Background: For almost 50 years, the U.S. National Health and Nutrition Examination Survey has measured Americans’ caloric consumption, and body heights and weight. This paper presents the first comprehensive analysis of that data, documenting how macronutrient consumption patterns and the weight and body mass index in the U.S. adult population evolved since the 1960s.
Alex’s Notes: The history of dietary guidelines is relatively short. Starting in the 1950s, a series of papers were published implicating dietary fat and cholesterol in the etiology of heart disease, leading the American Heart Association (AHA) in 1961 to issue the nation’s first guidelines that recommend limited the consumption of fat and cholesterol. In 1980 these recommendations were supported by the USDA’s Dietary Guidelines for Americans which called for a reduction of total fat intake to no more than 30% of calories, with a compensatory increase in carbohydrates. It wasn’t until the 2005 guidelines that this cap was elevated to 35% of calories.
At the same time that the government was making their recommendations, the rates of obesity and chronic disease have continued to increase. There are many explanations and causes, one of which is proposed to be the USDA’s dietary advice. For instance, the 1992 Food Guide Pyramid urged Americans to use fats, oils and sweets “sparingly,” and to consume between 6 and 11 servings of bread, cereal, rice, and pasta. To date, however, no comprehensive analysis of consumption levels both before and after the endorsement of reduced-fat diets has been undertaken.
The author of this paper, Adele Hite, uses all NHANES data from 1970 to the present (as well as a 1965 survey before NHANES started) to document patterns and changes in average adults’ consumption since the earliest recommendations. The primary findings are as follows.
- In 1965, fat consumption comprised 44.7% of adult Americans’ diets, compared with 39% for carbohydrate.By 1971, those numbers had changed significantly, with fat down to 37.5% and carbohydrate up to 45.6%. By 1999, fat consumption reached a low of 32.4%, while carbohydrate consumption hit its peak of 52.1%, and this has been maintained to the present.
- Protein consumption remains relatively constant, ranging from 15% to 17% of total calories.
- In 1971, saturated fat comprised 13.5% of total calories. By 2011, Americans were eating 10.7% of their calories as saturated fat, a 20.5% reduction since 1971.
- Cholesterol consumption is down from over 400 mg in 1971 to 300 mg in present day.
- The shift in the share of fat and carbohydrate is primarily due to an almost 65 gram, or about a 260 calorie, daily increase in Americans’ intake of carbohydrate from 1965 to present. In 1961, the average adult consumed ~109g of fat and ~213g of carbohydrate. In the present day, fat consumption is about 83g and carbohydrate 278g.
- Average BMI increased from about 24 in 1965 to about 29 in 2011. There is a strong relationship between the increase in carbohydrate share of total intake and obesity (85.3% for men and 91.2% for women).
- The increase in total caloric consumption since 1971 is not likely to offer any significant explanation for the increase in BMI over the last four decades.
This paper provides strong evidence showing that the USDA dietary guidelines have been effective in changing the way people eat. As such, it does appear that adherence to the guidelines is not a problem and that in reality people do listen to the government more so than not. At the same time this dietary shift was occurring, rates of obesity have drastically increased. This paper suggests that carbohydrate intake may be the cause, but provides weak evidence in favor of it.
It is important that we remain objective regardless of what we think of the government recommendations. Many things were going on in the last 60 years that could have easily confounded the results. One example is sedentariness and physical inactivity. Another is the type of food eaten, rather than its macronutrient distribution. Nonetheless, the current paper does provide a nice snapshot of the dietary trends that have occurred since the beginning of dietary recommendations.