Food is considered to be “Any substance eaten to provide
nutritional support for the body.
Obviously, since humans require certain essential nutrients in their diet, by both definitions of
diet (a plan for food intake, or a log of food consumed), the human diet must consist of foods.
Which foods and how much of each is one thing, among others, we hope you will learn from this
course. Those foods which are reasonably available are the “food supply.” The food supply
can be expected to vary by geography [grits are sometimes hard to find in the North, while Polish
sausage is uncommon in the South; more dramatically, American grocery stores do not normally stock
cats and dogs, yet some Southeast Asians consider tham to be normal human food] and by season
[although far less so in the 21st Century global marketplace]. It has been my observation
(therefore fact because it was observed) that many Americans perceive the food [and water] supply to
be unlimited, yet the prediction that the human population will ‘soon’ exceed the World's
agricultural capacity seems to be an annual event [usually around the celebration of Earth Day]. The
most famous such prediction was made by Malthus, a contemporay of Charles Dickens. Dickens even
refers to Malthus in A Christmas Carol when Scrooge says of the poor that they should
“die and decrease the surplus population.” The earliest reference to overpopulation
relative to food supply which I have found is Pliney, the Elder, in 33 BC [we know it was 33 B.C.,
because Pliney wrote the date quite clearly: “in 33 B.C.”]. In some parts of the World, the
food supply is far from endless, with sarvation locally wide-spread. So in parts of the World, food
is plentiful and, in other parts insufficient to sustain health or even life. The term “food
security” has been introduced to describe the reliability of the food supply. Food security [or
high food security] implies that there is a sufficient food supply to support an active and healthy
life, at least for everyone who can afford to buy food. Food insecurity [or low food security] occurs
when the food supply is either limited [insufficient, including too expensive for everyone to buy
their share] or uncertain [as in going to the grocery store without knowing whether or not there
will be food for sale]. I would suggest that it would be useful to add to the concept of food
supply that it should include the types of food [based on nutrient content] available, and the
quantities of each type in the supply.
Historically, or perhaps more accurately pre-historically, the food supply for the entire human species was seasonally uncertain. Once the growing season was well under way, hunting and gathering was relatively easy, because the food supply was in excess of what we needed, although we sometimes had to compete with other animals to get our share. As the growing season was ending, the food supply became steadily more limited. With the onset of winter, food became scarce. We developed several superstitions to account for this uncertainty, until we finally figured out that there are seasons that repeat on regular cycles, after which we learned to horde food to provide meals during the off seasons. Eventually we invented agriculture and food storage technology, such as storage facilities that could be somewhat protected from other animals, so we could grow and save surplus food for the off seasons. After the Industrial Revolution, we developed transportation infrastructure allowing transport of food long distances [from regions with short winters to regions with long winters]. Now we can transport foods between the northern and southern hemispheres, so effectively we have year-round growing seasons.
Appetite and Hunger describe “the drive to eat;” while
satiety describes the cessation of the drive to eat.
Appetite is “the desire to eat,” (text, pg. 8-9) or a
psychological drive to eat. Appetite may increase by thinking about food, hearing descriptions of
food, hearing sounds of food preparation or smelling food preparation, by circumstances normally
associated with eating (such as movies and popcorn, or watching television [probably related to
the movies], or for some people stress). I have successfully induced appetite in students by
suggesting the sounds and smell of coffee brewing and bacon frying, adding the image of a stack
of pancakes with butter melting on them and syrup flowing off the stack and onto the plate.
Hunger, on the other hand, is the physiological sensations that lead
people to acquire and ingest food (paraphrased from text pg 8-9). It has been shown that the
hypothalamus monitors blood temperature and serum glucose levels. When serum glucose drops below
a threshold, hunger is triggered.
It has been suggested that a genius, such as Einstein, uses only 10 -15% of his brain. Since I don't like the idea of owning useless body parts, I have hypothesized that some other functions must keep the other 85 - 90% of the brain amused. One of these is the management of hunger. The hypothalamus can monitor the serum concentration of nutrients other than glucose, and trigger subconscious memory of foods eaten and nutritional consequences [as well as how pleasant the taste was]. This would involve using part of the 85 - 90% of the brain not used for conscious thought. [I personally would not want such a large fragile brain encased in a heavy cranium creating balance problems unless I can use more than the 10 -15% used during thinking.] Then as nutrients become deficient in the serum, the hypothalamus triggers the brain to search the subconscious memory for foods that supplied those nutrients [and how good they tasted], so the brain can “crave” those foods which supplied those nutrients [and were pleasant to eat]. This would provide an “intuitive” correction of nutrition status in our caveman ancestors, who did not have a food guide pyramid to guide them in proper diet. Without some intuitive nutrition guidance, we probably would have failed to survive long enough to reproduce, leading to the early extinction of our species. As far as I know, we did not become extinct as cavemen.
