Why Ultra-Processed Foods Ramp Up Calorie Intake (+813 kcal!)
This Week’s Research Highlight
Background
You are probably well aware that so-called ultra-processed foods have been implicated in the obesity epidemic. Large prospective cohort studies generally show that higher consumption of these foods is associated with higher risk of gaining weight over time. In one such study, those in the highest quartile of ultra-processed food intake had a 79% greater risk of developing obesity.
From Beslay et al, 2020
But what precisely makes these foods so fattening?
Before I dive into this, let’s get some background on what exactly ultra-processed means, because it is kind of a contentious and confusing idea.
Back in 2009, Brazilian nutrition scientist Carlos Monteiro wrote a commentary in which he separated foods into categories based not on calories, or even micronutrients, but rather by how they are processed. He suggested that foods should be classified by the “type, intensity and purpose of food processing.”
Food processing is not binary — it occurs on a spectrum. To convey this nuance, the NOVA system has been developed, which classifies foods into four groups based on the type and purpose of processing.
- Group 1: Unprocessed or minimally processed foods (e.g., fresh fruits and vegetables, meat, eggs, grains, and milk)
- Group 2: Processed culinary ingredients (e.g., oils, butter, sugar, salt, and flour).
- Group 3: Processed foods (e.g., canned vegetables, salted nuts, smoked or cured meats, cheese, and freshly baked bread).
- Group 4: Ultra-processed foods (e.g., soft drinks, candy, mass-produced packaged snacks, instant noodles, sweetened breakfast cereals, frozen meals, and fast food)
From Crimarco et al, 2022
Okay, returning to the question of why ultra-processed foods are associated with weight gain. The answer is that we don’t really know, and that’s why the concept of “ultra-processed” remains troublesome, and authorities have been slow to formulate guidelines based on this paradigm.
You see, dietary recommendations are typically founded on a combination of three different research approaches which serve complementary functions:
- Epidemiological studies: Identify and define the scope of the problem
- Controlled clinical trials: Establish a causal relationship
- Mechanistic research: Unveil underlying mechanisms that drive the relationship
Basically, we have tons of epidemiological data showing a link between ultra-processed food intake and obesity. But so far, there have been very few rigorous clinical trials that examine the impact of ultra-processed foods on energy intake and weight regulation (they’re super expensive and hard to do). Indeed, the NIH study conducted by Kevin Hall, which we described previously in this newsletter, might be the only one. And although many plausible mechanisms have been suggested, it’s been difficult to directly link a consistent and specific attribute of ultra-processed foods to increased body weight.
Fortunately, a brand new trial has been published, which might help fill in both of those gaps: it appears to demonstrate a causal relationship between ultra-processed foods and weight gain, and it even provides insight into potential underlying mechanisms. Let’s take a look.
Study
To determine whether ultra-processed foods were causally related to energy intake and weight gain, Japanese researchers recruited nine healthy young men. These guys were all moderately overweight (mean BMI of 27.4) and weight stable (not in the process of either gaining or losing weight).
The trial in which these participants were enrolled was a randomized crossover design. That means that each participant is exposed to all treatments in a random order, and thus serves as their own control. This is advantageous because it reduces the impact of individual differences (age, genetics, etc), since the control group and the intervention group are literally the same people.
For this specific study, participants were admitted as inpatients to a metabolic ward at the University of Tokyo Hospital for two different 1-week phases, separated by a two week washout period.
During both phases, subjects were provided three meals daily, with a total caloric content that was double the estimated average energy requirement for a man of their size. They were instructed to eat as much or as little of the provisions as they wanted.
In one phase, all of the foods offered to participants were ultra-processed, meaning they would fall into NOVA group 4.
In the other phase, all foods were classified as non-ultra-processed. This did not mean no processing, but rather that they would be classed somewhere between NOVA groups 1 and 3.
Apart from processing methods, the meals were matched for total caloric content, macronutrient ratios (carbs/fat/protein), and energy density.
So this study was rigorously designed to fully control the diets of the participants, and to really zero in on the effects of processing — separate from any other nutritional or behavioral attributes.
Results
When participants consumed the ultra-processed diet, they consumed 813 more calories compared to when they were assigned to the non-ultra-processed foods.
Needless to say, that is a significant difference.
That is roughly the equivalent of adding a regular cheeseburger, medium fries, and 12 oz soft drink to your daily diet.
Unsurprisingly, that increase in energy intake translated into weight gain. During the ultra-processed diet period, participants gained 1.1 kg (almost 2.5 pounds) more weight, compared to the less processed diet.
That is statistically significant, but also meaningful from a real world standpoint when you consider that they were only on each diet for a single week! What might have happened if they remained on the regimen for longer?
Finally, while consuming the ultra-processed diet, participants chewed their food less, and concomitantly ate significantly faster, both in terms of energy intake and mass: on the order of +18.8 calories per minute and +8.2 grams of food per minute, respectively.
