My grandfather's generation were mostly employed by agriculture. They worked like hell and consumed a diet high in carbohydrates. Yet obesity and diabetes were rare. Michael Phelps consumes around 12,000 calories a day when he's in training. His diet is heavily weighted to carbohydrates because he needs the energy. He needs his glycogen reserves maxed out. I'd say he's in pretty good shape and is one hell of a competitor. He wouldn't be either of those if he didn't "carb up" like he does.
At the same time your maximum allowable consumption of protein is about 40% of your caloric intake. You should split the remaining 60% between fats and carbs. Some folks need more fats than others ~ actually, our Ice Age ancestors did, and even today there are groups that continue to need far more fats than carbs ~ they might even live in regions without carbohydrate resources.
BTW, Seal skin contains Vitamin C.