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Healthy humans have shockingly different digestive systems

A groundbreaking new study has revealed significant variations in the anatomy of the human digestive system, even among healthy individuals. 

The discovery carries important implications for our understanding of how the digestive tract’s anatomy can impact human health, potentially providing valuable insights into medical diagnoses and the gut’s microbial ecosystem.

The research, which resurrects a century-old exploration of human gut anatomy, has left the scientific community astounded at the extent of variability observed. 

Amanda Hale, co-first author of the study and a Ph.D. candidate at North Carolina State University, explained: “There was research more than a century ago that found variability in the relative lengths of human intestines, but this area has largely been ignored since then. When we began exploring this issue, we were astonished at the extent of the variability we found.”

Study co-author Professor Erin McKenney highlighted the uniqueness of the human gut. “If you’re talking to four different people, odds are good that all of them have different guts, in terms of the relative sizes of the organs that make up that system.” 

What the researchers learned

The researchers found wide variability in several digestive organs, including the cecum—an organ at the junction of the large and small intestine.

One striking finding was that women tend to have longer small intestines than men. According to Hale, this supports the canalization hypothesis, which suggests that women are better able to survive during periods of stress due to their enhanced ability to extract nutrients from their diet.

McKenney pointed out that the discovery of this variability raises numerous research questions that need to be explored. “Given that there is more variation in human gut anatomy than we thought, this could inform our understanding of what is driving a range of health-related issues and how we treat them.”

How the study was done

To carry out the study, researchers measured the digestive organs of 45 individuals who had donated their remains to the Anatomical Gifts Program at the Duke University School of Medicine. 

The project not only unveiled the unexpected variability in human anatomy but also emphasized the importance of teaching anatomical variation to medical students.

Roxanne Larsen, co-author of the paper and an associate professor of veterinary and biomedical sciences at the University of Minnesota, stressed the significance of this knowledge in medical training. “It’s particularly important in medical training because if students are only learning about a ‘normal’ or ‘average’ anatomy, that means they are not going to be familiar with the scope of human variation.” 

She added that as the medical field moves toward individualized medicine, understanding anatomical variation plays a critical role in improving patient outcomes and overall health and well-being.

McKenney expressed excitement about the discovery and its potential impact on future research. “It underscores just how little we know about our own bodies.”

The research article titled, “Hidden Diversity: Comparative Functional Morphology of Humans and Other Species,” is published in the open-access journal PeerJ. The co-authors of this paper include Janiaya Anderson, a former undergraduate at North Carolina State University; Colleen Grant, a former research scientist at NC State; and Rob Dunn, who holds the prestigious title of William Neal Reynolds Distinguished Professor of Applied Ecology and serves as the Senior Vice Provost for University Interdisciplinary Programs at NC State.

More about the human digestive system

The human digestive system is a complex series of organs and glands that process and break down food, allowing the body to absorb nutrients and eliminate waste. It plays a crucial role in maintaining overall health and well-being. Here is an overview of what we know about the human digestive system:

Components: The digestive system consists of the gastrointestinal (GI) tract, also known as the alimentary canal, as well as accessory organs, including the salivary glands, liver, gallbladder, and pancreas.


Digestion involves both mechanical and chemical processes. Mechanical digestion starts with chewing and breaking down food into smaller particles. Chemical digestion involves the secretion of enzymes and other chemicals that break down complex food molecules into simpler components that can be absorbed by the body.

Stages of digestion

The process of digestion can be divided into several stages, starting with ingestion (taking in food) and followed by propulsion (swallowing and moving food through the GI tract), mechanical and chemical breakdown, absorption of nutrients, and finally, elimination of waste through defecation.

