Why processed food makes people fat: calorie density and taste
- In a diet face-off between ultra-processed versus minimally processed food, those who ate the former consumed 500 more calories per day
- Researchers suggest it has a lot to do with people deciding how much to eat by gauging the amount of food, not its calorie content
For many years, I’ve steadfastly clung to a position for which there has been almost no evidence: processed food is the root of obesity.
This doesn’t mean that processed food is the sole cause. There’s also the ubiquity of food, changing social mores and what is probably a more sedentary lifestyle (though evidence for that, too, is surprisingly hard to come by). It also doesn’t mean that all processed food is bad. Whole-grain bread and cereal are excellent, and there are good versions of such things as frozen pizza and jarred pasta sauce. Also wine.
What it does mean is that modern industrial food processing – and only modern industrial food processing – has enabled the manufacture of the cheap, convenient, calorie-dense foods engineered to appeal to us that have become staples of our obesogenic diets. By one estimate, nearly 60 per cent of our calories come from ultra-processed food.
The case is that as our environment changed to surround us with delicious, cheap, convenient, calorie-dense food that’s specifically designed to be irresistible, we couldn’t resist it.
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Now, the very first randomised controlled trial of ultra-processed food versus minimally processed food is here.
Kevin Hall, a researcher at the National Institutes of Health, brought subjects into the lab for four weeks and fed them one of two diets: ultra-processed or minimally processed, both designed to have the same combination of carbs, fat and protein.
The ultra-processed menus included store-bought mac and cheese, chicken nuggets, canned ravioli, and frozen pancakes, while on the minimally processed side there was pasta with shrimp, salad with grilled chicken and grains, and oatmeal with nuts and bananas. Subjects were told to eat as much as they wanted. (Each subject spent two weeks on each diet.)
The result was that those who ate ultra-processed food consumed 500 more calories per day. Five hundred! They also gained a couple of pounds. Notably, though, subjects rated the meals as equally good tasting. So why the big increase?
“There are several potential hypotheses,” Hall told me. Top of his list? Calorie density. “There were about two calories per gram in the processed food,” excluding drinks, “and in the unprocessed it was closer to one.”
People also ate the ultra-processed meals a lot faster. “It might be softer, easier to chew and swallow,” Hall said. And that could mean that satiety signals, which take time, don’t get to your brain until after you’ve overeaten.
This is not a new idea. Barbara Rolls, a nutrition professor at Penn State University in the US, has been studying it for a couple of decades, and wrote the Volumetrics series of diet books based on the idea of calorie density. According to her, diets based on decreasing calorie density – eating foods that have more water and less fat – are more effective than any of the diets that manipulate macronutrients.
They have a different mechanism, she explained. “It’s behavioural. It’s visual.” You’re responding to cues about the amount of food you’re eating. So, for example, if you give research subjects the same cereal in two different forms – flaky (higher volume) and crushed (lower volume) – they eat a third more of the crushed version. Rolls said that on average, people tend to decide how much to eat by gauging the amount of food; the more there is available, the more they eat, and volume and weight both play a role. Visual cues matter.
When the food in question has a lot of calories for its size, that translates to simply consuming more. Diets that focus on carbohydrates or fat, by contrast, tend to focus on how different combinations of macronutrients trigger satiety hormones. But a decision to stop eating is more immediate, Rolls said. You often make it before hormonal cues have a chance to weigh in.
Calorie density is also part of the palatability equation – people just like those foods better, Rolls said. Any lover of baked goods, ice cream and cashews will find this easy to believe.
In a nutshell: the root of obesity is palatability and calorie density, combined with ubiquity and convenience. Satiety hormones and other metabolic machinations have much less to do with it. We’re responding to cues from without, not from within. One new study doesn’t prove it, of course, but it’s the hypothesis that best fits the preponderance of the evidence.
The most important thing we can do as a society is figure out how to make more nutritious food, more nutrient-dense food, in a manner that’s convenient, but to make them affordable and accessible
So what do we do about it? It’s a tough problem because, as historian Rachel Laudan, author of Cuisine and Empire, pointed out, “Processed food is what we eat.”
We’ve been processing food for the entirety of human history, and it was a huge boon – until it wasn’t. When it freed women from, say, having to bake their own bread, it was a win, but modern food processing is different. Books like Michael Moss’s Salt, Sugar, Fat and Mark Schatzker’s The Dorito Effect have detailed just how seriously food manufacturers take the challenge of winning consumer hearts, minds and stomachs.
I don’t think we’re going back to universal dinner from scratch any more than we’re going back to bread from flour and yeast. Insisting that we should isn’t terribly useful. Are you going to tell a parent (almost always a mum), struggling with a minimum-wage job and an erratic schedule and a picky kid, that she shouldn’t lay off the only chore she can afford to pay someone else to do? I’m sure not.
But the insistence on chopping onions and roasting chicken gives everyone the idea that the choices are either wholesome home-made dinner or lousy processed dinner. How about wholesome processed dinner? Granted, it’s not that easy to find, but a trip through a grocery store will yield plenty of choices. Grab a frozen veg assortment, complete with sauce, and you’re a rice mix and takeaway rotisserie chicken away from feeding your family.
The alternative to lousy processed food isn’t (always) home cooking. Sometimes it’s better processed food.
I asked Mehmood Khan, until recently the head of research and development at soft-drink multinational PepsiCo, what it would take to get more better processed food – whether that means something higher in nutrients or fibre, or lower in caloric density. Although he doesn’t pin all the blame for obesity on processed foods – he points to those changing social mores and our increasingly sedentary lives – he acknowledges that convenient, inexpensive processed food is one element.
“The most important thing we can do as a society is figure out how to make more nutritious food, more nutrient-dense food, in a manner that’s convenient, but to make them affordable and accessible,” he said.
But there’s a caveat. “When you actually do studies and give people options, they tend to always prefer tastier, and don’t like to compromise taste for health.”
I asked him if he could think of an example of a product that was formulated specifically to be more nutritious or healthful, and was a market success. There was a pause. “No,” he said. “No I can’t.”
It’s on us, people. Sure, there are a few things governments could do – how about a calories-per-gram label? – but we can’t expect more nutritious processed foods unless we’re willing to buy them.
As always, we get the food supply we demand.
The Washington Post
