One of the main problems with nutrition studies is that they often ask study participants to remember what they have eaten for a certain period of time. Another issue that seems to affect nutrition research is complexity. Sometimes, a study will focus on the impact of a single specific food or compound on a health outcome. This is a little easier to manage.
The science of nutrition has to be much more imprecise. It is full of contradictory studies that are fraught with flaws and limitations. The clutter of this field is one of the main reasons nutrition advice can be confusing. Nutritional research tends to be unreliable because most of it is based on observational studies, which are imprecise, have no controls and do not follow an experimental method.
As nutrition research critics Edward Archer and Carl Lavie have said, “'nutrition' is now a paradigm of degeneration research in which scientifically illiterate methods, meaningless data and consensus-driven censorship dominate the empirical landscape. Nutritional research has to make some compromises, since the perfect study is unattainable. Therefore, in “observational studies,” nutrition scientists look for links between what a person consumes and their current or future health status. To this day, his controlled experiments on human nutrition are considered a gold standard in nutrition science.
Problems with nutritional research can make it seem impossible to know anything about diet and nutrition.