Difference Between Absorptive and Postabsorptive State

The key difference between absorptive and postabsorptive state is that absorptive state is the state that digests foods and absorbs nutrients into our bloodstream while the postabsorptive state is the state in which the nutrient absorption does not occur, and the body relies on the energy reserves for energy.

Cells produce energy from glucose, lipids and amino acids. They store produced energy as fats, glycogen and proteins. During energy metabolism, chemical changes take place to make the energy available for use. There are three phases of energy metabolism. These three phases are the cephalic phase, absorptive phase and fasting phase or postabsorptive state. Therefore, our body undergoes absorptive and postabsorptive states throughout the day. The absorptive state takes place immediately after each meal while the postabsorptive phase takes places when the GI tract is empty and after the complete absorption of nutrients.

CONTENTS

1. Overview and Key Difference
2. What is Absorptive State
3. What is Postabsorptive State
4. Similarities Between Absorptive and Postabsorptive State
5. Side by Side Comparison – Absorptive vs Postabsorptive State in Tabular Form
6. Summary

What is Absorptive State?

Absorptive state or fed state is the time immediately after a meal. Once the ingested foods start digestion, nutrients are absorbed into the blood. Generally, this state runs for 4 hours after a typical meal. Therefore, per day, our body spends a total of 12 hours in the absorptive stage if we have three meals. In this state, our body depends on the energy that is absorbed from the food.

Glucose is the main energy source in this state. Apart from glucose, little amounts of fats and amino acids provide energy for our body during this state. Extra nutrients are not absorbed into our bloodstream. They undergo storage in tissues. Thus, the excess glucose converts into glycogen in the liver and muscle cells. The excess fat is deposited in the adipose tissue. Moreover, excess dietary fats are deposited as triglycerides in adipose tissues

In the absorptive state, insulin is the main hormone that helps in providing glucose for cellular consumption and storage. In addition to insulin, growth hormone, androgens and estrogens also participate in the nutrient absorption into the blood.

What is Postabsorptive State?

Postabsorptive state or fasting state is the time that starts after the completion of nutrient absorption. In simple words, the postabsorptive state is the state at which our GI tract does not contain food. Therefore, when there is an energy demand, our body relies on endogenous energy reserves. Internal energy reserves have to be broken down to fulfil energy demand during this state. Our body initially relies on glycogen stores for glucose. Then it depends on triglycerides. Glucagon is the enzyme that acts mainly during this state. Other than glucagon, epinephrine, growth hormone and glucocorticoids also participate in the postabsorptive state.

Similar to absorptive state, the postabsorptive state also runs 4 hours times in the late morning, late afternoon and the night. Therefore, per day, we spend 12 hours in the postabsorptive state.

What are the Similarities Between Absorptive and Postabsorptive State?

• Absorptive state and postabsorptive state are two functional metabolic states occurring in our body.
• We spend 12 hours in each state per day.
• Liver, muscle cells, and adipose tissue play major roles in both states.
• Cells demand energy in both states for their cellular activities.

What is the Difference Between Absorptive and Postabsorptive State?

Absorptive state starts immediately after the ingestion of foods. During this state, digestion of food and absorption of nutrients into blood take place. Meanwhile, the postabsorptive state starts after the complete absorption of nutrients. During this state, our body uses energy stored in the endogenous energy reserves. Thus, this is the key difference between absorptive and postabsorptive state. Moreover, insulin plays a major role in the absorptive state, while glucagon plays a major role during the postabsorptive state.

The below infographic provides more comparisons related to the difference between absorptive and postabsorptive state.

Summary – Absorptive vs Postabsorptive State

Absorptive state and postabsorptive state are two main states of energy metabolism. During the absorptive state, our body digests foods and absorbs nutrients into the blood. So, this state starts immediately after the food ingestion. In contrast, postabsorptive state starts after the complete absorption of nutrients and when the GI tract is empty. During this state, our body relies on the energy stored in reserves. Therefore, nutrient absorption does not take place during this time. When considering 24 hours time or a day, we spend nearly 12 hours in absorptive state and 12 hours in the postabsorptive state. This is the summary of the difference between absorptive and postabsorptive state.

Reference:

1.  “Anatomy and Physiology II.” Metabolic States of the Body | Anatomy and Physiology II, Available here.

Image Courtesy:

1. “2521 The Absorptive Stage” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “2522 The Postabsorptive Stage” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia