We'll start this module with the basics of nutrition and diet required for basic human functioning as well as good health. Nutrition basics start with the idea of a balanced diet, which should provide the essential nutrients for daily human activities, growth and tissue repair, and overall health, which have been demonstrated by years of research on human nutritional needs. Figure 3.1.1 shows one recent attempt to summarize this scientifically grounded view of a balanced diet in an accessible way as a "healthy eating plate". You'll notice that the sections addressing diet throughout module 3 will refer back to the concept of balanced combinations of nutrients from different food sources that create this balanced diet. It is also important to state that nutritional theories and the concept of the optimal diet have been somewhat changing over decades and centuries, which may give us reason to be careful about the certainty with which we hold to nutrition beliefs. See "High-quality fats and shifting paradigms around fat in diets [1]", further on in this module, on the changing attitudes from researchers towards different fat sources in human diets. Nevertheless, years of nutrition research up to the present have defined the requirements of a healthy diet that have been incorporated into the nutritional guidelines summarized in figure 3.1.1. and also published by the United States Department of Agriculture and other government agencies around the world.
What follows in the rest of module 3.1 is a summarized description of human nutritional requirements, intended to allow you to relate these to food systems as the source of human nutrition. Because of this, we will present both the requirements (e.g. vitamin A versus vitamin C versus amino acids) and also some major issues with particular nutrients that tend towards deficiency in many human populations and their related food systems. At the outset, we can already guide your learning by presenting an exceptionally simplified version of human nutrient needs that you will flesh out in the following pages. To a crude approximation, humans need the following components in their diets: energy, which in practice means carbohydrates, fats, and protein seen in relation to their energetic content; "building blocks" of growth and maintenance, which is generally protein linked to higher-protein foods but occurring within both the protein and whole-grain fraction of the healthy plate above; and promotion of health, proper development, and proper function, closely linked to vitamins and mineral intake. We'll delve into these elements of a balanced diet one by one in the following pages, and add a few details as well. An additional point that deserves mentioning now is the particular importance of proper nutrition for growth, mental development, and health promotion in children. Children are thus particularly vulnerable to nutrient deficiencies, and the consequences of deficiencies can be long-lived in their development into adulthood.
Carbohydrates (starches and sugars), fat, and protein within food can all function as sources of energy when they are metabolized to carbon dioxide and water in respiration processes in all of our body’s cells. This energy fuels everything from the production of neurotransmitters in our brains to the muscle contractions required to shoot a basketball or weave a basket. The energy content of food is expressed as “calories” (“calories” are in reality kcal or kilocalories as defined in chemistry; 1 kcal will heat one liter of water one degree C). Energy-dense foods with high caloric content are generally those with high carbohydrate, protein, or fat content - for example, pasta, bread, oatmeal, grits, and other cooked whole grains and porridges consumed around the world as staples; plant oils or animal lard present in cooked foods, or meat and cheese. It is interesting to note that gram for gram, fats contain over twice the energy density of carbohydrates or protein: about 9 kcal per gram for fats versus only about 4 kcal per gram for carbohydrates and protein. We’ll address the further role of high-quality fats as a nutrient, rather than just an energy source on a page further on.
Current U.S. Department of Agriculture (USDA) and other major nutritional guidelines promote the idea of accessing calories via a predominance of whole grains (e.g.. whole wheat and oats and flours made from these, brown rice) as these whole grains contain a mixture of carbohydrates, proteins, and indigestible fiber, as well as vitamins. These non-caloric contributions to nutrition are also important as discussed in the pages below, and combine well with the caloric content of food to produce better health outcomes. Calories are a fundamental consideration within nutrition because a negative calorie balance (calories consumed minus those expended in human sedentary activities and exercise) along with shortages of other associated food components described below leads to weight loss and faltering growth in children, including childhood stunting and permanent harm to a person’s developmental potential. By contrast, large excesses in a calorie balance over time lead to weight gain that is linked at a population level to increased rates of heart disease and diabetes. These diet-related diseases increasingly afflict populations in industrialized economies and urban populations worldwide with access to abundant, though often less healthy, food choices. Diet-related diseases as part of food systems will be taken up again in module 3.2.
