Why is the weight loss struggle so real?
I grapple with this question every time I see someone in my weight management clinic. Is the difficulty due to the foods we’re eating? Is exercise ineffective? Are some people genetically destined to have a hard time losing weight?
The answers to all of these questions are complex, variable, and poorly understood. However, a recent study in Cell Metabolism suggests that ultra-processed foods may play a pivotal role in the “weight loss struggle.“
So, what are ultra-processed foods?
Ultra-processed foods make up 60% of our calories in the US, yet there’s still a lack of awareness of what these foods are. I recently asked a group of medical students to define ultra-processed foods. None of the students were familiar with ultra-processed foods.
For clarity, ultra-processed foods are foods made with industrial processes/ingredients that bear little resemblance to naturally-occurring, whole foods. Think about the difference between raspberry gummy bears and raspberries. Or, think about how different maraschino cherries are from regular cherries:
A maraschino cherry (/mærəˈskiːnoʊ/ marr-ə-SKEE-noh or /mærəˈʃiːnoʊ/ marr-ə-SHEE-noh) is a preserved, sweetened cherry, typically made from light-colored sweet cherries such as the Royal Ann,Rainier, or Gold varieties. In their modern form, the cherries are first preserved in a brine solution usually containing sulfur dioxide and calcium chloride to bleach the fruit, then soaked in a suspension of food coloring (common red food dye is FD&C Red 40), sugar syrup, and other components.
The term ‘ultra-processed’ comes from the NOVA (not an acronym) classification. I gave a thorough introduction to ultra-processed foods in a previous post.
Here’s a quick recap of health concerns associated with ultra-processed foods:
- They are high in fat, sugar, salt, and random additives.
- There’s an association between higher consumption of ultra-processed foods and depression.
- Ultra-processed foods also have an association with increased mortality.
Why do people eat ultra-processed foods?
First, ultra-processed foods are everywhere. Supermarket, gas-stations, office kitchens, are all filled with ultra-processed foods. Ultimately, the reasons for the seemingly inescapable presence of ultra-processed foods are obvious. They are cheap, convenient, and tasty. Plus, ultra-processed foods typically have a long shelf life.
In a world in which people are cooking less, working longer, and are more accustomed to immediate gratification—reaching for ultra-processed foods is almost reflexive.
Can ultra-processed foods cause weight gain? Probably.
The study mentioned above attempted to answer this question.
How did the researchers design the study?
The researchers admitted 20 adults to the NIH Clinical Center. The adults had a mean age of 31.2 years and a mean BMI of 27. The people in the study received either ultra-processed diets for 2 weeks, followed by unprocessed foods for 2 weeks or vice versa. Both the unprocessed meals and ultra-processed meals had the same amount of calories, sugar, salt, fiber, energy density, and sodium. The participants on either diet could snack as much food or as little as they wanted to.
Here’s an example of ultra-processed meals in the study:
Here’s an example of unprocessed meals in the study.
Did the researchers find that people ate more when they consumed ultra-processed foods? Yes, they did.
The study’s participants ate 508 calories more per day while eating ultra-processed foods than when eating unprocessed foods. Subsequently, the adults gained an average of ~2 lbs during the ultra-processed part of the study. Additionally, the participants ate an extra 230 calories of fat and 280 calories of carbs while on the ultra-processed diet. The participants also ate less protein while consuming ultra-processed foods.
Of note, people lost an average of 2 lbs while consuming unprocessed foods.
Why did people eat more calories during the ultra-processed portion of the study?
Ultimately, the study wasn’t designed to answer this question. However, the study did reveal a few interesting findings.
For example, the participants did not rate the ultra-processed diet as being tastier than the unprocessed diet. Thus, palatability didn’t explain the difference in calorie intake between the two diets.
It’s also worth noting that the researchers found that the participants ate significantly faster while consuming ultra-processed foods. I’ve previously written about how the speed at which we eat can affect how much we eat.
The researchers also evaluated the effects of the different diets on various hormones. They found that the hormone PYY, an appetite reducing hormone, was lower while eating ultra-processed foods.
Hence, ultra-processed foods may impact your ability to stop eating.
What are some of the limitations of this study?
- Participants weren’t choosing and preparing their foods.
- There was no washout period between the two diets.
- The researchers performed the study in an inpatient environment. This environment is definitely different than being at home.
What should the average person who’s trying to lose weight take from this study?
- You may eat more calories when your diet is rich in ultra-processed foods. This increased calorie intake may lead to weight gain or at least make it harder to lose weight. Hence, the weight loss struggle is more real if ultra-processed foods are staples.
- The ultra-processed foods did cost less than the unprocessed diet per week ($106 vs. $151). In this instance, cheaper doesn’t necessarily mean better.
- Limiting ultra-processed foods may be a useful strategy when trying to lose weight.
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I am a physician and trained chef. I specialize in gastroenterology and nutrition. Currently I work as the Associate Director of Adult Nutrition at the University of Chicago.