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Are calories really important during weight loss?

Thus, the “calories in versus calories out” model is completely correct. You need a calorie deficit to lose weight.

Losing weight requires a calorie deficit
From a biological perspective, you need to eat fewer calories than you burn to lose weight. Once your body’s energy needs are met, the extra calories are stored for future use — some in your muscles as glycogen, but mostly as fat. Thus, eating more calories than you burn will lead to weight gain, while eating less than you need will result in weight loss.

Some studies make it seem as though what you eat matters more than how much you eat, which means that the calorie content of your diet has nothing to do with weight loss. However, these studies are based on some incorrect assumptions.

For example, those who insist that low-carb diets help people lose more weight despite eating the same number (or even more) of calories often rely on diet journals to estimate calorie intake.

The problem is that diet magazines are notoriously inaccurate, even when they are filled out by nutritionists. Furthermore, some studies only report the total weight lost, without stating whether the weight loss resulted from the loss of muscle, fat, or water.

Different diets affect muscle and water loss differently, which can make it seem like it’s more effective for fat loss when it really isn’t.

Studies that control for these factors consistently show that weight loss almost always results from a calorie deficit. This is true regardless of whether your calories come from carbohydrates, fats, or protein.

Health is more than just calories

While the “calories in versus calories out” model is important for weight loss, not all calories are created equal when it comes to your health.