The second main component conceptualized by nutritionists as a key ingredient of a healthy diet is protein, which is used in many different ways to build up and repair human tissues. Proteins are basically chains of component parts called amino acids, and it is these amino acids that are the basic “currency” of protein nutrition. Twenty amino acids are common in foods, and of these nine[1] are essential because humans cannot synthesize them from other nutrient molecules. Meat, fish, and eggs are animal-based and protein-dense foods that contain the complete profile of amino acids, basically because we are eating products that are very similar in composition to our own body tissues. In addition, some grains such as quinoa and buckwheat contain complete protein, while most legumes (peas, beans, soybeans, bean sprouts, products made from these) are high in proteins in a way that complements grains in the diet.
For people who do not eat meat (a vegetarian diet) or who avoid all animal-based foods (vegan diets), the full complement of amino acids are accessed by eating milk and egg products or by eating a diversity of plant-based foods with proteins such as whole grains, nuts, and legumes. Legumes are particularly protein-dense and important in addressing the lack of amino acids in other plant-based foods. The combination of rice and beans is an oft-cited example of the complementarity of amino acids for a complete amino acid profile. Eating a wide range of plant-based foods is an excellent strategy to access the full complement of essential amino acids, as well as the diversity of mineral, vitamin, and fiber needs discussed on the next pages. Many of the most problematic diets are those that are highly monotonous due to poverty and/or inadequate knowledge about diet, with an excess or a sole dependence on a single starch source without legumes or animal products, or overconsumption of processed foods in comparison to fresh plant and whole-grain foods. Where only a single grain is eaten, deficiencies of certain amino acids can result.
[1] These are phenylalanine, tryptophan, methionine, lysine, leucine, isoleucine, valine, and threonine, which you can find in many introductory nutrition texts or resources online, if further interested. A ninth amino acid, histidine, is important in child growth and may also be vital to tissue repair, while another, arginine is essential for some growth stages and can usually be synthesized by healthy adults.
In addition to the daily requirements for energy and protein, vitamins and minerals are required in relatively small amounts as part of a proper diet to ensure proper functioning and health and are especially important for childhood development. Vitamins and minerals deficiencies can lead to “hidden hunger”, where energy and protein needs are being met but the lack of vitamins and minerals prevents adequate development and health of child rent and saps the productive capacity of adults, for example via iron-deficiency anemia (see below). There are a large number of essential vitamin and mineral components in foods. In this module, we focus on a few that frequently pose major challenges within food systems. If you are interested, full details on the roles of many nutrients can be found in the excellent online text from the Food and Agriculture Organization (FAO) of the United Nations, Human Nutrition in the Developing World [4]. This module's formative assessment may also point to other vitamins and minerals that can become deficient in diets.
Although it is important for other functions, calcium is emblematic in its role in proper bone growth and maintenance. It is especially important for women to consume adequate calcium throughout life, and higher intakes of calcium from childhood on are associated with lower rates of osteoporosis and stronger bones later in life. Vitamin D is also essential for the proper absorption of calcium so that a vitamin D deficiency can lead to calcium deficiency. Dairy products and small fish that are consumed whole (so that fine bones are eaten) are highly calcium-dense foods around the world. Grains are low in calcium but are consumed in such volumes that they often contribute substantial calcium to diets. As is true for many other nutrients, women who are breastfeeding a child have an especially high calcium need because they export calcium in their breast milk to help grow the bones of a developing infant.
