For years, the standard advice for weight management has been simple: eat less, move more. However, new research published in the American Journal of Clinical Nutrition suggests that the composition of our meals—specifically the balance of fats and carbohydrates—may be more important for appetite control than sheer willpower.
The study, led by Jeffrey M. Brunstrom, Ph.D., of the University of Bristol, suggests that ultra-processed foods (UPFs) might actually “nudge” our biology toward overeating by providing a suspiciously perfect balance of energy sources.
Researchers conducted a post-hoc assessment of 20 weight-stable adults. These participants were given two weeks of an ultra-processed diet followed by two weeks of an unprocessed diet (or vice versa), with the freedom to eat as much or as little as they desired (ad libitum).
The results revealed two primary drivers of calorie intake:
The “Blend Index”: This measures how equal the ratio of energy from carbohydrates and fats is.
Energy Density: How many calories are packed into a specific weight of food.
One of the most striking findings was that participants on the unprocessed diet naturally selected meal components with a less balanced carbohydrate-fat intake.
In the world of nutrition, a “perfectly balanced” blend of carbs and fats (think of the ratio found in a donut or a bag of potato chips) is rare in nature but common in ultra-processed foods. This “equal blend” appears to bypass the body’s natural “fullness” signals, leading to higher energy intake.
Conversely, when eating whole foods, participants chose items that were more skewed toward one macro-nutrient or the other, which resulted in a lower “blend index” and a naturally reduced calorie intake.
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The study challenged the idea that overeating is simply a matter of eating too much physical food. In fact, participants on the whole-food diet consumed 57 percent more food by mass than those on the processed diet, yet they took in significantly fewer calories.
Whole Foods: High mass, low energy density (e.g., bulky fruits and vegetables).
Processed Foods: Low mass, high energy density (e.g., calorie-dense snacks).
“Overeating is not necessarily the core problem,” Brunstrom noted. “Our research clearly demonstrated consumers on a wholefood diet actually ate far more than those on a processed food one.”
The takeaway is that ultra-processed foods are engineered in a way that encourages higher calorie consumption even when the physical portion size is small. By pairing high energy density with a “perfect” blend of carbs and fats, these foods may be fueling the obesity epidemic by tricking the brain’s satiety mechanisms.
By shifting toward unprocessed meals, we aren’t necessarily eating “less” food—we are eating food that allows our bodies to recognize when we’ve had enough energy.
Based on Dr. Brunstrom’s findings, the goal isn’t just to eat “healthy,” but to avoid the specific nutritional combinations that trick your brain into overeating. Here is how you can apply these insights to your daily meals:
Ultra-processed foods often hit a “bliss point” by balancing fats and carbohydrates almost equally (e.g., pizza, pastries, or chips). This combination is rare in nature and highly addictive.
The Tip: Aim for meals that have a clear “identity.” For example, a high-protein/high-fiber meal with lower fat (like a bean chili) or a high-fat/high-protein meal with lower carbs (like grilled salmon and asparagus).
As the study noted, people on unprocessed diets ate 57 percent more food by weight but fewer calories.
The Tip: Use the “half-plate rule.” Fill at least half your plate with watery, fibrous vegetables (broccoli, leafy greens, peppers). This allows you to eat a large volume of food, physically stretching the stomach to trigger fullness signals without the calorie spike.
Processed snacks are engineered to be calorie-dense and low-mass.
The Tip: Swap a 200-calorie bag of crackers for two medium apples or three cups of air-popped popcorn. You’ll spend more time chewing and feel physically fuller due to the increased mass and water content.
Many processed dressings and sauces are the primary source of the “equal blend” of fats and sugars.
The Tip: Use simple acids like lemon juice or balsamic vinegar paired with herbs rather than creamy, sugar-laden bottled dressings. This keeps the energy density of your salad low.
The study suggests that balancing calorie consumption with micronutrient (vitamins and minerals) consumption helps regulate intake.
The Tip: If you are feeling hungry shortly after a meal, evaluate the “color” of your plate. If it’s mostly beige (bread, meat, cheese), your body may be hunting for the micronutrients found in colorful produce, leading to “false hunger.”
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