In this nationally representative sample, 45–59 year old adults who regularly consumed HFCS sweetened soft drinks had twice the likelihood of having CHD, independent of potential confounders, including diabetes and hypertension, while there was no association with diet drinks. The results of this cross sectional study are consistent with existing longitudinal epidemiology research [15, 16]. What differs in this study, relative to others, is that further adjustments were made for pre-diabetes and glycated hemoglobin (A1c). Notably, the association with CHD persisted after these adjustments, suggesting that the link between regular intake of HFCS sweetened soft drinks and CHD may be independent of blood glucose concentration.
Further, regular consumers of any combination of high excess free fructose beverages, including HFCS sweetened soft drinks, fruit drinks, and naturally high EFF apple juice were nearly three times more likely to have CHD than seldom or never consumers, independent of potential confounders, including pre-diabetes, glycated hemoglobin (A1c), and T2D status; higher than that for regular consumers of HFCS sweetened soft drinks alone. This is consistent with the hypothesis that regular intake of beverages with high ratios of fructose to glucose (excess free fructose) is associated with CHD. There was no association with low EFF beverages (diet drinks and citrus juice).
Although 5% or 10% more fructose in HFCS does not seem like a large amount [32, 33], HFCS that contains 60% or 65% fructose exceeds concentrations that are generally recognized as safe (55%) , and given average per capita intake (65 g/wk. or just under 1 lb./wk) [46, 47], it may be associated with above average fructose malabsorption (FM) in the general population [49–53]. Importantly, FM occurs after consumption of unpaired excess free fructose (EFF), but not with sucrose or equal monomers of fructose and glucose [49–51]. In the context of FM, these incremental amounts are significant. For example, in 65 g of HFCS (average per capita consumption) that is 55% fructose, there are 6.4 g of EFF. When the fructose content increases to 60%, the amount of EFF doubles to 13 g. When the fructose content increases to 65%, the amount of EFF triples to 19.4 g.
FM research indicates that 30% of healthy adults are FM positive after a 25 g EFF dose, and 10% are FM positive after a 12 g EFF dose, but not after consuming sucrose or equal amounts of fructose and glucose monomers . Children are at increased risk of FM at lower EFF exposure [49–51]. Moreover, these amounts do not consider EFF contributions from naturally high EFF apple juice (67% fructose, 33% glucose) , apple juice based drinks , or foods and beverages sweetened with agave syrup, which contains more than 60% fructose . Notably, one 8 oz. cup of apple juice contributes 9 g of EFF to the daily EFF load from HFCS , whereas the EFF contribution from orange juice is nominal (0.4 g).
From a glycemic perspective, orange juice, has a glycemic load (15) that is marginally lower than non-diet cola (16), and slightly higher than apple juice (12), per 250 ml serving . Yet, analyses with orange juice were not associated with CHD, rather, moderate consumption appeared protective. Interestingly, research on SSB and T2D from the Black Womens’ Health Study – a prospective follow-up study of 59,000 African American women – showed that regular intake of orange and grapefruit juice was not associated with T2D – a common comorbidity of CHD . Notably, other prospective studies with juice and T2D have not distinguished between juice types, and results have been mixed . In a recent meta-analysis of epidemiologic research with T2D and sugary drinks (SSB, fruit drinks, and fruit juices), two studies that adjusted for glycemic index (GI) as a potential confounder showed that the increased risk of T2D persisted, independent of GI. None of the other studies in the meta-analysis adjusted for GI . These results provide further evidence that another mechanism, independent of glycemic load and blood glucose, may be contributing to the increased risk of CHD, T2D and comorbidities among regular consumers of SSB.
From a total sugars perspective, orange juice (OJ) and HFCS sweetened cola are similar. Per 8 oz. cup, OJ contains 20.7 g of total sugars, and 10.1 g of total fructose , and cola contains 26.4 g of total sugars , and either 15.8 g (60% fructose), or 17.2 g (65% fructose) of total fructose, depending upon the HFCS formula used. However, per 8 oz. cup, cola contains 12 or 17.5 times the amount of EFF as OJ, depending upon the fructose percentage. Specifically, orange juice contains 0.4 g (NDB No. 09207) of EFF , whereas cola contains 4.7 g of EFF, when the HFCS formula contains 60% fructose, and 7.0 g of EFF when the HFCS formula contains 65% fructose; slightly lower than the 9 g in one cup of apple juice. Therefore, this substantial difference in EFF and underlying fructose malabsorption, rather than glycemic load, may explain why intakes of HFCS sweetened soft drinks, fruit drinks, and high EFF apple juice are associated with CHD, while intake of orange juice is not. More detail is available as Additional file 1: Table S2 and S3.
