Life Extension Magazine

Life Extension Magazine December 2008

Abstracts

Corn Syrup

Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity.

Obesity is a major epidemic, but its causes are still unclear. In this article, we investigate the relation between the intake of high-fructose corn syrup (HFCS) and the development of obesity. We analyzed food consumption patterns by using US Department of Agriculture food consumption tables from 1967 to 2000. The consumption of HFCS increased > 1,000% between 1970 and 1990, far exceeding the changes in intake of any other food or food group. HFCS now represents > 40% of caloric sweeteners added to foods and beverages and is the sole caloric sweetener in soft drinks in the United States. Our most conservative estimate of the consumption of HFCS indicates a daily average of 132 kcal for all Americans aged > or = 2 y, and the top 20% of consumers of caloric sweeteners ingest 316 kcal from HFCS/d. The increased use of HFCS in the United States mirrors the rapid increase in obesity. The digestion, absorption, and metabolism of fructose differ from those of glucose. Hepatic metabolism of fructose favors de novo lipogenesis. In addition, unlike glucose, fructose does not stimulate insulin secretion or enhance leptin production. Because insulin and leptin act as key afferent signals in the regulation of food intake and body weight, this suggests that dietary fructose may contribute to increased energy intake and weight gain. Furthermore, calorically sweetened beverages may enhance caloric overconsumption. Thus, the increase in consumption of HFCS has a temporal relation to the epidemic of obesity, and the overconsumption of HFCS in calorically sweetened beverages may play a role in the epidemic of obesity.

Am J Clin Nutr. 2004 Apr;79(4):537-43

Fructose ingestion enhances atherosclerosis and deposition of advanced glycated end-products in cholesterol-fed rabbits.

This study was performed to investigate whether the plasma concentration of phosphatidylcholine hydroperoxide (PCOOH), which is a marker of oxidized stress in the blood, increased in cholesterol-fed rabbits, and fructose ingestion promoted this process and aggravated atherosclerosis. Male Japanese white rabbits (age: 12 weeks, and body weight: around 2.0 kg, n = 15) were divided into three groups, (1) a NN group as a normal control fed a standard diet (n = 5), (2) a CN group fed 1.0% cholesterol, and (3) a CF group given both 1.0% cholesterol and 10% fructose-containing tap water. During 8 weeks, plasma PCOOH levels increased significantly in the CN and CF groups compared to the NN group and fructose further raised the PCOOH level. The atherosclerosis was significantly promoted and the deposition of advanced glycation end products (AGEs) was marked in the CF group compared to the CN group. Fructose worsened the atheromatous lesions caused by cholesterol feeding. The mechanism is most likely through lipid peroxidation, which was increased by cholesterol feeding-induced hyperlipidemia, and the formation of AGEs.

J Atheroscler Thromb. 2005;12(5):260-7

Effects of glucose-to-fructose ratios in solutions on subjective satiety, food intake, and satiety hormones in young men.

BACKGROUND: The greater prevalence of obesity and the metabolic syndrome in the past 35 y has been attributed to the replacement of sucrose in the food supply with high-fructose corn syrup (HFCS). OBJECTIVE: Two experiments were conducted to determine the effect of solutions containing sucrose, HFCS, or various ratios of glucose to fructose (G:F) on food intake (FI), average appetite (AA), blood glucose (BG), plasma insulin, ghrelin, and uric acid (UA) in men. DESIGN: Sugar solutions (300 kcal/300 mL) were (in %) G20:F80, HFCS 55 (G45:F55), sucrose, and G80:F20 (experiment 1, n = 12) and G20:F80, G35:F65, G50:F50, sucrose, and G80:F20 (experiment 2, n = 19). The controls were a sweet energy-free control (experiment 1) and water (both experiments). Solutions were provided in a repeated-measures design. AA, BG, and FI were measured in all subjects. Hormonal responses and UA were measured in 7 subjects in experiment 2. Measurements were taken from baseline to 75 min. FI was measured at 80 min. RESULTS: Sucrose and HFCS (experiment 1) and sucrose and G50:F50 (experiment 2) had similar effects on all dependent measures. All sugar solutions similarly reduced the AA area under the curve (AUC). FI and plasma UA concentrations were significantly (P < 0.05) lower after high-glucose solutions than after low-glucose solutions. The lower FI was associated with a greater BG AUC (P < 0.05) and smaller AA and ghrelin AUCs (P < 0.01). Insulin and BG AUCs were positively associated (P < 0.001). CONCLUSION: Sucrose, HFCS, and G50:F50 solutions do not differ significantly in their short-term effects on subjective and physiologic measures of satiety, UA, and FI at a subsequent meal.

