The liver is the largest organ in the body and has an impressive list of duties. Many of us only think of our liver when we feel we’ve overtaxed it with excessive alcohol or exposure to toxins, but the liver works full time every day. Beyond detoxification and purification of blood, the liver is the primary site for nutrient processing and the distribution of lipids, carbohydrates, and amino acids.
How the Liver Processes Food
The foods we eat are basically combinations of macronutrients. The macronutrients are carbohydrates, fats, and protein (as well as alcohol which is indeed a macronutrient in the sense that it contributes energy or calories to the diet).
Following digestion and absorption, these compounds all go through the “central processing plant” of the liver to be catabolized, converted, stored, or repackaged for delivery to other tissues and organs, depending upon the current needs of the body.
A useful model is to think of how an oil refinery works. Crude oil is delivered to the refinery and, depending upon the demands of the current market, is sent through the processing stream, which yields the most profitable end products; for example, petroleum, gasoline, diesel fuel, kerosene, petroleum gas, and jet fuels, among other products. Likewise, the liver senses which nutrients are needed by various tissues and organs and delivers the “building blocks” or assembled products to meet demands.
The liver produces and secretes bile, which mixes with ingested fat to promote absorption of fats from the gastrointestinal tract. Triglycerides (a type of fat found in our blood) can be metabolized in the liver to produce energy for this organ’s own use, after which it transports the breakdown products out to the blood for delivery to other tissues for their own needs.
The fate of carbohydrates, after being digested down to their simplest form (monosaccharides, mainly glucose), depends on the liver to store or use glucose as needed. It is vitally important to maintain the blood glucose level within a very narrow range, and the liver does a precise job of taking up excess glucose after a meal and storing it as glycogen. When the blood glucose level drops, the liver senses this change and releases glucose back into the blood.
The liver is also the place where amino acids from protein digestion get sorted and transformed by enzymes called deaminases and transaminases. These enzymes can add nitrogen to molecules in order to synthesize nonessential amino acids, or remove nitrogen to leave carbon structures that can then be used to make glucose or, less readily, be converted to fatty acids. The ammonia that is generated from the release of nitrogen from some of these reactions is converted to urea, a process that allows what was a toxic compound (ammonia), to be safely excreted from the body.
The liver produces a number of proteins, including albumin and fibrinogen, which are two major plasma proteins that circulate through the body. Albumin serves to regulate blood volume and may also be a means of transporting essential amino acids to other tissues. Fibrinogen is an important component of the blood clotting process. These plasma proteins, and the liver’s capacity to produce them, are affected by overall nutrition and excessive use of alcohol or other drugs.
There are many functions performed by the liver beyond filtering and neutralizing toxins. Efforts to limit exposure to these compounds, eat a nutrient-dense diet, and maintain a healthy body weight will go a long way towards keeping the liver healthy.