In nutrition, diet is the sum of food consumed by a person or other organism.

The word diet often implies the use of specific intake of nutrition for or reasons (with the two often being related).

Although humans are omnivores, each culture and each person holds some food preferences or some food taboos.

This may be due to personal tastes or ethical reasons.

Individual dietary choices may be more or less healthy.

A disease is a particular abnormal condition, a disorder of a structure or function, that affects part or all of an organism.

The study of disease is called pathology which includes the study of cause.

Disease is often construed as a medical condition associated with specific symptoms and signs.

It may be caused by external factors such as pathogens, or it may be caused by internal dysfunctions particularly of the immune system such as an immunodeficiency, or a hypersensitivity including allergies and autoimmunity.

Physiological or biological stress is an organism's response to a stressor such as an environmental condition.

Stress is the body's method of reacting to a .

Stimuli that alter an organism's environment are responded to by multiple systems in the body.

The autonomic nervous system and hypothalamic-pituitary-adrenal (HPA) axis are two major systems that respond to stress.

The sympathoadrenal medullary (SAM) axis may activate the fight or flight response through the sympathetic nervous system, which dedicates energy to more relevant bodily systems to acute adaption to stress, while the parasympathetic nervous system returns the body to homeostasis.

The second major physiological stress, the HPA axis regulates the release of cortisol, which influences many bodily functions such as metabolic, psychological and immunological functions.

The SAM and HPA axes are regulated by a wide variety of brain regions, including the limbic system, prefrontal cortex, amygdala, hypothalamus, and stria terminalis.

Through these mechanisms, stress can alter memory functions, reward, immune function, metabolism and susceptibility to diseases.

Definitions of stress differ; however, one system proposed by Elliot and Eisdorfer suggests five types of stress.

The five types of stress are labeled "acute time limited stressors", "brief naturalistic stressors", "stressful event sequence", "chronic stressors", and "distant stressors".

Food is any substance consumed to provide nutritional support for the body.

It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals.

The substance is ingested by an organism and assimilated by the organism's cells to provide energy, maintain life, or stimulate growth.

Life is a characteristic distinguishing physical entities having biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased, or because they never had such functions and are classified as .

Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria.

The criteria can at times be ambiguous and may or may not define viruses, viroids, or potential artificial life as "living".

Biology is the primary science concerned with the study of life, although many other sciences are involved.