FOOD AND HUMAN NUTRITION: an introduction

HUMAN NUTRITION

An overview (by Wikipedia)

Human nutrition is the provision to obtain the materials necessary to support life.
In general, people can survive for two to eight weeks without food, depending on stored body fat and muscle mass. Survival without water is usually limited to three or four days. Lack of food remains a serious problem, with about 36 million people dying every year from causes directly or indirectly related to hunger.[1] Childhood malnutrition is also common and contributes to the global burden of disease.[2] However, global food distribution is not equal, and obesity among some human populations has increased to almost epidemic proportions, thus, leading to health complications and increased mortality in some developed and a few developing countries. Obesity is caused by consuming more calories than are expended, with many attributing excessive weight gain to a combination of overeating of "unhealthy" (high fat, high sugar, high carbohydrate) foods and insufficient exercise. A major risk of obesity is becoming a type 2 diabetic.

Nutritional science investigates the metabolic and physiological responses of the body to diet. With advances in the fields of molecular biology, biochemistry, genetics, the study of nutrition is increasingly concerned with metabolism and metabolic pathways: the sequences of biochemical steps through which substances in living things change from one form to another.
The human body contains chemical compounds, such as water, carbohydrates (sugar, starch, and fiber), amino acids (in proteins), fatty acids (in lipids), and nucleic acids (DNA and RNA). These compounds in turn consist of elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus, calcium, iron, zinc, magnesium, manganese, and so on. All of these chemical compounds and elements occur in various forms and combinations (e.g. hormones, vitamins, phospholipids, hydroxyapatite), both in the human body and in the plant and animal organisms that humans eat.

The human body consists of elements and compounds ingested, digested, absorbed, and circulated through the bloodstream to feed the cells of the body.
Studies of nutritional status must take into account the state of the body before and after experiments, as well as the chemical composition of the whole diet and of all material excreted and eliminated from the body (in urine and feces).
Comparing the food to the waste can help determine the specific compounds and elements absorbed and metabolized in the body.
The effects of nutrients may only be discernible over an extended period, during which all food and waste must be analyzed. The number of variables involved in such experiments is high, making nutritional studies time-consuming and expensive, which explains why the science of human nutrition is still slowly evolving.