Use controlled, directional light and let the areas you don’t want to emphasize fall into shadow. In low-key portraits, broad flat light tends to reveal shape evenly, while side/back/rim lighting can define selected contours more selectively.

Helpful approaches:

• Use narrow, controlled light sources: small flashes, snoots, grids, flags, or masks/gobos to light only specific parts of the body.
• Position lights so they highlight stronger features and avoid spilling onto areas the subject wants minimized.
• Adjust pose first: posture matters a lot. Stretching the back, turning the body, and avoiding positions that compress the torso can reduce the appearance of belly or thighs.
• Change camera angle deliberately: lower angles can lengthen legs; longer focal lengths can be more flattering for facial proportions.
• Consider clothing and styling to support the lighting pattern.
• If needed, use subtle fill or a reflector to improve transitions without flattening everything.

In short, don’t try to light the whole body evenly. Build the image with selective light, flattering pose, and camera placement so attention goes to the subject’s best features.