April 19th is observed worldwide as a day to rise awareness about Liver disorders and we, as FOIE GRAS researchers, would like to contribute with this short piece on the importance of keeping a healthy liver.
Let’s start with a curious fact about the liver. Have you ever tried FOIE GRAS? Regardless of whether your palate has savored this French cuisine delicatessen or not, you are probably aware that it is made of the liver of a duck or a goose. Foie Gras literally means fatty liver and to produce it, these aquatic birds are usually force-fed a large amount of corn through a funnel for weeks on end. This over nutrition procedure has been carried out since the time of the Egyptians and it takes advantage of a very interesting metabolic feature of migratory birds. In the wild, before the migratory season, these animals prepare in advance and feed in excess to later be able to resist long periods flying oversea without running out of energy. But these ducks and geese are usually fed on sugary nutrients such as corn, so how do they produce a fatty liver? To be stored, sugars or carbohydrates need a large amount of water and therefore occupy a lot of space. The liver has a special mechanism that allows for the conversion of excess dietary sugars into fats, which repeal water and are stored much more efficiently. Given the accumulation of fat, the liver of these creatures enlarges and becomes yellowish and it is these reservoirs that are used in later stages of the migration period, when nutrients are scarce.
Our liver is also capable of the conversion of sugars into fats, a phenomenon called de novo lipogenesis. In humans however, the deposition of fat in the liver is not adaptive but pathologic. The accumulation of fat is clinically referred to as steatosis and it is the main feature of Non-Alcoholic Fatty Liver Disease (NAFLD), a condition that nowadays affects 1 in each 4 adults in Europe. This disorder stems from an energy imbalance for which an over-feeding behavior -voluntary and not forced like in the case of the ducks- is partly responsible. Ours and the rest of western societies have progressively shifted from the more traditional cuisine to the energy-dense Western Diet. This type of nutrition is characterized by foods and drinks rich in sugars that provide a very high value of calories (energy unit of foods) to the body. Additionally, the static work environments, the motorized transportation to commute to work and the increase of leisure activities in which physical activity is not necessary, for instance watching TV or playing video-games, have caused a huge decrease in the amount of energy that is being spent a day. This results in too much energy going into the body and not enough coming out, which leaves our organism with the need to retain these calories somehow.
At the beginning, sugars reconverted into fats by the liver are stored together with fats coming directly from the diet in the adipose or fat tissue. This is an adaptive situation, since through this depots, the human body can starve up to 40 days. However, when meals are big in size, frequent and energy-dense or hypercaloric on a daily basis, this situation becomes chronic and it may lead to Obesity. Over time, the fat tissue is unable to retain the vast amount of fat that is constantly consumed and produced by the liver and an excess of fat starts circulating in the bloodstream. These fat molecules can enter other organs that do not usually store big quantities of fats, such as the liver, the pancreas or the skeletal muscle. Fat inside these tissues, causes insulin resistance, which means that muscle and liver cells are no longer responsive to insulin, a signal that the pancreas sends when after a meal the body has absorbed large quantities of sugars and they need to be stored away. Insulin resistance is associated with Type II Diabetes, the Metabolic Syndrome and NAFLD. For the particular case of the liver and NAFLD, this event triggers a cascade of reactions that cause inflammation in the liver and the death of hepatic cells. This inflammation reaction towards the liver can originate from a stress response of the hepatic cells in trying to deal with the excess of fat, but can also come from the bacterial flora in the gut. The composition of the gut microbiota, or the collective of microorganisms that inhabit our intestines, is also affected by Western Diets, which allows for some pathogens to reach the liver and contribute to the inflammatory process. No matter the factors originating or contributing to the inflammation, if persistent can seriously compromise the function of the liver and lead to cirrhosis and liver cancer, both of which are life-threatening conditions.
NAFLD is referred to as a silent killer because it only shows symptoms at late stages of the disease and it is difficult to diagnose in the clinic. A healthy nutritional diet and an active lifestyle allow us to regulate and balance the energy cycles that our body handles every day and reduces the risk of suffering this dangerous fat deposition in the liver. The Mediterranean Diet, UNESCO’s intangible cultural heritage of humanity, is a proven treatment for NAFLD and associated diseases and its effects are better observed in combination with the practice of periodical physical activity of moderate to vigorous intensity, especially aerobic endurance training. Notwithstanding, the value of these recommendations does not only serve to those currently suffering from metabolic disorders, but to us all, if not for prevention, for reflection upon our life-choices.
Today, in WORLD LIVER DAY, it’s a good day to take a minute to reflect on how well we are taking care of our liver, and what small compromises we can incorporate in our life that help keep the health and well-being of this vital organ, and by extension, OURS!
See you liver 😉
Mireia Alemany i Pagès (ESR-13) is currently working at the Center for Neuroscience and Cell Biology (CNC) at the University of Coimbra, Portugal. Her project focuses on raising awareness on NAFLD through Science Communication.
Illustrations by: Rui Tavares (@ruidiastavares)