Apple has a negative 100 calories.

In real life, when you eat an apple before a meal, effectively it has -100 calories.

When a research study asked people to eat an apple before their all-you-can-eat pasta lunch, those people ate 200 calories less pasta. Usually, that group of people ate 1000 calories in a meal. However, when they ate an apple worth 100 calories, they could only eat 800 calories of pasta afterward, effectively saving 100 calories from their lunch. So, when paired with your lunch, an apple effectively has -100 calories.