In an editorial for Nature, Stephen J. Simpson (academic director of University of Sydney's Charles Perkins Centre) and David Raubenheimer (Leonard P. Ullman chair in nutritional ecology and nutrition theme leader at the Charles Perkins Centre) argue that the obesity epidemic isn't caused by sedentary lifestyles, but by overconsumption, because our appetite control systems are "fooled or subverted" by carbohydrates and fats that mimic proteins.
The ersatz proteins are much cheaper than the real thing, and have also made their way into the feed of livestock and pets. The authors state that "the range of processed food becoming available is evolving faster than our appetite control systems," and argue that the historic shortage of sugars caused us to evolve appetite systems that are bad at judging when we've had enough of them.
These arguments echo many of those raised in The End of Overeating (recently featured in a This Day in Blogging History post), in which former FDA commissioner and MD David A Kessler tries to understand how industrial food science has produced food that is exquisitely engineered to cause overeating and constant cravings.
Many processed food products are protein-poor but are engineered to taste like protein. Many people therefore eat far too much fat and carbohydrate in their attempt to ingest enough protein. In this way, engineered foods subvert the appetite control systems that should be helping to balance the consumption of macronutrients. The results are striking. In the United States, the typical diet saw a 0.8% decline in protein concentration between 1971 and 2006. During this same period, the consumption of calories from carbohydrates and fats increased by 8%, a trend reflected in the rising prevalence of obesity3, but protein intake remained almost unchanged.
The substitution of carbohydrates and fats for protein is driven by economics. Food manufacturers have a financial incentive to replace protein with cheaper forms of calories, and to manipulate the sensory qualities of foods to disguise their lower protein content. This leads to savoury-flavoured food that makes us think we're eating protein when in reality it is loaded with carbohydrates and fats. The manufacturers of animal feed have similar incentives to add carbohydrates, resulting in fatter livestock (and pets). The higher cost of protein drives consumers to buy cheaper processed food loaded with fat and carbohydrates — an effect that disproportionately affects people on tighter budgets.