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New Lustig Study on Fructose and Metabolic Syndrome in Kids

Dean Pomerleau

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Obesity researcher Dr. Robert Lustig, who is notorious for placing blame for the obesity epidemic on added sugar, especially fructose, has a new paper out [1] that is getting quite a bit of popular press attention on the link between added sugar/fructose in the diet of kids and obesity / metabolic syndrome.


Despite my distrust of Lustig and his "one underlying cause" thesis, believing as I do that many factors contribute to obesity, including 'mysterious' factors (see this thread), this was nevertheless a pretty interesting study.


He recruited ~40 obese kids suffering from metabolic syndrome and for 9 days had them eat a crappy diet with less added sugar/fructose than their normal crappy diet, keeping macronutrients the same, and measured how their markers for metabolic syndrome changed.


More specifically, at baseline these kids were on average eating 28% of daily calories from (presumably added) sugar, with 12% of it from (presumably added) fructose. Given where added sugar comes from in general in our culture, they were most likely eating a lot of sugar sweetened beverages, pastries, desserts and candy. In place of these, the authors substituted "kid-friendly" foods with less added sugar, which at one point in the paper they characterize as:


This “child-friendly” study diet included various no- or low-sugar added processed foods including turkey hot dogs, pizza, bean burrritos, baked potato chips, and popcorn that were purchased at local supermarkets.


Strangely, elsewhere in the paper the authors characterize the intervention diet in a way that sounds significantly less crappy:


The menu was planned to restrict added sugar, while substituting other carbohydrates such as those in fruit, bagels, cereal, pasta, and bread so that the percentage of calories consumed from carbohydrate was consistent with their baseline diet, but total dietary sugar and fructose were reduced... 


A diet enriched with "fruit, bagels, cereal, pasta, and bread" compared with their baseline diet (likely consisting of lots of soda, cookies and candy) sounds like a pretty big improvement to me, although fiber was only increased from 9g at baseline to 11g during the study, so it apparently wasn't that big an improvement. 


But digging a little further, the second set of substitution foods (fruit, bagels, cereal, pasta, and bread) sounds a lot more plausible to me than the first set (turkey hot dogs, pizza, bean burritos, baked potato chips, and popcorn), given that elsewhere the authors state that:


...compared with the baseline macronutrient distribution determined by FFQ, the total percentage of carbohydrate intake on the study diet decreased by 4%, protein increased by 2%, and there was no change in percentage calories from fat.


Substituting fat- and protein-laden processed foods in first set (pizza, bean burritos, baked potato chips etc) for sugary foods and soda, would not have left macronutrients virtually unchanged, as the authors claim. But substituting the high carb foods with little added sugar from the second set (fruit, bagels, cereal, pasta, and bread), would have left macronutrients nearly the same but reduced added sugar, as the authors claim. So if the substitutions were "fruit, bagels, cereal, pasta, and bread" for soda, pastry, and candy, perhaps the the intervention diet wasn't as crappy as Lustig claims, and that the popular press articles like the Wall Street Journal story are parroting:


Researchers from the University of California, San Francisco, and Touro University California took soda, pastries, sugary cereals and other foods and beverages sweetened with added sugar away from 43 Latino and African-American children and teens for nine days. They replaced those foods with pizza, baked potato chips, and other starchy processed foods.


Either way, it is a rather important ambiguity for the authors to not only leave open, but in fact bake right into the report on their study through the conflicting descriptions of the intervention diet. Since they gave the kids all their food during the intervention period, you would think they would have documented the details of the intervention diet in the paper (or at least in the supplemental material - which doesn't appear to exist), but apparently not. That's Lustig for you...


Given all that, what they found was that after 10 days, most indicators of metabolic syndrome improved significantly relative to baseline, including fasting glucose, insulin, OGTT, and blood lipids. They tried to maintain calories and avoid weight loss to make for a fair comparison, but on average the kids lost a couple pounds, which could account for some of the improvement. They separately analysed data from the kids who didn't lose weight, and found that the results weren't quite as strong, but many of the measures still improved, independent of weight loss.


So overall, this study seems to provide some (albeit relatively weak) support for the hypothesis that added sugar and fructose are particularly detrimental, and increase risk of metabolic syndrome.





