I think the problem is not the field, but your expectations from nutritional science research. Your comment is premised on the assumption that what you see in newspapers is representative of nutritional science. Like most research, the objective is seldom to immediately impact human health (exceptions: CDC, pharma companies, infectious disease researchers and others do that kind of stuff). Influencing human health outcomes is the hopeful eventual goal of most health-related research, but individual studies and projects are not designed to be end-all conclusions. I'd be suspicious of studies that claim this. But, read the quote by a co-author on that article. Each research project is designed to fit as a piece of puzzle into the larger picture. If you read the article, the Harvard public health professor puts it best:
> “We need more evidence, especially from clinical trials, to further verify these findings,” said a co-author, Dr. Lu Qi, an associate professor of nutrition at the Harvard T.H. Chan School of Public Health, “and we are looking forward to seeing data from other populations.”