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Human Nutrition Variation
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0:05
This is the Human Nutrition lecture and we are going to talk about quite a bit of different things that are related to nutrition, related to diet and how these things effect individuals but how they effect the overall variation between populations. So we are going to discuss human variation by looking at nutritional differences between populations. Diet and nutrition and understanding its role in human evolution is a very wide-spreading area of research.
0:48
Nutrition is something that represents the triad of those three components that contribute to variation that we discussed in the very beginning of the semester: culture, biology, and the environment. Nutrition is a great example of showing the interaction of these three things. It has not only affected our evolutionary history, when you think about period of time that nutrition has played a role in our biology (for example, the advent of agriculture, the
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fossil evidence for the beginnings of our species hunting for food). It also plays a big role in survival and reproduction. Not only that, nutrition is interesting in that it is one thing that can be drastically different between human populations, in terms of what is required for the survival of populations and the overall diversity in diets. These dietary differences between populations has evolved due to environmental circumstances
2:07
(what type of nutrition and/or food is available for a populations) and it has evolved due to culture (for example, think about the technological innovations for processing foods that differs between populations). So, for today we are going to begin by discussing the fundamentals of nutrition. I know that we often times just think of food or diet when we think of nutrition, but there are a lot more things that contribute to nutrition than just food.
2:50
This will lead us into the bulk of our discussion, which will be interpopulational variation in nutrition. Why and how do populations differ in their nutritional requirements? What evolutionary explanations do we have to help explain populational differences? What are the nutritional adaptations that have occurred due to human evolution? Humans and other animals require six different nutrients to sustain life. These include carbohydrates, protein, fats, vitamins, minerals, and water.
3:48
These nutrients are divided into 2 major groupings, macronutrients and micronutrients. Macronutrients are needed in large amounts and are highly critical for the body, while micronutrients are required in smaller amounts and play a bigger role in maintaining our everyday biological functions. The largest source of dietary energy for most humans in carbohydrates. This accounts for around 40-55% of our daily calories consumed among U.S. adults. There are 3 types of carbohydrates.
4:37
Monosaccharides are the simple sugars like glucose, fructose, and galactose. Disaccharides are sugars that are formed by the combination of 2 monosaccharides. Sucrose (which is the combination of glucose and fructose) is the most common and lactose (which is the combination of glucose and galactose), and is the sugar found in milk. Polysaccharides, often called NSPs, which stands for nonstarch polysaccharides are complex carbohydrates. These are a compound of 3 or more simple sugar molecules.
5:30
NSPs are not digestable to humans and passes through the GI tract as a dietary fiber. There are insoluble fiber NSPs and soluble fiber NSPs. The insoluble ones increase the bulk of ingested food and reduces the transit time for food to get through the GI tract, while soluble fiber NSPs are water soluble and therefore pass through the GI tract. They have been shown to reduce cholesterol levels in the bloodstream.
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Some of you may have heard of the Paleo lifestyle, which I honestly don’t know a great deal about, however, part of this diet is to restrict the insoluble fiber, since the biological makeup of our body isn’t made to properly digest them. Fats provide the largest store of energy in the body. They are divided into 3 main groups: simple, compound, and derived. Simple fats consist of triglycerides and fatty acids. Compound fats includes phospholipids and lipoproteins.
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These are important for blood clotting and for the transportation of fat in the bloodstream. Derived fats are synthesized from simple and compound fats. Cholesterol is the best known derived fat, and is necessary for normal development and function because it helps form tissues and organs during fetal development and also serves as a precursor in the synthesis of vitamin D. Proteins are essentially the compounds that we know as amino acids.
8:10
There are 20 different amino acids and 14 of these are known as ‘essential’ amino acids. Some of these can be synthesized in the body and some cannot be synthesized and therefore must be derived from food. The other 5 amino acids are known as nonessential because they can be produced by the body and do not have to be derived from the diet. Protein is very important component of maintaining adequate nutrition, but there is a balance
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between the body requiring a sufficient amount of protein and also requiring a protein that has sufficient quality. So, how do we know the requirements for adequate human nutrition? Well, I should first start by saying that the answer to this question is very complicated. There is a great deal of money and research that goes into answering this question. The answer to this question has also changed throughout the years.
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I’m sure you are all familiar with the food pyramid that tells us the appropriate proportion of food that we should be consuming. However, we know that through the years this pyramid has changed quite a bit and this is due to more research as well as cultural changes. To assess nutritional needs of human populations around the world, the World Health Organization is recognized as the voice for this. There are 2 standards that the World Health Organization evaluates: energy requirements
10:08
and nutrient requirements. I’m not som much concerned with knowing what the energy and nutrient requirements are, but I do want to briefly discuss how these are generally estimated. Estimating an individual’s daily energy requirements is determined by a number of things: basal metabolism, activity, thermoregulation, growth, reproduction, and these are just a few things that plays a role in a person daily energy requirements.
10:55
However, there is a recommendation of the WHO to assess human energy requirements. This is the standard procedure for adults. First, the basil metabolic rate (or BMR) is calculated. Remember, this is a calculation that provides the minimum amount of energy that is necessary for a person’s sustainability. This is calculated from body weight and based on a serior of age- and sex-specific predictive equations. Once BMR is calculated, the total daily energy expenditure (TDEE) is then calculated.
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This is based upon the individuals physical activity level index and is a reflection of the proportion of energy above BMR requirements that an individual spends over the course of a day. PALs are dependent upon the lifestyle of the individual, meaning do they have a sedentary or active lifestyle? PALs are also affected by energy costs for preproduction. In other words, there is a higher level of energy cost expected for a pregnant woman or a woman who is breast-feeding.
