Here you’ll find a sampling of current and important studies in nutrition research. We generally only share studies that are peer-reviewed, unbiased, and not funded by industry or special interests.
In a landmark study published October 27, 2015 in the journal Obesity, UCSF and Touro University researchers prove conclusively that dietary fructose restriction improves metabolic syndrome. Dr. Robert Lustig, was a primary investigator in the study and he offers answers to anticipated Frequently Asked Questions here.
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Q. What is sugar?
Dietary sugar (sucrose, high-fructose corn syrup, agave, honey, maple syrup) consists of two molecules — glucose (found in starch) and fructose (the sweet molecule). In sucrose, the two are bound together. In HFCS they are not bound together. It’s the fructose that makes sugar sweet, and the reason we like it so much. Although whole fruit has sugar, it generally has much more fiber and nutrients, and usually is not a problem. However, sugar that is added to processed foods by the food industry may lead to health problems. The fructose molecule is metabolized differently than the glucose molecule, and these differences have been implicated in the development of various chronic diseases. Research has also suggested that dietary sugar can be addictive.
Q. Who did this study?
A. Researchers at UCSF and Touro University performed this study in a team fashion. It took 5 years to complete. The study team consisted of Robert Lustig and Jean-Marc Schwarz (Principal Investigators), as well as Susan Noworolski, Kathleen Mulligan, and Alejandro Gugliucci (Co-Investigators). We also had many ancillary support staff that assisted with the protocol.
Q. Why did we do this study?
A. We knew that excessive added sugar consumption is associated with the development of the various diseases of metabolic syndrome, including cardiovascular disease, type 2 diabetes, hypertension, and lipid problems. However, other studies suggested that the detrimental effects of dietary sugar were due to extremely high dosing, excess calories, or because of effects on weight gain. If so, then sugar would not be different from any other foodstuff that provides calories. In order to clarify, we had to dissociate the metabolic effects of dietary sugar from its calories and its effects on weight gain. In other words, we focused on the metabolic impact of certain calories, versus the quantity of calories in the overall diet.
Q. How did we do this study?
A. We did not want to give sugar to people to see if they got sick; that has already been done (1-3), and critics would raise concerns about excessive dosing and excessive calories (4). Instead, we wanted to take sugar away from people who were already sick to see if they got well. But if they lost weight, critics would argue that the drop in calories or the weight loss was the reason for the clinical improvement. Therefore, the study was “isocaloric,” which means that we had to give back the same number of calories in starch as we took away in sugar, and we had to make sure that they did not lose weight.
Q. Who participated in the study?
A. A total of 43 children participated, ages 8-19, from the Weight Assessment for Teen and Child Health (WATCH) Clinic at UCSF, and from surrounding clinics. Of these, 27 were Latino, and 16 were African-American. Each person was obese, and had at least one other co-morbidity that demonstrated that they had metabolic problems. All were high consumers of added sugar in their diets (e.g. soft drinks, juices, pastries, breakfast cereals, salad dressings, etc.).
Q. What did we do in this study?
A. We assessed their home diets by two questionnaires to determine how many calories, and how much fat, protein, and carbohydrate they were eating. We had them come to the hospital for testing on their home diet. Then, for the next 9 days, we catered their meals. The macronutrient percentages of fat, protein, and carbohydrate were not changed. We fed them the same calories and percent of each macronutrient as their home diet; but within the carbohydrate fraction, we took the added sugar out, and substituted starch. For example, we took pastries out, we put bagels in; we took yogurt out, we put baked potato chips in; we took chicken teriyaki out, we put turkey hot dogs in — although we still gave them whole fruit. We reduced their dietary sugar consumption from 28% to 10% of calories, in accordance with the World Health Organization’s recommendation for free or added sugars. We gave them extra snacks. We gave them a scale to take home, and each day they would weigh themselves. If they were losing weight, we told them to eat more. The goal was to remain weight-stable over the 10 days of study. On the final day, they came back to the hospital for testing on their experimental low-added sugar diet. The study team analyzed the pre- and post-data in a blinded fashion so as not to introduce bias.
Q. How did the children do on the study diet?
A. Of the 43 children, 42 described the study diet as highly palatable. Despite our best efforts to stabilize these children’s weights for the 10 days, they lost an average of 0.9 kg or 2 pounds. Most of the children told us that they couldn’t eat more; they were too full. Because of the small weight loss, we adjusted all results statistically to control for the weight loss. We performed body composition analysis, which told us that the weight loss was in the fat-free mass compartment (either muscle or water), rather than in the fat compartment; so the weight loss was not body fat.
