Sources of Copper
It isn't hard to get enough copper-- unless you live in an industrial nation. I've compiled a chart showing the copper content of various refined and unrefined foods to illustrate the point. The left side shows industrial staple foods, while the right side shows whole foods. I've incorporated a few that would have been typical of Polynesian and Melanesian cultures apparently free of cardiovascular disease. The serving sizes are what one might reasonably eat at a meal: roughly 200 calories for grains, tubers and whole coconut; 1/4 pound for animal products; 1/2 teaspoon for salt; 1 cup for raw kale; 1 oz for sugar.
Note that beef liver is off the chart at 488 percent of the USDA recommended daily allowance. I don't know if you'd want to sit down and eat a quarter pound of beef liver, but you get the picture. Beef liver is nature's multivitamin: hands down the Most Nutritious Food in the World. That's because it acts as a storage depot for a number of important micronutrients, as well as being a biochemical factory that requires a large amount of B vitamins to function. You can see that muscle tissue isn't a great source of copper compared to other organs, and this holds true for other micronutrients as well.
Beef liver is so full of micronutrients, it shouldn't be eaten every day. Think of it in terms of the composition of a cow's body. The edible carcass is mostly muscle, but a significant portion is liver. I think it makes sense to eat some form of liver about once per week.
Modern Agriculture Produces Micronutrient-poor Foods
The numbers in the graph above come from NutritionData, my main source of food nutrient composition. The problem with relying on this kind of information is it ignores the variability in micronutrient content due to plant strain, soil quality, et cetera.
The unfortunate fact is that micronutrient levels have declined substantially over the course of the 20th century, even in whole foods. Dr. Donald R. Davis has documented the substantial decline in copper and other micronutrients in American foods over the second half of the last century (1). An even more marked decrease has occurred in the UK (2), with similar trends worldwide. On average, the copper content of vegetables in the UK has declined 76 percent since 1940. Most of the decrease has taken place since 1978. Fruits are down 20 percent and meats are down 24 percent.
I find this extremely disturbing, as it will affect even people eating whole food diets. This is yet another reason to buy from artisanal producers, who are likely to use more traditional plant varieties and grow in richer soil. Grass-fed beef should be just as nutritious as it has always been. Some people may also wish to grow, hunt or fish their own food.