A diet that is high in calories, not sugar-rich foods, may be key driver of non-alcoholic fatty liver disease, according to new research that contradicts current thinking.
The double-blind study of healthy but centrally overweight men compared the effects of high intakes of two types of sugar (glucose and fructose) in two conditions — weight-maintaining (moderate-calorie diet) and weight-gaining (high-calorie diet).
Published in the journal Gastroenterology, results from the study suggest that it is the level of total calories, rather than amount of sugar, in the diet that may be the main risk factor for the development of liver disease.
"In the isocaloric period, overweight men who were on a high-fructose or a high-glucose diet did not develop any significant changes in hepatic concentration of TAGs or serum levels of liver enzymes," wrote the authors. "However, in the hypercaloric period, both high-fructose and high-glucose diets produced significant increases in these parameters without any significant difference between the 2 groups."
"This indicates an energy-mediated, rather than a specific macronutrient-mediated, effect."
In a double-blind study, the team randomly assigned 32 healthy but centrally overweight men to groups that received either the high-fructose or high-glucose diet (25% energy).
The diets were provided during an initial isocaloric period of 2 weeks, followed by a 6-week washout period, and then again during a hypercaloric 2-week period.
Primary outcome measures were hepatic level of triacylglycerol (TAG), with additional assessments of TAG levels in serum and soleus muscle, hepatic levels of adenosine triphosphate, and systemic and hepatic insulin resistance.
In the weight-maintaining period, the team reported that men on neither diet developed any significant changes to the liver. However, in the weight-gaining period, both diets produced equivalent features of nonalcoholic fatty liver disease, including steatosis (fatty liver) and elevated serum transaminase and triglycerides.
Such findings, the authors said, indicate that fructose and glucose have comparable effects on the liver, and calorie intake is the factor responsible for the progression of liver disease.
"Based on the results of our study, recommending a low-fructose or low-glycemic diet to prevent nonalcoholic fatty liver disease is unjustified," said Professor Ian Macdonald, from the University of Nottingham, UK, who led the study. "The best advice to give a patient is to maintain a healthy lifestyle with diet and exercise."
"Our study serves as a warning that even short changes in lifestyle can have profound impacts on your liver."
Volume 145, Issue 5 , November 2013, Pages 1016–1025.e2, doi: 10.1016/j.appet.2013.08.014
"No Difference Between High-Fructose and High-Glucose Diets on Liver Triacylglycerol or Biochemistry in Healthy Overweight Men"
Authors: Richard D. Johnston, Mary C. Stephenson, Hannah Crossland, et al