America’s Great Dietary Divergence

This is a guest blog post by Richard Perlmutter, MS

Every so often it is useful to take a step back, and look at trends in what people choose to eat. One especially interesting trend is what I call America’s Great Dietary Divergence.

Because animal foods contain both protein and fat, one would expect that increasing consumption of animal protein, would be accompanied by
increasing consumption of animal fat. But that is not what has been happening. Increasing consumption of animal protein has been accompanied by decreasing consumption of animal fat.

Similarly, decreasing consumption of protein from plant sources has been accompanied by increasing consumption of fat from plant sources.

Compared to a hundred years ago more of our protein is from animal sources, and much more of our fat is from plant sources.

The U.S. Department of Agriculture (USDA) has been tracking the availability of the various classes of food and food nutrients since the early nineteen hundreds. Much of this discussion relies on the Department’s data.

The Former Importance of Wheat

In the period 1909–1919, animal sources (meat, dairy, eggs) supplied
about 50 percent of the protein in the American diet. Plant foods supplied the
other 50 percent. Grains, mostly wheat, were the major sources of protein, supplying about 37 percent of the total. At 30 percent, meat was the number
two source of protein.

A USDA graph shows that wheat flour consumption peaked at about 225 lb per person per year in the late 1800’s. During the period 1909-1919 consumption was decreasing, and the yearly average was about 190 lb.

Over the same ten year period, animal sources supplied about 85 percent of the fat. This percentage included the fat in meat, dairy, and eggs; as well as the fat contributed by butter, lard, and tallow.

Wealth, Refrigeration, and Health

Increasing income and the introduction of refrigeration were responsible
for rising meat and milk consumption during the first half of the twentieth century. At the same time foods based on wheat became less popular.

In the decade 1950–1959 animal sources supplied about 64 percent of the protein in the diet, up from 50 percent. Grains, around 20 percent.

But fat from animal sources declined. That was the net result of two opposing trends. Consumption of fat in meat and dairy increased. But the consumption of butter and lard decreased, mainly due to the increasing popularity of margarine and shortening made from vegetable oils.

Between 1950 and 1959 animal sources supplied about 69 percent of the fat, down from 85 percent.

Animal fat has suffered an even more serious fall that began around 1980. That was the year the Dietary Guidelines for Americans, the federal government’s official guide to healthy eating, was first published. The Guidelines did not think highly of animal fat. (And they still don’t.)

Cardiovascular disease had become the major cause of death among older Americans. Public health officials believed animal fat in the diet was the major controllable cardiovascular disease risk factor. The Guidelines recommended decreasing one’s intake of fat, saturated fat, and cholesterol. These recommendations, especially with regard to saturated fat, continue to be emphasized.

Consumers did not reduce their intake of meat and dairy, but they began wanting them to contain less fat.

Producers responded to the change in demand. Red meat (beef and pork) is now much lower in fat. Poultry, a source of low fat and low cost meat, has surged in popularity. Except for cheese, low fat versions of most dairy products now sell better than the full fat versions.

During the years 2000 -2005, animal sources contributed 63 percent to protein availability- similar to fifty years ago. Grains, mostly wheat, contributed about 22 percent- also similar to fifty years ago.

Very recently gluten, the main protein in wheat, has been demonized as the cause of numerous maladies. In reaction, wheat consumption is probably deceasing. For the years 2000-2005, annual wheat consumption was about 135 lb per person.

In the early 1900’s wheat was mostly sold for home use. By the latter part of the 1900’s most was sold to commercial bakeries. There was probably much less loss due to discarded stale product in the earlier time compared to the more recent times. In consequence recent wheat consumption estimates may be somewhat overstated.

For the years 2000-2005, animal sources supplied only 39 percent of the fat in the diet. This was down from 69 percent for the years 1950-1959.

Besides the switch to leaner animal foods, increased production of foods fried in vegetable oils are most responsible for the lower percentage of animal fat. The frying oil of choice is soybean oil, an oil that was not even a factor in food use seventy-five years ago. French fried potatoes have become the most popular fried food. Production has increased by a multiple of ten since the 1950’s.

Soybean Oil and More Soybean Oil

Soybean oil has also become the oil of choice for most other food uses, such as in salad dressings and baked goods. It accounts for about eighty-five percent of the vegetable oil used in food. Among all food ingredients it is the third greatest source of calories in the American diet, after wheat flour and added sugars.

I should add a note of caution regarding vegetable oil data. Unlike protein, there is tremendous waste with vegetable oil. When used in deep fat fryers, oil has a short life. It is discarded and replaced with fresh oil on a regular basis. For this reason food availability estimates for oils are thought to be considerably higher than their actual consumption.

Comparing the Changes

Comparing data for 1909-1919 and 2000-2005, the percentage of protein coming from animal sources rose from about 50 to about 63 percent.

Over the same period, the percent of fat coming from animal sources declined from
about 85 to about 39 percent.

What are the health related results of these changes?


The mortality rate for cardiovascular disease has certainly come down. Public health officials believe this has been a positive outcome of the shift from animal fat to vegetable oil.

But obesity has increased.

More fat is now found in foods that are high in carbohydrates. This combination produces foods that are both high in calories and low in satiety. Eating these foods can cause weight gain.

And osteoporosis has become a major concern among older adults. Animal protein is more acidic than plant protein and some researchers believe that calcium is pulled from bone to neutralize the acid. This weakens bones, making them more susceptible to fractures.

It appears that both good and not-so-good have followed in the wake of America’s great dietary divergence.

Richard Perlmutter is the owner of Abington Nutrition Services LLC which prepares nutrition labeling for products manufactured by food and beverage companies. He also takes an interest in seeing that government nutrition policy is in line with nutritional science.

(References to this article are available on request from the author.)

  • Laurel Ebert

    Can we say how much of the rate of mortality from cardiovascular disease is down due to dietary changes, and how much is from better drugs, like statins and better procedures like stents? I would be interested in seeing how the rate of cardiovascular disease overall compares.

  • kelly Perkins

    My reaction is similar to Laurel’s below. Cardiovascular disease is rampant, but medical interventions have cut down on the mortality rates due to cardiovascular disease. The obestity increase is a good reminder that there is alot of hidden fat, more than imaginable often, in carb based “treats” like muffins, etc.

  • The Candid RD

    We just can’t win can we?!

  • Brian Klein

    I’m curious why the correlation wasn’t made to vegetable oil as a reason more obesity? What were the rates for heart disease in 1909 when animal fats made up over 80% of the fats in the american diet? You should also note the consumption rates of sugar. That could very well be the main cause of obesity.

    An the discussion about osteoporosis comes out of nowhere. It seems as though you are just looking for a reason to indicate meat as an evil in the diet. Could the rates of osteoporosis be linked to lower magnesiums levels? Which would also balance out the acidity of meat? What about the near absence of vitamin k2 in our diets? This is a very simplistic explanation for something much more complex.

  • Mike Luque

    The comments about medical advances being much more important to the mortality rate are on the mark, as far as I’m concerned. Also, I’m prone to looking at sugar being the primary culprit as far as our obesity rates as well.
    However, I was really surprised by the levels of protein from wheat previous to 1919. Just goes to show the whole “no gluten” thing might not be a problem with wheat itself but instead with the current varieties of wheat that are in mass production as well as the heavily proccessed nature of so many “food” choices at supermarkets.
    I was also really surprised by the growth in the use of soy oil. Since the majority or soy is GMO, I’d be wiling to bet many people are consuming GMO products without even knowing it.