[gadders]

The calorie counts on food packets themselves are +/- 20%, so it's inaccurate all the way down.

Some of the value also just comes from writing down what you eat, and noting the snacks, dressings, glasses of wine etc that you forget about but all add up.

[sumeno]

+/- 20% is way better than being off by 3x like in the example in this article