When considering toxic substances that are eaten, the reason most fats should be included as toxic is because all fats become highly carcinogenic when heated. Even rancid fats, as in stale nuts or seeds, are harmful and should not be eaten. Nuts or seeds should never be eaten roasted, either. | When considering toxic substances that are eaten, the reason most fats should be included as toxic is because all fats become highly carcinogenic when heated. Even rancid fats, as in stale nuts or seeds, are harmful and should not be eaten. Nuts or seeds should never be eaten roasted, either. |