What does the liver do?

The liver is an important metabolic organ that performs over 500 functions. It receives and processes all of the blood leaving the stomach and intestines. It can break down alcohol and metabolize drugs into forms that can be easily put to use by the body. The liver functions as an energy reserve by pulling excess glucose from circulation and storing it in the form of glycogen. This glycogen can be used as a future source of energy. The liver also helps to regulate amino acid levels in the blood, metabolize some nutrients, remove toxins, and excrete bile. With over 500 responsibilities, having a properly functioning liver is key to good health.

What is fatty liver and who is at risk?

Fatty liver is a condition that can interfere with the proper functioning of the liver. Fatty liver occurs when the fat builds up in the liver to the extent that fat comprises between 5 and 10 percent of the total weight of the liver. There are two main forms of fatty liver disease: non-alcoholic fatty liver disease (NAFLD) and alcohol-induced fatty liver disease. Non-alcoholic steatohepatitis (aka NASH) is a specific type of NAFLD that includes inflammation along with the buildup of fat. This type is particularly problematic as the inflammation can cause scaring (fibrosis) and increase the risk of developing liver cancer. This article will focus on NAFLD as it relates to metabolic health.  

NAFLD impacts approximately 33% of American adults and 10-12% of American children. While pre-existing conditions are not a prerequisite for NAFLD, fatty liver does impact people with diabetes at a significantly higher rate than non-diabetics. Approximately 55% of people with type 2 diabetes develop fatty liver. Obesity is also a risk factor, with 50 to 90% of people who are obese developing fatty liver disease. Individuals with insulin resistance, metabolic syndrome (which impacts 1 in 3 adults), and high cholesterol are all at risk of developing fatty liver.

What does insulin resistance have to do with the liver?

In healthy individuals, a high level of insulin in the blood signals the liver to pull glucose from circulation and store it in the form of glycogen.  When this happens, the liver uses some of the glucose it pulls from circulation and stores it in the form of fat. This mechanism is meant to plan ahead for future energy needs. At a later time, if blood sugar drops too low, we can turn glycogen back into glucose and release it into the bloodstream in order to provide us with energy to power our brain, muscles, or other bodily functions. However, for one in three Americans that have developed insulin resistance, it is likely that this insulin resistance impacts the liver.

The liver can develop what is called selective insulin resistance. In this case, insulin no longer works effectively. Insulin does not prompt the removal of glucose from the blood. Instead, glucose is permitted to linger in the bloodstream, allowing unhealthy high blood sugar levels to persist. As part of this insulin resistance, the liver may also malfunction, break down glycogen, and release it into the blood, even when it is not needed. This compounds the already high blood sugar levels, resulting in excess glucose and ineffective insulin in circulation.

Even though the insulin in circulation is ineffective at pulling glucose from the blood, it is not completely ignored. Instead, the insulin incorrectly triggers the liver to make fat. This additional fat combines with the fat released from our own insulin-resistant fat cells and results in fatty liver. 

How can fatty liver be prevented?

Many of the same steps we take to improve our metabolic health will also aid in the prevention of fatty liver. Consuming healthy food that is not processed and performing regular exercise are common suggestions that benefit general health. Since fatty liver impacts overweight and diabetic individuals at a disproportionate rate, maintaining a healthy weight and regular exercise can significantly reduce the likelihood of developing fatty liver. Limiting fructose consumption has also been tied to improved liver health. One of the liver’s many tasks is that of a metabolizer. Fructose is a monosaccharide sugar that is primarily metabolized in the liver because very few other tissues can use fructose. Thus, consuming an abundance of fructose can overwhelm the liver and prompt it to turn fructose into fat, and this is exacerbated in the context of a caloric surplus. Fructose is especially prevalent in sugary drinks like fruit juices, sodas, or beverages sweetened with high fructose corn syrup. Research has shown that consuming a high volume of these fructose-sweetened drinks increases fat deposits in the liver and other deep visceral organs.

How can fatty liver be reversed?

While there is no medication specifically designed to combat fatty liver disease, in most cases, fatty liver is reversible with some diet and lifestyle changes. Research has shown that one of the most effective ways to reverse fatty liver is to lose weight (with the support of a physician). Assisting with this weight loss effort can be exercise, which helps to burn fat and decrease the production of fatty acids. Low-carbohydrate and high-protein diets have also been shown to be beneficial in reducing the amount of fat in the liver. One study found that low-carbohydrate diets act by improving liver fat metabolism, shifting the gut microbiota, increasing circulating folate, and increasing folate-dependent metabolism gene expression in the liver.  Reducing cholesterol and triglycerides can also reduce the amount of fat in the liver. If blood tests show elevated liver enzymes, eliminating fructose and alcohol intake can go a long way.  Beyond maintaining a healthy body weight, engaging in regular exercise, reducing fructose and overall carbohydrate, and reducing alcohol consumption, exogenous ketone supplements may be an emerging preventative and/or treatment option. Since NAFLD is a serious health concern with no FDA-approved therapies, and is an independent risk factor for cardiovascular disease, liver failure, and all-cause mortality, it is important to understand proper diagnosis, treatment and biomarker monitoring for optimal liver health when putting this information into practice. 

Author: Dr. Colleen Gulick

Colleen Gulick, Ph.D., MS, BS (BioE), EIT (ME), CSCS, is a science researcher and writer with a Ph.D. in exercise physiology. She is the life science writer for GOOD IDEA, Inc; she’s also a professional cyclist.