Organs involved:

  • Mouth: The process begins in the mouth, where food is broken down by chewing and mixed with saliva, which contains enzymes to begin the breakdown of carbohydrates.
  • Esophagus: The esophagus is a muscular tube that connects the mouth to the stomach. Food is transported through the esophagus via peristalsis, a series of coordinated muscle contractions.
  • Stomach: The stomach is a muscular, sac-like organ that stores and breaks down food. Gastric juices, including hydrochloric acid and enzymes, mix with the food to form a semi-liquid substance called chyme.
  • Small intestine: The small intestine is a long, coiled tube where the majority of nutrient absorption takes place. It is divided into three sections: the duodenum, jejunum, and ileum. Bile from the liver and gallbladder, as well as pancreatic enzymes, aid in the digestion and absorption of fats, proteins, and carbohydrates.
  • Large intestine: The large intestine, or colon, absorbs water, electrolytes, and vitamins produced by enteric bacteria. It also forms and stores feces, which are eliminated through the rectum and anus.


The human gut is home to trillions of microorganisms, collectively known as the gut microbiome. These microbes play a crucial role in digestion, metabolism, immune function, and overall health. Imbalances in the gut microbiome have been linked to various health issues, including obesity, inflammatory bowel disease, and mental health disorders.

Diet and lifestyle

The human digestive system is influenced by factors such as diet, hydration, exercise, and stress. A balanced diet rich in fiber, lean proteins, healthy fats, and a variety of fruits and vegetables can promote optimal digestion and overall health.

In recent years, researchers have discovered significant variation in the anatomy of the human digestive system, even among healthy individuals. This variability can impact how the digestive system functions and how the body processes food, which has implications for understanding and treating various health issues.

What we know about the human gut and microbiome

The human gut microbiome is an incredibly complex and diverse community of microorganisms, including bacteria, fungi, viruses, and other microbes, that reside within our gastrointestinal tract. These microorganisms play a crucial role in various aspects of our health and bodily functions. Some of the key roles of the gut microbiome include:

Digestion and metabolism

Gut microbes aid in breaking down complex dietary components, such as carbohydrates and fibers, that our bodies cannot digest on their own. They also produce essential short-chain fatty acids, which serve as an energy source for our intestinal cells and have anti-inflammatory properties.

Nutrient synthesis

The gut microbiome is involved in the synthesis of essential vitamins, including vitamin K and some B vitamins, which are important for blood clotting, energy metabolism, and neurological functions.

Immune system regulation

The gut microbiome plays a significant role in shaping and regulating our immune system. It helps to maintain a balance between pro-inflammatory and anti-inflammatory responses, protecting the body from harmful pathogens while preventing excessive inflammation that can lead to autoimmune diseases.

Gut barrier function

The gut microbiome contributes to the integrity of the gut lining, which acts as a barrier to prevent the entry of harmful substances and pathogens into the bloodstream. Imbalances in the gut microbiome can compromise this barrier function, leading to a condition known as “leaky gut,” which has been linked to various health issues, including autoimmune disorders and chronic inflammation.

Brain-gut axis

The gut microbiome communicates with the central nervous system through the brain-gut axis, which is a complex network of nerves, hormones, and signaling molecules. Research has shown that the gut microbiome can influence our mood, behavior, and cognitive function, leading to the concept of the “gut-brain axis.” Imbalances in the gut microbiome have been associated with mental health disorders, such as anxiety and depression.

Weight management and obesity

The gut microbiome can impact energy balance, fat storage, and appetite regulation, which are crucial factors in weight management and obesity. 

Studies have shown that individuals with obesity often have a different gut microbial composition than lean individuals, suggesting that the gut microbiome may contribute to the development of obesity and metabolic disorders.

Maintaining a healthy gut microbiome is essential for overall health and well-being. Factors such as diet, exercise, stress, and antibiotic use can influence the composition and diversity of the gut microbiome. 

A balanced diet rich in fiber, fruits, vegetables, and fermented foods can promote a healthy and diverse gut microbiome. Additionally, regular physical activity, adequate sleep, and stress management can contribute to a healthier gut environment.


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