Good and bad nutrition research:

My purpose here is to definitively (wherever possible) or tentatively (where the data are incomplete or nonexistent) answer a series of key questions about adult human nutrition using relevant rigorous scientific principles and methods. The data clearly show that much current advice about dietary pyramids, food supplements, megavitamins, and weight loss regimens is frequently unproven, erroneous, or even harmful and is often based on pseudoscience or derivative incorrect professorial opinion.

Bottom line:

First, a healthy person (given RDA intake of the substances in Table 1) can proceed with a normal (see below), stable weight by eating predominantly fat or carbohydrates or protein or various combinations of these because of the body’s ability to interconvert and utilize carbohydrates, fats, and proteins (amino acids) as needed. In other words, fat, carbohydrate, or protein can serve as the principal source of calories.

Second, the body has a remarkable ability to maintain relatively constant blood levels (homeostasis) of many nutrients. Even more remarkable is the ability of the central nervous system, testicles, and ovaries to maintain nutrient homeostasis. For example, in two carefully studied cases, even huge fluctuations in (orally) ingested potassium or vitamin C barely changed the concentrations of these substances in cerebrospinal fluid (CSF) or the brain. We now understand the biochemical, molecular, and genetic bases for such remarkable homeostasis in the CSF and brain. This has profound implications for attempting to prevent cognitive decline with certain nutrients as discussed below.