:I heard that lettuces are low in nutrients. People who fed largely lettuce to their tortoises and reptiles, such as iquanas and bearded dragon, that eat plants often get a sick and malnurished animals. And I think you are thinking about tomatoes. When you cook tamatoes for a long time it release certain chemical that is good for your heart. Usually, the dietitian recommend for people not to cook any kind of food, even meat, for to long because it destroys a lot of nutrients. Rare stakes contain much more vitamins and minerals than an overcook pieces fo meat. I think you can grow your own algaes, that hey can graze on, and feed them taddy food and some fish foods.