Macros vs Calories

Yes. Calories are all that matter for weight loss.

You should eat at least a portion of them back, especially if you're burning a lot. Take a 25-minute walk and don't be overly concerned; that's probably going to be in the neighborhood of 100 calories, give or take (variables include your weight, the speed of your walk, and the type of terrain). A 60-minute walk or a 30-minute run? Different story.

Calorie burns can be hard to estimate accurately. I generally eat back about half and keep the rest as a buffer against inaccurate calculations, both on my food intake and exercise burns.

The thing to remember is that when you exercise, your body needs more fuel. Otherwise, there's a limit to how much fat you can burn in a given period of time. Once you hit that, if your deficit is too aggressive, your body will start in on muscle. Other side effects of not adequately fueling your workouts include:

• Not having the energy to work out as hard, so you're burning less than you think
• Overall depleted energy to get you through the rest of the day
• Increased hunger
• Thinning hair, brittle nails, and other issues as your body stops fueling less-essential systems

Note that these effects don't always hit right away. A lot of people go through a "honeymoon" phase, where they feel great despite running too high a deficit. Problem is, it doesn't last and when the crash hits, it often hits hard.