Q. What were the results of this study?
A. We looked at three types of data. 1) Diastolic blood pressure decreased by 5 points. 2) Baseline blood levels of analytes associated with metabolic disease, such as lipids, liver function tests, and lactate (a measure of metabolic performance) all improved significantly. 3) Fasting glucose decreased by 5 points. Glucose tolerance improved markedly. Fasting insulin levels fell by 50%. Every one of these changes was highly significant. In sum, virtually all aspects of their metabolic health improved. These indicate that these children improved their metabolic status in just 10 days, even while eating processed food, by just removing the added sugar and substituting starch. The metabolic improvement was unrelated to their caloric intake, and unrelated to changes in weight or body fat.
Q. What are the limitations of the study?
A. 1) We did not do an external control group; this would have been nearly impossible to do, because their calorie counts are underestimated, and you would not be able keep them from knowing what they ate, unless you tube-fed them, which is unlawful. 2) The children did lose an average of 2 pounds, although based on the pattern of weight loss and the body composition analysis, we believe this was water and not fat, and water loss should not lead to metabolic improvement. Of the 43 children, 10 did not lose weight. We analyzed them separately (called sensitivity analysis) and showed that their metabolic health improved as well. Thus, the metabolic improvement is not due to weight loss or caloric deficit.
Q. What does this study show?
A. 1) This study conclusively proves that all calories are not the same (“a calorie is not a calorie”); because substituting starch for sugar improved these children’s metabolic health unrelated to calories or weight gain. 2) This study shows that we can improve the metabolic health of obese children in just 10 days by removing the added sugar from their diet. 3) This study demonstrates that added sugar contributes to metabolic syndrome in children. This study does not prove that sugar is the sole, or even primary cause of metabolic syndrome; but it is clearly a modifiable cause. Based on the results of this and other studies, a compelling case is made for appropriate public education and rational policy change to improve the lives and health of children (and adults) worldwide.
Q. What implications can we derive from this study?
A. When it comes to chronic disease, the quality of our food is as important, and possibly even more important, than the quantity of food consumed. Restriction of added sugar should be a first step in the prevention or treatment of chronic disease in children. Although we did not study adults, other studies demonstrate similar improvements when sugar is restricted. Sugar is added to processed food for palatability, convenience, cost, and shelf life. Of the 600,000 items in the American food supply, 74% have been adulterated by added sugar (5). Processed food is directly implicated in the rise of the various aspects of metabolic syndrome unrelated to calories. The food industry has said that we only have correlation, not causation, for sugar and chronic disease. However, these data, when taken with other studies, provide causation. This study bolsters the evidence that the food industry argument of added sugar being no more harmful than other components of processed food is fallacious. It is now clearer than ever that recommended limits on added sugar, provided by leading health organizations (WHO, AHA, USDA/DGAC, etc.) should be taken seriously. Additionally, added sugar should be included on all food labels, so that consumers can make informed decisions about their children’s health.
3. Maersk M, Belza A S-JH, Ringgaard S, Chabanova E, Thomsen H, Pedersen SB, Astrup A, Richelsen B. Sucrose-sweetened beverages increase fat storage in the liver, muscle, and visceral fat depot: a 6-mo randomized intervention study. Am. J. Clin. Nutr. 2012;95:283-289.
4. Sievenpiper JL, de Souza RJ MA, Yu ME, Carleton AJ, Beyene J, Chiavaroli L, Di Buono M, Jenkins AL, Leiter LA, Wolever TM, Kendall CW, Jenkins DJ. Effect of fructose on body weight in controlled feeding trials: a systematic review and meta-analysis. Ann. Int. Med. 2012;156:291-304.
- Global mean BMI and obesity prevalence have risen from 1975 to 2014, while underweight has fallen. If trends continue, the probability of meeting the global obesity target is virtually zero. Targets in Adult Body-mass Index in 200 Countries from 1975 to 2014: A Pooled Analysis of 1698 Population Based Measurement Studies with 19.2 Million Participants.
- Fewer than 3 percent of American adults meet criteria for a healthy lifestyle of being sufficiently active, eating a healthy diet, having a normal body fat percentage, and not smoking. Healthy Lifestyle Characteristics and Their Joint Association with Cardiovascular Disease Biomarkers in US Adults.
- Removing added fructose from the diets of obese teens with metabolic syndrome for 10 days improved every marker of metabolic health measured. Isocaloric fructose restriction and metabolic improvement in children with obesity and metabolic syndrome.
- Americans consume 58% of their calories as ultra-processed foods which contributes 90% of added sugars. 60% of Americans consume more than the recommended calories from added sugars. The average American consumes 292 calories from added sugar/day. Decreasing consumption of ultra-processed foods may be an effective way to decrease added sugars. Ultra-processed and added sugars in the US Diet: evidence from a nationally representative cross-sectional study.
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