Non-Alcoholic Fatty Liver Disease (NAFLD) is a condition not only highly associated with metabolic syndrome, but is also on a meteoric rise as a global health concern and is every bit as ominous as it sounds. A recent meta-analysis suggests that as much as a quarter of the world’s population may be suffering from this condition, which is a strong presage of future cardiovascular problems, yet you’ve likely never even heard of it. But you probably should familiarize yourself with it, as recent research suggests it is highly correlated with heart health and insulin resistance.
The liver is one of the most vital of your vital organs. Nestled behind your ribs is the wedge-shaped, reddish-brown cleansing wonder that is tasked with filtering blood, regulating various chemical levels, and metabolizing drugs. It is also the site for production and excretion of bile, a liquid substance that helps process lipids for absorption and transport waste products out of the body. While a normal liver does contain a small amount of fatty tissue, NAFLD is characterized by fat composition exceeding 5%. As liver composition becomes increasingly fatty, it gets into a cycle of continuous inflammation, which can lead to fibrosis, the formation of scar tissue, apoptosis (cell death), and ultimately, full-blown liver disease. This condition is also highly correlated with diabetes and heart disease risk. It is estimated that as much as 90% of those who have been diagnosed with metabolic syndrome, due primarily to a combination of poor diet and lack of physical activity, also suffer from NAFLD and are on a runaway train to a wide array of blood glucose regulation and cardiovascular issues.
Although liver dysfunction is most often associated with excess alcohol consumption, drinking alcohol is not the most influential lifestyle behavior in overall liver health. That would be your diet, or more specifically, your sugar consumption. A recently published randomized, two-way crossover study examined the influence of sugar consumption on liver composition and other biomarkers of health. Researchers recruited 25 men, 11 who had already been diagnosed with NAFLD and 14 who had relatively low levels of liver fat. Using a computer-generated sequence, participants were randomized into either a high- or low-sugar diet. The high-sugar diet included 650 calories from “simple” carbohydrates (26% of total energy intake, approximating the amount in an “average” contemporary diet), including sources that are commonly accepted as “healthy,” such as dried fruit, fruit juices, and low-fat dairy. Those in the low-sugar diet were restricted to 140 calories per day (6% of total energy intake, approximating recommended guidelines for sugar intake) from simple carbohydrates, replacing most of it with whole grains and vegetables. The diets were iso-energetic (contained the same amount of total calories and created to match each participant’s basal needs) and were identical in overall macronutrient composition (proportion of carbohydrates, protein, and dietary fat were similar). Participants were also asked to maintain their regular levels of physical activity. Following the initial 12-week trial period, there was a 4-week washout period in which all participants returned to their habitual diet before they were then asked to switch to the alternative diet for another 12-week trial period. Basic biomarkers of health (weight, body fat percentage, plasma lipids, glucose and serum insulin) were measured before and after each trial period while specific metrics of liver health and composition were determined only after each dietary trial. What the researchers found was that initial liver composition had little influence on how participants responded to the high-sugar diet in terms of weight management. The participants already diagnosed with NAFLD and those with relatively healthy livers both gained weight (approximately 4 lbs. during the 12-week period) and experienced expected increases in liver fat accumulation. They then experienced the opposite effect during the low-sugar trial periods (losing, on average, nearly 4 lbs.), but the influence on lipid metabolism was quite different. Of particular concern was very low-density lipoprotein (VLDL), a “bad” cholesterol that contains a large amount of triglycerides and is a major factor in the accumulation of cholesterol on arterial walls and in the development of heart disease. Participants previously diagnosed with NAFLD experienced significant increases in plasma VLDL concentration following the high-sugar diet, while those with normal liver fat levels showed insignificant changes in plasma cholesterol levels.
The weight changes, although not initially expected because both diets were iso-energetic, have a logical theoretical explanation. Researchers posited that the high-sugar diet, which was also lower in fiber, was less satiating and therefore more difficult to adhere to; participants were likely eating more on a day-to-day basis during the high-sugar trial period. What is not so easily explained is the variances in influence on production of VLDL. While the study did not provide much information to help us understand the mechanisms behind the effect (other than some theories about de novo lipogenesis and alterations in intra-hepatic fatty acid storage), it is clear that how fatty one’s liver is can have significant effects on how you break down fat. It may be possible for a “healthy” liver to temporarily adjust to maintain homeostatic plasma lipid levels during periods where dietary habits may not be so good, but a liver with abnormally high levels of fat reacts to increased sugar intake by altering lipid metabolism to increase production of “bad” cholesterol. In essence, a healthy liver provides a buffer to deal with times when your normal healthy dietary habits go to the wayside, but an already dysfunctional liver is just a holiday season away from significantly increasing your risk for heart disease and insulin resistance.
There are so many distinct takeaways from this recent finding, but most of them are difficult to explain without coming off like a human biology textbook and are probably of little relevance to you. The fundamental theme is simple and, in my opinion, the single most important concept in all of health science. Health is holistic. Being healthy makes it easier to stay healthy. Feel like spending Halloween week binge-watching all of Stranger Things season 2 with your children’s trick-or-treating buckets at arm’s reach? Probably not a big deal if you are otherwise healthy, but for one with NAFLD, it may be opening the door for some haunting health issues. A lifestyle with a solid foundation of good dietary decisions and daily physical activity allows one the freedom to have an off day (or two or three or even 84, as in this study) and it not result in real, long-term, negative health consequences. Get off the sugar-paved road to NAFLD and heart disease and onto the path of lifelong health and vitality.
Dr. Damian Rodriguez is the health and exercise scientist for doTERRA International, LLC. He holds a doctorate in health science, a master’s degree in exercise physiology, and countless professional certifications. He has spent most of his life researching nutrition, exercise, and the lifestyle behaviors associated with optimal health. Along with his passion for health, as someone who lives with Asperger’s Syndrome, he is also involved in bringing awareness to autism spectrum disorders. There are varying opinions about many health and fitness topics. His opinions are his own and not necessarily that of doTERRA International, LLC. Consult your healthcare provider before making any changes to diet and exercise.