tionship of marketing to diet-related health. Studies that intentionally used television viewing as a measure of exposure to marketing (advertising) and employed similar correlational designs had already been included in the systematic evidence review for the relationship of marketing to precursors of diet and for the relationship of marketing to diet. Moreover, television viewing is well related to exposure to food and beverage advertising because, as explicated in Chapter 4, food and beverage marketing messages are common across the television landscape, particularly in programming with the highest concentrations of youth in the audience. For this reason, any correlation reported between young people’s time watching television and precursors of diet, diet, or diet-related health may be caused by exposure during television viewing time to commercial messages for food and beverage products, which are likely to be high in calories and low in nutrients.
It becomes more difficult to infer causality in an individual study and to arrive at findings about causality from a group of studies as the outcome moves from precursor to diet to health. The increasing difficulty arises from two conditions. First, due to the decreasing proportion of experimental studies in the evidence for precursor, diet, and health outcomes, respectively, the ability to use the correlational studies to confirm results from experimental studies and arrive at findings about causality decreases from precursor to diet to health outcomes. Second, as one moves from precursor to diet to health outcomes, there is a substantial increase in the number of plausible alternative explanations for any correlation between the outcome and advertising exposure as measured by television viewing. Accordingly, for any given study that employs television viewing as a measure of exposure to television advertising, as one moves from precursor to diet to health it becomes increasingly difficult to infer causality.
In drawing on the available research to assess the influence of exposure to television advertising on adiposity, as measured by television viewing, three challenges were paramount, given the fact that all but one of the studies were correlational. One challenge is the fact that television viewing may represent or be highly associated with several other factors that could influence adiposity. In addition to exposure to commercial food and beverage advertising, a measure of television viewing may indicate or be closely associated with physical activity, snacking, propensity to engage in other sedentary activities (e.g., reading, videogaming), reduced metabolic rate, exposure to food and beverage consumption within programs, and blunting of physiological cues to satiety. A second challenge, given the correlational design of these studies, is the possibility of reverse causation. Perhaps heavier young people watch more television because it demands less of them physically. A third challenge is the possibility that television viewing and weight status are unrelated to each other, but well related to a third variable that