Foods engineered to be cheap and tasty might make you eat more

There are dozens of contestants in the fight for the title of “optimal diet”: vegetarian, vegan, paleo, keto … and the list goes on. The question of what diet is “best” is far from settled—and it’s quite possible that there’s no such thing as a single “best” diet for everyone. Focusing on which diets are “best” makes it very easy to overlook an important point: almost all of these diets agree that ultra-processed foods should be avoided.

Ultra-processed foods^[1] are mixtures of specific parts of different foods, generally constituents that have undergone multiple processing steps after harvesting and are subsequently low in fiber, protein, and various micronutrients, and high in added fats, sugars, or salt. These foods have been described not as foods at all, but as—“formulation(s) mostly of cheap industrial sources of dietary energy and nutrients plus additives …”^[1] Doesn’t sound too appealing when phrased that way, does it?

Yet, as shown in Figure 1, the sales^[2] of ultra-processed foods have been inching upward from 2002-2016 in all major regions of the world except North America, Australasia, and Western Europe. Sales may have stagnated in the latter three regions, but they also exhibit the highest sales of ultra-processed food, by volume, in the world. After all, the purpose of ultra-processing is to create convenient and highly palatable food products from low-cost ingredients.Their convenience, taste, and generally low cost can be quite alluring.

But, convenient, tasty food may have a downside. Increases in sales of ultra-processed foods are positively associated with population-level BMI trajectories. In fact, ultra-processed food consumption has been associated with higher risk of overweight and obesity^[3], hypertension^[4], cancer^[5], and even mortality^[6] in prospective studies. These foods have been associated with addictive-like eating behaviors^[7] and have been suggested to facilitate overeating^[8]. The problem is that these studies only establish a predictive correlation, not causation.

Since no causal relationship between ultra-processed food intake and obesity or excess energy intake has been established, researchers from the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland conducted a randomized controlled trial comparing ad libitum energy intake on diets based primarily on ultra-processed compared to unprocessed foods.

Ultra-processed foods are food products that have undergone multiple processing steps after harvesting. They are often designed for convenience, palatability, and low cost. However, these foods have been linked to overeating and the ever-increasing global burden of noncommunicable diseases. To determine whether there might be a causal relationship between ultra-processed foods and energy intake, the researchers of the study under review conducted a randomized controlled trial comparing ad libitum energy intake during an ultra-processed diet, compared to a minimally processed diet.