Am J Clin Nutr. 2007 Nov;86(5):1354-63

Potential role of sugar (fructose) in the epidemic of hypertension, obesity and the metabolic syndrome, diabetes, kidney disease, and cardiovascular disease.

Currently, we are experiencing an epidemic of cardiorenal disease characterized by increasing rates of obesity, hypertension, the metabolic syndrome, type 2 diabetes, and kidney disease. Whereas excessive caloric intake and physical inactivity are likely important factors driving the obesity epidemic, it is important to consider additional mechanisms. We revisit an old hypothesis that sugar, particularly excessive fructose intake, has a critical role in the epidemic of cardiorenal disease. We also present evidence that the unique ability of fructose to induce an increase in uric acid may be a major mechanism by which fructose can cause cardiorenal disease. Finally, we suggest that high intakes of fructose in African Americans may explain their greater predisposition to develop cardiorenal disease, and we provide a list of testable predictions to evaluate this hypothesis.

Am J Clin Nutr. 2007 Oct;86(4):899-906

A critical examination of the evidence relating high fructose corn syrup and weight gain.

The use of high fructose corn syrup (HFCS) has increased over the past several decades in the United States while overweight and obesity rates have risen dramatically. Some scientists hypothesize that HFCS consumption has uniquely contributed to the increasing mean body mass index (BMI) of the U.S. population. The Center for Food, Nutrition, and Agriculture Policy convened an expert panel to discuss the published scientific literature examining the relationship between consumption of HFCS or “soft drinks” (proxy for HFCS) and weight gain. The authors conducted original analysis to address certain gaps in the literature. Evidence from ecological studies linking HFCS consumption with rising BMI rates is unreliable. Evidence from epidemiologic studies and randomized controlled trials is inconclusive. Studies analyzing the differences between HFCS and sucrose consumption and their contributions to weight gain do not exist. HFCS and sucrose have similar monosaccharide compositions and sweetness values. The fructose:glucose (F:G) ratio in the U.S. food supply has not appreciably changed since the introduction of HFCS in the 1960s. It is unclear why HFCS would affect satiety or absorption and metabolism of fructose any differently than would sucrose. Based on the currently available evidence, the expert panel concluded that HFCS does not appear to contribute to overweight and obesity any differently than do other energy sources. Research recommendations were made to improve our understanding of the association of HFCS and weight gain.

Crit Rev Food Sci Nutr. 2007;47(6):561-82

Fructose consumption as a risk factor for non-alcoholic fatty liver disease.

BACKGROUND/AIMS: While the rise in non-alcoholic fatty liver disease (NAFLD) parallels the increase in obesity and diabetes, a significant increase in dietary fructose consumption in industrialized countries has also occurred. The increased consumption of high fructose corn syrup, primarily in the form of soft drinks, is linked with complications of the insulin resistance syndrome. Furthermore, the hepatic metabolism of fructose favors de novo lipogenesis and ATP depletion. We hypothesize that increased fructose consumption contributes to the development of NAFLD. METHODS: A dietary history and paired serum and liver tissue were obtained from patients with evidence of biopsy-proven NAFLD (n=49) without cirrhosis and controls (n=24) matched for gender, age (+/-5 years), and body mass index (+/-3 points). RESULTS: Consumption of fructose in patients with NAFLD was nearly 2- to 3-fold higher than controls [365 kcal vs 170 kcal (p<0.05)]. In patients with NAFLD (n=6), hepatic mRNA expression of fructokinase (KHK), an important enzyme for fructose metabolism, and fatty acid synthase, an important enzyme for lipogenesis were increased (p=0.04 and p=0.02, respectively). In an AML hepatocyte cell line, fructose resulted in dose-dependent increase in KHK protein and activity. CONCLUSIONS: The pathogenic mechanism underlying the development of NAFLD may be associated with excessive dietary fructose consumption.

