Inside Story: The Digestive Adventure of Your Steak and Fries
“You're digging your grave with your teeth," warn the new Puritans, eager to spoil our fun. But let's not get bogged down by their gloom.
Eating is crucial for our well-being; it's how we provide our bodies with essential nutrients. Instead of extolling the virtues of broccoli, let's embark on a lighthearted adventure through your digestive system to see how your body makes the most of what you eat.
So, what is digestion?
Picture your digestive tract as an 8 to 9-metre-long assembly line. Food enters at one end, and unusable waste exits at the other. Along the way, your body extracts and absorbs nutrients into the bloodstream. This intricate process is called digestion (and when things go awry, we call it indigestion!).
The goal of digestion is to break down the food on your plate into tiny particles that can pass through the wall of your intestine and into your blood. Your body uses a mix of mechanical actions and chemicals to achieve this. By understanding how this system works, you can improve your gut health and overall well-being. So, let's follow the path of a food item – say, a steak and fries – from start to finish.
It takes just five to ten seconds for food to travel down your esophagus and enter your stomach, where it hangs out for two to six hours for partial digestion. The real magic of digestion and nutrient absorption happens in the small intestine over five to six hours. Within 12 to 24 hours, any leftovers make their way through the large intestine, and out they go as faeces.
Digestion Starts in Your Mind
Even before you take a bite, your brain gets the ball rolling. You imagine how delicious your meal will be, and suddenly, your eyes are on high alert for anything edible. Your nose leads you to the delightful scent of the sizzling steak. These sensory cues are essential as they prepare your brain and body for eating: just thinking about food triggers the secretion of digestive juices. Your mouth waters, and your stomach starts to rumble in anticipation of that first juicy bite of grilled steak.
Chew, Chew!
Your mom was right when she told you to chew well. When that piece of steak enters your mouth, the breakdown process begins. Your teeth chop the meat into smaller pieces, increasing the surface area for digestive enzymes to work on.
Chewing breaks down the food's fibres and removes protective coatings, allowing enzymes to access the nutrients inside. Saliva, already flowing in your mouth, coats the steak and fries with the first digestive enzyme, salivary amylase, which starts breaking down carbohydrates into small sugar molecules. These sugars are ready to be further broken down if needed to cross the intestinal barrier and enter your bloodstream. Fat digestion also begins in your mouth with the help of lingual lipase, an enzyme that dissolves fat.
As you continue down the digestive tract, you'll notice that enzyme names often end in "ase" and are based on the nutrients they help digest: lipase for lipids, proteinase for proteins, and lactase for lactose (milk sugar).
Saliva does more than just moisten food; it helps your steak and fries slide smoothly down your oesophagus, the tube connecting your mouth to your stomach. Saliva is a magical potion of the body, aiding in digestion and containing epidermal growth factor, which helps heal and regenerate intestinal tissues. This might explain why animals lick their wounds. Good news: your body produces about a liter of saliva daily!
Eating smaller bites, chewing thoroughly, and swallowing slowly not only aid digestion but also reduce air intake (less belching) and make you more aware of when you're full, preventing a "traffic jam" in your digestive system. Your mom's advice to chew well and eat slowly was spot on.
The Oesophagus: A Funny Tube
The esophagus, a 30-centimeter-long tube, "pushes" food toward the stomach. It's smooth inside and covered with mucus, allowing food to glide easily. The food you swallow forms a pellet, which is pushed into the esophagus by muscle contractions. These muscles, resembling rings, tighten sequentially every 9 seconds to move food forward, even if you're lying down or doing a handstand.
Mix, Mix!
When food reaches your stomach, it mixes with whatever's already there. The stomach acts like a food processor, blending food mechanically and chemically. It's a pouch formed by crisscrossing muscles that contract to mix food in all directions, similar to kneading bread dough. The stomach lining secretes gastric juices, including:
Hydrochloric acid: dissolves food
Pepsin: breaks down proteins
Lipase: dissolves fat
Just like fruits and vegetables in a food processor, the food is stirred and mixed with digestive juices until it resembles a thick soup called chyme.
