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Basics of Physiology

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Basics of Physiology

March 10, 2024, 11:07 AM IST 

After exploring various myths about diet and lifestyle, we will now delve into the fundamentals of human physiology and nutrition. Every living organism, from single cells to primates, has two primary objectives: (1) survival and (2) propagation. For survival, two elements are crucial, which in Vedanta are termed PRANA and APANA. Prana represents the life-giving force, including food and air (oxygen) for energy, while Apana refers to the elimination of waste produced by metabolism, driven by Prana. In this and the next three blog posts, we will examine the four basic systems of human physiology:

1. Gastrointestinal Tract: It ingests and processes food.

2. Respiratory System: It inhales fresh air and exchanges oxygen for carbon dioxide.

3. Blood Circulatory System: It distributes nutrients and oxygen to every cell in the body.

4. Lymphatic System: It acts like a janitorial system, removing waste from all body parts due to metabolic processes.

Gastrointestinal Tract

This tract is the path from our mouth to the anus, through which food passes, is consumed, digested, absorbed, and eventually, waste is excreted.

As depicted above, food enters our mouth where it is mixed with saliva and chewed into a fine slurry before moving through the esophagus to the stomach via a sphincter valve. In the stomach, food mixes with acids and digests over a period that can range from two to six hours. The total transit time of food, from ingestion to defecation, can vary from 10 to 72 hours, primarily depending on the type of food and gut health. Here’s a breakdown:

– Gastric emptying: 2-6 hrs.

– Small Intestine transit: 2-6 hrs.

– Colonic transit: 6-60 hrs.

– Total Gut transit: 10 to 72 hrs.

This transit time largely depends on how nutrients are embedded within the food’s fibers. Food lacking fiber moves slowly but is quickly absorbed. In contrast, plant-based whole foods move quickly due to the motility created by undigested fibers but are absorbed slowly, as extracting nutrients like sugars and starches from fibers takes time. This dynamic results in a significant challenge for animal and processed foods, as they are quickly and completely absorbed, leading to liver overload and potential weight gain, with little left for the colon’s microbial inhabitants.

When this pattern repeats, our microbial guests become starved and agitated, starting to consume the mucosal layer they inhabit, eventually leading to inflammation and conditions like “Leaky Gut Syndrome” or “Irritable Bowel Disorder.”

Epithelial Cell Lining

The human gastrointestinal tract is lined with a single layer of epithelial cells with tight junctions, protected by an inner mucus layer containing goblet cells that produce mucus. Adjacent to this inner layer is an outer mucus layer, home to various microbes.

The importance and roles of these colon microbes are becoming increasingly clear, giving rise to a new field called epigenetics. Surprisingly, our bodies host more foreign cells (38 trillion microbes) than our own cells (37 trillion). These microbes play a significant role in our health, overshadowing our genetic makeup. This was highlighted in the January 14, 2010, issue of TIME magazine.

“Microbiota” refers to the collective microbes (sometimes called a microbial garden), with “Microbiome” denoting their genetic makeup. These terms are often used interchangeably. An analogy to understand the human microbiome versus genome is comparing computer hardware and software: despite similar hardware, the software dictates the functionality, akin to how our epigenome, the body’s software, influences gene expression.

To make my point clear I like to give an example of cell phones.

All cell phones in use today are very similar in terms of hardware however, how this hardware expresses itself visually on the screen or audibly on the speaker depends upon what software is being used. For example Facebook, WhatsApp and Instagram all express very differently on the same phone. So our epigenome is our body’s software and it determines how our genes are expressing at any given moment.

This understanding is revolutionizing medical science, leading to groundbreaking practices like fecal transplantation which was not even in the realm of our wildest imagination. An overweight woman, who has tried everything in her life to lose weight, loses weight simply upon receipt of a fecal transplantation from a slim woman. Some of the lessons we have learned with this new science suggest:

  1. Same cause can manifest as different symptoms in different people.
  2. Same symptoms can be due to different causes in different people therefore diagnosing problems based on symptoms is an imperfect science distraught with many hits and misses.
  3. A different diet for different diseases doesn’t make sense but a different diet for different individuals could make sense. It is conceivable that soon in future, we may create meal plans based on one’s fecal sample analysis.

Refined vs. Whole Food

Consider the example of identical twins T1 and T2, consuming the same ingredients (wheat, peanuts, and apples) in different forms for breakfast. T1 opts for porridge in peanut milk with fresh apples, while T2 consumes refined flour kachori fried in peanut oil with apple juice. T1 maintains health, but T2 may gain weight and risk developing diabetes, liver, and kidney issues. This disparity arises because T1’s body might leave some calories for the microbiome, keeping them happy and satisfied, whereas T2’s body absorbs all calories in the small intestine, leaving nothing for microbial digestion. This causes microbes to consume the mucosal layer in which they reside. Over time, this can lead to leaky gut and autoimmune diseases.

Sugar spikes due to Apple juice and refined flour would result in new fat formation in liver (de novo lipogenesis) causing non alcoholic fatty liver disease and visceral fat and insulin resistance (Diabetes type-2). Ultimately both the kidney and liver will be affected shortening his lifespan.

The impact of diet on health is profound, yet often overlooked, with many attributing health issues to bad luck. However, chronic diseases are less about luck and more about the consequences of dietary choices, particularly the consumption of refined and highly processed foods.


The transition from whole foods to refined and processed options during the past century is a primary contributor to lifestyle-related diseases. These diseases affect our body on a daily basis in small ways that are rarely noticeable until it is often too late. They are not impervious as we often like to believe. Taking medications to suppress symptoms is not the solution. The diet has to be modified.

To Read this article on Times of India click here

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