Fructose and metabolic syndrome, hypertension and renal disease
In animal studies, an intake of fructose over four weeks as compared with intake of glucose, results in heightened levels of uric acid in the blood, reduced urinary excretion of uric acid, heightened levels of triglycerides, heightened fasting insulin levels, increased production of insulin after a glucose tolerance test and a lowered insulin sensitivity index . All these differences even out after intake of the xanthine oxidase inhibitor allopurinol (15). Intake of fructose results in a significantly accelerated progression of chronic renal failure, enlarged kidneys, glomerular hypertrophy with focal segmental sclerosis and increased interstitial fibrosis when compared with glucose (16).
Increased peripheral insulin resistance can be explained as an effect of uric acid and/or fructose inhibiting the production of nitric oxide, thereby causing reduced peripheral circulation. Stimulation of the production of MCP-1 and ICAM-1 can explain the renal effect.
Glucose tolerance tests undertaken on adult, overweight persons following nine weeks of treatment with equivalent quantities of glucose or fructose show significantly higher values of glucose and insulin after preceding intake of fructose compared with glucose. The same applies to de novo lipogenesis in the liver and visceral adiposity (13).
In a follow-up study of 46 000 men over 12 years, with self-reported nutritional case history , it was found that intake of sugared beverages and fructose, including fruits and fruit juices with a high fructose content, was strongly associated with an increased risk of gout (17). A cross sectional study from the US showed that a daily intake of ≥ 75 grams of fructose is independently associated with elevated blood pressure in adults (18). In a controlled intervention study, adult men were given 200 grams of fructose for 14 days, with or without added allopurinol. Both groups developed findings that were consistent with metabolic syndrome, and allopurinol was shown to have a clear effect in reducing blood pressure (19).