Is raw tuna bad for nonalcoholic fatty liver disease?

What is NAFLD?

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This term refers to a group of conditions that cause excess fat to accumulate in the liver.

The buildup of fat can injure the liver, leading to permanent scarring and irreversible damage to liver cells. These effects are called cirrhosis. Cirrhosis may lead to liver failure and liver cancer.

People who are more likely to have NAFLD include those with:

• more body weight
• obesity
• type 2 diabetes
• abnormal levels of fat in their blood
• metabolic syndrome

Sometimes, heavy alcohol use can cause alcohol-associated liver disease. By contrast, people with NAFLD may drink little or no alcohol. There are two types of NAFLD:

• Nonalcoholic fatty liver. People may refer to this as “NAFL.” There is fat in the liver but minimal or no inflammation, and no liver damage.
• Nonalcoholic steatohepatitis. People may refer to this as “NASH.” There is inflammation and liver damage, as well as excess fat, in the liver.

Raw tuna and NAFLD

Older research suggests that raw tuna is a good source of many nutrients, including selenium and anti-inflammatory omega-3 polyunsaturated fatty acids (PUFAs).

However, eating raw fish comes with health risks. And some types of cooking retain more nutrients than others. A person might consider speaking with a doctor or registered dietitian for advice.

Tuna contains healthy fats, including the omega-3 fats docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Most of these fats contain omega-3 fatty acids, which fish synthesize from their consumption of marine plants.

Other fish that are rich in omega-3 fatty acids include:

• salmon
• mackerel
• herring
• sardines

No significant evidence suggests that raw tuna can improve NAFLD. Fish oil supplements are a more concentrated source of EPA and DHA, and so may be helpful.

Fish oil and NAFLD

Fish oil contains omega-3 PUFAs. The main types of these acids are:

• alpha-linolenic acid
• DHA
• EHA

Fish oil may protect against harmful effects of a high fat and high cholesterol diet. A 2015 study on the dietary treatment of NAFLD listed the following health benefits of consuming oily fish and fish oil:

• increased insulin sensitivity
• increased levels of a hormone that breaks down fatty acids and reduces inflammation, called adiponectin
• reduced inflammation
• reduced levels of fats in the blood, such as serum cholesterol
• reduced blood pressure
• improved liver function tests
• increased breaking down of fatty acids in the mitochondria
• reduced fat in the liver, or hepatic steatosis

A 2018 study found that omega-3 long-chain PUFA supplementation led to significant improvements in people with NAFLD.

The improvements concerned:

• liver enzyme levels
• liver fat contents
• measures of hepatic steatosis
• metabolic risk factors

A 2020 review supported the findings above. It also suggested that omega-3 long-chain PUFA supplementation improves levels of fat in the liver, as demonstrated by a reduction in body mass index scores among people with NAFLD.

In a 2021 study, people with NAFLD and type 2 diabetes took 2000 milligrams of omega-3s every day for 12 weeks. The researchers found significant improvements in the participants’ fatty liver index, lipid accumulation product, and visceral adiposity index scores, compared with those of participants who had received a placebo.

Managing NAFLD

Weight loss is key for managing NAFLD. But rapid, significant weight loss may induce liver dysfunction and inflammation. Instead, the best approach is to lose weight through regular exercise and a low-calorie diet that includes healthy foods.

A healthcare professional may recommend that a person with NAFLD loses 7–10% of their body weight.

A 2021 review recommends that people with NAFLD focus on eating whole, nutrient-dense foods. These are rich in proteins, complex carbohydrates, and unsaturated fats and include, for example:

• fruits
• vegetables
• whole grains
• legumes, such as beans and chickpeas
• nuts and seeds, including walnuts, pistachios, and sunflower seeds
• healthy fats, such as from healthy oils
• lean sources of protein
• fatty fish

People with NAFLD should limit:

• foods high in sodium
• foods high in simple sugars, such as pastries and cakes
• sweetened beverages, including juices and sodas
• sweeteners, such as corn syrup and fructose
• sources of refined carbohydrates, such as white rice and white bread
• foods high in saturated fat and trans fat, such as fried foods
• processed foods

A registered dietitian or a doctor can help create a diet plan that allows a person to reach their health goals.

The Mediterranean diet, in particular, may benefit people NAFLD by improving liver fat levels.

Exercise may help:

• boost the immune system
• improve liver enzyme levels
• reverse insulin resistance
• prevent hepatic steatosis and liver injury

Regular exercise might involve:

• walking
• gardening
• light jogging
• housework

However, a 2020 study found that moderate-intensity physical activity led to more significant improvements in NAFLD than low-intensity physical activity.

Exercising on its own may improve NAFLD and glucose tolerance. However, diet and lifestyle changes are usually necessary.

The Centers for Disease Control and Prevention (CDC) recommend that adults get at least 150 minutes of moderate-intensity physical activity each week. A person may need more or less than this, depending on their health status and goals.

Summary

NAFLD is caused by fat building up in the liver, potentially causing inflammation and liver damage.

Raw tuna and other oily fish contain high amounts of omega-3 fatty acids. These may reduce inflammation and the amount of liver fat. They may also prevent further liver damage.

A healthy diet and regular exercise are the best ways to manage and prevent liver damage that stems from NAFLD. A registered dietician or a doctor can help a person tailor a dietary plan that helps them reach their weight loss goals safely. A doctor or dietitian can also advise about whether it is safe to eat raw tuna.