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The total number of people with diabetes worldwide is projected to double by 2030.1,2 Given the increasing prevalence of obesity, these fgures probably underestimate the future prevalence of diabetes. The risk for developing type 2 diabetes mellitus (T2DM) and premature cardiovascular disease are strongly linked to the metabolic syndrome, a condition characterized by excess central adiposity, elevated triglycerides, reduced high-density lipoprotein (HDL) cholesterol, hypertension, and impaired glucose tolerance.3
A number of dietary factors have been implicated in the development and progression of this cardiometabolic phenotype. Chief among them have been sugars containing fructose: fructose, sucrose, and high-fructose corn syrup (HFCS). Since a temporal relationship was frst demonstrated between the increasing availability of HFCS and the prevalence of overweight and obesity in the US nearly a decade ago,4a fructose-centric view of cardiometabolic diseases has emerged. We aim to review the scientifc evidence supporting the role of fructose-containing sugars in the epidemics of diabetes and its related cardiometabolic complications.
Current Dietary Advice Regarding Sugar Intake
Various dietary guidelines have addressed sugars (see Table 1). Most have focused on the reduction of added fructose-containing sugars to maintain a healthy bodyweight.5–14 Recent American Heart Association lipid guidelines15 and international diabetes guidelines16–18 have singled out fructose by setting upper thresholds for fructose intake based on putative adverse lipid effects, although the American Diabetes Association acknowledges that fructose produces a lower postprandial glucose response when it replaces sucrose or starch in the diet.17 The guidelines implicate all fructose-containing sugars. There is now broad scientifc consensus that sucrose and most forms of HFCS are nutritionally and metabolically equivalent.19–21 Differences in the thresholds for harm set by the different guidelines, however, re"ect some uncertainty in the evidence on which the guidelines are based.
Dietary Sugar Sources/Typical Intake Patterns
Sugars are found naturally in fruit and fruit products (fructose) and are added to foods mainly as sucrose (50 % bound fructose) or HFCS (42 % to 55 % free fructose) during preparation or processing to improve their palatability. HFCS is available at various fructose levels. HFCS 42, used in beverages, processed foods, cereals, and baked goods, comprises 42 % fructose and 53 % glucose. HFCS 90 comprises 90 % fructose and 10 % glucose. It is used in small quantities for specialized applications, but is primarily blended with HFCS to produce HFCS 55, which is used in soft drinks. The most important sources of fructose are nonalcoholic beverages (46 %) followed by grain products (17.3 %), and fruit and fruit products (13.4 %) (see Figure 1). The introduction of corn sweeteners in the early 1970s led to the progressive replacement of sucrose with HFCS in sugar-sweetened beverages (SSBs), so that the availability of sucrose (44 %) and HFCS (42 %) in the US market is roughly equal.22 The use of fruit sugar concentrate is also increasing.23
Although the availability of sugars has increased considerably over the last 50 years,24 total added sugar intake has begun to decrease over the last decade in the US. According to an analysis of the National Health and Nutrition Examination Survey (NHANES) III from 1999 to 2008 (n=42,316), the intake of added sugars in the US has decreased from 100.1 g/day (18.1 % energy) to 76.7 g/day (14.6 % energy), with a reduction in the intake of SSBs accounting for two-thirds of this reduction.25 The contribution of fructose to the diet has followed these trends. Total fructose intake is 49 g/day (9.1 % energy intake) at the 50th percentile and 87 g/day (14.6 % energy intake) at the 95th percentile.22 The highest intakes of fructose are among males 15–18y and 19–22y, each of whom consumes 75 g/day at the 50th percentile and 121 g/day and 134 g/ day, respectively, at the 95th percentile. On a per bodyweight basis, the highest intakes of fructose are in non-breast-fed infants and toddlers.22