In the United States and other Western countries, ultra-processed foods such as potato chips make up an increasingly large percentage of the overall calories that children and adults consume. Photo / Peggy Cormary, The Washington Post
A small but rigorous new study found that eating ultra-processed foods caused otherwise healthy men to quickly gain body fat and led to reductions in their sex hormones. The men also seemed to have accumulated higher levels of a chemical found in plastics and food packaging.
Many previous studies have found that ultra-processed foods are linked to higher rates of obesity, heart disease, Type 2 diabetes and other chronic health conditions. But the new study, published on Thursday in Cell Metabolism, is striking because it suggests that ultra-processed foods can have detrimental effects not only on metabolic health but on reproductive health as well.
The study found that when it comes to weight gain, all calories are not created equal. When men in the study were assigned to eat a diet of ultra-processed foods that contained the number of daily calories they needed for their age, weight, height and physical activity levels, they still gained weight and body fat – which did not happen when they consumed a diet of largely unprocessed foods.
“This is a major finding because it means that the nature of the food itself is at play here,” said Romain Barrès, a professor at the University of Copenhagen and the senior author of the study. “Calories from minimally processed foods and calories from ultra-processed foods are not equal, so to speak. They don’t have the same consequences on our bodies.”
The findings add to what is becoming overwhelming evidence that diets based on ultra-processed foods are not good for us, said Marion Nestle, an emeritus professor of nutrition, food studies and public health at New York University, who was not involved in the new study.
“But the big shocker here is the potential effect on male fertility.”
She said that the study was relatively short, and that there was a lot of individual variation in how people responded to the different diets. But on average people did much worse when they were eating ultra-processed foods, she said.
The authors of the new study said that they wanted to look at the impact these foods might have on reproductive health because sperm counts in men around the globe have declined at the same time that consumption of ultra-processed foods has rapidly increased.
In the United States and other Western countries, ultra-processed foods make up an increasingly large percentage of the overall calories that children and adults consume – roughly 55%, a recent study found. These foods consist of things like hot dogs, soft drinks, potato chips, sweetened breakfast cereals and packaged snacks. Unlike whole foods such as fruits, vegetables, fresh meats, whole grains, nuts and seeds, ultra-processed foods are mostly industrial formulations that contain many additives, including salt, sugar, oils, preservatives, emulsifiers and synthetic ingredients.
These foods typically contain a lot of refined grains and flours and are often devoid of health-promoting nutrients like fibre. This makes them less nutritious but cheaper and more shelf-stable.
The researchers recruited 43 relatively healthy men between the ages of 20 and 35 and split them into groups.
One group was assigned to eat a diet of largely ultra-processed foods for three weeks and a diet of largely unprocessed foods for three weeks, separated by a “washout” period of three months, when they went back to eating their usual diets. The researchers provided all their meals.
Another group of men was assigned to do something very similar, except in this case the ultra-processed and unprocessed diets were designed to be high in calories. The researchers provided them 500 more calories per day than they needed.
For each arm of the study, the researchers designed the two diets to contain equivalent amounts of calories, protein, carbohydrates and fat. This was so they could see whether the extent of ultra-processing had any health effects separate from the impact of calories and specific macronutrients.
Compared to when they ate the unprocessed diets, men gained about 3lbs (1.360kg) on average and 2.2lbs (997g) of body fat when they were assigned to eat the ultra-processed diets.
– When men ate the high-calorie, ultra-processed diet, they had lower levels of follicle-stimulating hormone, or FSH, a hormone produced in the brain that plays a critical role in male fertility. FSH stimulates sperm production and helps to regulate testicular function.
– The researchers found trends toward lower testosterone levels when men ate the normal-calorie, ultra-processed diet and a reduction in sperm motility when they ate the high-calorie, ultra-processed diet.
– In another trend, men who ate the ultra-processed diets had higher levels of a chemical called cxMINP, a type of phthalate that’s added to food packaging and other plastics to make them more stretchy, soft and flexible. Phthalates are known as endocrine-disruptors because they can cause hormonal changes in the body, leading to health problems. Barrès said that the accumulation of phthalates in the body could be one reason eating ultra-processed foods caused weight gain and changes to sex hormones.
– The men had higher amounts of lithium in their blood and seminal fluid when they ate the unprocessed diets. The researchers said this was a good thing because lithium helps to regulate mood and is often prescribed to treat mood disorders such as depression and bipolar disorder.
– Eating the diet of mostly unprocessed foods did have some downsides. Men had higher levels of mercury when they ate the unprocessed diets, likely because they were consuming more tuna and other types of seafood, the researchers said. At the same time, when men ate the unprocessed diets, they accumulated higher levels of two so-called “forever chemicals”, also known as per- and polyfluoroalkyl substances, or PFAS. The researchers said they suspected this was because the foods they ate were cooked and prepared in nonstick pots and pans that were coated in PFAS.
Although the ultra-processed and unprocessed diets were matched for calories and macronutrients, they could not have looked more different.
The unprocessed diet contained many colourful whole foods and fibre-rich plants. Here is a typical day of meals on this diet:
Breakfast: Scrambled eggs, tomatoes, roasted potatoes, toasted rye bread and a banana.
Lunch: A salad with chickpeas, chicken and sesame dressing, along with falafel and hummus
Snack: Things like cheese, hard-boiled eggs, hummus, whole wheat crackers, smoked salmon, sliced red peppers and fresh fruit
Dinner: Whole wheat pasta with mixed vegetables and Danish meatballs with beans. Or fresh salads served with avocados, salmon or tuna, and chopped mango or pineapple on the side.
The ultra-processed diet, on the other hand, contained a lot of packaged foods. The researchers said they designed it to look like a typical diet in countries where people regularly eat a lot of ultra-processed foods.
Breakfast: Pastries, protein bars, sweetened breakfast cereals, toasted white bread with butter, instant mashed potatoes and orange juice.
Lunch: Sandwiches on white bread, juices, chocolate milk and mixed candies.
Snack: Sour cream and onion potato chips, salted potato chips, chocolate snack bars, chocolate milk, crackers, dried apricots and mixed candies.
Dinner: A hamburger with ketchup on a bun, creamy pasta, or pulled pork on a bun with barbecue sauce, with coleslaw, baked potatoes and lemonade.
Barrès said that one notable difference between the diets was that the ultra-processed meals contained a lot less fibre, which is very common with ultra-processed foods. This makes them easier to chew and gives them a longer shelf life. But it also means that we eat them more quickly, they enter our guts much faster, and we absorb them more rapidly. Studies have found that people absorb more calories from ultra-processed foods than unprocessed foods, and that they tend to cause larger blood sugar and insulin spikes, which may contribute to weight gain.
Barrès said that the findings from the study have caused him and his family to eat fewer ultra-processed foods. He said that for most people, it’s not practical to avoid all ultra-processed foods, because they’re so convenient and accessible. But he recommends that people start thinking differently about the foods that they eat.
“What we’re finding is that quantity is perhaps not as important as food quality.”
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