Liquid calories, energy compensation and weight: what we know and what we still need to learn

Roughly 10,000 years ago, sugar was first domesticated in New Guinea. Roughly 8,000 years ago it was transplanted to India. Sometime around the seventh century, cultivation and some industrial production began in southern Europe, and the crusades subsequently acquainted more Europeans with sugar imported from Arab lands. Through the 16th century, sugar was often viewed by Europeans as having medicinal properties. Colonization of the new world led to mass production and distribution and sugar as a major foodstuff(1–5). By 1713, a writer in a scholarly journal was extoling the health virtues of high levels of sugar consumption, including in beverages(6). In 1893, Harley(7) conducted self-experiments and concluded that consumption of 250 g (~4184 kJ, or ~1,000 kcal) of sugar greatly increased muscular work capacity. In 1899 it was reported that in a controlled trial in soldiers, those given a ration of sugar were in better health, felt more vigorous, and gained more weight (presumably judged to be a good thing at the time)(8). As the century turned, Gardner(9) described sugar as a nutritional necessity that increased the health and vigor of populations. Yet the positive health halo of sugar would not last. A generation later, authors of scientific papers would write about “The social problem growing out of the overconsumption of sugar” and described school-based programs to teach children to consume less sugar(10). Sugar consumed in liquid form has come to be seen by some as especially deserving of scrutiny. In 1990, Tordoff and Alleva(11) published seminal trial results showing that persons required to consume additional sugar in the form of a beverage gained more weight than did a control group given a noncaloric beverage. Thirteen years later, suspicion was increasing that metabolizable energy, perhaps especially sugar, consumed as liquids promoted less satiety, less energy compensation, and more weight gain than did the same energy consumed in solid form(12). The topic has become controversial to say the least(13), and there is substantial evidence that the strength of the supporting data has often been exaggerated and distorted(14,15). Newspaper articles offer statements such as “People who drink sugary soft drinks do not appear to compensate by reducing calories somewhere else in their diets, so they tend to pack on extra pounds”(16) and “Study after study has shown that like experimental animals, people do not compensate for extra liquid calories by eating less food”(17). This concept, that people do not adjust their energy intake (or expenditure) to compensate for energy consumed as liquids is at the heart of the matter. Yet, is it true? Though opinions on matters of energy compensation in response to various forms of sugar intake and/or liquid energy have been offered for over 70 years(18) (19), convincing data on these issues has been scarce. In this issue of the Journal, Reid et al.(20) offer a new and valuable piece of evidence on this question. In a study of obese adult women, those consuming sugar in liquid form at a level of 1800 kJ (~430 kcal) per day gained far less weight than expected and no more weight than did women in a control group drinking zero-calorie beverages. The study has several strengths. It was a controlled trial that was run for long enough to observe weight changes and that was at least partially conducted in a blinded fashion. It also has several limitations, including a modest sample size, incomplete blinding, and the fact that it was not strictly randomized. I will not belabor those points here as Reid and colleagues discuss them in their article. Note also that the study only concerns adult women and cannot necessarily tell us about effects in men or children.