Why Ultra-processed Foods Are Fattening 🍟
You are no doubt well aware that so-called ultra-processed foods are implicated in the obesity epidemic, and with good reason. Large prospective cohort studies show that higher consumption of ultra-processed foods is associated with higher risk of gaining weight over time, and those in the highest fourth of ultra-processed food intake had a 79% greater risk of developing obesity. Given the ever-growing dominance of ultra-processed foods in the US food supply — now constituting 57% of caloric intake on average — this is a major concern.
But what isn’t addressed as often is why they are so fattening. There are probably many factors at play here, but recent research points to one major underappreciated element: ultra-processing tends to make foods softer.
That might sound kind of…obvious, but here’s why it matters for energy intake. We’ve known for a long time that various forms of processing speed up consumption. A classic experiment from the 1970s compared three test meals:
- 482 grams of whole apples, cored and quartered
- 482 grams of apples, pureed in a blender
- 444 mL of apple juice
As you would expect, it took way longer to eat the whole apples (17 minutes) compared to the puree (5.9 minutes) and the juice (1.5 minutes). That's important, because a ton of research has shown that faster eating rate is associated with greater total energy intake, and food texture is a key mediating factor. Harder foods require more chewing, and thus take longer to consume. When researchers instruct people to double the amount of chewing in a test meal, their food intake has been shown to drop by nearly 15%, and they show lower concentrations of ghrelin (a hormone that stimulates appetite) and higher concentrations of GLP-1 and CCK (hormones that tend to suppress hunger).
Basically, eating slower, and letting each bite hang around in your mouth longer, seems to lead to lower energy intake, possibly due to differences in post-meal gut peptides that regulate appetite.
This Week's Research Highlights
🍟 A diet high in ultra-processed foods results in much higher caloric intake compared to an unprocessed diet.
In an inpatient clinical trial conducted by Kevin Hall and colleagues at the NIH, 20 adults were admitted to the NIH Clinical Center and were randomized to receive either an ultra-processed or unprocessed diet for two weeks, followed immediately by the alternate diet for two weeks (yeah, this is about as rigorous as nutrition research gets). Meals were designed to be similar in calories, macronutrients, fiber, sugar, and sodium, in order to isolate the effects of processing. Energy intake was substantially higher when participants ate the ultra-processed diet (more than 500 calories per day greater on average). But why exactly? You might assume palatability was the difference here, but participants rated the ultra-processed and unprocessed meals as being similarly pleasant and familiar when surveyed. One thing that jumps out is the eating rate. Participants ate the ultra-processed meals significantly faster than the minimally processed foods, and faster eating rate was in turn associated with higher overall energy intake.
🪨 Consuming harder foods leads to a sustained reduction in total energy intake over the course of a day.
Researchers recruited 53 young Chinese participants who visited the lab on two separate days. On one day, they were presented with a lunch with soft foods, and on the other day they were given a lunch with hard foods. Both meals were the same (hamburger with rice salad), same energy density and ingredients, with only the texture being manipulated, and participants were allowed to eat as much as they pleased. Unsurprisingly, the hard lunch required quite a bit more chewing, leading to a 32% slower eating rate than that of the soft lunch. The hard meal also led to a 13% reduction in energy intake at lunch, compared to the soft meal. Finally, ratings of hunger and fullness did not differ following the two lunches, suggesting that the hard lunch was more satiating. And that effect seemed to endure, as the increased energy intake from the soft lunch was not compensated for when the subjects were served dinner later.
🥦 Differences in texture independently influence eating rate and energy intake in both ultra-processed and minimally processed meals.
Researchers in Singapore recruited 50 healthy young participants and had them consume four different meals on four separate occasions: “soft minimally processed,” “hard minimally processed,” “soft ultra-processed,” and “hard ultra-processed.” Eating speed was monitored via camera, and every meal was all-you-can-eat. The soft ultra-processed meal was consumed the fastest and led to the highest total energy intake. But when comparing all the meals head-to-head, food texture seemed to be the most important factor in eating rate and energy intake. The soft minimally processed and ultra-processed meals were both consumed faster than their hard counterparts, and people consumed more total calories (21 26% more) when eating both soft textured meals, regardless of processing. And like the previously described study, the increased energy intake at the soft lunches was not compensated for with lower energy intake at subsequent meals. The researchers conclude that ultra-processed foods lead to greater energy intake due in large part to their texture, and also their higher energy density. Incorporating more hard-textured foods, along with less processing, could be a useful lever for weight management.
Random Trivia & Weird News
🌭 Human performance in hot dog eating competitions has ramped up remarkably over the past four decades.
An exercise physiologist who analyzed four decades of data from Nathan’s Famous Hot Dog Eating Contest found that the winning consumption rate had increased by about 700%, despite minimal changes to the size or composition of the hot dogs themselves. No other sport has observed such a meteoric rise.
Podcasts We Loved This Week
- Stephan Guyenet: Neurobiology of Obesity. Via Docs Who Lift Podcast.
- Patrick Collison: We Know Shockingly Little About What Makes Humanity Prosper. Via Ezra Klein Show.
Products We Are Enjoying
These are super cool. They’re smart bulbs that you can directly connect to Google Assistant or Alexa, and can dim or change colors at your command.
Obviously some fun possibilities, since you can make them whatever color you like, but also very useful from a circadian standpoint, which is what we’re interested in here. During the day, you can make them more of a bright blue, for alertness, and during the evening you can make them a dim amber.
humanOS Catalog Feature of the Week
Thanks for reading, enjoy the weekend, and we will see y'all next week!