J Hepatol. 2008 Jun;48(6):993-9

Fructose and the metabolic syndrome: pathophysiology and molecular mechanisms.

Emerging evidence suggests that increased dietary consumption of fructose in Western society may be a potentially important factor in the growing rates of obesity and the metabolic syndrome. This review will discuss fructose-induced perturbations in cell signaling and inflammatory cascades in insulin-sensitive tissues. In particular, the roles of cellular signaling molecules including nuclear factor kappa B (NFkB), tumor necrosis factor alpha (TNF-alpha), c-Jun amino terminal kinase 1 (JNK-1), protein tyrosine phosphatase 1B (PTP-1B), phosphatase and tensin homolog deleted on chromosome ten (PTEN), liver X receptor (LXR), farnesoid X receptor (FXR), and sterol regulatory element-binding protein-1c (SREBP-1c) will be addressed. Considering the prevalence and seriousness of the metabolic syndrome, further research on the underlying molecular mechanisms and preventative and curative strategies is warranted.

Nutr Rev. 2007 Jun;65(6 Pt 2):S13-23

Adverse effects of dietary fructose.

The consumption of fructose, primarily from high-fructose corn syrup (HFCS), has increased considerably in the United States during the past several decades. Intake of HFCS may now exceed that of the other major caloric sweetener, sucrose. Some nutritionists believe fructose is a safer form of sugar than sucrose, particularly for people with diabetes mellitus, because it does not adversely affect blood-glucose regulation, at least in the short-term. However, fructose has potentially harmful effects on other aspects of metabolism. In particular, fructose is a potent reducing sugar that promotes the formation of toxic advanced glycation end-products, which appear to play a role in the aging process; in the pathogenesis of the vascular, renal, and ocular complications of diabetes; and in the development of atherosclerosis. Fructose has also been implicated as the main cause of symptoms in some patients with chronic diarrhea or other functional bowel disturbances. In addition, excessive fructose consumption may be responsible in part for the increasing prevalence of obesity, diabetes mellitus, and non-alcoholic fatty liver disease. Although the long-term effects of fructose consumption have not been adequately studied in humans, the available evidence suggests it may be more harmful than is generally recognized. The extent to which a person might be adversely affected by dietary fructose depends both on the amount consumed and on individual tolerance. With a few exceptions, the relatively small amounts of fructose that occur naturally in fruits and vegetables are unlikely to have deleterious effects, and this review is not meant to discourage the consumption of these healthful foods.

Altern Med Rev. 2005 Dec;10(4):294-306

High fructose consumption combined with low dietary magnesium intake may increase the incidence of the metabolic syndrome by inducing inflammation.

