Cohen,E., Cragg,M., deFonseka,J., Hite,A., Rosenberg,M. and Zhou,B., (2015) Nutrition 31:727-732 10.1016/j.nut.2015.02.007
OBJECTIVE: To document patterns and changes in average adult consumption in the USA since the earliest US government dietary recommendations for reduced fat intakes were issued (late 1970s) to current intakes, based on National Health and Nutrition Examination Survey (NHANES) data. Also to investigate the correlation between long-term consumer dietary patterns and obesity rates.
DESIGN: Dietary intake data were taken from 10 NHANES surveys. Additional data were included from the 1965 USDA household consumption survey. Potential demographic biases were corrected for.
SETTING: USA, free living.
PARTICIPANTS: Free living adults aged 18-64 years, excluding pregnant women, participating in NHANES 1971-1974, 1976-1980, 1988-1994, 1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008, 2009-2010, and 2011-2012 (released in 2014).
MAIN OUTCOME MEASURES: Relative and absolute macronutrient intakes. Correlation between long-term consumer dietary patterns and BMI distribution.
RESULTS: History of macronutrient recommendations is reviewed.
Percent energy from fat decreased from 44.7% in 1965 to 37.5% in 1971, further decreasing to 32.2% in 1999 and is currently at 33.6% (2011 survey). Percent energy from carbohydrate was 39% in 1965, increasing to 45.6% in 1971, peaking at 52.1% in 1999, and is 50.5% in the 2011 survey. Percent energy from saturated fat has also decreased from 13.5% in 1971 to 10.7% in 2011. The changes in share of fat and carbohydrate are primarily due to a 65g (260kcal) increase in absolute carbohydrate intake between 1965 and 2011. While absolute fat intake fell by approximately 26g between 1965 and 1971 (authors note data from different survey types and hence different methodologies), it has since remained relatively unchanged.
The primary objective for introducing the dietary recommendations was to decrease coronary heart disease (CHD). Though mortality from CHD has declined the goal of reducing risk of CHD has not been achieved on an absolute per capita basis. The authors refer to recent conclusions that guidelines on saturated fat were not supported by the available science at the time, a disconnect which may explain this finding for CHD. However the authors refer to a correlation between dietary shift and a significant increase in rates of obesity. Average adult BMI has increased from 24 in 1965 to 29 in 2011 and there is a strong relationship at the individual level between increase in percent energy from carbohydrate and obesity: 85.3% for men and 91.2% for women. In 1971 BMI distribution was tighter around the median (24.1) with a small skew at higher BMI at the end of the tail. However in 2011 median BMI was 27.4 with a much more evident skew to severe obesity. In 1971 42.3% of adults were overweight, 14.7% obese and 1.6% severely obese; in 2011 the figures were 66.1% overweight, 35.2% obese and 7.2% severely obese.
To explore whether this shift in BMI distribution to higher obesity can be explained by an increase in overall calorie intake, the authors collected cross-sectional data in two subsamples of participants. These were adults who consumed average calorie intake between 1971 and 2011, i.e. 2400-2500 kcal/day for men (1.5-1.6% of participants) and 1700-1800 for women (3.6 and 2.5%), and those who consumed higher intakes i.e. 3400-3600 kcal/day for men and 2400-2600 for women. Macronutrient shares trended consistently with the pattern seen in all participants and BMI rose in line with the full sample. This was taken by the authors to indicate that an increase in total caloric consumption since 1971 was not likely to offer any significant explanation for the increase in BMI in following decades.
CONCLUSIONS: Since 1971 the shift in macronutrient share from fat to carbohydrate is primarily due to an increase in absolute consumption of carbohydrate as opposed to a fall in absolute fat intake. General adherence to US government dietary recommendations to reduce % total energy from fat has been accompanied by a rapid increase in obesity rates. There is a high correlation at the individual level between % total energy from carbohydrates and adult BMI: 85.3% for men and 91.2% for women.
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