[thebrid]

Harvard's Nutrition Source web site [0] is the best source I've found. It has a wealth of evidence-based information. The accompanying book "Eat Drink and Be Healthy" discusses what features make a study reliable or not. The web site will be more up-to-date on specific dietary advice.

The Harvard School of Public Health are behind 2 of the biggest ongoing studies on diet, the Health Professionals Follow-Up Study[1], which has followed 50,000 men for over 30 years, and the Nurses' Health Study which has included 275,000 people over 40 years.

[0] https://www.hsph.harvard.edu/nutritionsource/

[1] https://www.hsph.harvard.edu/hpfs/

[2] http://www.nurseshealthstudy.org/