Why Green Leafy Vegetables May Protect Liver Health

New research featured in the journal Proceedings of the National Academy of Sciences (PNAS) discovers that a compound found in green leafy vegetables helps prevent non-alcoholic fatty liver disease in mice.

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Green leafy vegetables, such as lettuce and spinach, contain high levels of nitrate, a compound that may prevent fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD), or fatty liver disease, is a condition in which fat builds up in the liver. Included between 30 and 40 percent of adults in the United States are living with NAFLD.

The condition is one of The most common causes of chronic liver disease in Western countries, and experts link it to obesity, overweight and metabolic risk factors.

Currently there is no approval treatments for NAFLD, which can progress to more serious conditions, such as steatohepatitis, fibrosis and cirrhosis. Health professionals recommend losing weight, making healthy food choices, and getting more physical activity to reduce fat in the liver.

However, new research could pave the way for a new treatment. Scientists from the Karolinska Institutet in Sweden have just published a study in which they show that inorganic nitrate – a compound found naturally in green leafy vegetables – can reduce fat accumulation in the liver.

Mattias Carlström, an associate professor in the Department of Physiology and Pharmacology at Karolinska Institutet is one of the principal investigators and corresponding authors of the study.

Carlström and his colleagues studied the effects of supplementing a high-fat, high-sugar Western diet with dietary nitrate in mice.

They divided the mice into three groups and fed each of them a different diet. The control group received a normal diet, while the high-fat diet group ate the equivalent of a Western diet, and the third group received a high-fat diet with nitrate supplementation.

As expected, the mice in the high-fat diet group gained weight and fat mass, and their blood sugar levels increased. However, all of these markers were significantly lower in the group that also received nitrate.

Carlström reports the results, saying, “When we supplemented mice fed a high-fat, high-sugar Western diet with dietary nitrate, we noticed a significantly lower proportion of fat in the liver.”

The researchers also found that rodents given the nitrate had lower blood pressure and better insulin sensitivity than those fed a high-fat, nitrate-free diet.

Previous research, the researchers explain, has shown that dietary nitrate boosts cellular metabolism. He also suggested that green leafy vegetables may protect against metabolic conditions, such as type 2 diabetes.

Scientists also know that a higher consumption of fruits and vegetables has a positive effect on cardiovascular function.

“We think these diseases are linked by similar mechanisms,” Carlström hypothesizes, “where oxidation stress causes compromised nitric oxide signaling, which adversely impacts cardiometabolic functions.

The researchers explain that the medical community still doesn’t know exactly which compounds make leafy greens so healthy. “No one has focused on nitrate yet, which we think is key,” Carlström continues.

We now want to conduct clinical studies to investigate the therapeutic value of nitrate supplementation in reducing the risk of fatty liver disease. The results could lead to the development of new pharmacological and nutritional approaches.

Mattias Carlstrom

Further studies are needed to clarify which compounds are responsible for these healthy properties and to confirm that nitrate is essential for liver and metabolic health. In the meantime, the team advises people to consume more green leafy vegetables.

Those with the highest concentration of inorganic nitrate include “celery, spinach, lettuce and arugula”.

“[I]It doesn’t take huge amounts to get the protective effects we’ve seen — only about 200 grams a day,” says Carlström. “Unfortunately, however, many people are choosing not to eat enough vegetables these days,” he adds.

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