Iron is most important as an ingredient in hemoglobin that causes the red color of blood, and the role of red blood cells in carrying oxygen. Iron deficiency thus leads to anemia from a lack of red blood cells, including shortness of breath and overall weakness. Women require more iron than men because of blood loss in menstruation, and pregnant and lactating women require especially high amounts of iron as they expand their blood supply and provide for a growing fetus. During lactation or breastfeeding, mothers pass substantial amounts of iron to their growing infants, so that iron need for women is also high during the period when mothers are nursing their children. When shortage arises during pregnancy or lactation, a woman’s iron stores tend to be sacrificed to the benefit of the child, which can leave a mother who lacks adequate food due to poverty with acute iron deficiency and anemia that greatly complicates other daily activities such as economically important work. The best sources of iron in foods are meat, fish, eggs, green leafy vegetables, and whole grains. Cooking food cast iron utensils is also an easy way to supplement iron in food.
Zinc is an essential mineral that is important in a large number of human cellular enzyme processes. It is important for proper tissue growth, cell division, wound healing, and the functioning of the immune system, among other functions. As such it is very important for children’s health, growth, and development. Zinc is an example of a nutrient that is often used to fortify processed foods and is also naturally present in a wide variety of foods such as red meat, poultry, beans, nuts, and whole grains. One goal of plant breeders recently has been to breed or identify traditional varieties of whole grains and potatoes that are high in zinc and iron. This way of enhancing diets by way of the properties of crop plants is called a biofortification strategy. Because these staple foods are usually present even in the most rudimentary diets associated with extreme poverty, biofortification can be an effective strategy to ease access to these important mineral nutrients in the most vulnerable populations.
Vitamin A or retinol (linked to the word ‘retina’ or part of the eye) is famous for the popularized connection between eating carrots and good eyesight. Vitamin A deficiency is the cause of reduced vision in dim light, called night blindness, as well as a broad correlation to increased infant mortality in children from a variety of causes. True vitamin A is not in fact directly present in carrots and other dark green or pigmented vegetables (collards, squash, sweet potatoes, tomatoes, and even yellow maize) but is readily synthesized in the body from the orange pigment (beta-carotene) that these plant sources contain. True retinol is found in eggs as well as meat and fish products. Like zinc, vitamin A is another crucial nutrient for growth and development that can become deficient in the diets of children and other vulnerable groups (Figure 3.1.2), and has been targeted as a priority for resource-poor populations around the world through the promotion of orange-fleshed sweet potato, other orange vegetables, and yellow maize within smallholder diets and "golden rice" as a genetically engineered innovation in maize varieties that was developed to address vitamin A deficiency. While not all biofortification approaches utilize genetic engineering, golden rice is a further example of a biofortification strategy.
Vitamin C is not a major deficiency challenge worldwide, though in the 1700s vitamin C deficiency was linked to the disorder scurvy in sailors due to highly monotonous diets. Rather it is presented here because of its iconic association with fresh fruits and vegetables, especially citrus fruit but also potatoes, bananas, spinach, collards, cabbage, and many of the weeds that are consumed around the world as leafy vegetables. True deficiency is thus uncommon in most diets around the world, though vitamin C’s role as an antioxidant and health-promoting vitamin that “cleans up” harmful free radicals in the body has been promoted. Also, vitamin C is an excellent example of a positive interaction between nutrients. Vitamin C promotes iron absorption. Since most plant sources of iron are much less available than so-called heme iron in animal iron sources, fruits and vegetables with vitamin C in the same meal with plant-based sources of iron are an excellent way for people that eat meat-free diets (or just individual meals without meat) to absorb sufficient iron.
A number of other vitamins and minerals are essential, and in general, the way that a food system can work to provide these to human populations is to make a wide variety of plant-based foods as well as a few meat options, available to consumers. As we will see soon, this is in contrast to what certain sectors of the food system often make available to consumers. Some of these important vitamins and minerals are Vitamin C, Vitamin D, the B-complex vitamins, potassium, and magnesium, and you may see these arise as concerns in the formative assessment below.
A complete description of vitamins, minerals, and other diet components in an accessible format can be found in the online book from the FAO, Human Nutrition in the Developing World [4].
