In this special interlude, I lay down the framework of the five core principles that make a good marker of nutritional status. This is to lay down the framework for a series of podcasts in the future about managing nutritional status for specific vitamins and minerals. Since these core principles will be referred back to as a general reference in so many other episodes, this one has a special place outside of the sequence and you can reach it at any time with the easy-to-remember URL chrismasterjohnphd.com/interlude. This episode is brought to you by Kettle and Fire Bone Broth. Use the link kettleandfire.com/chris to get $10 off your first order. This episode is also brought to you by US Wellness Meats. Head to grasslandbeef.com and enter "Chris" at checkout to get 15% off your order as long as the final price is over $75 and you order fewer than 40 pounds of meat. You can use "Chris" to get the same discount twice. In this episode, you will find all of the following and more: 37:23 Cliff Notes 09:25 Purpose of this podcast and its place in the upcoming series on managing nutritional status; 11:54 What are the five core principles? 12:05 Principle #1: We understand its biochemistry and physiology; 15:04 Principle #2: It has been validated against changes in nutritional status; 17:17 Principle #3: Sensitivity; 17:52 Principle #4 Specificity; 19:45 Principle #5: It must be interpreted in the overall context of other markers and the clinical and health history, current signs and symptoms, and diet and lifestyle analysis; 23:20 Example of principle #1: Spectracell vs dp-ucMGP as tests of vitamin K2 status; 27:20 Example of principle #2: 25(OH)D vs. calcitriol; 29:20 Example of principle #3: transferrin saturation vs. ferritin 31:08 Example of principle #4: specificity of 25(OH)D and contexts where its specificity fails; 32:50 Example of principle #5: distinguishing between calcium and vitamin D deficiencies as causes of 25(OH)D by testing PTH, calcitriol, and analyzing the diet and lifestyle; 37:50 Shotgun approaches to nutritional testing; 40:30 Whether to act on leads from shotgun approaches should depend on the risks and other costs of the actions.