Caloric Balance

A basic premise of the 2005 Dietary Guidelines is that nutrient needs should be met primarily through consuming nutrient-dense foods that provide substantial amounts of vitamins and minerals (micronutrients) and relatively few calories. "Foods that are low in nutrient density are foods that supply calories but relatively small amounts of micronutrients, sometimes none at all. The greater the consumption of foods or beverages that are low in nutrient density, the more difficult it is to consume enough nutrients without gaining weight, especially for sedentary individuals. The consumption of added sugars, saturated and trans fats, and alcohol provides calories while providing little, if any, of the essential nutrients."

Maintaining weight requires balancing "energy input" (calories taken in through eating) with "energy output" (calories burned). Losing weight requires a sustained effort to curtail dietary intake and, if possible, boost physical activity so that you are consistently burning more calories than you are taking in. Over time, this will produce weight loss. However, many aspects of modern life influence how easy or difficult it is to balance "calories in" with "calories out." Three developments that deserve special consideration are the increase in portion sizes, the increase in the amount of sugar-sweetened beverages that children and adults consume, and the increase in the amount of time that Americans spend watching television.

Portion sizes — Portion Distortion

The following table demonstrates the difference in portion size for many foods over the past 20 years. To give you a clear picture of the caloric costs of this inflation in portion sizes, the table calculates the extra calories in the larger portions and translates them into the amount of exercise that is needed to burn off those extra calories. Since the majority of Americans are less active than they were in the past (when portion sizes were smaller), the consequence of this portion distortion is weight gain in people of all age groups.

Sugar-Sweetened Beverages

From 1947 to 1997, the per capita consumption of carbonated soft drinks in the US increased from approximately 10 gallons to more than 50 gallons per year. Consumption of sugar-sweetened soft drinks has become particularly high among children and adolescents.

The possible role of soda or soft drinks and other sugar-sweetened beverages in the development of childhood obesity is a matter of great interest. A meta-analysis of 88 studies conducted by Vartanian et al. (2007) found associations of soft drink intake with increased energy intake and increased body weight. Soft drink intake was associated with lower intakes of milk and calcium and with an increased risk of diabetes. Since not all studies have implicated soda as a cause of childhood obesity, Vartanian et al. (2007) attempted to explain the discrepant results. Their analysis suggested that study design significantly influenced the results. Larger effect sizes were found in studies using a stronger experimental design, i.e., longitudinal and experimental studies. Studies of weaker design, i.e., cross-sectional or observational studies, were less likely to find an association. They concluded that population-based strategies to prevent childhood obesity by limiting soft drink consumption are "strongly supported" by the available scientific evidence.

The authors also found a link between soft drink consumption and type 2 diabetes. For example, in one study of 91,249 women followed for 8 years, daily consumers of one or more servings of soft drinks were twice as likely as those who consumed less than 1 serving per month to develop diabetes. That this finding is specific to consuming sugared soft drinks is suggested by the disappearance of the effect among those using diet drinks.

In point of fact, only two of the 88 studies were designed to directly test whether reductions in soda consumption would improve BMI. One study by James et al (2004) targeted soft drink consumption in 644 children ages 7 to 11 years old in six primary schools in southwest England from August 2001 to October 2002. The intervention consisted of one hour for each class each term delivered by a trained health educator. Drink diaries covering two week days and one weekend day prepared at baseline and at the end of the study showed that carbonated soft drink consumption decreased slightly but significantly in the intervention group as compared to the controls. Height and weight were measured every six months. After one year the percentage of overweight and obese children increased in the control group by 7.5% and decreased in the intervention group by 0.2%. This study has been criticized because the documented decrease in soft drink consumption was very small (~50 ml per day, not even a 1/4 cup).

The second study was an intervention by Ebbeling et al. (2006) conducted during the 2003-2004 academic year. This was a small study of 103 teens, 13 to 18 years old, who were daily consumers of at least 12 oz. of soft drinks or other sugar sweetened beverages. The subjects were randomized into two groups and calorie-free soda was delivered to the homes of the intervention subjects for 25 weeks. The intervention subjects received written instructions on how to avoid sugar sweetened beverages and monthly phone calls to reinforce instructions, answer questions and address concerns. These subjects also received refrigerator magnets with messages related to weight control, tooth decay, hunger, misleading beverage labels and advertisements. Control subjects were asked to continue usual beverage consumption habits for 25 weeks. Consumption of sugared soft drinks decreased by 82% in the intervention group and was unchanged in the controls. Change in BMI was not different between the two groups as a whole. However, an analysis of the heaviest subjects in the two groups showed a greater beneficial effect of reduced soda consumption in the intervention group as compared to the heaviest subjects in the control group.

Because of the complexity of obesity and the many factors contributing to overweight there is a low likelihood that a single change (such as reducing sugar-sweetened beverages) is all that is necessary to stem childhood obesity on a population basis. But, decreasing soda consumption is not a harmful strategy and it may be helpful. The findings of the two interventions discussed above are of great interest and further studies of the value of reducing soft drinks as a prevention strategy should be pursued as a high priority.

Television

Parents surveyed in 2000 reported that American children typically spent more than four and a half hours each day watching television or videos, playing computer or video games, or surfing the internet; of this "screen time," more than half was spent watching television. Time spent watching television is positively associated with overweight among children. Proposed mechanisms to explain this association include the possibility that the time spent watching television may displace physical activity, thus decreasing energy output, and the possibility that television viewing may result in increased energy intake either because children eat snacks while watching TV or because they are exposed to, and respond to, more advertising promoting high-calorie foods. Research has shown that children who reduce the amount of time they spend watching television and video tapes and playing video games also reduce their BMI. According to the 2007 YRBS, approximately 1 of 4 Montana high school students spend three or more hours watching TV on an average school day, and YRBS trend data shows that younger students (7th and 8th graders) are consistently spending more time watching TV than high school students. The American Academy of Pediatrics recommends that television and video time be limited to a maximum of two hours per day. The report from the Institute of Medicine, Preventing Childhood Obesity: Health in the Balance reaffirmed that recommendation. Here again, reducing TV viewing is a strategy that is not harmful and can be helpful in managing weight.

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