You may be familiar with the idea that fats are perhaps "delicious yet harmful" for most humans, and to be consumed in moderation (see the balanced plate in figure 3.1.1). Recently there has been increased attention focused on the role that “good fats” play in health and development, in addition to the awareness that most diets in more affluent areas of the world contain excessive fat, especially saturated fats of animal origin. Unsaturated fatty acids of plant origin are generally considered essential healthy nutrients, and there is evidence that fatty acids derived from plant sources and fish are important in promoting better neural development and nerve function. For consumers that tend to face food-insecure conditions, also, fats are a highly concentrated energy (calorie) source and therefore a valuable addition to a diet. Where calories are already in excess such as in many urban diets around the world and particularly in the industrialized first world, the calorie content is not a benefit of high-fat diets. Recently it has been found that excessively processed or hydrogenated fats often included in processed foods (trans-fats) are harmful to health, and so labeling now specifies the trans-fat content of foods. For example, you can find the trans-fat content of diets in the diet tool used with this module's formative assessment.
Fat in foods as a case study of shifting paradigms in nutrition
(this section is adapted from a contribution by Human Geographer Mark Blumler at Binghamton University)
Most of us have probably absorbed the current overall thinking that fat in diets needs to be treated with caution, that it is synonymous with "divine" or "sinful" food in a joking way, or perhaps that there is something suspect about fat. Because of evolving in limited nutrition environments, most humans are primed to take in fats and other high-calorie foods as a nutritional bonanza and store it away in an evolutionarily "thrifty" way to confront future calorie shortage. However, western nutrition scientists’ beliefs regarding different types of fat in diets have undergone drastic fluctuations over the past century (Table 3.1) that may potentially shake our confidence in exactly what is known about "good" and "bad" in nutritional terms. The advice coming out of the nutritional science community, as filtered through government proclamations such as the food pyramid, have also caused enormous changes in the American diet, which have benefited some such as the vegetable oil processing industry, while hurting others such as cattle ranchers and the beef lobby.
To recap this sometimes bewildering history: around the 1960s, scientists discovered a relationship between cholesterol and cardiovascular disease and noticed that saturated fats have more cholesterol than other oils. Consequently, there was a big push to replace butter with margarine and to cut back on the consumption of red meats, lard, and other animal fats. Initially, it was believed that polyunsaturated fats such as safflower oil are most heart-healthy and so there was a major promotion of such oils. Later, interest developed in the “Mediterranean diet” because of the presence of many very old people in Mediterranean Europe, and nutritionists came to believe that monounsaturated fats such as in olive oil were best for us. Polyunsaturated oils, on the other hand, were increasingly shown to be not beneficial. Meanwhile, further research showed that cholesterol in the blood does not correlate with cholesterol in the diet, undermining the assumption that saturated fats are unhealthy. Trans fats, high in margarine and other processed fatty foods, were shown to be very inimical to heart health. Also, fish oils were recognized as being high in omega 3 fatty acids, which are deficient in the typical American diet today. Recently, butter has been officially accepted as “good” fat, reversing a half-century of denigration of its nutritional value. While other saturated fats are not yet accepted, there is nothing to distinguish butter from the others that would explain how it could be “good” and the others “bad”.
Fat | 1900 | 1960 | 1970 | 1980 | 2000 | 2015 |
---|---|---|---|---|---|---|
Butter | Good | Bad | Bad | Bad | Bad | Good |
Egg Yolks | Good | OK | Bad | Bad | Bad | OK? |
Lard | Good | bad | Bad | Bad | Bad | Bad? |
Fish oil | Good | Good | Bad? | OK? | Very Good | Very Good |
Coconut oil | Good | Good | Bad | OK? | OK? | Good? |
Olive oil | Good | Good | OK | Best | Best | Good |
Safflower oil | OK? | Good | Best | Good | OK | ??? |
Margarine | - | Good | Good | Bad | Bad | Bad |
It is interesting to compare these shifting attitudes against traditional diets: The Japanese have the longest life span of any nation. Within Japan, the longest-lived are Okinawans. On Okinawa the only fat used for cooking is lard (of course, being on an island Okinawans also consume considerable fish oil although they do not cook with it). So, what is going on here? Why can science and scientists not "make up their minds" about fat in diets? Are findings on diet overly influenced by lobbying groups of major food industries, as some have charged for the case of margarine or dairy fats?
