[MUSIC] The liver is important in the regulation of both glucose and lipid concentration in the blood. There is a positive relationship between the degree of liver fat accumulation and the occurrence of elevated fasting blood glucose and lipid levels. For individuals with increased liver fat dietary treatment regimens as a goal to reduce liver fat, to target the metabolic disturbances. We know that excess caloric intake increases liver fat while on the other hand, caloric restriction decreases liver fat. So an important question is whether the content of fat and carbohydrate in the diet plays a role in regulation of liver fat. This appears to be the case. Studies suggest that without restriction of energy intake to induce weight loss, a change in carbohydrate and fat intake can affect liver fat content and also liver function. A reduction in liver fat could inquire for a reduction in fat intake. But is it so? The role of dietary composition has mainly been assessed in obese individuals and individuals with already elevated liver fat. Such studies are informative in treatment perspective. Studies investigating the role of diet composition in regulation of liver metabolism must be carefully controlled. Also to ensure that energy balance is maintained. This can be done by delivering all experimental foods, weigh to one gram of accuracy, ensuring a higher degree of compliance. Along with my two research associates, Annemarie Lundsgaard and Andreas Fritzen, we have performed several well-controlled dietary intervention studies in humans, in which we have changed the content of carbohydrate and the content of fat in the diet in order to look at liver function. So Andreas, what has the most effect on liver fat? Is it the reduction in body weight or is it changing the distribution of carbohydrates and fat in the diet? Prolonged calorie restricted diets promote weight loss and at the same time clearly reduce liver fat content. So weight loss in itself is definitely a factor in regulation of liver fat. However, at the same time, macronutrient composition also is a factor in regulation of liver fat content and that is shown in a study by Kirk et al, who showed in obese individuals, that a 48 hour calorie restriction induced by lowering of either the carbohydrate or the fat intake, induced a lowering of liver fat. When reducing the fat content of the diet, a minor lowering of liver fat was observed. But as you see here on the graph, when reducing the carbohydrate intake a much more pronounced lowering of liver fat was observed. Are there other studies supporting these findings? Yes, in a study by Browning and co-workers, they found in obese individuals suffering from NAFLD, that a two weeks diet low in carbohydrate containing only 10E% of carbohydrate, lowered the liver fat content by 12%. This was observed to a greater extent than a large calorie restriction of their normal diet. Also this was observed, together with an improvement in several markers of liver function. So this suggests that altering macronutrient composition of the diet, lowering carbohydrate, increase fat intake will affect liver fat content. So Andreas, now we have been discussing a lot about the energy restriction, but what about if you are in an energy balance? Yes, this has also been investigated during conditions where the calorie intake is not restricted and energy balance is maintained. In a study from Sweden from 2018 by Mardinoglu and co-workers, they investigated a very low-carbohydrate diet containing only 4E% of carbohydrates in individuals with NAFLD. Being on this very low-carbohydrate diet, lowered liver fat content in all these individuals. On the x-axis we see the days on the diet, and this clearly shows that already within three days on this low-carbohydrate diet, liver fat content was reduced in most of these individuals. Importantly, in the same study, they also found that together with this lowering of liver fat content, they also observed a lowering of blood fat. So Annemarie, how is it, is there a relationship between the changes in fat content in the liver and fat content in the blood? >> Yes, so it is well documented that there is a positive association between fat content in the liver and the fasting levels of fat in the blood. So when liver fat increases, blood triglyceride levels also increases and they can potentially reach dyslipidemic levels. So this increase triglyceride levels in the blood, they are believed to reflect an increased secretion of fat rich lipoproteins from the liver. Such an increase in fat in the blood is not beneficial as it has been associated with an increased risk of cardiovascular disease and also insulin resistance. So, how much should we reduce carbohydrates in the diet then? Yes, so in the Swedish study by Mardinoglu et al, they found out that both liver fat and also the blood triglyceride levels, they were reduced within a few days of changes in the diet, but in that study, their carbohydrate intake was very low. But in more prolonged studies, also in obese individuals with elevated liver fat, it has been shown that liver fat is reduced, when the carbohydrate intake is reduced from the typical 50-60E% in the diet to around 30-40E% as applied in the different studies, so around 30-40E% has an effect in studies. These individuals that you have been discussing now are all obese individuals, and all the data from those have been obtained in obese individuals. So the question is, with the macronutrient distribution, has it a similar or played it a similar role in lean individuals without elevated fat in the liver? Yes, so studies in non-obese healthy individuals are very important in a prevention perspective. As you know, to further understand the role of macronutrient distribution and the relative role of carbohydrate and fat in the diet, we have studied how healthy lean individuals responded to changes in carbohydrate and fat intake. And we investigated markers of liver function, and such measures include glucose output from the liver, secretion of fat to the blood and also insulin clearance by the liver. Because it is actually so that the liver clears a great fraction of the insulin that is secreted from the beta cells, as this insulin passes the liver before it reaches the systemic circulation. We know that when liver fat content increases, the hepatic insulin clearance decreases, or becomes impaired if you will, and that is not appropriate as this will lead to high systemic insulin levels, which in turn can mediate insulin resistance or other metabolic maladies. So in the context of our dietary intervention