intake and limit excess and unhealthy fats while also taking adequate carbs. Of course, these dietary modifications must be combined with optimal physical activity.

You need about 1gram of protein per pound of body weight per day to ensure optimal muscle growth. An average man can obtain this protein requirement across 4-6 meals per day. However, some research has shown that protein intake does not have to be balanced through meals. Thus, even eating two meals that provide all the protein you need for a day will aid muscle growth.

Some suggest that protein-rich meals should be eaten in the daytime for better muscle building. However, research suggests that proteins can be taken at any time of the day and still have the desired effect on muscle building. Here are the best meals to take at different times.

Morning meals

The following high-protein breakfasts will aid your muscle growth efforts

  • Grain-free banana protein pancakes
  • Overnight oats with fruits
  • Turkey sausage and egg sandwich
  • Blueberry greek yogurt pancakes
  • Breakfast smoothie
  • Yogurt with pumpkin granola


These high-protein snacks will help you build muscle

  • Yogurt with whey protein and berries
  • Dark chocolate
  • Protein shakes
  • Protein bars
  • Protein pancakes

Bedtime meals

Protein-rich meals to help build muscle overnight include

  • poultry
  • fish and seafood
  • tofu
  • legumes, lentils, and peas
  • Greek yogurt
  • cottage cheese and ricotta cheese
  • eggs
  • nuts


Bodybuilding Digestion

Take Away

Digestion provides nourishment for the body. Glucose needed for cell energy, amino acids needed for DNA and protein synthesis, and fatty acids needed for building cell membranes are all end products of food digestion. Exercising maintains digestive health, allowing nutrients that aid exercise performance to be absorbed. In addition, protein-rich diets are needed in abundance for muscle building. However, these should not preclude the intake of carbohydrates and fats, which are equally important in the body.


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