Individuals who consume higher levels of saturated fats are more likely to feel the effects of a range of health conditions, including non-alcoholic fatty liver disease. Although this link is well-known, exactly how and why it develops is not yet clear.
Non-alcoholic fatty liver disease (NAFLD), as the name suggests, is a condition in which excess fat is stored in the liver of an individual who drinks little or no alcohol.
Marked by liver inflammation, NAFLD most commonly affects people in their 40s and 50s, and especially those who are obese. It can cause scarring of the liver and permanent damage. At its worst, it can lead to liver failure.
NAFLD is primarily characterized by an increased buildup of fat in the liver, and this buildup is often accompanied by insulin resistance, thereby increasing the risk of type 2 diabetes and cardiovascular disease.
Although a diet high in saturated fats is linked to NAFLD, it is not clear how fatty foods initiate these changes in the liver.
Because of the unerring rise in obesity, NAFLD is predicted to become the number one reason for liver transplantation in the near future. It is already the most common chronic liver disease; NAFLD affects an estimated 20-30 percent of the Western population and 90 percent of individuals who are morbidly obese.
Currently, the reasons why high-fat diets cause NAFLD and metabolic disorders are not known. Similarly, it is not understood why certain people who eat a high-fat diet do not develop these conditions, and why some people who eat a healthful diet, do. Since the burden of metabolic disorders in Western countries is rising sharply, researchers are working to understand the exact processes behind these metabolic changes in the liver.
A recent study, published in The Journal of Clinical Investigation, set out to investigate this interaction at a molecular level.
Researchers from Michael Roden’s laboratory at the German Diabetes Center in Germany, led by Elisa Álvarez Hernández, examined how a single episode of high saturated fat intake would affect insulin sensitivity and other markers of metabolism in humans and mice.
In total, 14 lean and healthy participants were involved in the study. The researchers provided a quantity of fat (palm oil) equivalent to a single rich meal. Following the meal, they analyzed each individual’s hepatic metabolism. They carried out a similar, parallel experiment on mice.
An immediate increase in fat accumulation and changes in liver metabolism were observed. This single meal also led to elevated triglycerides, insulin resistance, and increased glucagon (a hormone that increases glucose levels) in the bloodstream.
The high-fat palm oil meal was found to decrease insulin sensitivity across the board. Findings show that:
- Whole body insulin sensitivity decreased 25 percent
- Hepatic insulin sensitivity decreased 15 percent
- Adipose (fat) tissue insulin sensitivity decreased 34 percent.
Hepatic triglycerides – the main constituent of body fat in humans and a marker for metabolic and cardiovascular disease – also rose by 35 percent.
The study shows that consuming saturated fat lays the foundation for metabolic disease by influencing liver metabolism and the storage of fat. As the authors conclude:
“Saturated fat ingestion rapidly increases hepatic lipid storage, energy metabolism, and insulin resistance. This is accompanied by regulation of hepatic gene expression and signaling that may contribute to development of NAFLD.”
Because the current study only utilized male mice and human participants, the team hope to extend their findings in females. It is possible that the uptake of fatty acids by the liver is greater in men. In future investigations, the team also plan to make changes to their choice of control; in the current study, they compared saturated fat intake to water, but their next project will compare saturated fat with unsaturated fat and protein.
By understanding the metabolic machinery behind NAFLD, medical science may uncover novel ways to treat this prevalent and destructive condition.