If swimming is so healthy for you why are whales so fat?

For whale’s blubber is useful for a number of different things besides keeping them warm.

As stated earlier the whale's blubber helps protect their vital organs from the cold/freezing waters.

This blubber is the reason whales are able to remain comfortable in freezing temperatures while other animals (such as humans) would easily freeze to death.

Another less talked about use for blubber is that it can also help protect whales against attacks from predators such as killer whales and sharks.

While these attacks are rare they do occur and the thick layer of blubber can provide some defense against these attacks and deter would-be predators that are looking for an easy meal.

Blubber also provides whales with additional buoyancy when they are in the water and makes it easier for them to rise to the surface of the water after making a deep dive.

Because whales are such large and heavy animals their ability to remain buoyant allows them to swim more effectively rather than just sinking to the bottom of the ocean like a rock.

Lastly, a whale’s blubber can be used to store additional calories during times when there are food shortages or when migrating to other areas.

Depending on the thickness of the blubber some marine animals can survive for months without food.

In order to minimize their expenditure of calories whales are very efficient swimmers and will limit their speed and body movements in order to use the least amount of calories during their long trip or during food shortages.

To a lesser degree, humans and other animals are also survive for weeks without food by utilizing their body fat for energy and minimizing the number of physical activities being performed.

Fat is healthy,  dingus. 

Good question. I always wondered- if vegetables are so low in calories, why are cows fat???? But for the whales, I would say that they expend a lot less energy swimming than people do. 

Because fat is a good way for a mammal that lives in water to not die from the cold. If a human lived in the water it would have a lot of fat to survive the cold.  

Because "fat" is the correct body size and shape for a whale.