Circular muscles surround the top and bottom of your stomach to keep food from rising or falling before it's fully processed into liquid. Sometimes, these muscles can misbehave. The lower muscle, called the pylorus, can be too tight in infants, causing a condition called pyloric stenosis, which leads to frequent and severe vomiting. The upper muscle, known as the gastroesophageal sphincter, can become too loose, allowing stomach contents to escape during digestion, leading to gastroesophageal reflux disease (GERD).
The Stomach: Your Body's Blender and Disinfectant
Hydrochloric acid in the stomach is strong enough to dissolve meat and kill most harmful bacteria in your food. So, your stomach not only digests but also disinfects. However, not all bacteria are destroyed. Some hardy bacteria survive and make their way to the intestine, where they contribute to health and digestion in exchange for a steady food supply.
The Delicate Balance of Stomach Acid
For smooth digestion, the stomach lining must secrete just the right amount of acid at the right time. If it produces acid when the stomach is empty (which can happen when you're stressed), the acid irritates the mucous membrane, causing discomfort. Without food to neutralize it, the acid can also enter the sensitive duodenum (the upper part of the intestine) and even start to digest it, leading to ulcers. Consuming substances like alcohol or coffee on an empty stomach can exacerbate this issue, essentially causing you to "eat yourself from the inside out." Excess acid can also travel back up to the oesophagus, causing heartburn or reflux.
Handy Tips for Happy Digestion
The mouth and stomach mainly prep food for absorption in the small intestine. However, some substances, like alcohol, caffeine, and certain medications (like aspirin), can be absorbed directly through the stomach lining. This explains why you might feel tipsy or jittery even before finishing your drink or coffee. Consuming these on an empty stomach speeds up their absorption.
Gurgling and Other Noises
When your stomach is empty and expects food, it starts to contract but only kneads air, causing gurgling sounds. Burping, tummy noises, and vomiting are the "work accidents" of an overactive digestive system.
The vomiting reflex protects the intestines from unwanted substances by sending the food back up. The brain triggers muscles in the diaphragm, abdomen, and stomach to contract abruptly, emptying the stomach from above, which is why vomiting often brings relief.
Eat the Right Amount
To digest well, don't eat more than your stomach can handle. To gauge your stomach's size, open your hand and hold your thumb and fingers together. Your stomach is about as wide as your palm and twice as long. Next time you're tempted to overeat, compare your hand to your plate. (For perspective, compare it to a baby's tiny fist, and you'll see why little stomachs can easily get overwhelmed).
The entire digestive system is designed for small meals rather than big feasts.
Now that your ribeye steak has been chewed, stirred, and liquefied, it's ready to move from the stomach to the small intestine, where the real digestion happens. Most proteins and carbohydrates move on from the stomach after a few hours, but fats linger longer because they are digested more slowly. This slower digestion is because fats are not water-soluble and require emulsification by bile for proper digestion. Consequently, a high-fat meal tends to keep you feeling full longer than a high-carbohydrate or high-protein meal.
As chyme (the "soup" made in your stomach) enters the small intestine, the most crucial part of digestion begins. The first section of the intestine is called the duodenum, named after its length being about twelve fingers long in adults. This is where most digestion occurs.
For your body to absorb nutrients, food must pass through the intestinal lining since your gastrointestinal tract is technically outside your body.
Here's where things get exciting:
Neutralizing Acidity: The intestine lining, delicate and sensitive to stomach acid, secretes bicarbonates (antacids) to neutralize the acidity.
Digestive Juices: As food moves through the intestine, it receives digestive juices that break proteins into pieces small enough to pass through the intestinal wall and into the bloodstream. The blood then carries these nutrients to different parts of the body for energy or assimilation.
Fat Digestion and Absorption
Meanwhile, back in the stomach, the fats are finally ready to move on. Entering the small intestine, they are sprayed with bile from the gallbladder and lipases from the pancreas. Bile acts like soap, forming an emulsion with the fat, breaking it into small particles. Lipases then further break these particles down so they can pass into the bloodstream.
Fatty acid molecules pass through small doors in the intestinal lining, but instead of going directly into the bloodstream like carbs and proteins, they enter a microscopic airlock in special cells in the intestinal mucosa. Here, they are packed into small bags and exit through the back door onto lipoproteins, tiny molecular barges that transport fats in the blood.