The story of fat recommendations illustrates the nature of science, that it proceeds piece by piece, and also seems to have a penchant for identifying single causes that are later shown in the context of a complex system to be overly simplistic. Each research finding, such as that cholesterol is associated with cardiovascular disease, may have been correct. But that gave rise to recommendations that were wrong, because other facts, such as that dietary cholesterol does not correlate with blood cholesterol, were not yet known. Given that many of us would like to eat healthy diets and may also believe that science should guide better nutritional policy, there is a need for principles that emerge from current science to inform dietary recommendations, rather than the confusion that is perhaps caused by this tangled story about the history fats in nutrition. In the summary below, we try to provide some ballpark recommendations regarding fats, other dietary constituents, and lifestyle choices. They summarize many of the same principles from the "balanced plate" at the beginning of this module or the "healthy plate" from the USDA and other nutritional recommendations of government organizations.
In addition to these nutrients that contribute to particular functions within the human body, fiber is the mostly undigestible component of food that moves through the human digestive tract but also provides remarkable benefits. Undigestible cell wall components of plant foods (fruit membranes, bean and grain seed hulls, most of the plant cell wall, etc.) are examples of dietary fiber. In addition to its famous role in avoiding constipation by moving masses of foodstuffs through the digestive tract as a bulking agent, fiber helps to feed beneficial gut bacteria that produce beneficial substances. Over the last few decades fiber consumption associated with the benefits of avoiding certain cancers, heart disease, and diabetes. Emerging knowledge regarding fiber highlights the role played by the gut microbiome --many billions of non-human cells that inhabit our digestive tract in promoting human health and avoiding disease. These cells are more in number than the human cells in our body, due to the small size of bacteria compared to human cells. Much like the other areas of nutrition described here, the importance of fiber links directly to the importance of eating a varied diet with whole grains, legumes, fruits, and vegetables. It is interesting to view fiber and these microbes not as a direct nutrient for human life processes, but as a "helper nutrient" or "catalyst" for human nutrition. Dietary fiber is relatively inert as a source of protein, minerals, or vitamins, but helps our digestive system do its job.
For more on the role of fiber and nutrition generally in an accessible format, you can see the following page: "Dietary Fibre" [5] from the British Nutrition Foundation.
In this assessment, you will use an online diet assessment tool to test how different foods contribute to the total nutrients in a daily diet. You will follow along in the instruction sheet, and log the nutrient content (e.g. calories, total fat, vitamin C) for each diet option in an excel spreadsheet, to be able to compare the diets.
Download both the instructions and worksheet [6] (word doc) and the excel spreadsheet [7] for logging the results. The spreadsheet has color-coding of cells to transform the data you log into a color that indicates deficiency or sufficiency, which will help you to interpret the result.
We will use the tool My Food Record [8] for this assessment. Important: you should use the "one-day analysis" under the "analyze" tab so that you do not have to create an account and can just log in as a guest. You should open this online nutrition assessment tool in an adjoining window or a different browser so you can see the instructions for the assessment and the online tool at the same time.
Please submit your assignment in Module 3 Formative Assessment in Canvas.
Links
[1] http://www.e-education.psu.edu/geog3/node/1199
[2] http://www.thenutritionsource.org
[3] http://www.health.harvard.edu
[4] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/Mod3/Human%20nutrition%20in%20the%20developing%20world%201997.pdf
[5] https://www.nutrition.org.uk/healthyliving/basics/fibre.html
[6] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/Formative_3.1_worksheet_Edit_August2016.docx
[7] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/FormEvaluation_Module3_1.xlsx
[8] http://www.myfoodrecord.com/