Fat is the primary source of fuel when you engage in low-intensity movements - from sitting in front of the computer to walking the dog. Not only does the body burn fat during calorie deficits, but it also burns fat during normal day-to-day activities. When this happens, your body taps into its own fat stores, breaking them down for energy through a process called “beta oxidation.” This process requires glucose, which can come from carbohydrates or protein, and is most efficient when you’re mildly restricting calories. In a healthy adult, calorie deficits occur mainly by restricting calories consumed or by undergoing a tough workout.

Not surprisingly, significant fat breakdown occurs when your body runs on a calorie deficit. If you go right to bed, they’ll be stored in fat tissue until they’re needed. If you need energy right away - say you take a walk after dinner - they’ll be used to meet those demands. Once the chylomicrons arrive, fatty acids are again released to be taken up by muscle and fat cells.

The fatty acid chains are picked up by intestinal cells, reassembled and packaged into vessels called chylomicrons, which are sent to muscle or fat tissue. Dietary fat is digested into small chains of fatty acids. This makes sense, since one of the biggest roles of fat is energy storage. At 9 calories per gram, fat is the most calorie-dense of the macronutrients (carbs and protein each have 4 grams).

Nutrition infographic healthy fat