Notably, our prior epidemiologic research with high EFF beverages suggested that adults who regularly consumed HFCS sweetened soft drinks were nearly twice as likely to have chronic bronchitis as never/ seldom consumers , and that young adults who consumed any combination of high EFF beverages were three times as likely to have autoimmune arthritis as seldom/ never consumers, independent of lifestyle, dietary and socio-economic factors, diabetes and glucose status . Our prior research with high EFF beverages and asthma/ chronic bronchitis was motivated by results of an HFCS food elimination diet , and research with young adult, auto-immune arthritis and CHD was motivated by the fact that chronic respiratory conditions are common comorbidities of arthritis and CHD [6–11].
Multiple hypotheses have been suggested to explain the mechanisms responsible for the association between SSB and chronic disease. In addition to glycemic load, researchers have hypothesized that high intake of fructose may increase the risk of CHD, because fructose increases triacylglycerol concentration, which promotes dyslipidemia – a risk factor for CHD. Researchers have also postulated that fructose consumption may promote endothelial dysfunction and vascular damage, possibly due to the production of uric acid, which may reduce endothelial nitric oxide and, thereby, increase oxidative stress [14–16]. However, our results suggest that these hypotheses do not fully explain the association between SSB and CHD. The higher probability of CHD among apple juice versus orange juice drinkers is not likely explained by antioxidant properties either, as post pasteurization vitamin C content is comparable between apple juice (95.5 mg/c) and orange juice (75 mg/c) . We hypothesize that the mechanism involves malabsorption of unpaired excess fructose, as occurs when the fructose to glucose ratio exceeds 1:1.
Despite ongoing research, the exact cause of fructose malabsorption is not completely understood, but may result from EFF consumption that exceeds an individual’s EFF transport (GLUT5) capacity.  Notably, few natural foods contain significantly more fructose than glucose. Exceptions include apples, pears, watermelons, and mangoes . According to the “fructositis” hypothesis, underlying fructose malabsorption and unabsorbed EFF may contribute to the intestinal in situ formation of AGE (enFruAGE). GI generated AGE may be an overlooked source of immunogens that travel to other tissues and promote inflammation by binding the pro-inflammatory receptor of advanced glycation end-products (RAGE) , known to be concentrated in the lungs, heart, connective tissues, lymph nodes  and, as recently discovered, the pancreas, in the presence of AGE [58, 59].
Intestinal enFruAGE may be an overlooked source of pro-inflammatory AGE that is separate from dietary AGE, and AGE that form in the systemic circulation of diabetes patients, under high blood glucose conditions . The pH of the duodenum and jejunum, under high EFF conditions, appears to be more conducive to AGE formation than the systemic circulation of diabetes patients under high glucose conditions , and recent murine based research provides evidence of AGE formation in the jejunum [60, 61]. There is also evidence that the way excess free fructose is transported and absorbed into the body differs than when fructose is consumed in relatively equal proportions with glucose . For many people, consumption of excess free fructose results in unabsorbed fructose in the intestines. Importantly, the intestinal environment after a meal may be highly conducive to AGE formation in the presence of unabsorbed excess free fructose, as transition metals including iron (Fe2+) are known to accelerate the Maillard reaction [63, 64]. Further, anionic ligands including the phosphates in soft drinks, particularly colas, and the bicarbonate from pancreatic juice, are potent catalysts of glycation at specific sites on proteins [65–68].
There is evidence that AGE are deposited in arterial walls, accumulate over time, and contribute to stenosis and atherosclerosis ; AGE accumulate in the coronary artery of heart disease patients with  and without [69, 70] diabetes and contribute to CHD [20, 69, 70]; AGE accumulate in the pancreas and contribute to pancreatitis and impaired ß-cell function; [58, 59] AGE are elevated in connective tissues including the synovium, sub-lining, and cartilage of autoimmune arthritis sufferers [71–75]; and the receptor of advanced glycation end-products (RAGE) is a key mediator of asthma .
