853. A recent study on ultra-processed foods seems to be yet another nail in the coffin for UPFs. But all is not as it seems.
853. A recent study on ultra-processed foods seems to be yet another nail in the coffin for UPFs. But all is not as it seems.
References
Effect of ultra-processed food consumption on male reproductive and metabolic health
Related Episodes:
Maybe “hyperpalatabilty” isn’t the problem after all
The surprising links between UPFs and diet quality | Nutrition Diva
Find a transcript here.
If ultra-processed foods really drive weight gain, then giving people a high-calorie, mostly ultra-processed diet should make them gain weight. Right? And at a glance, this recent study seems to show exactly that. Except, that’s not really what happened. Now, I may be just a stickler for details. But let me explain why I think it’s so important to get the details right.
Hello! This is Monica Reinagel and you are listening to the Nutrition Diva podcast, a show where we take a closer look at nutrition news, research, and trends and help you make more informed decisions about what you eat.
A recent study on ultra-processed foods seems to be yet another nail in the coffin for UPFs. Media outlets generally presented it as more evidence that UPFs drive weight gain and have other harmful effects on things like cholesterol and blood pressure. That, of course, fits perfectly into the prevailing wisdom about UPFs as the root-of-all-evils. The actual findings, however, are a little less tidy–and a lot more interesting.
The design of the study is a little complicated, but in order to understand the larger point I want to make here, you really need to understand the set-up. So here goes:
First of all, the subjects were all healthy males between the age of 20 and 35. This is actually pretty typical for university-based research labs because universities tend to have a lot of healthy, young men lying around–but obviously, this sample is hardly representative of the general population.
In any case, subjects were divided into two main groups: The young men in the first group were provided with meals that contained enough calories to maintain their current weight. The fellows in the second group were given meals that provided about 500 extra calories per day. (So, all other things being equal, we’d expect those guys to gain around a pound a week.)
They then tested two different diets in each group. One diet was very high in ultra-processed foods and the other had virtually no ultra-processed foods. For those keeping score, we now have 4 different test diets in our study: UPF maintenance diet, UPF +500 calories, unprocessed maintenance level, and unprocessed + 500 calories.
The subjects had all of their food provided for them over the course of the study, and each diet was consumed for a period of three weeks. The subjects also filled out detailed questionnaires each day, documenting what they had and hadn’t consumed. And they pretty much ate what they were provided.
So, what do you think happened? Perhaps you’d expect the two groups that ate the extra calories to have gained weight. That would certainly be a reasonable expectation, based on what we’ve been told about excess calories causing weight gain. And based on what you’ve heard and read about UPFs, maybe you’d also think that the diets high in ultra-processed foods would lead to more weight gain than the minimally processed diets.
But that’s not quite what happened.
The first surprise was that the extra calories did not produce the expected weight gain. On average, the guys eating the higher-calorie ultra-processed diet gained less than a pound, all told. That’s only about a quarter of what the calorie math would have predicted. Maybe we can chalk that up to those 25 year old metabolisms.
The second surprise was that the groups eating the unprocessed diets both lost weight. Remember, half of them were given enough calories to maintain their weight–and they lost about 3 pounds on average. The other was given 500 extra calories per day–they lost an average of about 2 pounds. Again, according to the calorie math, this is not what we would expect to see.
In fact, the only result that was about what you would expect was the group eating the UPF-diet, the one that was calibrated for them to maintain their weight, which basically did.
That’s what actually happened. But the way these results were presented suggested something totally different. The researchers reported that body weight in the UPF diet groups was about 3 pounds higher than in the unprocessed diet groups, which was true. But not because eating the UPFs caused people to gain weight (which is definitely what the media heard), but because eating only unprocessed foods caused people to lose weight.
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A lot of researchers have been trying to figure out what exactly it is about processed foods that drives us to overeat them. Several theories have been advanced.
1. Processing reduces the amount of effort required to eat foods, which causes us to eat them more quickly and consume too much of them.
2. There’s the hyper-palability argument: It’s just so tasty we can’t stop. (See my recent episode for more on that one.)
But neither of those arguments gets much support from this study because the subjects didn’t choose how much to eat. They simply ate the calories they were provided.
3. Another theory is that food processing disrupts the food matrix, making the energy more absorbable. Let’s take a closer look at this one.
The food matrix refers to how the nutrients in a food are packaged. For example, maybe you’ve seen those machines in healthfood stores where you put nuts into a hopper, and nut butter comes out the spout. This does not change the nutritional composition in any way but it does change the matrix. And changing the matrix can affect how nutrients and energy or calories are absorbed–especially for foods that are higher in fiber.
When we eat whole nuts for example, up to 20% of the calories they contain are not absorbed because they remain “trapped” in the fiber. When we grind them into nut butters, however, we break some of that fiber, releasing more of the calories to get absorbed.
So, could that explain why the people eating 500 excess calories every day but from unprocessed foods mysteriously lost weight? It might. Higher fiber diets tend to trap more calories than lower fiber diets. But that’s true whether the fiber comes from unprocessed foods like nuts and legumes or from highly processed foods like breads made with resistant starch.
Unfortunately, in this study, the unprocessed diet had 4 times as much fiber as the UPF diet. In fact, that difference in fiber could explain why one group lost weight and the other didn’t. So instead of a smoking gun, we have an unloaded weapon.
Had the two diets contained similar amounts of fiber, we’d be in a better position to talk about the effects of processing on energy absorption. Instead, what this really suggests is that eating more fiber may help you lose weight (even if you don’t reduce the number of calories you take in!).
I know I’m starting to sound like a broken record here, but when we are considering the benefits (or harms) of food processing, it’s just not enough to ask how processed it is. We need to consider the nature and purpose of the processing. Because just like magical powers, food processing can be used for good or evil.
There were a few other findings from this study that bear brief mention. They reported that cholesterol levels were higher after the UPF diets. But this appears to have been mostly because they decreased during the unprocessed diet. Moreover, the UPF diets were also significantly higher in saturated fat, which is known to drive up cholesterol and lower in fiber, which tends to decrease it. So how much of that was about the processing and how much was simply about the nutrient composition? Hard to say.
Finally, I want to mention something that was outside the scope of this study–which is what those minimally processed diets that were provided to the subjects actually cost, not just in dollars but in the time, equipment, and skill required to turn raw ingredients into 3 meals a day, day in and day out.
And here's why I think this matters: one of the reasons that a lot of Americans consume so many UPFs is that they can be relatively cheap and very convenient. And not everyone has the resources required to cook all their meals from scratch. So we can proselytize for "real food" all we want, but it’s unlikely to change behavior if we aren’t willing to acknowledge and address the fact that this way of eating, may be out of reach for many Americans.
More to the point, studies have also shown that it is actually not that hard to build a healthy, nutritious diet that relies heavily on ultra-processed foods. And that such a diet would actually be cheaper and require much less time to produce. So perhaps it would be more realistic and helpful to show people how convenient, affordable, processed foods can be used to create a healthy meal plan.
If you have a topic you’d like me to tackle on the podcast or a comment or a question about this one, you can email me at nutrition@quickanddirtytips.com.
This is also a topic I present on quite a bit. And if you would like to find out about having me speak at your next live or virtual event, you can find out more at https://wellnessworkshere.com/
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