The liver as a biochemical hub
How the liver, digestion, and the enterohepatic circulation are connected.
An organ in the background
The liver works continuously in the background. It receives substances from the intestines, processes them, converts them, and distributes them throughout the body. Everything absorbed from the intestines first travels to the liver via the portal vein before entering the systemic circulation.
You can think of the liver as a large internal distribution center: not a static storage facility, but a place where substances are processed, sorted, converted, and redistributed. It plays a role in the metabolism of carbohydrates, fats, and amino acids, produces bile components, and regulates the biotransformation of both exogenous and endogenous substances.
Biotransformation: What the Liver Does to Substances
The liver plays a key role in chemically modifying foreign substances, dietary components, metabolic intermediates, and the body’s breakdown products so that they can be reused, transported, or excreted.
This usually happens in two steps: First, substances are enzymatically modified to make them more accessible for further reactions. Then, they are often conjugated to other molecules to make them more water-soluble and easier to excrete.
From a biological perspective, it is not only the excretion itself that is interesting, but also the body’s ability to convert substances into a form that can be processed. The liver does not make conscious decisions—but it creates the biochemical conditions necessary for substances to be properly processed.
The Close Interaction Between the Liver and Digestion
The liver cannot be meaningfully considered in isolation from the digestive system. The intestines continuously supply material and information. The liver plays a key role in the subsequent processing.
This applies to nutrients, but not only to nutrients. Microbial metabolites, food breakdown products, and numerous small molecules from the intestinal contents also enter the liver’s metabolic processes via the portal vein. If the digestive environment becomes disrupted, this also alters what is presented to the liver for further processing—and what it must do with it. The better the material delivered from digestion, the easier the liver’s job becomes.
The enterohepatic cycle
A particularly interesting mechanism links the liver and the intestines: the enterohepatic circulation. Substances are released by the liver into the intestines via bile, where they are partially altered, bound, excreted, or reabsorbed—and then return to the liver.
Bile acids are a classic example. They are produced in the liver, released into the intestines via bile, and, after fulfilling their function, are largely reabsorbed. We now know that bile acids are not only aids to digestion—they are also involved in signaling processes, metabolic regulation, and communication between the intestines, liver, and microbiome.
This creates a circular system: The intestines influence what is delivered to the liver. The liver, through bile, influences the environment in the intestines. The microbiome alters parts of this delivery. The returned material then goes back to the liver.
A Perspective from Traditional Chinese Medicine and Empirical Medicine
In TCM, the liver is understood not merely in anatomical terms, but as part of a functional system: flow, distribution, tension, and internal dynamics all play a role. This perspective differs significantly from modern biochemistry—yet the two converge on a fundamental level: metabolism is not merely the conversion of substances, but a process of coordination.
In traditional European medicine, bitter herbs, rhythms, and dietary habits have always been considered in relation to liver function, digestion, and distribution—rarely as isolated measures.
What that means
In this context, research is focusing on bitter compounds, sulfur-containing plant compounds, choline-related nutritional factors, and certain amino acids. Not as isolated solutions, but as substances that are integrated into the broader metabolic context of the liver.
In the next post, we’ll turn our attention to blood—not just as a collection of lab results, but as an internal transport and distribution system.