The main driver of the obesity epidemic has been increased intake, rather than decreased energy expenditure, Stephen J. Simpson and David Raubenheimer say:
The obesity problem is best understood not as the result of the overconsumption of a single macronutrient, but from a skewing of the proportion of each macronutrient in our diet — notably the dwindling quantity of protein in processed food products. The paucity of protein relative to fats and carbohydrates in processed foods drives the overconsumption of total energy as our bodies seek to maintain a target level of protein intake.
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 obesity, 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.