Remove the light cream cheese from the refrigerator and allow it to soften so it can be mixed smoothly. If needed, cut it into several small pieces to help it soften more quickly.
Wash and dry the lemon thoroughly. Use a fine grater or microplane to collect approximately 1 tablespoon of finely grated lemon zest, taking care to grate only the yellow outer peel and avoid the bitter white pith.
Cut the lemon and squeeze 1 tablespoon of fresh lemon juice. Set the zest and juice aside while you prepare the creamy base.
Place the softened cream cheese in a medium mixing bowl and beat it with an electric hand mixer or sturdy spatula until completely smooth.
Add the powdered zero-calorie sweetener, vanilla extract, and pinch of salt to the cream cheese. Mix thoroughly until the sweetener is evenly incorporated and the mixture looks smooth and creamy.
Add the fresh lemon zest and lemon juice. Mix again until the lemon is evenly distributed throughout the cream cheese mixture. Taste a small amount and add a little additional lemon zest if you want a stronger citrus flavor.
Add approximately half of the whey protein isolate and mix until incorporated. Add the remaining protein powder and continue mixing until no dry powder remains.
Sprinkle the coconut flour over the mixture and mix thoroughly. Allow the mixture to sit for one to two minutes so the coconut flour can absorb moisture and help thicken the mixture.
Check the consistency. The mixture should be thick enough to press together and shape. If it remains too soft or sticky, add another teaspoon of coconut flour, mix, and allow it to sit briefly before deciding whether another small amount is needed.
If the mixture becomes too dry or crumbly, add a small amount of softened cream cheese and mix again until the texture becomes pliable. Avoid adding a large amount at once because the mixture can become too soft.
Cover the bowl and refrigerate the mixture for approximately 20–30 minutes. Chilling allows the protein powder and coconut flour to absorb moisture and makes the mixture much easier to shape.
Line a small plate or tray with parchment paper. Use a small cookie scoop or tablespoon to portion the mixture into approximately 12–16 small pieces, keeping the pieces as evenly sized as possible.
Gently roll each portion between your palms to form a smooth ball. If the mixture begins sticking to your hands, return it to the refrigerator for another 10 minutes before continuing.
If desired, roll each truffle lightly in unsweetened shredded coconut. For the lowest-carbohydrate version, leave the truffles plain and finish them with a tiny amount of fresh lemon zest instead.
Place the finished truffles on the parchment-lined tray and refrigerate for at least another 30 minutes. This second chilling period helps the truffles firm up and gives them a more satisfying bite.
Serve the lemon truffles chilled. Store any leftovers in an airtight container in the refrigerator and enjoy within approximately 3–4 days for the best quality.