These lipoproteins circulate until they find a cell dock to deliver the fat. If a cell doesn’t need fat, it closes its docks, forcing the lipoprotein to keep circulating until it finds a place to unload. The liver and fat cells are the primary recipients. Excess fat is stored around the waist, hips, thighs, or in the liver. In the liver, bile dissolves the fat, which is then evacuated into the intestine as waste.
The Law of Supply and Demand: Digestion Edition
Enzymes involved in digestion work like a supply-and-demand system. If your intestines and pancreas produce enough enzymes to break down and absorb all the food, everything goes smoothly. But if there's more food than enzymes, the extra food heads to the lower intestine, leading to indigestion. How can you keep things balanced? Simple: eat reasonable portions to give your enzymes a fair chance. And if you know you're going to indulge in a big meal, like at a family gathering, consider taking digestive enzymes about half an hour before you sit down to eat.
The Inner Workings of Your Gut
The inner lining of your gut is like a plush mat with trillions of tiny folds, increasing the surface area for nutrient absorption. It’s only one cell thick, which has its pros and cons. The thin mucous membrane allows nutrients to pass through easily, but it’s also fragile and easily irritated or infected. When this happens, food isn’t well absorbed, leading to diarrhea, abdominal pain, gas, and bloating. Damaged cells might lack enzymes needed to digest certain foods, like lactose, which is why avoiding hard-to-digest products after an intestinal infection is recommended. The epithelial cells lining the gut can regenerate within 3 to 5 days, but complete healing of the gut may take a few weeks depending on the extent of the damage.
Water & Waste: The Colon's Role
After your ribeye steak and fries complete their 7-meter, 10-hour journey through the small intestine, most nutrients are absorbed. What’s left starts a 1.7-meter journey through the colon, or large intestine. This is the calm after the storm. While digestion slows down, the colon is still very active and crucial for your health.
The colon’s first vital function is to regulate hydration. It absorbs water from food and delivers it to your body. If there isn’t enough water in your food, the colon pulls water from your body into the stool to prevent constipation. A good fluid balance in the colon means healthy bowel movements. One noticeable change after adopting a balanced diet is having less abundant, flexible stools several times a day, rather than the typical large bowel movement once a day or every other day.
Microbes in the Gut: Your Tiny Helpers
Billions of bacteria reside in your intestines, especially in the large intestine. Known as gut flora, these microbes play a crucial role in the health of your colon and entire body. These beneficial bacteria are called probiotics because they support life.
The Probiotic Stars: Lactobacilli and Bifidobacteria
The two main categories of healthy bacteria in the colon are lactobacilli and bifidobacteria. They live in a symbiotic relationship, meaning they provide mutual benefits. In exchange for a warm place to live, they offer numerous advantages to our bodies. These include keeping harmful bacteria at bay, fermenting soluble fibre in food, producing short-chain fatty acids (SCFAs) that nourish colon cells, stimulating healing, and reducing the risk of intestinal cancer. SCFAs are also absorbed through the intestines and travel to the liver, where they help lower cholesterol production. If you have recurring digestive issues, consider trying dietary supplements with lactobacillus and bifidus, available in most pharmacies and health stores.
Gas Production: A Side Effect of a Healthy Gut
When the normal bacteria in your colon digest certain foods (like the polysaccharides in beans), they produce gas. Their favorite foods include polysaccharides from starchy foods such as beans, Brussels sprouts, prunes, and most grains (except rice, which is gentler in social settings). Milk galactose and pectin are also popular with these bacteria. However, the amount of gas produced varies greatly among individuals and is more influenced by the volume of food consumed than the type.
The Final Journey: Waste Elimination
Colon contractions move waste products (faeces) into the top five centimeters of the intestine, called the rectum, where they are eliminated. Their presence triggers a highly effective eviction reflex, as long as you don't disrupt the process. Eating too little fibre, drinking too few fluids, consuming too much fat (which slows bowel movements), or ignoring the urge to evacuate can hinder this reflex. (Children between ages five and ten, especially boys, often ignore these signals.)
Feed your bowels properly, listen to their signals, and they will serve you well.
To your health!