Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century

Abstract

Background: The consumption of omega-3 (n-3) and omega-6 (n-6) essential fatty acids in Western diets is thought to have changed markedly during the 20th century.

Objective: We sought to quantify changes in the apparent consumption of essential fatty acids in the United States from 1909 to 1999.

Design: We calculated the estimated per capita consumption of food commodities and availability of essential fatty acids from 373 food commodities by using economic disappearance data for each year from 1909 to 1999. Nutrient compositions for 1909 were modeled by using current foods (1909-C) and foods produced by traditional early 20th century practices (1909-T).

Results: The estimated per capita consumption of soybean oil increased >1000-fold from 1909 to 1999. The availability of linoleic acid (LA) increased from 2.79% to 7.21% of energy (P < 0.000001), whereas the availability of α-linolenic acid (ALA) increased from 0.39% to 0.72% of energy by using 1909-C modeling. By using 1909-T modeling, LA was 2.23% of energy, and ALA was 0.35% of energy. The ratio of LA to ALA increased from 6.4 in 1909 to 10.0 in 1999. The 1909-T but not the 1909-C data showed substantial declines in dietary availability (percentage of energy) of n-6 arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Predicted net effects of these dietary changes included declines in tissue n--3 highly unsaturated fatty acid status (36.81%, 1909-T; 31.28%, 1909-C; 22.95%, 1999) and declines in the estimated omega-3 index (8.28, 1909-T; 6.51, 1909-C; 3.84, 1999).

Conclusion: The apparent increased consumption of LA, which was primarily from soybean oil, has likely decreased tissue concentrations of EPA and DHA during the 20th century.

FIGURE 1

Trends in the estimated per capita consumption of major food commodities (A), major fat commodities (B), and vegetable and seed oils (C) between 1909 and 1999. kg/p/y, kilograms per person per year.

FIGURE 2

Major sources of calories between 1909 and 1999. Fats included shortening, butter, lard, margarine, and beef tallow. Soybean oil was considered separately from other oils because of its disproportionate contribution. Dairy included all milk, buttermilk, condensed milk, cream, sour cream, yogurt, cheese, and eggnog. Butter was not included in the dairy category to avoid double counting.

FIGURE 3

Availability of essential fatty acids from 1909 to 1999. Inputs to the equation of Lands et al (2) to estimate US tissue compositions: P₆, P₃, H₆, and H₃ indicate linoleic acid (LA), α-linolenic acid (ALA), n−6 highly unsaturated fatty acids (HUFAs), and n−3 HUFAs, respectively. 1909-T data are indicated by solid arrows for LA (2.23% of energy), ALA (0.35% of energy), arachidonic acid (AA) (0.67% of energy), docosahexaenoic acid (DHA) (0.033% of energy), eicosapentaenoic acid (EPA) (0.028% of energy), and docosapentaenoic acid (DPAn−3) (0.018% of energy).

FIGURE 4

Regression analysis for the availability of linoleic acid (LA) between 1909 and 1999. The linear relation [LA percentage of energy (en%) = −115.4221 + 0.0617 × x] was significant at P < 0.000001 with a coefficient of determination of r² = 0.95 (STATISTICA for Windows version 8.0; StatSoft, Tulsa, OK).

FIGURE 5

Changes in ratios of n−6 to n−3 fatty acids in the US food supply from 1909 to 1999. Linoleic acid (LA)/α-linolenic acid (ALA) is indicated by a solid line, total n--6/total n--3 fatty acids by a dashed gray line, and n--6 highly unsaturated fatty acids (HUFA)/n--3 HUFAs by a dotted line. 1909-T (foods produced by traditional early 20th century practices) data are indicated by the solid arrow for the LA/ALA ratio and by a dashed gray arrow for the ratio of total n−6 to n−3. The LA:ALA ratio was lowest for 1909-T foods (6.4) and highest for 1999 foods (10.0). The ratio of total n−6 to n−3 was 5.4 in 1909-T and 9.6 in 1999.

FIGURE 6

Sources of linoleic acid (LA) (A) and α-linolenic acid (ALA) (B) between 1909 and 1999. Fats included shortening, butter, lard, margarine, and beef tallow. Oils included cottonseed, corn, olive, coconut, canola, peanut, palm, safflower, sunflower, and sesame oils. Soybean oil was considered separately because of its disproportionate effect. Dairy included all milk, buttermilk, condensed milk, cream, sour cream, yogurt, cheese, and eggnog. Butter was not included in the dairy category to avoid double counting.

FIGURE 7

Sources of arachidonic acid (AA) (A), eicosapentaenoic acid (EPA) (B), docosapentaenoic acid (DPAn−3) (C), and docosahexaenoic acid (DHA) (D) from current foods between 1909 and 1999.

FIGURE 8

Omega-3 tissue highly unsaturated fatty acid (HUFA) predictions over the 20th century. Solid arrows indicate the percentage of n−3 in HUFA (36.8%) and the estimated omega-3 index (8.3) calculated from available nutrient intakes for 1909 traditional foods (1909-T).

FIGURE 9

Time-series determination of the dependence of the percentage of n−3 in highly unsaturated fatty acids (HUFA) on linoleic acid (LA) (A) compared with on α-linolenic acid (ALA) (B). Slopes of suggested regression lines between contrived series plots (dashed lines) and original functions (bold lines) were similar in direction and magnitude for LA. For ALA, slopes of regression lines were opposite in direction and lower in magnitude than the original prediction plot. Therefore, the tissue percentage of n−3 in HUFA was dependent on changes in dietary LA rather than in ALA.

FIGURE 10

The historical event immediately preceding the largest increase in apparent consumption of soy oil in the United States was the 1961 American Heart Association (AHA) Central Committee Advisory Statement (32) that advised Americans to replace their saturated fat intake with polyunsaturated fats. Vegetable oils and, to a lesser extent, shortening and margarine were recommended as replacements for animal fats such as butter, cream, and cheese. kg/p/y, kilograms per person per year; WWI, World War I; WWII, World War II; USDA/HHS, US Department of Agriculture/US Department of Health and Human Services.