Clams themselves are a healthy food even when you have high cholesterol.
But clam chowder is not all that good when you have high cholesterol unless you make the clam chowder homemade and don't add a bunch of fatty ingredients to it.
Clams are a great source of protein, are low in calories and fat, and filled with minerals that we need to stay healthy but when you add all the other ingredients to make clam chowder it becomes unhealthy especially if eaten too much.
When eaten in moderation clam chowder shouldn't raise your cholesterol levels all that much and my husband has high cholesterol and he does eat a bowl of clam chowder twice per week and his cholesterol levels have been okay.
Just don't eat too much clam chowder when you have high cholesterol and you should be okay.