“Lose That Extra Weight — While Eating the Foods You Love!”

For decades, such headlines were fixtures of supermarket checkout lanes, to be taken no more seriously than claims of alien abduction. But times have changed. High-protein, low-carbohydrate diets have become wildly popular because they help adherents lose dozens of pounds without having to gnaw on rice cakes.

It seems too good to be true, and some critics say it is. The debate over the long-term health effects of Atkins and similar weight-loss plans might grind on for years with no satisfactory conclusion. But it is possible to predict some ecological consequences if more of us adopt high-protein, low-carbohydrate diets, forcing the earth and sea to produce more of the “foods we love.”

Let’s start with the Worldwatch Institute’s estimate that 1 billion of Earth’s inhabitants are overweight. Assume that on average they each eat 56 grams of animal protein a day. That is the average in Western countries, and most overweight people eat Western diets.

If all those people went on an Atkins-style diet, their requirement for animal protein would rise to about 100 grams. A billion dieters each eating an extra 44 grams could not easily be satisfied by giving them a bigger share of current animal protein production. As it is, humans worldwide average only 28 grams per day. Instead, by our calculations, the meat, dairy, poultry and seafood industries would have to increase output by 25 percent.

The dieters would no longer get much of their protein from plants, so less cropland would be required for that. Still, the net result of their big switch to animal protein would require almost 250 million more acres for corn, soybeans and other feed grains. That’s because feeding grain to animals and then eating the meat, milk, eggs or farm-raised fish is much less efficient than eating plant products directly. The dieters could not expect to get more from the oceans: the global catch has fallen since the mid-1980s, from overfishing.

Finding a quarter-billion acres for adequate feed grain harvests would mean at least a 7 percent increase in cropland worldwide at a time when farmers are already using most of the better land. Much of the newly plowed acreage would likely be marginal, subject to greater erosion and requiring extra generous applications of fertilizer and pesticides.

Furthermore, feeding that grain to all those extra animals would lead to greater pollution from feedlots, poultry and hog confinement operations, and slaughterhouses.

And that’s not all. Cattle and other ruminant animals, whose numbers would have to rise by 25 percent to supply our dieters, get a large share of their food from pasture and rangeland. If most of the additional animals were raised on current range and pasture that are already fully stocked, the result would be overgrazing and degradation.

If new pastures were to be created for, say, half of the additional animals, a billion more acres would have to be found. Most of this would probably be obtained by deforestation, meaning that 10 percent of Earth’s remaining forests would have to go.

It’s unlikely that all 1 billion of the world’s overweight people will have the desire or the means to make the move to expensive animal-based food. Nevertheless, the kind of ecological damage we have described will occur in direct proportion to the number of people who do adopt the diet.

Already, industry analysts give much of the credit for this fall’s sharply higher beef and egg prices to high-protein, low-carb dieters. Stepped-up production is sure to follow.

While it’s true that overconsumption in America doesn’t exactly qualify as “breaking news,” we’re now seeing a new twist to an old story. The obesity epidemic, caused largely by excess food consumption, has proven to be one of our society’s most vexing problems. The diets now in vogue may be a breakthrough in curbing obesity, but their success entails even greater consumption of global resources.

Marty Bender and Stan Cox are scientists at the Land Institute in Salina, and members of the institute’s Prairie Writers Circle.