Fat does more than pad your waistline — in fact, your body needs some fat to function. For example, in addition to being a reserve source of energy that can be taken out of storage and converted into glucose if needed, fat can help your body absorb certain vitamins. And because fat is broken down more slowly than carbs, it can also help you feel full longer than carbs can.
But there’s no doubt that fat is high in calories. In fact, it’s the most calorie-dense of the macronutrients, weighing in at 9 calories per gram.
Of course, like carbs, not all fats are created equal. Unsaturated fats are typically found in fats that are liquids at room temperature — oils such as olive oil and canola oil — as well as foods such as nuts and fish. These fats are considered heart healthy, and can certainly be considered a part of a healthy diet for weight loss.
But saturated fats (such as butter), which are usually solid at room temperature, and trans fats (such as hydrogenated oils) are largely considered unhealthy, mainly because of their effects on heart health.
Fat that goes unused by the body ultimately has the same fate as carbs and protein: It’s stored as fat.