Energy balance

When total energy deficit is strictly matched, adding structured aerobic exercise to caloric restriction provides no additional benefit for fat mass loss or abdominal fat distribution compared to caloric restriction alone.

If your goal is purely fat loss and you are willing to restrict calories, adding exercise will not make you lose more fat than dieting alone, provided the total calorie deficit is the same. However, exercise is still valuable for improving cardiovascular health and aerobic fitness, which are independent benefits of weight loss. Do not feel guilty if you skip the gym; your fat loss progress depends on your net energy balance, not the source of the deficit.