The American Diet has shifted from primarily unprocessed whole foods to primarily processed foods in the last century.

In 1890, obesity prevalence was 3.4% [1]. Western diets have shifted in the last 120 years, particularly since WWII, to include more meat and vegetable oil. Looking at the United Nations data on U.S. food availability, which serves as a proxy for actual consumption, you can see where Americans get their calories today (grains, vegetable oils, sugar / sugar equivalents, and meat) and how this has changed since 1961.

U.S. Food supply (kcal/capita/day)

U.S. Food supply (visualization of chart on left for scale)

Reviewing USDA food availability data going back further, we can see how Americans got their calories in 1900 - the large majority (approximately 1200 calories per day) coming from cereal grains.

USDA meat availability (kg)

Per capita meat availability has nearly doubled in the last century largely because of factory farms and processing equipment.

USDA grain availability (kg)

In the first half of the 20th century, increased prosperity and transport led to increased competition from other food groups and grain consumption declined. With the growth of the fast food industry and 1977 dietary recommendations emphasizing low-fat diets grains have since gained back some share.

USDA fat availability (kg)

Animal fats declined partly as a result of the first recommendations against saturated fat came out and found the public spotlight in the mid-20th century.

USDA cheese availability (kg)

Most dairy products have gone down in consumption since the 1960. In contrast, cheese availability has increased dramatically and 60% comes from commercially prepared food.

USDA bev availability (kg)

From the end of WWII to 2000, carbonated soft drink consumption grew approximately five-fold.

As established above, cereal grain has long made up the largest portion of calories in the diet of Americans. Wheat makes up an outsized share of U.S. cereal grain consumption. In the late 1800s, the way wheat was processed changed drastically. The purpose of grain milling is to separate the high calorie endosperm from the bran and germ. Up to that point, grains were primarily stone ground and some bran made it into the endosperm, discoloring it - and at the time the whiter the flour, the more value it got on the market. In 1880, John Stevens was awarded the patent for the roller mill which significantly improved yield and completely separated the more nutritious bran and germ from the endosperm flour. Today, an estimated 99% of wheat is ground in roller mills [2], [3].

U.S. Grain Supply (kcal/capita/day)

What we feed the animals we eat has also changed dramatically with the growth of the food processing industry. Though wheat remains the most consumed grain, heavily subsidized corn and soybeans are the two most widely produced crops. A large portion of both corn and soybeans are now used as animal feed in concentrated animal feeding operations. From 1995 to 2014, the government has paid out $322 Billion in farm subsidies, supporting the continued production of these crops [4].

American behavior has also shifted in the last century from consuming the large majority of meals at home to consuming the majority of meals away from home. Factors leading to the growth of food away from home include higher incomes, larger % of women employed outside the home and more affordable and convenient fast food. Food consumed away from the home has been found by the USDA in a number of studies to be on average more caloric and of lower nutritional value (less fiber, more saturated fat) than food consumed at home. [5], [6], [7], [8].

Source: https://www.ers.usda.gov/data-products/food-expenditures.aspx

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