The metabolic syndrome is a cluster of common pathologies: abdominal obesity linked to an excess of visceral fat, insulin resistance, dyslipidemia and hypertension. This syndrome is occurring at epidemic rates, with dramatic consequences for human health worldwide, and appears to have emerged largely from changes in our diet and reduced physical activity. An important but not well-appreciated dietary change has been the substantial increase in fructose intake, which appears to be an important causative factor in the metabolic syndrome. There is also experimental and clinical evidence that the amount of magnesium in the western diet is insufficient to meet individual needs and that magnesium deficiency may contribute to insulin resistance. In recent years, several studies have been published that implicate subclinical chronic inflammation as an important pathogenic factor in the development of metabolic syndrome. Pro-inflammatory molecules produced by adipose tissue have been implicated in the development of insulin resistance. The present review will discuss experimental evidence showing that the metabolic syndrome, high fructose intake and low magnesium diet may all be linked to the inflammatory response. In many ways, fructose-fed rats display the changes observed in the metabolic syndrome and recent studies indicate that high-fructose feeding is associated with NADPH oxidase and renin-angiotensin activation. The production of reactive oxygen species results in the initiation and development of insulin resistance, hyperlipemia and high blood pressure in this model. In this rat model, a few days of experimental magnesium deficiency produces a clinical inflammatory syndrome characterized by leukocyte and macrophage activation, release of inflammatory cytokines, appearance of the acute phase proteins and excessive production of free radicals. Because magnesium acts as a natural calcium antagonist, the molecular basis for the inflammatory response is probably the result of a modulation of the intracellular calcium concentration. Potential mechanisms include the priming of phagocytic cells, the opening of calcium channels, activation of N-methyl-D-aspartate (NMDA) receptors, the activation of nuclear factor-kappaB (NFkB) and activation of the renin-angiotensin system. Since magnesium deficiency has a pro-inflammatory effect, the expected consequence would be an increased risk of developing insulin resistance when magnesium deficiency is combined with a high-fructose diet. Accordingly, magnesium deficiency combined with a high-fructose diet induces insulin resistance, hypertension, dyslipidemia, endothelial activation and prothrombic changes in combination with the upregulation of markers of inflammation and oxidative stress.

Magnes Res. 2006 Dec;19(4):237-43

Fructose, weight gain, and the insulin resistance syndrome.

This review explores whether fructose consumption might be a contributing factor to the development of obesity and the accompanying metabolic abnormalities observed in the insulin resistance syndrome. The per capita disappearance data for fructose from the combined consumption of sucrose and high-fructose corn syrup have increased by 26%, from 64 g/d in 1970 to 81 g/d in 1997. Both plasma insulin and leptin act in the central nervous system in the long-term regulation of energy homeostasis. Because fructose does not stimulate insulin secretion from pancreatic beta cells, the consumption of foods and beverages containing fructose produces smaller postprandial insulin excursions than does consumption of glucose-containing carbohydrate. Because leptin production is regulated by insulin responses to meals, fructose consumption also reduces circulating leptin concentrations. The combined effects of lowered circulating leptin and insulin in individuals who consume diets that are high in dietary fructose could therefore increase the likelihood of weight gain and its associated metabolic sequelae. In addition, fructose, compared with glucose, is preferentially metabolized to lipid in the liver. Fructose consumption induces insulin resistance, impaired glucose tolerance, hyperinsulinemia, hypertriacylglycerolemia, and hypertension in animal models. The data in humans are less clear. Although there are existing data on the metabolic and endocrine effects of dietary fructose that suggest that increased consumption of fructose may be detrimental in terms of body weight and adiposity and the metabolic indexes associated with the insulin resistance syndrome, much more research is needed to fully understand the metabolic effect of dietary fructose in humans.

Am J Clin Nutr. 2002 Nov;76(5):911-22

Fructose intake at current levels in the United States may cause gastrointestinal distress in normal adults.

