Many nutritional studies also suffer from funding bias in which the result reported conforms to the interest of whomever funded the study. In addition, studies based on randomized controlled clinical trials can be affected by their study population selection criteria, with participants commonly limited to those without other potentially confounding illnesses. Although this makes for cleaner study design and easier analysis, observational studies with a more natural participant population will tend to include people who may benefit from nutritional supplementation due to other ailments.
Similar to the govt.-funded scientists that conclude without a doubt the "settled science" of global warming.