The paper discusses this: However, there are some limitations to our paradigm. Athough inclusion of a separate external control group would have been optimal,

The paper discusses this: However, there are some limitations to our paradigm. Athough inclusion of a separate external control group would have been optimal, it would have presented novel challenges of its own, such as: 1) if subjects under- or over-estimated their baseline fructose consumption, then providing them their reported daily fructose content would be problematic; 2) altering each subject's diet while trying to maintain the baseline fructose content would require changes in liquid versus solid, which may also result in caloric change, altered absorption, and altered satiety; and 3) our participants were all patients in an obesity program. We did not believe that maintaining fructose at the same level, even within a study, is commensurate with the message that the change in macronutrient composition is important for their health, and in order to use the study as an “educational moment.” Furthermore, others have looked longitudinally at children with obesity over time without any intervention, but still within the confines of a study, and had seen no changes in metabolic outcomes [39]. Rather, each participant served as his or her own control. Our paradigm of dietary sugar and fructose restriction, which included mid-study dietary adjustments to compensate for weight loss, resulted in a 4% decrease in percentage of calories from carbohydrate, a 2% increase in percentage of calories from protein, and a small increase in dietary fiber, which could have reduced macronutrient absorption [18], flux of fructose to the liver, and also increased satiety. Recognizing that consumption data by recall is routinely underestimated [24], we made every effort to maintain our participants' baseline weight throughout the 10-day study interval, and even increased the caloric allotment partway through the cohort, yet a decline of 0.9 ± 0.2 kg was noted during the 10 days.