Fructose, Obesity, and Children’s Metabolic Syndrome

Childhood obesity is one of the most pressing public health challenges facing the world today. According to the World Health Organization (WHO), the problem is global and is steadily affecting many low- and middle-income countries, particularly in urban settings. The WHO defines overweight and obesity as ”abnormal or excessive fat accumulation that presents a risk to health.” So, what are the health risks of overweight and obesity? The answer includes a long list of disorders, as for example cancer, reproductive problems, and metabolic syndrome.

Metabolic syndrome is the name for a group of risk factors that raises the risk for heart disease and other health problems, such as type 2 diabetes and stroke. Below is the list of the metabolic risk factors. A diagnosis of metabolic syndrome is usually made when at least three of these risk factors are present.

  • A large waistline. This also is called abdominal obesity or “having an apple shape.” Excess fat in the stomach area is a greater risk factor for heart disease than excess fat in other parts of the body, such as on the hips.
  • A high triglyceride level. Triglycerides are a type of fat found in the blood.
  • A low HDL cholesterol level. HDL sometimes is called “good” cholesterol. This is because it helps remove cholesterol from the arteries. A low HDL cholesterol level raises the risk for heart disease.
  • High blood pressure. If this pressure rises and stays high over time, it can damage the heart and lead to plaque buildup.
  • High fasting blood sugar. Mildly high blood sugar may be an early sign of diabetes.

In the US, nearly 35% of all adults and 50% of those aged 60 years or older are estimated to have metabolic syndrome, a worrisome observation given the increasing aging US population. Metabolic syndrome also occurs in children, although only recently it has been identified as a condition of childhood obesity. Other diseases associated with metabolic syndrome, such as non-alcoholic fatty liver disease, now occur in children — this disorder, along with type 2 diabetes, was previously unknown in the pediatric population.

Consumption of drinks and foods with added sugars — and especially fructose, either as sucrose or high-fructose corn syrup — is linked to the development of metabolic syndrome. Dietary fructose is naturally present in fresh fruits — thus, many people think of fructose as a “healthier” alternative to other types of sugar. However, fruits contain very small amounts of this sugar. In contrast, fructose is present in much larger amounts in sweetened products such as sodas.

To ascertain whether or not cutting consumption of dietary fructose would improve metabolic syndrome in obese children, a group of researchers at UC San Francisco and Touro University California designed a study in which they modified the diet of 43 obese children, aged nine to 18, who had at least one other metabolic disorder — foods with added sugar were replaced with other carbohydrate-rich foods, such as bagels, cereal and pasta, so that the children’ weight and overall calorie intake remained about the same.

The study results were published online in the journal Obesity on October 27, 2015. After just 9 days on the sugar-restricted diet, virtually every aspect of the children’ metabolic health improved, without change in weight. Thus, the researchers concluded that the health detriments of sugar, and fructose specifically, are independent of its caloric value or effects on weight.

Robert Lustig, lead author of the study, said in a press release: “This study definitively shows that sugar is metabolically harmful not because of its calories or its effects on weight; rather sugar is metabolically harmful because it’s sugar.” He added: “All of the surrogate measures of metabolic health got better, just by substituting starch for sugar in their processed food — all without changing calories or weight or exercise. This study demonstrates that ‘a calorie is not a calorie.’ Where those calories come from determines where in the body they go.”

Jean-Marc Schwarz, senior author of the study, said, “I have never seen results as striking or significant in our human studies; after only nine days of fructose restriction, the results are dramatic and consistent from subject to subject. These findings support the idea that it is essential for parents to evaluate sugar intake and to be mindful of the health effects of what their children are consuming.”

Interestingly, results from previous research show that fructose helps our brains to find high-calorie foods more appealing — in other words, it leads to overeating. In addition, excess fructose cannot be converted into energy by the mitochondria inside our cells. Instead, our cells turn excess fructose into liver fat, thus starting a cascade of insulin resistance that leads to chronic metabolic disease, diabetes and heart disease.


  1. More and more studies, including the one discussed in this blog post, show the deleterious effects of fructose.

    Last Spring, a paper published in The American Journal of Clinical Nutrition reported that only two weeks of modest consumption of high-fructose corn syrup causes cholesterol and triglycerides levels to rise, and the more consumed, the greater the increases. In other words, modest consumption of high-fructose corn syrup significantly increased risk factors for cardiovascular diseases.

    Although the study discussed in this blog post is based on a small group size and lacks a negative control group, it still adds to what we need to know about fructose.

    As more and more studies come out on this subject, we can finally hope that regulations will be put in place to discourage consumption of soda and foods containing fructose.

  2. As referenced in Doctor Lustig’s study, fructose is primarily metabolized the liver, through biochemical pathways that favor lipogenesis. Therefore, over consumption will have a causal effect on fatty liver and metabolic disease. However, metabolic disease is only part of what constitutes Metabolic Syndrome: Immune dysregulation, closely meshed with an abnormal intestinal microbiome also comprise necessary and sufficient causes for metabolic syndrome. It has been demonstrated through a variety of animal and human studies that the development and proper function of the immune system depend on the presence and interaction of resident intestinal cells with the population of a healthy intestinal microbiome. Should the composition of the microbiome be altered, either through the elimination of symbiotic bacteria, or their replacement by deleterious strains, the development and proliferation of resident dendritic and macrophage cells will be compromised, and a phenotype susceptible to inflammation and infection will result.

