Summarize complex carbohydrates in one sentence.
Complex carbohydrates are long chains of sugar molecules that provide sustained energy, and are found in foods such as whole grains, fruits, and vegetables.
Complete the following task based on the instruction and optional input provided.### Instruction:
Summarize complex carbohydrates in one sentence.

### Output:
Complex carbohydrates are long chains of sugar molecules that provide sustained energy, and are found in foods such as whole grains, fruits, and vegetables.