People are different. They react differently to stress, to the physical environment… and to nutrients. No two bodies are exactly alike – even identical twins, who share the same genetic material, have differences.

When it comes to diet, one person may actually need more or less of a particular nutrient than the next person. Smokers and people under stress have increased vitamin C needs. Some people gain weight easily while others can't seem to keep weight on. People react to foods differently, they have different likes and dislikes, different metabolisms, and different appetites. People respond differently to different dietary regimens. A diet plan that "works" for one person may be a disaster in terms of compliance for another.

Bottom line? It’s hard to make global nutrition recommendations that apply to everyone.