If women who aren't very overweight add aerobic exercise to a calorie-reduced diet, they get noticeably better at exercising — like being able to bike or walk harder — but just dieting alone doesn't help much with fitness.

What we've found so far is that adding aerobic exercise to a low-calorie diet appears to improve fitness in women who are not or only moderately obese. Our analysis of the available research suggests this benefit is clear when compared to dieting alone. We reviewed 46 studies or assertions, and all of them support the idea that aerobic exercise combined with reduced calorie intake helps these women become noticeably more fit [1]. This means they can exercise harder—like biking longer or walking faster—after following this combined approach. In contrast, cutting calories without aerobic exercise does not seem to lead to the same level of improvement in physical fitness [1]. Our current analysis shows the evidence leans strongly toward aerobic exercise making a meaningful difference in fitness when added to a low-calorie diet. We have not found any studies that contradict this pattern. Still, our understanding is based on what has been studied so far, and future research could add nuance. For now, the consistent message across the evidence we’ve reviewed is that exercise plays a key role in boosting fitness, even if weight loss is the shared goal of both diet and exercise. Practical takeaway: If you're a woman who isn't very overweight and want to feel stronger and more capable during physical activity while eating fewer calories, adding regular aerobic exercise—like brisk walking or cycling—may make a noticeable difference.