Your body on ultra-processed foods: Subtle weight gain, muscle loss, stubborn fat

• Ultra-processed foods are associated with all kinds of poor health outcomes.
• But they're probably not all equally bad.
• An ongoing study suggests adding more high-volume foods into your ultra-processed diet could help.

It's no secret that ultra-processed foods aren't the greatest for our health.

"What we're trying to figure out is, very specifically, what is it about ultra-processed foods that seems to drive over-consumption and weight gain?" metabolism researcher Kevin Hall recently told Business Insider.

Hall works at the National Institutes of Health, where he is conducting an unusual experiment. He brings people into a tightly controlled food lab for one month, and tests out how four different diets — one unprocessed, and three ultra-processed, but all with the same levels of key nutrients — impact people's hunger, fullness, calorie consumption, weight gain, and fat loss.

While his study is still ongoing, he's been sharing some initial results with colleagues in the US and in Europe.

The early findings offer some hints about why UPFs can not only lead to weight gain but also make it hard to dump fat. The study is also showing that simple tweaks could make a huge difference. Perhaps, Hall says, you don't need to cut out ultra-processed products to have a satisfying, relatively healthy plate of food.

On an ultra-processed diet, patients gained 2 lbs a week

When Hall's patients switched diets, their calorie intake shifted dramatically.

During their week of unprocessed meals, full of fresh vegetables, beans, legumes, and whole grains, participants ate an average of 2,700 calories per day. They also tended to lose a little weight, about a pound of fat.

That changed when they switched to an 80% ultra-processed diet. Same amount of food offered, same levels of sugar, salt, fat, carbs, protein, and fiber on the plate.

The patients ended up consuming more food to achieve the same level of fullness — ingesting about 3,700 calories per day on average. On ultra-processed foods, the patients' weight shot up by over two pounds in a single week.

The results, while still preliminary, are even more striking than the last experiment Hall did like this, when patients ate 500 extra calories per day on ultra-processed diets.

People might not even feel like they're eating more when they consume those ultra-processed meals. Generally speaking, each bite of ultra-processed food is far more calorie-dense than a homemade meal.

Adding moisture made ultra-processed meals 'healthier'

Cutting out ultra-processed foods isn't realistic in the US, Hall said. But what if you could make a Western diet less bad?

Hoping to reduce people's weight gain and improve satiety with fewer calories, Hall (and his team of clinical chefs) devised two new diets to test this time.

Both diets were 80% ultra-processed but with some crucial adjustments.

In the first new diet, researchers lowered the amount of what are called "hyper-palatable foods" — foods that combine sugar, salt, and fat in ways that aren't typically seen in nature (think: rich, salty ice cream, a donut, or veggies in cream sauce).

Addiction researcher Tera Fazzino coined the term "hyper-palatable" as a way to collect data on the irresistibility of junk food. She hypothesizes that hyper-palatable ultra-processed foods might mess with our minds, and drive people to eat more than they would otherwise.

But that didn't ring true in Hall's new study. The patients who cut out hyper-palatable foods only saved themselves 200 calories a day, and gained over 1 lb in a week.

In the second diet, the chefs lowered the amount of hyper-palatable foods again, but also upped the moisture of people's ultra-processed meals, making them less energy-dense. Often, this meant adding more high-volume, non-starchy vegetables like a side salad to the ultra-processed plate.

"Basically, add very low-calorie mass," Hall told BI. "That typically is non-starchy vegetables."

On an ultra-processed diet with fewer energy-dense foods and less hyper-palatable items, people lost about a pound in one week — just like on the unprocessed diet. They also consumed about 830 fewer calories per day, very close to the 1,000 fewer calories consumed on the unprocessed diet.

"I thought, OK, gosh, we've solved this problem, this is great," Hall said during a presentation at Imperial College London in November, when he first revealed the new results.

There was a catch, though.

"A little bit of a monkey wrench was thrown in because we decided to look at the body composition changes," Hall said.

The nut we haven't cracked: Achieving the right kind of weight-loss

Only people on the 100% unprocessed diet lost body fat.

On the "healthier" ultra-processed diet, people lost about a pound of weight in a week, but it was coming from fat-free mass. That means muscle, bone, tissue, or maybe just water weight.

Hall is not yet sure why this is happening, but he says it could have to do with the "digestability" of the ultra-processed foods — in other words, how they are handled inside our bodies, compared to whole foods.

"If we can learn what those mechanisms are, then the really smart people who are ingenious food technologists and scientists can maybe re-engineer some of these foods," he told BI.

"There's so many narratives and hypotheses that sound reasonable, but until you actually do the studies to test that, then you don't know."

5 simple ways to make your meals healthier today

While it's still too early to say for sure exactly why people eat more calories and store more fat on ultra-processed diets, Hall says we can already begin to use his early findings to make some educated guesses.

Here are some tips:

• Bulk up a meal, any meal, by adding some vegetables to your plate. Could be salad. Could be a side of cooked broccoli or some carrots. They don't have to be fresh. Frozen is also just fine.

• Try some beans. You could whip up a hearty longevity-friendly minestrone soup, but if you don't have the time even ultra-processed refried beans are a decent option.

• Pick out whole grains, like oatmeal, brown rice, and quinoa.

• Pay attention to how much added sugar is in items like yogurt, granola, and salad dressing, and try to limit how much of it you consume. (Olive oil makes a great dressing, and it's filled with healthy fats and beneficial plant compounds.)

• Prioritize the satiating, nutrient-rich foods we know are associated with good health, like eggs (even the ultra-processed liquid kind might be fine).

"It's possible that there's some weird additive or some ingredient in that food that is not good for you," Hall said. "We don't have the science on that yet, but applying what we do know, I think you can still make educated choices."