Yeah, a bit confusing, isn’t it. However, all will be made clear.
Consuming some food because it contains something beneficial will have much more detrimental effects if it contains an allergen or something else that the body does not tolerate.
Let me give you an example. Nut allergy. Need I say more?
Ok, here’s a less drastic and more common example. Imagine this scenario: you are middle aged and lactose intolerant. You are scared of osteoporosis. Everyone tells you to eat more dairy in order to put more calcium in your diet. So you put up with the consequences and have your daily dose of milk or cheese. You also succumb to the fat-scare and choose low or no-fat milk.
What is wrong here? First of all, low fat milk has a higher concentration of lactose. Skim milk powder can contain up to 52% lactose. Most of dairy products like cheese, cream, yoghurt, spreads etc are made from low fat milk powder. So if you feel you must have dairy, have full cream. At least it tastes better 🙂
Secondly, if your digestive system is upset from the lactose, do you think that it will process all the other stuff, especially with all the symptoms going on? No. The calcium in the milk, together with other contents of the guts will be speedily evacuated. After all, there is no filter in the guts that can seperate the offending material and dispose of only that.
As you can see, taking that calcium in the form of dairy in this situation is not only pointless, it is actually depriving this person of proper digestion of all other nutrients taken at the same time. Food intolerances and allergies are actually pretty common these days so more examples can be thought of. Fructose intolerance is another common one. And, of course, gluten.
So what is the alternative for the calcium example? Well, let me ask you a question. Where do cows get the calcium from? I am not suggesting to eat grass like cows but grean leafy vegetables. So the calcium is less concentrated than in milk but at least it will be absorbed better.
In the long run, it is better for the body to avoid the offending food. You can always find an alternative, however, sometimes it may be difficult because of lifetime habits and beliefs.