studies, we have after the interventions done some metabolic testing. On these experimental days we have applied blood samplings, we have also provided infusion of tracers, typically glucose tracers, to evaluate changes in glucose metabolism, and we have also applied indirect calorimetry, where we analyse the expiration air of the subjects to evaluate changes in glucose or fat combustion. So, in our first study, we overfed lean healthy individuals in only three days with excess carbohydrates. We also overfed them with excess fat intake. Here with low carbohydrate and a control mixed diet. In this trial, they were in energy balance, in comparison to the two other ones, where they were in energy surplus. And we found that excess carbohydrate intake led to increased glucose output from the liver, increased fat in the blood and decreased insulin clearance. But on the contrary, low carbohydrate combined with excess fat intake, but still at energy surplus led to decreased glucose output, reduced fat in the blood and increased insulin clearance. All of which are health beneficial effects expected to reduce the risk of developing metabolic diseases. So importantly, we learned from this trial that, we saw beneficial effects with low carbohydrate intake, even under conditions of marked calorie surplus, as the subjects ingested high amounts of fat, and that tells us that it is changes in carbohydrate intake that is most important in regard to liver function or liver health. Further proving the liver beneficial effects of low-carbohydrate availability, we have also shown that in healthy overweight individuals low-carbohydrate intake combined with high fat intake over six weeks and this time notably under conditions of energy balance, had similar beneficial effects. The bars to the left show data obtained at preintervention, and the bar to the right show data obtained at six weeks after a changed diet. So in this study, a low-carbohydrate intake of 20E%, was associated with reduced liver glucose output, reduced levels of fat in the blood and increased insulin clearance indicating a healthy liver after prolonged intake of a low-carbohydrate but high fat. The main evidence thus points to the role of carbohydrate in the diet in regulation of liver fat content. When you eat a high fat meal, the fat is absorbed from the intestine via the lymph vessels draining the gut. Therefore, the fat enters the bloodstream and is taking up in the muscle and adipose tissue before it reaches the liver. This could be one mechanism explaining that fat intake seems not causally related to fat storage in the liver. Actually studies have shown that only 10-15% of the stored fat in the liver originates from dietary fat, but rather comes from adipose tissue on neosynthesis of fat from carbohydrates. The most important mechanism, linking carbohydrate intake to fat content in the liver and dysregulation of liver function, may be that carbohydrates can be converted to fat in the liver. If the carbohydrates are not used as energy fuel in the body or in the liver itself. Carbohydrates can also be stored as glycogen in the liver and muscle, but this is limited. Therefore, carbohydrates in excess are rerouted to new synthesis of fat, and accumulated in the liver. Until now, carbohydrates have only been referred to in general. Dietary carbohydrates are mainly in the form of polysaccharides, disaccharides or monosaccharides. Excess consumption of refined sugars has been viewed as particularly potent to induce NAFLD. Refined sugar is typically in the form of sucrose, which consists of glucose and fructose in a ratio 1:1. Sugar intake is typically high in the western population, and in Denmark sugar intake is close to 10E%. In a Danish study, overweight individuals were provided with either 1L of regular coke, 1L of milk with the same energy content as in the coke, 1L of diet coke or a water, and that was done daily for six months. No body weight gains were observed in any of the groups, so total energy intake appeared to be similar. The regular coke group, which ingested large amounts of sucrose, and thus glucose and fructose, increased liver fat by 140%, whereas the other groups remained unchanged. Especially fructose has been negatively associated with liver fat accumulation, particularly in rodent studies. From such studies we know that metabolism of fructose in the liver increases new-synthesis of fat, especially when energy intake is positive, and also decreases the burning of fat in the liver. Fructose is a simple sugar that is present in table sugar and sweetened beverages, besides being present in fruits. The summarised evidence to suggest that fructose negatively influences liver fat is not consistent. It has been shown in overweight individuals, that replacement of a high amount of fructose in the diet with complex carbohydrates had positive effects on liver fat and liver glucose output. However, when lean individuals ingested either 150 gram fructose, or 150 grams of glucose with a weight maintenance diet, there were no effects on liver fat. The effects of fructose methods depend on the degree of fat in the liver. To further nuance a picture, fruit derived fructose ingestion may not have the same detrimental effect as fructose from sweetened drinks. Finally, low doses of fructose, may be well tolerated. Taken together, there's some evidence to suggest that restricted intake of sugar or fructose sweetened beverages could be an advantage, if you have elevated liver fat. So Andreas, would all groups benefit from reducing carbohydrates in the diet? No, not all groups benefit from lowering their carbohydrate intake. Individuals that are regularly performing high intensity exercise, they use carbohydrates stored as glycogen in their liver and in their muscle during these exercise bouts. They need to replenish their glycogen stores in their liver and muscles, after they have been exercising. So in regularly active people, that are performing high intensity exercise, we recommend a high carbohydrate intake. So in conclusion, it seems that if you have elevated liver fat, a reduction of carbohydrate intake, it can have beneficial effects on liver fat accumulation. Notably, independent of caloric restriction. A diet induced reduction in liver fat can thereby have beneficial effects on hepatic glucose regulations and levels of fat in the blood. Less research has been conducted in lean healthy subjects, but recent studies suggest that also in this population group, reduction of dietary carbohydrates, availability and increases in dietary fat, can regulate liver function. [MUSIC]
