A recent article published in Harvard Heart Letter1 recommended that readers cut back on fructose. Though the article adequately summarized how the body handles fructose, “especially when there is too much in the diet” or when researchers “give the liver enough fructose,” it did not state clearly enough that these observations were observed largely in test subjects consuming highly exaggerated versus normal fructose exposures.
Fructose always appears in the diet in tandem with equivalent amounts of glucose, whether from added sugars (i.e., sucrose, high fructose corn syrup, honey and fruit juice concentrates) or from naturally occurring sources (fruits and vegetables). It has been known for many years that fructose is metabolized differently when tested alone than in the presence of glucose.2 And while fructose makes up 9.4 and <18% of calories at mean and 95th percentile levels, respectively,3 studies reporting untoward effects commonly expose human and animal subjects to 25-40 and 60+% of calories as fructose, respectively. Such effects have only been observed with contrived laboratory diets; they have not been demonstrated in real-world diets with more realistic, mixed sugars exposures.4-7
Cutting back on all non-essential caloric sources in the diet is inarguably good advice that all readers will find beneficial. But singling out fructose for specific action in liver and heart disease is simply not scientifically justified.