The internet is full of weight loss tips, advice, and claims, but not all of them hold up to scientific scrutiny. One of the most common—and misleading—claims is that obesity is caused solely by insulin resistance and that weight loss can be achieved without considering caloric intake. Today, we’re going to tackle this myth head-on and reveal the truth: while insulin resistance is a real condition with important implications for health, sustainable weight loss still fundamentally depends on creating a caloric deficit. What is Insulin Resistance? Insulin resistance occurs when your cells stop responding effectively to insulin, a hormone that regulates blood sugar. As a result, the pancreas produces more insulin to compensate, leading to elevated insulin levels (hyperinsulinemia). Over time, this can cause metabolic dysfunction, including prediabetes, type 2 diabetes, and an increased risk of cardiovascular disease. While insulin resistance is more common in people with obesity, it is not the sole driver of weight gain. Instead, it is a consequence of prolonged energy surplus—consuming more calories than your body needs. To understand why, we need to look at how energy balance governs weight. The Role of a Caloric Deficit in Weight Loss A caloric deficit occurs when you consume fewer calories than your body burns. This is the primary mechanism for weight loss, regardless of whether you are insulin sensitive or insulin resistant. Energy balance—calories in versus calories out—remains the foundation of fat loss. What Does the Science Say? Insulin and Weight Loss Research consistently shows that weight loss improves insulin sensitivity, even without specifically targeting insulin spikes. In a caloric deficit, the body begins using stored fat for energy, which reduces fat mass and improves metabolic health. Key Study: A 2011 study in the New England Journal of Medicine compared low-fat and low-carb diets and found that while both improved weight loss and insulin sensitivity, the total calorie intake was the most significant factor influencing results.