I feel the need to preface this post to implore that no piece of research, thought, post, blog or authority is infallible. As with everything, approach with caution, read critically, keep an open mind and question question question.
Bad Science: Not specifically related to health and fitness per se, but a good blog that draws attention to the need to be critical and open minded when presented with research findings.
Fat Head: The blog of the movie 'Fat Head' a rebuttal of the docu-movie Supersize Me.
Hyperlipid: Provides critique of mainstream 'high carb' 'low fat' research and commentary on important nutritional issues.
Junkfood Science: Critical analysis and commentary of health and diet issues from a medical perspective.
Livin' La Vida Low Carb: Blog on low carb living; also provides commentary and critique of mainstream research.
Mark's Daily Apple:The blog of the Primal Blueprint's creator Mark Sisson. For all information relating to the Primal Blueprint diet and lifestyle.
Son of Grok: A primal living blog with some interesting looking primal recipes.
What if it's all been a Big Fat Lie? / The Soft Science of Dietary Fat (both articles by Gary Taubes)
Intermittent Fasting 101: Info on how to fast, the benefits of fasting and the research behing fasting.
Paleo in a nutshell part 1 / part 2
The Quality of Calories: What Makes Us Fat and Why Nobody Seems to Care (Gary Taubes' UC Berkeley Lecture)Forums:
Active Low-Carber Forums