It has long been suspected, based on observational studies and lab research, that increased consumption of highly processed (also called ultra-processed) foods in recent decades has contributed to rising rates of obesity, diabetes, hypertension, and possibly other disorders.
While experts have blamed the high fat, calorie, and sodium content of such foods, some have theorized that there are other things about highly processed foods that also encourage overeating, though this has been hard to prove—until now.
What are ultra-processed foods?
Food processing is any procedure that alters food from its natural state, such as heating, freezing, milling, mixing, and adding flavorings. Cooking and preparing raw ingredients at home is also processing them, but the term “processed” is almost always reserved for commercial foods, usually packaged.
NOVA, the classification system used by food scientists and researchers, defines ultra-processed foods as ready-to-eat, packaged products with five or more ingredients, including sensory-enhancing additives, that have gone through a number of processes to combine and transform them. They include everything from processed meats, margarine, jarred sauces, and frozen entrees to most baked goods, chips, breakfast cereals, ice cream, and candies. Think of them as multi-ingredient industrially formulated mixtures that are no longer recognizable as their original plant or animal sources. It’s estimated that such foods provide about 60 percent of the calories consumed by the average American.
Putting ultra-processed foods to the ultimate test
The first randomized, controlled trial to compare ultra-processed and unprocessed diets in terms of calorie consumption and weight gain appeared in the journal Cell Metabolism in May. It involved 20 healthy volunteers (average age 31, most overweight but not obese) who stayed in a metabolic ward for four weeks, where all food was provided and monitored. Each participant was given either an ultra-processed diet or an unprocessed diet for two weeks, and then switched. They got three meals a day plus snacks and were allowed to eat as much as they wanted.
To develop the two diets, the researchers used a food classification system called NOVA to categorize foods by the extent of processing. The unique thing about the study was that the two diets were matched for carbohydrates, fat, sugar, sodium, calorie density, and fiber, so differences in these factors couldn’t be responsible for the outcomes. Because highly processed foods tend to be low in fiber, fiber was added to beverages in that diet to equal the fiber in the unprocessed diet. During the two weeks that they ate ultra-processed foods, participants consumed more food and about 500 more calories per day, on average, than when they ate unprocessed foods; the extra calories came from fat and carbs, not protein. Thus, they gained two pounds, on average, on the ultra-processed diet, compared with a weight loss of two pounds after two weeks on the unprocessed diet. There were no significant differences in other measures of health, such as liver fat or blood glucose.
The researchers hypothesized that people ate more on the ultra-processed diet in part because they ate much faster, due to the softer texture and enhanced sensory properties of the foods. Eating quickly doesn’t give your gastrointestinal tract enough time to signal your brain that you’re full, so it’s easy to overeat. Another possible explanation: Blood tests showed that the highly processed diet altered levels of appetite-related hormones in ways that could lead to overeating.
One limitation of the study: Because all the food was prepared for the participants, convenience and cost didn’t play a role in food choices. In the real world, ultra-processed foods tend to be less expensive and more convenient than cooking with whole, fresh foods. That may also contribute to overeating them.
“Our data suggest that eliminating ultra-processed foods from the diet decreases energy intake and results in weight loss, whereas a diet with a large proportion of ultra-processed food increases energy intake and leads to weight gain,” the researchers concluded. “Whether reformulation of ultra-processed foods could eliminate their deleterious effects while retaining their palatability and convenience is unclear. Until such reformulated products are widespread, limiting consumption of ultra-processed foods may be an effective strategy for obesity prevention and treatment.”
Dying for processed foods?
The latest observational research linking ultra-processed foods to poor health is a French study in JAMA Internal Medicine. It included 44,551 people, ages 45 and older, whose customary diet was analyzed via food questionnaires. Over the next seven years, a high intake of ultra-processed foods was associated with higher mortality rates, even after the data were adjusted for the participants’ body weight, education, income, smoking, physical activity level, and other factors. Each 10 percent increase in ultra-processed food intake was associated with a 14 percent higher mortality rate.
The researchers pointed to the usual culprits: the added sugar and sodium in ultra-processed foods, their lack of fiber, and the unhealthy dietary patterns associated with them. They also suggested that heavy use of additives may play a role, along with compounds created during processing (such as acrylamide) and others migrating into food from packaging (such as bisphenol A, or BPA).
This being France, only about one third of the participants’ daily calories came from ultra-processed foods, a much lower proportion than in most other industrialized countries. Even so, intakes have been increasing there, leading to a report on the problem done for the French National Assembly last year and the introduction of a public health goal of reducing ultra-processed food consumption by 20 percent in France by 2021.
‘Process’ it yourself
Food companies sometimes try to develop ultra-processed foods that are healthier, though they haven’t had a good track record with this, and consumers often don’t like the results. The alternative: Buy more whole or minimally processed foods and do the “processing” yourself. It’s called home cooking, done from scratch as much as possible.