SECULAR TRENDS: CHANGES IN CARBOHYDRATE INTAKE DURING THE TIME PERIOD THAT OBESITY RATES HAVE RISEN

9.3 SECULAR TRENDS: CHANGES IN CARBOHYDRATE INTAKE DURING THE TIME PERIOD THAT OBESITY RATES HAVE RISEN

9.3.1 T OTAL C ARBOHYDRATES

As the prevalence of overweight and obesity has risen in the U.S. since the 1970s, so has the average per capita intake of carbohydrates. To estimate intake, we examine both national food supply and intake data. National food supply refers to the amount of food available for human consumption in the U.S., whereas intake data refers to the amount actually eaten based on a random sample of self-reported intakes. Both methodologies have their strengths and weaknesses. Food supply data are not subject to recall bias, but do not completely account for waste. Food intake data, on the other hand, are subject to many biases on the part of the individual, but have the advantage that they directly measure the variable of interest, i.e., intake. The increase in carbohydrate intake can be illustrated on the basis of both national food supply (Figure 9.2) and intake data (Figure 9.3). Since the late 1970s, total carbohydrate intake has increased in absolute terms as well as in proportion to total energy intake. According to data from the National Food Consumption Survey (NFCS) and the Continuing Survey of Food Intake by Indi- viduals (CSFII), the percent of calories consumed as carbohydrates has increased among adults from about 40% in the late 1970s to about 50% in the mid-1990s. 42 Over this same time period, carbohydrate intake has increased from 47 to 54% of calories among adolescents. 43

9.3.2 S UGARS AND R EFINED C ARBOHYDRATES

Of course, total carbohydrates are not a single entity but are a class of dietary compounds, some of which, on the basis of their chemical and metabolic properties,

Functional Food Carbohydrates

Energy 3000

Total fat 2000

Carbohydrate Protein

Kilocalories per capita per day

FIGURE 9.2 Energy sources in U.S. food supply. (From Lisa Bente, USDA Center for Nutrition and Policy Promotion, personal communication, 2003.)

% Kilocalories 20 10

1994-95 FIGURE 9.3 Trend in carbohydrate intake among adults (NFCS and CSFII). (From Enns,

1977-78

1989-91

C. et al., Fam. Econ. Nutr. Rev., 10, 27, 1997.) may have quite different and even opposite effects on energy balance. Sugars, other

refined carbohydrates, and fiber are three types of carbohydrates of particular interest. Food supply data suggest that Americans on average have increased their intake of

all of these types of carbohydrates. Since the early 1970s, added sugars in the food supply have increased by 20% (Figure 9.4) and intake of foods that are classified

as sugars and sweets have increased by 12%. 42 The rise in the intake of soda has been particularly precipitous (Figure 9.5), up from about 25 gallons per capita per year in the mid-1970s to almost 40 gallons per capita in the late 1990s. The intake of soda in the 1990s is therefore equivalent to about 400 calories per day, or 20% of the daily energy requirement for a sedentary adult. According to a 1994–1996 national survey, Americans get about 43% of their added sugars from soft drinks and fruit drinks. 44

9.3.3 F IBER

Concomitantly, fiber intake has increased by 5 g or 26% (Figure 9.6), and intakes of total flour and cereal products have increased by 48%. 45 Nevertheless, a very

Carbohydrates and Obesity

1970-74 1975-79

1980-84

1985-89

1990-94 1995-99 2000-

FIGURE 9.4 Per capita annual average of total caloric sweeteners. (From USDA, Nutrient content of the U.S. food supply, available online at http://147.208.9.134.)

FIGURE 9.5 Per capita annual carbonated soft drink consumption in the U.S. (From USDA/ERS, Food availability spreadsheets, available online at http://www.ers.usda.gov/data/ FoodConsumption/FoodAvailSpreadsheets.htm.)

Grams/person/day

FIGURE 9.6 Fiber in U.S. food supply. (From USDA, Nutrient content of the U.S. food supply, available online at http://147.208.9.134.)

Functional Food Carbohydrates

small proportion of the total flour and grain intake is in the form of whole grains. Although food supply data indicate that over 10 servings of grain products per day

are available for consumption in the U.S., in the mid-1990s two thirds of the U.S. population over 2 years of age ate less than 1 serving of whole grain foods per day. 45 Secular trends in food intake therefore suggest that more than one type of carbohy- drate may be contributing to Americans’ weight gain, most particularly refined flour products and liquid forms of sugar.