What you eat is only half the equation, absorbing and delivering nutrients is the other half. In other words, just because you ate something, doesn’t mean that you absorbed and extracted its nutrients and delivered them to specific parts of your body.
The digestive system is 26ft long, it starts at your mouth and ends in your butt. The GI tract selectively absorbs nutrients while protecting you from toxins and pathogens. In a nutshell, the way it works is by involuntary muscular contractions that breakdown food down into small molecules, which then make their way into cells to be useful, the rest that is not useful or what your body doesn’t want to use is excreted. Amongst the many roles of the GI tract, here are a few of them:
-Process nutrients and minerals
-Acts as a barrier for chemical and physical pathogens
-Detoxifies harmful substances
-It contains the enteric nervous system, also known as “the second brain”
-Regulates immune system
-Its involved in social engagement and emotions
Our behavior, diseases and intolerances tend to mess with digestion, which in turn makes the absorption of nutrients and nutrient delivery an uphill battle.
It all starts in our brain. Hunger activates systems in our brain that essentially makes us search for food. When we start smelling or seeing food, or body starts getting ready to start the digestion process. Digestion is controlled by the autonomic nervous system, which is divide in two sides:
-The sympathetic nervous system (SNS) or “fight or flight” mode. SNS activates through intense activity or stress. When SNS is activated, digestion shuts down via norepinephrine.
Norepinephrine actives when the sympathetic response is activated, shuts down digestive process, so more energy goes to your limbs to “ fight for flight”.
-The parasympathetic (PSNS) or “relax and digest” mode. PSNS activates through rest and relaxation, it promotes digestion.
This is the main reason why high-performers or people who are constantly internally or externally stressed have a hard time with any physiological adaptation. They are constantly interrupting the digestion process, which in turn messes with their appetite, hunger and fullness.
Once your brain got you to eat food, chewing it breaks down your food into smaller pieces. Your saliva, moistens these pieces and saturates them with digestive enzymes like lipase and amylase that help break them down once you swallow.
Once you swallow, the esophagus transports the shredded pieces into your stomach.Most carbohydrates are then broken down into glucose and exit the stomach first, most proteins follow carbohydrates and are broken down into amino acids and finally, most fats are broken down into fatty acids and are the last ones to leave the stomach.
This is good to know because someone who might need a quick energy boost without wanting a big meal might only need carbohydrates, versus someone that has a hard time with feeling hungry all the time might need meals that are higher in fat so they feel satisfied for longer.
After spending time in the stomach, a semi-fluid mass containing the partially digested food called chime, is transported into the small intestine where most of the nutrients are absorbed via the villi. A healthy villi is crucial for nutrient absorption.
I will stop here as processes like this keep unfolding until you excrete whatever your body doesn’t use. They key take away here is that digestion is a very complex system and although genetics, activity levels, microbiome, age and food allergies play a role, the main reason we mess it up is because our behaviors are sometimes messed up.
The one running the show behind-the-scenes is the endocrine system. It is a system that communicates with your body via hormones.
A lot of times, people complain that they are always hungry, essentially whats happening is that their endocrine system is signaling ghrelin. Ghrelin is your “hungry” hormone - Whereas when people don’t feel hungry at all, leptin is the one to blame. Because leptin its secreted by fat cells, the more fat cells you have, the less hungry you are going to feel. On the other hand, the less body fat the more “hungry” you are going to feel.
Leptin also regulate