The side effects of apple fruit are due to the glycemic load.
Apple fruit contains both stimulants and depressants, so there can be a range of reactions. Young children in particular have adverse reactions when they consume an excessive amount of apple juice, which is typically unpleasant for them.
The unpleasant methedside effects are usually attributed to the high sugar content, but these side effects may be caused by eating too many ripe/over-ripe apples or drinking juice that has not been filtered properly…