If you want to lose weight, you need to get better at knowing how many calories you eat. With some foods, like peanut butter or ice cream, that's actually really hard to do. Here's why it's important to be a little more accurate than "Eh, that looks like one serving" if you want to lose weight.
As I demonstrate in the video, a bagel, two tablespoons of peanut butter, or any other serving size is hard to imagine if you don't know exactly what it looks like. Test it out: make a peanut butter and whatever sandwich, using only one serving of peanut butter (that's two tablespoons, or 32 grams). Go ahead and use a measuring spoon, which is still prone to a lot of error. Now weigh out your portion in grams. What did you get?
If you've never paid attention to this stuff before, it could very well be twice the serving size, or twice the calories! If you're off by even 10 grams, that's still extra calories you never accounted for. Clearly, it's easy to overdo it on your favourite foods without even realising it. If you nailed the perfect serving size, congrats!
Tracking and weighing foods aren't for everyone and a lot of work, but they're a powerful process for weight loss. Note that calorie information can have up to a 25% margin of error and you'll never be truly accurate (which is ok).
Be careful not to be obsessed with weighing and tracking every leaf of lettuce, cereal flake, and anything else you eat. That's overkill. Just do it for a couple of weeks with your most commonly eaten foods to get a sense of what appropriate serving sizes should look like.