Athletes and physically active people have increased needs for

They have increased need to carbohydrates, protein, water and iron.

Carbohydrates is the primary source for energy and active people apparently need more energy for their daily activities.

Protein helps build muscles, even though they only need a small amount more of protein than normal people, they still require protein for muscle buildings.

Water has to be needed as they may excrete more sweat by active activities in the day time. Water can also help remove waster material from body.

Iron helps the production of hemoglobin, which is in the red blood cells that help transport oxygen. As they exercise more, they need more oxygen supply for respiration, therefore there is a need for iron supply.

Very hard to understand

Then it is june the conclusion to the second sentence is just restating "if it is june then it is summer"