Calories vs. Food Quality? What Matters More for Fat Loss?

There’s a long-running debate in the nutrition world:

🧮 “It’s all about calories in vs. calories out!”

🥦 “Food quality is what really matters!”

But of course like anything else in nutrition, it's not black and white. The laws of thermodynamics absolutely stand when it comes to losing weight: calories in must be less than calories out.

But where these calories come from can absolutely impact one's ability to lose weight or change their body composition.

A new study published in Diabetes, Obesity & Metabolism shed light on how ultra-processed-food (UPF) intake affects our hunger and appetite regulation.

The results were crystal clear: Intake of ultra-processed-foods leads to higher caloric intake even when calories and macros available were matched.

Let’s break down the research and what it means for your fat loss goals, energy, and appetite.

The Study: Same Calories Offered, But Ultra-Processed Food Group Ate More

Researchers in Japan designed a randomized crossover trial with 9 men classified as overweight or obese.

Each participant completed two different 1-week diet phases:

1. Ultra-processed food (UPF) diet — Think packaged snacks, soft breads, sweetened beverages.

2. Minimally processed (non-UPF) diet — More whole foods, less industrial processing, more texture.

   
   

The important stuff:

• Both diets were matched for calories and macronutrients, but the UPF diet was lower in fiber and higher in sodium.

• Participants received identical food quantities for all meals and snacks, but they were allowed to eat ad libitum (as much or as little as they wanted).

• The only variable? How processed the food was.

The Outcome: Calories vs. Food Quality - BOTH Matter

Here’s where it gets interesting:

• On the ultra-processed diet, participants chose to eat 813 more calories per day on average. (Note, this was a crossover trial, meaning the same person chose to eat 813 calories more on UPF than they did on natural, whole foods diet).

• Most of the excess intake came at lunch and dinner, which suggests that UPFs may bypass typical satiety mechanisms later in the day (a time where individuals are prone to consuming UPFs already)

• As a result, they gained 1.1 kg (about 2.4 lbs) in just one week.

And perhaps the most significant finding of this study that helps us link why UPFs lead to overeating:

• Participants chewed significantly less and ate way faster when consuming the UPF diet

  • 0.6 fewer chews per calorie on UPF

  • 18.8 kcal more consumed per minute on UPF

• Despite eating more, participants didn't report feeling hungrier on the UPF diet. However, their hormonal profiles suggested otherwise:

  • Appetite suppressing hormones (leptin and adipnectin) rose during the UPF diet

  • Peptide YY (fullness hormone), trended lower during UPF diet - consistent with faster eating and lower fiber consumption

👉 When it comes to calories vs. food quality, turns out they both matter! The weight gain didn’t come from the food itself being inherently more fattening — it came from eating more of it. Reduced chewing and faster eating likely resulted in participants consuming more calories before their fullness signals could catch up.

Why Ultra-Processed Foods Are Easier to Overeat

This research finally confirms something we already suspected: not all calories are experienced the same way, even when they look identical on paper.

Ultra-processed foods are often:

⏩ Easier and faster to eat

🧠 Hyper-palatable (engineered to taste irresistible)

🥣 Less filling per bite

That doesn’t make them “bad” by any means, but it does make them easier to overeat (often without realizing it). This matters even more when you're trying to stick to a calorie deficit or manage hunger.

And most people aren’t weighing every bite or tracking perfectly 100% of the time. Which means things like chewing, food texture, and satiety truly can impact your results.

Limitations of the Study

As with any research, context matters. Here are a few key limitations to consider:

• Small sample size (only 9 men)

• Men were classified as overweight/obese

• Short timeframe (1 week per diet)

• Participants knew which diet they were on (no blinding)

• Results need to be replicated over multiple demographics

That said, this study adds important depth to a growing body of evidence showing that ultra-processed foods can lead to higher calorie intake.

What This Means for You (and Your Goals)

We don't believe in good vs. bad food mentality, and there is a time and place for processed foods in a healthy diet, regardless of your goals.

But if you're someone who:

• Is trying to lose weight or lose body fat

• Struggles with appetite regulation, cravings and hunger swings

• Wants to improve energy and consistency w

… then reducing ultra-processed foods can make your goals easier to stick to.

Here’s how to apply this in real life:

1. Build meals that slow you down.

Foods that require more chewing (lean protein, fibrous veggies, whole grains) give your body time to register fullness. Focus on eating slowly, chewing your food fully and eating without distraction as much as possible.

2. Pay attention to how meals impact your hunger.

Start noticing if some meals leave you satisfied for hours… or ravenous 30 minutes later. As this study shows, food quality impacts our hunger and satiety, so focus on the meals that leave you feeling satisfied as much as possible.

3. Use processed foods strategically — not by default.

Protein bars and packaged snacks can be great tools. But when they make up the bulk of your diet, they may make staying in a deficit much harder.

4. Support your biology, not just your willpower.

Eating mostly whole foods not only provides you with additional benefits from fiber and micronutrients - but makes sticking to a calorie deficit or maintenance calories a lot easier. Maybe you don't need more willpower after all.

Bottom Line: You Eat More When Food is Easier to Overeat

The study doesn’t mean ultra-processed foods are “bad” — but it does show they make overeating more likely, even when you're offered the same amount of food.

So while calories still count, food quality absolutely matters.

If you want to feel more in control, more satisfied, and less snacky — focus on whole, nutrient-dense meals most of the time.

No guilt. No rigid rules.Just smarter choices that support your body and your goals.

Want to better understand your hunger and energy? Check out our blog on tracking biofeedback.

Struggling to balance food quality and your macros? Book a free nutrition strategy call 📞