The interaction of AGE with the receptor for advanced glycation end products (RAGE) is well studied. Cytokines, known to be associated with AGE/RAGE pro-inflammatory signaling, are involved in the inflammatory process in asthma and other comorbid conditions, including RA, CHD and T2D . There is evidence that regular consumption of SSB elevates the same pro-inflammatory cytokines associated with AGE/ RAGE pro-inflammatory signaling. For example, in the Health Professionals Follow-up study with 42,883 men, intake of HFCS sweetened, but not artificially sweetened beverages, was significantly associated with higher C-reactive protein (CRP), IL6, and tumor necrosis factor receptors . These biomarkers are consistent with the transcriptional activation of genes associated with AGE/ RAGE/ pro-inflammatory signaling and are known to be involved with chronic inflammation . Importantly, a similar investigation of sucrose found no association with CRP, and high consumption of sucrose-sweetened foods and drinks had only a limited association with CRP .
Notably, our study of EFF in children showed that regular consumers of any combination of high EFF beverages were five times more likely to have asthma as seldom/ never consumers; and that moderate (1–4 times/wk) and regular (≥5 times/wk) apple juice consumers were more than twice as likely to have asthma as seldom/never consumers. There was no association with orange juice . It is possible that enFruAGE contribute to inflammation beginning in childhood, as inflammation is commonly observed in children with asthma , including mild and moderate asthma . EnFruAGE may begin to accumulate in arterial walls and in the pancreas in childhood, as recent research indicates that acute pancreatitis is more common in children than previously thought [70, 79]. The intestinal in situ formation of pro-inflammatory enFruAGE, resulting from regular EFF consumption, could explain why children with asthma have an increased risk of T2D, and why adults with asthma have an increased risk of T2D and CHD. It is a potential pathway that could explain the connection between the gut and asthma, idiopathic chronic bronchitis, RA, T2D, and CHD.
Importantly, while this study was undergoing peer review, results of a proof of concept experiment were published, which provide evidence of possible enteral enFruAGE formation. Incubation of amino acids with fructose - but not glucose - at concentrations and pH that would be present in the intestines after a meal, led to a time and dose dependent formation of AGE intermediates, as measured by fluorescence, after just 1 h of incubation – a time frame well compatible with the digestive process .
This study is subject to limitations. First, the associations are cross-sectional, limiting causal inference. Although cross sectional and longitudinal studies are both observational studies, cross sectional studies provide only a single “snapshot” in time. Second, the NHANES data have some degree of error which may have affected our results. Third, our models did not include adjustment for triglycerides or LDL - known risk factors of CHD - as these were measured only in a subset of respondents. Fourth, fruit and vegetable intake - a covariate included in analyses - may be underestimated, as responses that measure intake of individual foods do not always capture intake from mixed dishes. However, our results are consistent with existing largescale study results, wherein intake of HFCS sweetened soft drinks, and fruit drinks increased CHD risk, independent of dietary quality [15, 16]. Fifth, CHD status in NHANES is based on self-report, so there is potential for reporting bias. However, our results are comparable to findings from existing large-scale longitudinal studies of HFCS sweetened soft drinks and CHD. [15, 16] Sixth, high EFF beverages are only one food category that contributes to daily EFF load. Associations between dietary EFF and CHD may be higher when other food sources of EFF are considered. For example, a 20 oz. (590 ml) bottle of cola contains 65 g (240 kcal) from HFCS. Coincidentally, average daily HFCS intake during the study period was approximately 65 g/d. However, only adolescent boys consumed this amount of HFCS (kcal/d) from SSB (12–19 y boys, 273 kcal; girls, 138 kcal), relative to other age groups: (2–5 y boys, 71 kcal; girls, 70 kcal; 6–11 y boys, 141 kcal; girls 112 kcal; 20–39 y men, 252 kcal; women, 138 kcal; 40–59 y men, 159 kcal; women, 86 kcal; 60 y ≥ men, 70 kcal; women 42 kcal) . Therefore, for many people, HFCS sweetened foods (other than beverages) may be major sources of high fructose corn syrup. Lastly, the extent to which high EFF agave syrup and crystalline fructose – increasingly popular HFCS alternatives – are contributing to fructose malabsorption prevalence is unknown.