Due to this tolerance that the body develops to certain food that are harmful, in order to experience if a certain food is really good or bad for us, it could be a good idea to avoid eating it during a certain time. The length of time is the necessary amount until the body looses its apparent “tolerance” to it. Then it must be reintroduced again.
When removing a harmful food it is possible that the person feels better or worse, depending on several factors. But in the reintroduction, it is the moment when the person will feel a worsening, which could happen in some hours or even in some days after the reintroduction started.
Taking into account the following list of possible links, we can be aware and make the relationship between disease and food easily.
I have got this information from my experience as nutritionist. Some links are known by most nutritionists, but most of them are the fruit of my observations, and they are new contributions.
 

Diseases	Food
Breast cancer	soy (when it is removed from the diet after it has been taken during several years)
Osteoporosis	dairy, meat, fish, grains
Cardiovascular diseases	fats and oils
Nervousness, insomnia, tachycardia	coffee, tea, chocolate
Constipation	gluten, carrot, rice, fish. In lesser degree: meat, green leafs
Laxative	avocado, citric fruits, fats, dried fruits
Circulatory problems, cold sensitive, Raynaud syndrome	fast carbs (sugar, syrup, honey, dried fruit) and slow carbs (starch)
Brittle nails	fast carbs (sugar, syrup, honey, dried fruit) and slow carbs (starch)
Nightmares	nuts, seeds, grains, seeds, dairy
Premenstrual syndrome	eggs, nuts, seeds, grains, dairy, meat, fish
Lack of memory, mental sluggishness	meat, fish
Fatigue and/or muscular pain	tomato, bell peeper, citric fruits, kiwi, pineapple
Diuretics	vegetables
Somnolence, fatigue, bags under the eyes	alcohol, dairy, meat, fish. In lesser degree: green leafs, salt
Headaches	dairy, smoked products, alcohol, coffee (withdrawal effect). In lesser degree: salt
Leg pain	eggs
Dermatological diseases	oils, avocado, coconut, olives, nuts, seeds
Liver inflammation	dairy, chocolate, fats, alcohol, banana
Muscular cramps	sugar, syrup, honey, dried fruit, excess of fruit
Ophthalmological diseases, conjunctivitis	sugar, syrup, honey, dried fruit
Joint disorders	fats and oils
Hemorrhoids	fats and oils
Intestinal worms	sugar and syrups
Gastrointestinal diseases	gluten, dairy, legumes
Kidney diseases	teas and infusions
Heart diseases	drugs

After reading this list you may ask yourself: then, what can we eat? I think that our best food are fruits and vegetables, knowing that they can have some undesirable effects too, although the repercussion is much lower compared with the other food. For example, citrus may be excessively laxative and result in some muscular pain and fatigue, as well as tomate and bell peeper; and vegetables are quite diuretic.