Obesity rates in the US climbed steadily over the last four decades, from 13% of the population in 1970 to more than 34% in 2009. While some blame an increase in dietary fructose, a recent study published in the Nutrition Journal used food availability data over the past four decades to set the record straight on what’s to blame for the obesity epidemic.
Drawing on data from the USDA Economic Research Service for 1970-2009, the authors found that total energy availability in the US food supply increased 10.7% during the period, though the net change in total fructose availability for the period was 0%.
During the same period, energy available from total glucose (from all digestible food sources) increased 13%. Furthermore, glucose availability was more than three times greater than fructose. The food categories that increased the most during this period were grains (up 24.2%) and fats & oils (25.3%).
“Our findings indicate that fructose per se was not a unique causal factor in promoting obesity during 1970-2009,” the authors wrote. “Rather, increased total energy intake, due to greater availability of foods providing glucose (primarily as starch in grains) and fat, were significant contributors to increased obesity in the US.”
Carbohydrate availability increased more than any other macronutrient during the 40-year period tracked by the researchers. In 2009, 32.3 grams per day more carbohydrates were available than in 1970, suggesting that carbohydrates alone contributed 129 more calories per day in 2009 than 1970 with a range of 253 calories per day. The cumulative change in carbohydrate-derived energy across the study period as measured by the area under the curve (AUC) was 9.8%.
The caloric sweeteners category—which consists mainly of sucrose, HFCS-55, and HFCS-42—increased 1.3% over the 40-year period. Unlike sucrose, which dropped in availability, the availability of both types of HFCS increased since their introduction into the US food supply. Still, the data indicate that sucrose and HFCS, used as added sweeteners, are the major sources of fructose in the US diet.
The impact of low-carb diets
Dietary fat and oil availability also increased from 1970 to 2009, with a cumulative change in fat-derived energy of 14.6% across the period. Notably, fat and oil availability charted a sharp incline starting in 1999, while carbohydrate availability began to decline, a shift that could be due to the explosion of low-carb, high-fat diets around that same time.
Before this shift, carbohydrates had accumulated to a greater extent than fats and oils regarding both mass and energy contribution to the US diet. Post-1999, the fats and oils category was a bigger contributor to the energy increase.
Source: Nutrition Journal
“Food availability of glucose and fat, but not fructose, increased in the US between 1970 and 2009: analysis of the USDA food availability data system”
Authors: Trevor J Carden and Timothy P Carr