Do I need to lift weights to change my physique?
If your goal is only to reduce scale weight, you do not strictly need to lift weights. But almost nobody wants weight loss in that abstract sense. Most people want fat loss, a leaner shape, better proportions, more visible muscle, or a body that looks and performs more athletically. For that, resistance training is one of the highest-leverage tools available.
The reason is partitioning. Diet controls much of fat loss through calorie balance, but training helps determine what the weight change is made of. A calorie deficit without resistance training can reduce both fat and lean mass. A deficit with enough protein, adequate carbs to support training, and progressive resistance training is more likely to preserve muscle while fat is lost.
This is why "skinny fat" is a real concern. The phrase usually means someone has relatively low bodyweight but also low muscle mass, so the body can still look soft, weak, or undefined. The issue is not merely how much fat they have, but the ratio of fat to muscle and where they are on the spectrum of muscularity. Losing more scale weight without building or preserving muscle can make that problem worse, not better.
Hypertrophy-style training is especially useful here, even if your goal is not to become visibly large or bodybuilder-muscular. Training that challenges muscles through appropriate volume, effort, range of motion, and progression sends a strong "keep this tissue" signal during a deficit. You can think of it less as "trying to get huge" and more as telling the body which tissue is expensive but worth keeping.
You do not need an advanced bodybuilding program to start. Two or three simple full-body sessions, done with good technique and gradual progressive overload, can change the direction of your body composition. If you cannot lift because of pain, disability, injury, or equipment constraints, other forms of resistance can still help: machines, bands, bodyweight progressions, weighted carries, or aquatic resistance. Persistent pain should be evaluated by a qualified clinician.