    Therefore, while the direct metabolic effect of fructose ingestion is clearly a factor in metabolic syndrome, the indirect effects a high fructose diet exerts on the development and function of the immune system: producing the low-grade chronic inflammation characteristic of metabolic syndrome are almost certainly a factor as well. The effect substituting complex carbohydrates for a specific type of simple sugar can exert in distorting the makeup of microbiota and immune function is well documented. Additionally, emulsifiers commonly used in food have also been demonstrated to alter the composition and phenotype of microbiota to one that induces inflammation, disrupt intestinal mucus and allow infiltration of hitherto protected intestinal areas. Added to Dr. Lustig’s study, this suggests that microbial-immune factors associated with the sugars and food additives in junk food could have contributed to the phenotypes seen the children. Collectively, this makes it clear that public schools and other organizations interacting with low-income children should treat providing a healthy diet as a matter of public health importance.

    Bibliography: 1. Di Luccia B, Crescenzo R, Mazzoli A et al. Rescue of Fructose-Induced Metabolic Syndrome by Antibiotics or Faecal Transplantation in a Rat Model of Obesity. PLOS ONE. 2015;10(8):e0134893. doi:10.1371/journal.pone.0134893.

    Bibliography: 2. Khitan Z, Kim D. Fructose: A Key Factor in the Development of Metabolic Syndrome and Hypertension. Journal of Nutrition and Metabolism. 2013;2013:1-12. doi:10.1155/2013/682673.

    Bibliography: 3. Choi M. The Not-so-Sweet Side of Fructose. Journal of the American Society of Nephrology. 2009;20(3):457-459. doi:10.1681/asn.2009010104.

    Bibliography: 4. Wu H, Wu E. The role of gut microbiota in immune homeostasis and autoimmunity. Gut Microbes. 2012;3(1):4-14. doi:10.4161/gmic.19320.

    Bibliography: 5. Chassaing B et al. Dietary emulsifiers impact the mouse gut microbiota promoting colitis and metabolic syndrome. – PubMed – NCBI. Ncbinlmnihgov. 2015.

    Bibliography: 6. Roberts C, Keita A, Duncan S et al. Translocation of Crohn’s disease Escherichia coli across M-cells: contrasting effects of soluble plant fibres and emulsifiers. Gut. 2010;59(10):1331-1339. doi:10.1136/gut.2009.195370.

  3. It is unfortunate that children from developed countries have to suffer from childhood obesity due to diets high in sugar, fat and carbohydrates. In developed countries like the United States there is access to healthy foods such as fruits, vegetables and whole grains especially to the middle class. There is no good reason why educated middle class parents and schools in America don’t provide nutritious food for children to reduce the chances of metabolic syndrome. I do understand that parents from low income backgrounds struggle to provide fresh food but the cost of fruits and vegetable is cheaper that junk food. At Wal-Mart the cost for bag of chips ahoy cookies is $2.50 and while the cost for 2 or 3 bananas is under a dollar. Parents need to realize that providing unhealthy foods to children has negative immunological consequences especially when children develop diabetes. Diabetes impairs the immune system’s ability to heal after an infection or injury and often children get cuts and bruises when playing. In addition, patients with diabetes have increased complications with pneumococcal infections that can be deadly (1). Studies have shown patients with type 2 diabetes have a weakened pathogen-specific memory CD4+ and Th17 response and reduced CD+T-cells in response to S. pneumoniae (2).

    1. Kornum JB, Thomsen RW, Riis A, Lervang HH, Schonheyder HC, Sorensen HT. Type 2 diabetes and pneumonia outcomes: a population-based cohort study. Diabetes Care. 2007;30:2251–2257.
    2. Martinez PJ, Mathews C, Actor JK, et al. Impaired CD4+ and T-helper 17 cell memory response to Streptococcus pneumoniae is associated with elevated glucose and percent glycated hemoglobin A1c in Mexican Americans with type 2 diabetes mellitus. Translational research : the journal of laboratory and clinical medicine. 2014;163(1):53-63.

  4. While I don’t consider myself a “health nut”, I exercise 3-5 times a week and I eat “clean” 90% of the time. Clean eating refers to having no fried foods, no fast food, minimally processed foods, and eating lots of fresh/flash frozen fruits and vegetables along with whole grain. When I go grocery shopping, I make sure to shop the edges i.e. the produce section, fresh meats, breads, and frozen foods. The middle aisles we clean eaters like to refer to as “filler aisles.” The contain mostly things that are processed and have additives so that they may remain on the shelves for an extended amount of time. And unfortunately, eating healthy is not the cheapest option. But America is about money not doing what’s right. Along with these additives, I have also found evidence that these filler aisles also contain “nutritional information” that are LIES. And what is worst is that the children were found to be the targets of these nutritional lies. An example of the data found is in baby food there was found to a range of 88% less sugar to 82% more sugar in the products than listed on the jars. I personally made my sons baby food when he started whole foods, but every parent is not like me. How can we protect our children from unnecessary sugars when companies add sugar to infant formula and baby foods? More so, how can we be sure that they are not getting too much sugar if the nutritional label is not providing accurate information? I guess the best thing for our kids is for everyone to eat clean. When my kid ask for dessert, he gets berries and he loves it.

    Works Cited:
    Walker RW, Goran MI. Laboratory Determined Sugar Content and Composition of Commercial Infant Formulas, Baby Foods, and Common Grocery Items Targeted to Children. Nutrients. 2015 Jul; 7(7): 5850-5867.

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