Beyond Calories: How Insulin Shapes Our Weight and Health

As most of you in this particular community already know, for years our patients, clients, neighbors, family members and coworkers have been told that weight loss is a simple equation: burn more calories than you consume, and the pounds will melt away. So why do so many people struggle with weight despite counting calories, exercising, and following conventional advice?

The problem isn’t just about calories in, calories out—it’s about what those calories do inside our bodies. And that comes down to insulin.

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Teaching This Concept to Others

Consider this: 200 calories from a doughnut and 200 calories from a steak might be equal on paper, but they trigger vastly different responses in our bodies. A doughnut—high in sugar and refined carbs—spikes insulin, your body's key fat-storage hormone. A steak, on the other hand, has little impact on insulin and provides protein that helps preserve lean muscle.

This is why two people can eat the same number of calories but experience dramatically different weight and health outcomes. Insulin controls how your body partitions energy—whether you burn it for fuel or store it as fat.

The Insulin-Obesity Connection

When insulin levels remain elevated over time (often due to frequent carb-heavy meals, snacks, and sugar-laden drinks), fat loss becomes nearly impossible. Instead of using stored fat for energy, your body is locked into fat-storage mode.

This explains why some people gain weight easily despite eating a “normal” amount of calories—their bodies are metabolically primed to store rather than burn.

The Proof: Low-Carb vs. Low-Fat Diets

Let’s look at the research. The UK’s Public Health Collaboration analyzed 67 randomized controlled trials, comparing low-carb diets to low-fat, high-carb diets. The results?

• 58 out of the 67 studies found low-carb diets to be significantly more effective for weight loss and metabolic health (references below).
• Low-carb eaters experienced greater fat loss, better blood sugar control, and improved metabolic markers.

Explaining Weight Loss: Focus on Hormones, Not Just Calories

If insulin plays such a central role in weight gain and metabolic health, it makes sense that the key to sustainable fat loss isn’t about cutting calories across the board but about managing insulin levels strategically.

This means:

• ✅  Prioritizing protein and healthy fats to maintain muscle and satiety
• ✅  Avoiding refined sugars and ultra-processed carbs that spike insulin
• ✅  Eating in a way that allows insulin levels to naturally drop between meals through intermittent fasting and time-restricted eating

When insulin is low, our bodies can access stored fat for energy—leading to effortless fat burning, steady energy, and better metabolic health.

Calories do matter, but they don’t tell the whole story. What you eat affects how your body responds hormonally, and insulin is at the center of it all.

If someone’s goal is to lose weight, improve their metabolic health, or simply feel better, understanding insulin is far more powerful than just counting calories.

References:

https://phcuk.org/evidence/rcts/ 

• https://phcuk.org/wp-content/uploads/Meta-Analyses-Comparing-Low-Carb-To-Low-Fat-Diets.pdf 
• https://phcuk.org/wp-content/uploads/Summary-Table-Of-Randomised-Controlled-Trials-Comparing-Low-Carb-To-Low-Fat-Diets.pdf 
• https://phcuk.org/wp-content/uploads/LC-v-LF-RCTs-26.10.2023.png 
• https://phcuk.org/wp-content/uploads/2018/02/Summary-Table-Of-Randomised-Controlled-Trials-Comparing-Low-Carb-To-Low-Fat-Diets-26.02.2018.pdf 

Metabolic Classroom Lecture 36: “Insulin Alters Metabolic Rate” - https://youtu.be/JbgvgjStxFA?si=Ej_QP_YPyIQWEQM1