Food is considered, by Nutritionists, to be “any substance which
can provide nutrients.” Obviously, since humans require certain essential nutrients in their
diet, by both definitions of diet, 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 them 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 most 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. 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.
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 blood glucose levels. When blood 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. I sugggest that the hypothalamus also monitors other nutrients. As food is aborbed, the hypothalamus can trigger formation of subconscious memory of foods eaten and the nutritional consequences (or what nutrients were provided to the blood stream) [as well as how pleasant the taste was]. Then as nutrients become deficient in the blood stream, the hypothalamus can trigger 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. In the 1990's, there was an interesting study related to the issues of satiety causation. It was reported from a limited clinical trial that an increase in fatty acids in the blood stream 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].
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 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, measuring the heat produced in calories. 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. In a later lecture I will suggest that the minimum Calories required to maintain Human Life to be 800 Calories, because that is the lowest number I have seen for third world people without nutrient deficiencies. The lowest number I have seen for maintaining 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 “typical American” you are likely to become (or already be) overweight and will need to reduce your weight to maintain wellness, since being overweight has been identified as a major risk factor in a number of diseases which limit life expectancy and reduce quality of life.
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 later). 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 substances.
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 & 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 legislation creating income tax limits income tax collection by the IRS to individuals, so the IRS successfully created 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. Hence the USDA pamphlet describing the benefits of Concord grape juice was written by Welch's® (Welch Foods, Inc) [This does not say that the information in that pamphlet is not true, nor does it say that it is true].
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, the over-weight
population [including children] has risk factors for several disease processes, and places a
financial burden on the Health Care system (including insurance rates the acceptable weight
population has to pay for health insurance [and life insurance]). 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 are capable of maintaining a stable near average (or less, within
acceptable limits) weight, weight management is a simple matter: if you consume more Calories than
you burn, you will gain weight.
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, because of the Biology of weight loss. 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. This will be a superficial review, with the expectation that you, the student, will complete a more thorough examination of the needs and issues that affect you and your prospects for maintaining an acceptable quality of life for your entire life span.
TABLE OF CONTENTS
© 2004-2011 TwoOldGuys
revised: 22 Jun 2011