Satiety is the cessation of the drive to eat. Most texts suggest that this is driven primarily by distention of the stomach during eating, and more recently [mostly in ads for weight control programs] both driven by and blocked by hormones produced by adipose tissue and/or by stress. Within the last decade, there was an interesting study related to the issues of satiety causation. It was reported from a limited clinical trial that an increase in serum fatty acids causes the hypothalamus to trigger satiety (by producing one of the hormones that adipose is claimed to produce).
Since the 1950’s, the USDA [United States Department of Agriculture] has published dietary guidelines, as the “Food Guide Pyramid.” The USDA has attempted to simplify these guidelines and, in 2011, published new guidelines titled “My Plate.” The USDA is now requesting that website owners “Join MyPyramid’s online campaign by placing this graphic link on your website.” The major change is to a more user-friendly image, showing a divided plate, with plate divisions sized to suggest the amounts of each food type [fruits, vegetables, grains, & protein], plus a circle to the side for dairy [like a glass of Milk]. For students in this course, I suggest that you use the link to their “For Professionals” to get suitable materials for patient education.
Biological individuals must spend energy merely to remain alive for 24 more hours. Warm-blooded animals spend more energy than cold-blooded animals and plants, due the necessity of maintaining a reasonably consistent internal body temperature. Specifically, for humans, the metabolic cost of living one more day is between 800 and 1,000 Calories. A Calorie, with a capital “C”, or dietary calorie is a kilocalorie [1,000 calories, with a small “c”, or scientific calorie]. But nobody on a diet [in the sense of a plan to lose weight] wants to eat only 1,000,000 calories per day! A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 Celsius degree starting at 20 °C. We determine the calorie content of food by burning a sample in a bomb calorimeter [pronounced “cal-o-rim'-e-ter”]. The bomb calorimeter is two halves of a hollow steel ball that screw together, and enclose a platform for the sample and electrodes for sufficient electricity to burn the sample to ash. The ball is immersed in a known quantity [in grams] of water at 20 °C. The water temperature after ashing the sample is measured to calculate the number of calories released. All foods, and many non-foods contain calories. This, however, does not tell you how many Calories are available for metabolic processes, because only some of these Calories will be used to maintain Life or to engage in exercise. Earlier (above) I suggested that the minimum Calories required to maintain human Life is 800 Calories, because that is the lowest number I have seen for third world people without clinical nutrient deficiencies. The lowest number I have seen for maintaing a good quality life, as opposed to merely existing, is 1,000 Calories. The USDA used the 1,000 value in the 1950's, yet four methods of estimating minimum Calorie needs from Nutrition textbooks yield numbers in the 1300 - 2000 range. By one method, a 158-pound, 5-foot 11-inch adult male with 18.5% body fat, would need “only” 9,762 Calories per day for basal metabolism plus ADL's [Activities of Daily Living], although 1,200 Calories is more realistic. Your text quotes (pg 8-4) 1,350 Calories for a 135-pound adult female and 1,870 Calories for a 170-pound adult male just for basal metabolism [the “energy required to maintain normal body functions while at rest” (table 8.1 pg 8-3)]. Based on my library research on this subject, the value for females is about 135% of actual, and the male is about 187% of actual; so why is the American population becoming increasingly overweight? I will revisit this question repeatedly throughout this course because as a health care professional you will, without any doubt, encounter overweight patients who need to reduce their weight to maintain wellness.
If I were reading [rather than writing] this, I would infer from the definition of food above that
food is digested to “nutrients,” but other than that “humans require certain essential
nutrients in their diet” I might not be clear about what a nutrient is. For those of you who
are taking notes… By the way, for those of you not taking notes, you should be. Yes, I know
this is on-line and you can reread it as many times as you want. Did you know that you retain [as in
long-term memory] only 20% of what you read (or hear), but more like 60% of what you write?