Interestingly, the aforementioned trial from Kevin Hall found almost the exact same difference in eating rate — 17 calories per min, or 7.4 grams per minute — as this study, when he and his colleagues compared diets comprised of either ultra-processed or unprocessed foods.
And as you’ll see, that’s probably a major driver of the observed rise in energy intake.
Underlying Mechanisms
We’ve known for a long time that food processing can affect eating speed. This makes sense intuitively, and has been proven experimentally.
For instance, 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). And there was no doubt a lot more chewing involved with consuming the apple quarters.
This is important from the standpoint of weight gain, because a ton of research has shown that a faster eating rate is associated with greater total energy intake. You’ve probably heard that before.
And food texture seems to be a key mediating factor in how fast people eat. For example, in an earlier study, researchers compared mashed versus whole versions of the exact same meal. When subjects ate mashed potatoes/carrots and minced steak, their eating rate went up by 20%, which led to them consuming 12% more calories, compared to eating whole vegetables and intact steak. This is, in part, because harder foods demand more chewing, and thus take longer to consume. In fact, when people were instructed to deliberately double the number of chews they took in a test meal, their food intake dropped.
Chewing less and eating faster may lead to overeating by affecting satiety signaling. An array of gut hormones work together to regulate hunger and appetite. As food travels through the gastrointestinal system, hormones like CCK (cholecystokinin) and peptide YY are secreted which promote satiation. However, it takes time for all of these signals to be transmitted and integrated in the brain. For instance, plasma peptide YY levels rise within around 30 minutes of food reaching the small intestine. If you're eating too rapidly, you may, in effect, outrun those satiety signals.
Notably, in this study, peptide YY levels did tend to be higher during the non-ultra-processed period (albeit not statistically significant).
Of course, any level of processing can make foods easier to consume and thus accelerate eating rate. But ultra-processed foods in particular are usually much softer, and practically designed to facilitate fast consumption. Next time you order fast food, or eat a frozen prepared meal, take note of the texture and how easy it is to wolf down.
This mechanism could explain why sugar-sweetened beverages usually jump out in observational studies as being more harmful than other types of ultra-processed foods. These drinks basically yield a metabolic trifecta: high energy density, rapid rate of consumption, and zero chewing.
Finally, it's worth remembering that differences in texture have been shown to independently influence energy intake, regardless of processing. In a prior study in Singapore, people consumed four different meals on four separate occasions, which included minimally processed and ultra-processed foods whose texture had been manipulated to be either hard or soft.
The soft minimally processed and the soft ultra-processed foods were both consumed faster than harder counterparts, and participants consumed more total calories (21-26% more) when eating both soft textured meals.
So another key takeaway here is that incorporating more hard-textured foods could be a useful lever for weight management, even if you're already eating a generally healthy diet and limiting junk food. One easy way to achieve this would be consuming more whole raw fruits and vegetables (which is a smart move anyway, right?)
Random Trivia & Weird News
🦀 Some Japanese crabs have shells that resemble human faces — and some think that they evolved this way to discourage fishermen from preying upon them.
Heikegani (ヘイケガニ) is a species of crab notable for highly distinctive markings on their shells. And indeed, if you take a look and squint a bit, you can see a person’s face — more specifically, the face of a scowling samurai.
According to legend, the defeated Heike warriors, after being defeated at the naval Battle of Dan-no-ura, drowned in the sea, and were subsequently reincarnated as the Heikegani (literally, Heike crabs).
More recently, it has been suggested that Heikegani may be an example of inadvertent artificial selection. The idea here is that Japanese fishermen were more inclined to throw back crabs that reminded them of the samurai. Over time, crabs with face-like markings were more likely to survive and reproduce, reinforcing and perpetuating the characteristic appearance. In this respect, Heikegani are an interesting intersection between folklore and biology.
Via Wikimedia Commons
Podcasts We Loved This Week
- Josh Turknett & Tommy Wood: Does high intensity interval training have unique brain benefits? Via Better Brain Fitness.
- Laura Cinti: A lonely and ancient plant needs a female partner and researchers are using drones and AI to find it. Via The Conversation Weekly.
Products We Like
Promixx Pro Shaker Bottle
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humanOS Catalog Feature of the Week
Optimizing Nutrition with Smoothies
One thing to keep in mind, when talking about the impact of ultra-processed food, is that altering the structure of food isn’t necessarily a bad thing per se. In fact, certain forms of processing can actually enhance the health-promoting properties of whole foods, in some respects.
In this course, we take a deep dive into phytochemicals in plants, where they are found, their powerful health effects, and how intelligently-devised smoothies can help optimize our intake of these awesome compounds. For a practical breakdown on building nutritious smoothies, please refer to our How-to Guide for smoothies.
Wishing you the best,