[1] Lustig, R. H., Mulligan, K., Noworolski, S. M., Tai, V. W., Wen, M. J., Erkin-Cakmak, A., Gugliucci, A. and Schwarz, J.-M. (2015), Isocaloric fructose restriction and metabolic improvement in children with obesity and metabolic syndrome. Obesity. doi: 10.1002/oby.21371


Free Full Text: http://onlinelibrary.wiley.com/doi/10.1002/oby.21371/full




Dietary fructose is implicated in metabolic syndrome, but intervention studies are confounded by positive caloric balance, changes in adiposity, or artifactually high amounts. This study determined whether isocaloric substitution of starch for sugar would improve metabolic parameters in Latino (n = 27) and African-American (n = 16) children with obesity and metabolic syndrome.
Participants consumed a diet for 9 days to deliver comparable percentages of protein, fat, and carbohydrate as their self-reported diet; however, dietary sugar was reduced from 28% to 10% and substituted with starch. Participants recorded daily weights, with calories adjusted for weight maintenance. Participants underwent dual-energy X-ray absorptiometry and oral glucose tolerance testing on Days 0 and 10. Biochemical analyses were controlled for weight change by repeated measures ANCOVA.
Reductions in diastolic blood pressure (−5 mmHg; P = 0.002), lactate (−0.3 mmol/L; P < 0.001), triglyceride, and LDL-cholesterol (−46% and −0.3 mmol/L; P < 0.001) were noted. Glucose tolerance and hyperinsulinemia improved (P < 0.001). Weight reduced by 0.9 ± 0.2 kg (P < 0.001) and fat-free mass by 0.6 kg (P = 0.04). Post hoc sensitivity analysis demonstrates that results in the subcohort that did not lose weight (n = 10) were directionally consistent.
Isocaloric fructose restriction improved surrogate metabolic parameters in children with obesity and metabolic syndrome irrespective of weight change.
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The New York Times has an article on the Lustig sugar study, that provide interesting additional insights into the ambiguity of the intervention diet that I discuss above. The NYT article quotes Dr. Lustig himself. Here is the relevant section (painstakingly saved to Evernote first to allow cutting-and-pasting, since the way the NYT displays articles now, you can't cut-and-paste directly from the browser, grrrr...):


On average, the subjects had been getting about 27 percent of their daily calories from sugar. By comparison, the average American takes in about 15 percent, though children typically consume much more than this in part because they have the highest intake of sugar-sweetened beverages.


The study authors paired the subjects with dietitians. They then replaced the sugary foods in their diets with other foods purchased from local grocery stores. The goal was not to eliminate carbohydrates, but to reduce sugary foods and replace them with starchy foods without lowering body weight or calorie intake.


“Wherever there was food with added sugar in their diets, we took it out and we replaced it with a no-added-sugar version,” Dr. Lustig said.


So instead of yogurt sweetened with sugar, the children ate bagels. Instead of pastries, they were given baked potato chips. Instead of chicken teriyaki – which typically contains a lot of sugar – they ate turkey hot dogs or burgers for lunch. The remaining sugar in their diet came mostly from fresh fruit.


So if this characterization is correct, the substitution the researchers did was to replace foods and soda containing added sugar with no-added-sugar equivalents, and compensating for the resulting reduction in carbs by adding fresh fruit and (processed) starches to their diet. Obviously the processed starches aren't great, but overall that sort of switch is definitely a step up in nutritional quality as far as I'm concerned, so it isn't too surprising they saw the metabolic improvements that they did.


Of course this doesn't detract from the legitimate message of the study that added sugar is pretty toxic.



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Here is a good article out today in the Guardian with some substantive criticism from other nutrition scientists about Lustig's claim that his study (discussed above) shows "a calorie is not a calorie" and that added sugar is particularly toxic. 


Here are some quotes from the article:


But in spite of Lustig’s assertions that he has proved his thesis, the reaction to the study was muted. “The results are not convincing to me – this is a very small study, and it has not been statistically well-controlled,” said Naveed Sattar, professor of metabolic medicine at Glasgow University.
“Also, when people are losing weight, even if modest, their metabolic changes can seem larger than they actually are – one needs to see results once folk return to their habitual state after they’ve finished losing weight. Overall, this study is of modest interest but is far from convincing.”
The comparison instead was made with their weight and health before the study while on their usual diet. “But it is well known that obese children underestimate and under-report food intake, particularly of soft drinks and snack foods,” said Sanders.
“This is a fundamental flaw in the study. It is likely that the changes in metabolic outcomes observed can be explained by the experimental diet providing fewer calories than the children’s usual intake.”
Given that sugar and starch contain roughly the same amount of calories per gram, he said: “It is just inconceivable that isocaloric substitution of sugar from starch would have such a large effect on metabolism. In fact it denies the basic laws of thermodynamics.”
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