Assuming you are here [in my virtual world] on a quest for knowledge, your notes as written by
you will improve your odds of success. Meanwhile back at the ranch, I was complaining that reading
these lectures so far has left me uncertain as to what the writer [me] means by nutrient. This
illustrates why we like to define our terms. Had I defined nutrient sooner, you probably would
have some idea about that of which I speak. A nutrient is “any
chemical substance that is necessary for the proper function of the body, yet is not made in
sufficient quantities (if at all) by the body.” Since nutrients are chemical substances, we
can classify them on the basis of their chemical characteristics into the following six classes:
♦ carbohydrates (can be digested to saccharides, such as glucose)
♦ lipids [fats & oils] (can be disgested to fatty acids)
♦ proteins (can be digested to amino acids)
♦ vitamins (are not digested, but absorbed intact)
♦ minerals (must be bio-available)
♦ water (is a solvent)
Nutrients can also be classified on the basis of their function, or role in metabolic processes:
Based on the physiology of energetics in living systems, the only sources of energy are
carbohydrates and lipids (and, in plants, sunlight). Protein is an energy source of last resort
(you will learn why in the lecture on protein). Protein provides the building blocks for growth
and development (including repair). Those chemicals manufactured in the body to regulate
metabolism (enzymes and hormones) are derived from dietary protein and lipids. Vitamins and
minerals appear to be involved in regulating metabolism, but are not manufactured in the body,
or are manufactured in smaller quanities than are needed. Water is the solvent used to transport
nutrients and waste (metabolic byproducts), and the fluid medium of transport for insoluable
A few other chemical substances, for example, phytochemicals (and other herbal products) have been hypothesized to limit or repair damage to cells. If this can be shown to be true in clinical testing, we may see additional nutrients added to dietary guidelines. Until then, we must, as scientists, remain skeptical of these claims.
Those nutrients which have been proven in numerous clinical tests to be necessary for proper metabolic function, and which humans produce little or none of naturally are called essential nutrients. Nutritional needs vary with age, sex, growth status, body mass, genetic traits; plus pregnancy (including pre-pregnancy) & breast-feeding, illness, drug use, environmental contaminants. Governments, for example United States and Canada, publish nutrient intake standards, based mostly on reasonably current research. I say “mostly” here because the United States publishes their standards as regulations. U.S. regulations are first published in draft form in the Federal Register, for public comment. Any individual may comment on any proposed regulations, where “individual” includes corporations, because the law authorizing a tax on income limits the imposition (and collection) of this tax to individuals, so the IRS successfully enacted regulations declaring corporations to be individuals so they can be taxed. Since corporations are considered to be individuals by one Federal agency, they are individuals for all Federal agencies. As such, they may, and do, comment on proposed Federal regulations. As a result, those corporations with vested interests in promoting their products [such as National Dairy Council, National Pork Producers Council, National Cattlemen's Beef Association, American Egg Board, etc.] routinely comment on all regulations concerning the quantities of their products recommended in the guidelines. You also should know that the USDA (U. S. Dept of Agriculture) “publishes” informative pamphlets written by individuals, but neither authored by, edited by, nor approved by the USDA.
The current nutrient intake standards in the United States are grouped into 5 categories as follows:
DRIs: Dietary Reference Intakes, based on clinical research
RDAs: Recommended Dietary Allowances, based on large data sets
AIs: Adequate Intakes, hypothesized values
EARs: Estimated average requirements, based on large population data sets
ULs: tolerable Upper Levels of intake, based on large data sets, or clinical trials
Note that only DRIs and some ULs are based on clinical research, and that AIs are based solely on opinion. The RDAs, EARs and some ULs are statistical estimates from large data sets.
Unless you have been pretending to be a caveman, you are probably already aware that there has
been a steady increase in the weight of the average American. I need to remind you that
statistically an average is a better estimate than are the individual
weights of many Americans, and not that there is such a thing as an average American [the
average American would be about 50% male and 50% female, an individual I have not met]. Still, as
a health care professional, you will have to deal with an over-weight population [including
children], and will need to know more than a little about how to help this population. It has also
been reported that the “westernization” of international diets has contributed to
over-weight populations throughout the World, except in Third World countries where starvation
is still the major issue. For those of us, such as me, who have been able to maintain a stable
weight which is somewhat less than “normal [average] weight” for several decades, weight
management is a simple matter: if you consume more Calories than you burn, you will gain
The bad news for the rest of the world is that weight management is difficult and requires a lifetime commitment to maintaining wellness. The worse news is that, for the over-weight population, as you begin to lose weight, it becomes more difficult, not easier, to lose more weight. A quick check of the the outline will reveal that we will spend two full lectures on weight management. We will look at three different models for predicting weight change, and will cover both sides of the energy balance: Calories ingested, and Calories expended.
Assuming we can consider weight gain to be a form of eating disorder [not recommended], we could discuss it as a psychological disorder, but this turns out to enable the severely over-weight to continue their behaviors that caused them to become over-weight. We will also consider the classic examples of eating disorders; those involving obsessive or impulsive under eating, with potentially severe nutritional consequences, including death.
Finally, we shall review the changing nutritional needs and issues through the typical life span of a human [from maturing egg (which has a yolk to store nutrients for the embryo it hopes to become before it implants, becomes a fetus and draws its nutrients from the maternal serum) to the elderly ‘until death do they depart’]. This will be a superficial review, with the expectation that you, the student, will complete a more thorough examination of the needs and issues for the population [by age] that you expect to deal with primarily during your career in health care, or the individual whose diet you will be assessing as your final exam.
TABLE OF CONTENTS
© 2004-2011 TwoOldGuys
revised: 22 Jun 2011