Can excessive protein intake affect liver function?

From the Guidelines

Excessive protein intake can indeed affect liver function, particularly in individuals with pre-existing liver conditions, and the recommended daily protein intake should be tailored to individual needs to avoid putting unnecessary stress on the liver. The liver plays a crucial role in processing protein by metabolizing amino acids and producing urea to eliminate excess nitrogen. When protein consumption is significantly higher than needed, the liver must work harder to process this excess, potentially leading to increased stress on the organ. This is particularly concerning for individuals with pre-existing liver conditions such as non-alcoholic fatty liver disease or hepatitis.

According to the most recent and highest quality study, the recommended protein intake for adults with cirrhosis is 1.2-1.5 g/kg/day, as stated in the 2021 practice guidance by the American Association for the Study of Liver Diseases 1. This recommendation is based on the finding that patients with cirrhosis have increased protein needs, and a positive protein balance was achieved above a protein intake of 1.2 g/kg/day.

Some key points to consider include:

• The type of protein consumed may also play a role, with some studies suggesting that vegetable and casein-based protein diets may be beneficial in reducing hepatic encephalopathy (HE) 1.
• Protein restriction is not recommended in cirrhotic patients with HE, as it can increase protein catabolism 1.
• The liver's ability to process protein can be affected by various factors, including the presence of liver disease, and individual protein needs may vary accordingly.

Overall, it is essential to consume a balanced diet with moderate protein intake, tailored to individual needs, to protect liver health and avoid putting unnecessary stress on the organ. Consuming protein well beyond one's body's requirements can force the liver to convert excess amino acids into glucose or fat, and the nitrogen waste must be filtered and excreted, which can burden both the liver and kidneys. Signs of liver stress from excessive protein may include fatigue, digestive discomfort, and in severe cases, elevated liver enzymes.

From the Research

Excess Protein Intake and Liver Function

• Excessive protein intake can affect liver function, as the liver plays a crucial role in deaminating proteins and producing urea for excretion of excess nitrogen 2.
• High protein diets, which can exceed the liver's capacity to convert excess nitrogen to urea, may lead to dangers such as hyperaminoacidemia, hyperammonemia, hyperinsulinemia, nausea, diarrhea, and even death 2.
• The liver's capacity to handle excess protein intake is limited, and excessive intake can put a strain on the liver, particularly in individuals with pre-existing liver conditions.

Protein Requirements and Liver Disease

• Protein requirements may be elevated in individuals with liver disease, such as cirrhosis, and diets supplying less than 60g of protein per day should not be prescribed in long-term treatment of cirrhotic patients 3.
• Insufficient protein intake has been linked to increased mortality in patients with cirrhosis awaiting liver transplantation, and protein intake below 0.8g/kg/d was an independent predictor of malnutrition and mortality 4.
• Protein deficiency is often associated with liver disease, and the principal cause of protein deficiency is decreased dietary intake, which can contribute to protein deficiency in alcoholic liver disease 5.

Dietary Protein Insufficiency and Fatty Liver Disease

• Dietary protein insufficiency has been linked to excessive TAG storage and non-alcoholic fatty liver disease (NAFLD) in developing countries, and may be due to altered peroxisomal, mitochondrial, and gut microbiota function 6.
• The methyl donor amino acid composition of dietary protein is an important contributor to liver function and lipid storage, and the presence and abundance of dietary branched-chain amino acids can modulate the composition and metabolic activity of the gut microbiome 6.
• Specific amino acid supplementation can ameliorate fatty liver disease in preclinical animal models fed with low-protein diets, highlighting the importance of adequate protein intake for liver health 6.