Nutrition is a science which
studies the relationship between diet and states of health and disease.
Dieticians are Health professionals who are specialized in this area of
expertise. They are also the only highly trained health professionals able to
provide safe, evidence-based and accurate dietary advice and interventions.
Between the extremes of optimal
health and death from starvation or malnutrition, there is an array of disease
states that can be caused or alleviated by changes in diet. Deficiencies,
excesses and imbalances in diet can produce negative impacts on health, which
may lead to diseases such as scurvy, obesity or osteoporosis, as well as
psychological and behavioral problems. Moreover, excessive ingestion of
elements that have no apparent role in health, (e.g. lead, mercury, PCBs,
dioxins), may incur toxic and potentially lethal effects, depending on the
dose. The science of nutrition attempts to understand how and why specific
dietary aspects influence health.
Nutrition is the body of science
that seeks to explain metabolic and physiologic responses to diet. With
advances in molecular biology, biochemistry, and genetics, nutrition is
additionally developing into the study of integrative metabolism, which seeks
to connect diet and health through the lens of biochemical processes.
The human body comprises chemical
compounds such as water, amino acids (proteins), fatty acids (lipids), nucleic
acids (DNA/RNA), and carbohydrates (e.g. sugars). These compounds in turn
consist of elements such as carbon, hydrogen, oxygen, nitrogen, and phosphorus,
and may or may not contain minerals such as calcium, iron, or zinc. Minerals
ubiquitously occur in the form of salts and electrolytes. 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 organisms (e.g. plants, animals) that humans eat.
The human body necessarily
comprises the elements that it eats and absorbs into the bloodstream. The
digestive system, except in the unborn fetus, participates in the first step
which makes the different chemical compounds and elements in food available for
the trillions of cells of the body. In the digestive process of an average
adult, about seven litres of liquid, known as digestive juices, exit the
internal body and enter the lumen of the digestive tract. The digestive juices
help break chemical bonds between ingested compounds as well as modulate the
conformation and/or energetic state of the compounds/elements. However, many
compounds/elements are absorbed into the bloodstream unchanged, though the
digestive process helps to release them from the matrix of the foods where they
occur. Any unabsorbed matter is excreted in the feces. But only a minimal
amount of digestive juice is eliminated by this process; the intestines reabsorb
most of it; otherwise the body would rapidly dehydrate; (hence the devastating
effects of persistent diarrhea).
Study in this field must take
carefully into account the state of the body before ingestion and after
digestion as well as the chemical composition of the food and the waste.
Comparing the waste to the food can determine the specific types of compounds
and elements absorbed by the body. The effect that the absorbed matter has on
the body can be determined by finding the difference between the pre-ingestion
state and the post-digestion state. The effect may only be discernible after an
extended period of time in which all food and ingestion must be exactly
regulated and all waste must be analyzed. The number of variables (e.g.
'confounding factors') involved in this type of experimentation is very high.
This makes scientifically valid nutritional study very time-consuming and
expensive, and explains why a proper science of human nutrition is rather new.
In general, eating a variety of
fresh, whole (unprocessed) foods has proven hormonally and metabolically
favourable compared to eating a monotonous diet based on processed foods. In
particular, fresh, whole foods provide higher amounts and a more favourable
balance of essential and vital nutrients per unit of energy, resulting in
better management of cell growth, maintenance, and mitosis (cell division) as
well as regulation of appetite and energy balance. A generally more regular
eating pattern (e.g. eating medium-sized meals every 3 to 4 hours) has also
proven more hormonally and metabolically favourable than infrequent, haphazard
food intake.