There are many different sugars in foods including fructose and glucose. Some people can't absorb fructose properly, and so the sugar passes through the digestive tract. Bacteria in the digestive tract try to digest these sugars, fermenting them and releasing gas into the digestive tract. This gas causes bloating and generally makes a person feel unwell and down in energy.
The best way to tell if you're one of those people that can't absorb fructose properly is to either
- record everything you eat and how you feel after each meal. This can help you track down if it's the apples that are causing the problem, or if it's something else that you tend to eat at the same time as apples.
- take a hydrogen breath test.
The hydrogen breath test is the only diagnosing test around at the moment. It involves testing how much hydrogen is present in your breath in general, and then again at multiple times after consuming some fructose. If the hydrogen level rises, it's most likely because the person isn't absorbing the fructose properly.