I’ve been eating pretty much nothing but fish and vegetable soup for the past couple of weeks and I’ve honestly never felt better. I don’t feel any weakness or anything like that.
A lot of it has to do with what you’re eating with your fish. I’ve found that if I include foods that are dense in carbohydrates—like rice or fried potatoes—with my meal, then I’ll feel weak later on during the day. This is because carbohydrates trigger an insulin response in your body that raises your blood sugar. Afterwards, your blood sugar drops to lower than normal levels which results in you feeling weak.
If I eat just the fish and other foods that are low in carbohydrates, I find that not only do I not have any weakness but I also don’t feel as hungry throughout the day.