25/11/2025
Can Food Quality Change Your Body?
(Even When Calories Are The Same)
You’ve probably heard people say this more than a thousand times: “A calorie is a calorie.”
While calories are one of the primary mechanisms that determines weight gain or loss, a new study should make you change how you think about what’s on your plate!
In mid-May, Dr. Kevin D. Hall, a senior investigator with the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) published a study on the first randomized, controlled trial at the NIH Clinical Center.
The study found that when people eat the exact same number of calories, those whose diet consists primarily of ultra-processed foods gain more body fat and have worse cholesterol levels than those who eat whole, unprocessed foods.
The researchers compared a diet of mostly ultra-processed foods (think packaged snacks, frozen meals, refined grains, and sugary drinks), and one made almost entirely of unprocessed foods like fruits, vegetables, and whole grains. Every meal was calorie-matched and had the same amount of protein, carbs, and fat. The ONLY difference in diet was food quality.
Each participant followed both diets for three weeks each (with a 3-month washout period in between), allowing researchers to compare how the same person responded to each diet.
After just three weeks, participants on the ultra-processed diet gained about 1kg of fat (about 1.5kg total weight). They also had worse cholesterol levels (among those eating the normal set calories) and higher blood pressure (among those eating excess calories), suggesting that different aspects of metabolic health were affected by caloric intake.
And the reproductive hormone (FSH) dropped in the group eating ultra-processed foods with extra calories, but the study was too short to say whether that would affect fertility in the long term.
"Though we examined a small group (20 people), results from this tightly controlled experiment showed a clear cut and consistent difference between the two diets," said Hall. "This is the first study to demonstrate causality — that ultra-processed foods cause people to eat too many calories and gain weight."
So why the difference? The researchers suggest the ultra-processed foods were digested faster and had less fiber, resulting in your body reacting differently to a plate of whole foods than to a plate of refined ones, even if the calorie count matches.
If you want to improve your long-term health, you don’t need to swear off all processed foods. Just start tilting the balance in favour of whole foods: pick more single-ingredient foods, choose whole grains, beans, fruits, and vegetables whenever possible, and eat lean sources of protein. You don’t need to chase perfection, just small, consistent upgrades will make a real difference.
The Study: https://www.cell.com/cell-metabolism/fulltext/S1550-4131(19)30248-7
