Why "Calories In, Calories Out" Isn't the Whole Story

Hi, I’m April, one of the nutritionists here at Protea Medical Center in Tempe. A topic that comes up a lot with my patients is the idea that weight loss is just about calories in versus calories out. It’s a simple equation we’ve all heard before, and I used to believe it too. But the truth is, our bodies aren’t that simple.

We’re not machines.

Our bodies are incredibly complex and unique. Each person has their own metabolic chemistry, hormonal profile, stress levels, and lifestyle. These variables all influence how our bodies gain, lose, or maintain weight.

Let’s take metabolism as an example. It’s not just about how many calories you consume and burn. Metabolism is influenced by age, genetics, hormone levels, stress, and sleep. Two people can eat the exact same meals and lead similar lifestyles, yet their bodies may respond in completely different ways. That’s how individualized our systems really are.

One of the analogies I like to use during appointments is that your metabolism acts like a thermostat. If you lower your calorie intake, your body might respond at first by shedding a few pounds. But eventually, it adapts. It “resets the thermostat” to this new lower intake and tries to maintain your weight at that level. The body doesn’t want to let go of energy stores unless it feels safe, which is why many people plateau or even start gaining weight again despite staying in a calorie deficit.

When patients tell me they’re frustrated because they’re counting calories and not seeing progress, I like to dive deeper. I don’t just look at the numbers—I look at the bigger picture. What are their stress levels like? How is their sleep? What types of calories are they consuming?

This brings me to another important point: not all calories are created equal.

Let’s say you eat a 200-calorie snack. One version could be a pack of crackers, while the other could be raw vegetables and hummus. Your body will respond to these two snacks very differently. The refined carbs in the crackers might spike your blood sugar, trigger an insulin response, and leave you hungrier sooner. The balanced option with fiber, protein, and healthy fat is more likely to stabilize your blood sugar and keep you full longer.

When I meet with patients, we often go through a “diet recall,” looking at what they typically eat in a day. This helps us identify small changes that can make a big impact. I’m not looking to overhaul anyone’s lifestyle overnight. Instead, we set simple, attainable goals—like increasing protein intake or shifting meal timing slightly.

Protein is a big one.

A lot of people struggle to eat enough protein, especially if they’re not very hungry. One easy trick is to double the scoop of protein powder in your morning shake. That way, you’re starting your day with a solid base instead of playing catch-up later. Another small step could be adding an ounce or two more protein to your meals, or sprinkling seeds and nuts onto salads and bowls. These changes don’t feel overwhelming, but they can make a difference.

Now, back to the bigger picture. Calories in and calories out is a part of the conversation, but it’s just one piece. Gut health, for example, is an emerging area of research that we now know plays a role in weight management. If you have issues like IBS or SIBO, that inflammation can affect digestion, nutrient absorption, and your ability to lose weight.

The truth is that every body is different. What works for one person may not work for someone else. That’s why I love having these one-on-one conversations with patients—to really uncover what’s going on in their unique lives and bodies.

Thanks for reading. If you have questions or want to learn more, we’re here for you. I hope to connect with you soon.