Diet / zero-sugar cola

One serving of Diet / zero-sugar cola — 1 can (300 ml) — comes to 0 kcal, 0 g protein, 0 g carbs and 0 g fat. Scaled to 100 g it works out to 0 kcal and 0 g protein, which makes it not a meaningful protein source on its own for a beverage item. That single serving is about 0% of a 1,500 kcal day and 0% of a 2,000 kcal day, so it's more of a filler than a target-hitter on protein without much extra planning.

Walking off Diet / zero-sugar cola takes roughly 0 steps, using the rough approximation of 0.04 kcal burned per step (a population-average estimate for a moderate walking pace, not a personalised number). Cost data for this item wasn't reliable enough to price per gram of protein, so treat it as a calorie source rather than a protein strategy. It fits nearly every Indian diet type, including vegetarian, Jain, vegan. It works at lunch, the evening snack slot and dinner. It's a packaged/processed item, worth checking the label against this estimate.

If you want variety without changing the macros much, the closest swaps in the beverage category are Black coffee (no sugar), Tender coconut water, Cold drink (cola/soda, regular), Energy drink (Red Bull type) — each keeps a similar role on the plate while shifting the exact protein-to-carb balance a little.