OBJECTIVE: Fructose intake has increased considerably in the United States, primarily as a result of increased consumption of high-fructose corn syrup, fruits and juices, and crystalline fructose. The purpose was to determine how often fructose, in amounts commonly consumed, would result in malabsorption and/or symptoms in healthy persons. DESIGN: Fructose absorption was measured using 3-hour breath hydrogen tests and symptom scores were used to rate subjective responses for gas, borborygmus, abdominal pain, and loose stools. SUBJECTS/SETTING: The study included 15 normal, free-living volunteers from a medical center community and was performed in a gastrointestinal specialty clinic. INTERVENTION: Subjects consumed 25- and 50-g doses of crystalline fructose with water after an overnight fast on separate test days. MAIN OUTCOME MEASURES: Mean peak breath hydrogen, time of peak, area under the curve (AUC) for breath hydrogen and gastrointestinal symptoms were measured during a 3-hour period after subjects consumed both 25- and 50-g doses of fructose. STATISTICAL ANALYSES: Differences in mean breath hydrogen, AUC, and symptom scores between doses were analyzed using paired t tests. Correlations among peak breath hydrogen, AUC, and symptoms were also evaluated. RESULTS: More than half of the 15 adults tested showed evidence of fructose malabsorption after 25 g fructose and greater than two thirds showed malabsorption after 50 g fructose. AUC, representing overall breath hydrogen response, was significantly greater after the 50-g dose. Overall symptom scores were significantly greater than baseline after each dose, but scores were only marginally greater after 50 g than 25 g. Peak hydrogen levels and AUC were highly correlated, but neither was significantly related to symptoms. CONCLUSIONS: Fructose, in amounts commonly consumed, may result in mild gastrointestinal distress in normal people. Additional study is warranted to evaluate the response to fructose-glucose mixtures (as in high-fructose corn syrup) and fructose taken with food in both normal people and those with gastrointestinal dysfunction. Because breath hydrogen peaks occurred at 90 to 114 minutes and were highly correlated with 180-minute breath hydrogen AUC, the use of peak hydrogen measures may be considered to shorten the duration of the exam.

J Am Diet Assoc. 2005 Oct;105(10):1559-66

Advanced glycation end-product pentosidine accumulates in various tissues of rats with high fructose intake.

The slowly metabolized proteins of the extracellular matrix, typically collagen and elastin, accumulate reactive metabolites through uncontrolled non-enzymatic reactions such as glycation or the products arising from the reaction of unsaturated long chain fatty acid metabolites (possessing aldehydic groups). A typical example of these non-enzymatic changes is the formation of advanced glycation end-products (AGEs), resulting from the reaction of carbohydrates with the free amino group of proteins. The accumulation of AGEs and the resulting structural alterations cause altered tissue properties (increased stiffness, reduced elasticity) that contribute to their reduced catabolism and to their aging. Posttranslational nonenzymatic modifications of the proteins of the extracellular matrix (the formation of a typical AGE product--pentosidine) were studied in three types of tissue of three rat strains subjected to a high-fructose diet. Chronic (three-week) hyperglycemia (resulting from fructose loading) caused a significant increase in pentosidine concentration mainly in the aorta and skin of the three rat strains (Lewis, Wistar and hereditary hypertriglyceridemic rats).

Physiol Res. 2008;57(1):89-94

Long-term fructose consumption accelerates glycation and several age-related variables in male rats.

Fructose intake has increased steadily during the past two decades. Fructose, like other reducing sugars, can react with proteins through the Maillard reaction (glycation), which may account for several complications of diabetes mellitus and accelerating aging. In this study, we evaluated the effect of fructose intake on some age-related variables. Rats were fed for 1 y a commercial nonpurified diet, and had free access to water or 250 g/L solutions of fructose, glucose or sucrose. Early glycation products were evaluated by blood glycated hemoglobin and fructosamine concentrations. Lipid peroxidation was estimated by urine thiobarbituric reactive substances. Skin collagen crosslinking was evaluated by solubilization in natural salt or diluted acetic acid solutions, and by the ratio between beta- and alpha-collagen chains. Advanced glycation end products were evaluated by collagen-linked fluorescence in bones. The ratio between type-III and type-I collagens served as an aging variable and was measured in denatured skin collagen. The tested sugars had no effect on plasma glucose concentrations. Blood fructose, cholesterol, fructosamine and glycated hemoglobin levels, and urine lipid peroxidation products were significantly higher in fructose-fed rats compared with the other sugar-fed and control rats. Acid-soluble collagen and the type-III to type-I ratio were significantly lower, whereas insoluble collagen, the beta to alpha ratio and collagen-bound fluorescence at 335/385 nm (excitation/emission) were significantly higher in fructose-fed rats than in the other groups. The data suggest that long-term fructose consumption induces adverse effects on aging; further studies are required to clarify the precise role of fructose in the aging process.

J Nutr. 1998 Sep;128(9):1442-9