A bidirectional cell signaling pathway that may regulate cell function, metabolism, or other aspects of physiology. Most signaling pathways are unidirectional. However, an axis may involve two or more signaling proteins and their secreting organs or cells in a type of feedback loop. For example, the growth hormone/IGF axis, also known as the Hypothalamic–pituitary–somatotropic axis, is a highly regulated pathway involving IGF-1 (produced by the liver), growth hormone (produced by the pituitary), and growth hormone-releasing hormone (produced by the hypothalamus).

A measurable substance in an organism that is indicative of some phenomenon such as disease, infection, or environmental exposure.

The practice of long-term restriction of dietary intake, typically characterized by a 20 to 50 percent reduction in energy intake below habitual levels. Caloric restriction has been shown to extend lifespan and delay the onset of age-related chronic diseases in a variety of species, including rats, mice, fish, flies, worms, and yeast.

One of the most potent natural activators of the AKT signaling pathway. IGF-1 stimulates cell growth and proliferation, inhibits programmed cell death, mediates the effects of growth hormone, and may contribute to aging and enhancing the growth of cancer after it has been initiated. Similar in molecular structure to insulin, IGF-1 plays a role in growth during childhood and continues later in life to have anabolic, as well as neurotrophic effects. Protein intake increases IGF-1 levels in humans, independent of total caloric consumption.

An essential mineral present in many foods. Iron participates in many physiological functions and is a critical component of hemoglobin. Iron deficiency can cause anemia, fatigue, shortness of breath, and heart arrhythmias.

A diet that causes the body to oxidize fat to produce ketones for energy. A ketogenic diet is low in carbohydrates and high in proteins and fats. For many years, the ketogenic diet has been used in the clinical setting to reduce seizures in children. It is currently being investigated for the treatment of traumatic brain injury, Alzheimer's disease, weight loss, and cancer.

An enzyme that participates in genetic pathways that sense amino acid concentrations and regulate cell growth, cell proliferation, cell motility, cell survival, protein synthesis, autophagy, and transcription. mTOR integrates other pathways including insulin, growth factors (such as IGF-1), and amino acids. It plays key roles in mammalian metabolism and physiology, with important roles in the function of tissues including liver, muscle, white and brown adipose tissue, and the brain. It is dysregulated in many human diseases, such as diabetes, obesity, depression, and certain cancers. mTOR has two subunits, mTORC1 and mTORC2. Also referred to as “mammalian” target of rapamycin.

Rapamycin, the drug for which this pathway is named (and the anti-aging properties of which are the subject of many studies), was discovered in the 1970s and is used as an immunosuppressant in organ donor recipients.

A chemical that causes Parkinson's disease-like symptoms. MPTP undergoes enzymatic modification in the brain to form MPP+, a neurotoxic compound that interrupts the electron transport system of dopaminergic neurons. MPTP is chemically related to rotenone and paraquat, pesticides that can produce parkinsonian features in animals.

The highest level of intake of a given nutrient likely to pose no adverse health effects for nearly all healthy people. As intake increases above the upper intake level, the risk of adverse effects increases.