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So, lots of different factors are taken into account when estimating daily energy requirments. Also note that the estimates for children and adolescents is different than that of adults, which makes sense because children are using energy for proper growth. This changes throughout childhood and into adolescence. The energy demands for growth are higher early in life and slow down as the child reaches adolescence. Daily protein requirements have been established based on controlled studies.
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These studies monitor the amount of nitrogren (from protein) consumed and measures the amount excreted from the body. Currently for adults, it is recommended that to maintain safe levels of protein, .8 grams of protein per kilogram of weight should be consumed daily. This is substantially higher for children and adolescents since they, again, are in a period of rapid growth and development. This is a table taken directly from a textbook that shows the recommended protein intakes by age and sex.
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Notice that protein intake is the same for males and females up until the age of adolescence. It is the highest during infancy, when growth rates are highest. During later childhood (7-10 years of age) recommendations are lower, and then adult recommendations are beginning to be reached at the end of adolescence. You can also see that males require slightly more protein intake during adolescence than females.
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I should also note that there are other times during life that protein is required at higher rates, for instance, additional protein is required from women during pregnancy and lactation (with an increase in protein intake from the beginning of pregnancy to the end). Protein intake also must be adjusted for diets that do not receive protein from the consumption of meat, like vegetarians. The requirements for this type of diet must be adjusted.
15:18
Now that we have a basic, fundamental understanding of nutrition, I want us to move into our discussion of the inter-populational variation in nutrition. What are the major differences in nutrition that we see between populations and how can some of these differences be accounted for from our evolution as a species? Compared to other mammalian species, humans are unique in that we are able to survive and flourish on a remarkably wide range of diets and subsistence patterns.
16:05
Some of these can be accounted for due to the adaptations to distinct cultural practices. For instance, the various types of food being processed by native people of various regions has established “staple” foods for various populations. Some examples include processing corn in America, potatoes in South America, and soybeans in Asia. have developed techniques for processing corn in the Americas. Another thing that can account for the wide range of diets and subsistence patterns is
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simply human biological variation. There are interpopulational differences in BMR, ability to digest lactose properly, the ability to digest starches, and various metabolic adaptations. All of these examples reflect basic adaptations to specific dietary selective pressures that are now a part of human biological variation. So, for the remainder of this lecture we are going to discuss a number of examples of dietary
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variations between populations and how these variations have contributed to biological variations between populations. The first example is that of dietary intake and energy expenditure. These are two things that interact with one another, but human diets have a great amount of range in the human species, from completely vegetarian (a large number of populations in South Asia are vegetarian) to the other extreme, a diet that is almost entirely based on meat and animal foods.
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For example, Inuit populations have a diet that is heavy in meat consumption. On average, agricultural populations tend to have the lowest consumptions of animal foods. For many hunting and gathering populations, this is variable, primarily based upon where the population is located. The !Kung San, for example, have the lowest levels of animal food consumption among hunter-gatherer populations due to the very desert, arid environment that they occupy.
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Hunter-pgatherer Populations in the arctic, on the other hand, have diets that are rich in meat and rely on obtaining most of their daily energy from animal foods. Another variable aspect of dietary intake is macronutrient composition. Here is a table that shows the composition of macronutrient composition for various populations. As you can see, Americans, for instance, consume a lot less protein than foraging or herding populations.
20:14
Foragers and pastoralists consume less carbohydrates than Americans. In fact, the biggest difference in terms of diet between industrialized and subsistence-level societies is the type of carbs that are consumed. A large portion of the America diet consists of simple sugars or refined grain products. This contributes to a much more rapid increase in blood glucose levels. This process, over time, can lead to insulin resistance, where the body’s ability to
20:56
take up glucose from the bloodstream is limited. Insulin resistance contributes to type II diabetes, obesity, hypertension, and coronary heart disease. These are all things that are on the rise in America. It these differences in diet that contribute not only to variation in health but it can lead to variation that is genetically-linked. Another example of inter-population variation that is related to nutrition is that of energy expenditure and activity patterns.
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How we get our food, whether we grow it ourselves, hunt for it, or buy it, can have drastic impacts on the energy expenditure, which directly effects daily caloric needs and weight. Men in western populations, on average, are about 26 pounds heavier than men from subsistence populations, yet they have a caloric intake that is significantly less. Industrial societies also tend to have lower PALs. All of these factors contribute to the ongoing issues that I previously discussed on the last slide.
21:35
A lot of factors are contributing to a lot of the health factors that are prevalent in the U.S. when compared to other countries. Research has shown that BMR is correlated with mean annual temperature, meaning that it shown interpopulational variation. Populations occupying warmer climates have relatively lower metabolic rates, while those occupying colder climates have higher metabolic rates. What is interesting is that there is little understanding on the adaptive significance
22:09
of this and/or whether or not the population differences are due to genetics or some type of short-term acclimatization. Now that we have discussed some expamples of interpopulational variation, I want to briefly discuss the environmental and genetic factors that a play a role in producing interpopulation variation. Environmental factors play a huge role in contributing to the populational differences in nutritional adaptations.
22:50
I think one of the most prevalent nutritional transitions (especially seen here in the U.S.) is that of obesity. Environment, of course, plays a big role in this transition. Urbanization and rising incomes throughout much of the developing world has contributed to a shift in diet, to one that is higher in simple carbohydrates and fat. There is also the environmental/social aspect of a reduction in physical activity that is contributing to a steady increase in rates of obesity.
23:30
There is also evidence which shows that genetic differences contribute to the obesity trend. Today, our environment is sometimes referred to as obesogenic, which means that its an environment that is providing abundant food energy and requiring less work or activity to obtain energy. Our genes are therefore being introduced to new nutritional environments that are drastically different from the ones that our bodies became accustomed to in an evolutionary sense.
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So, some individuals are more susceptible to weight gain than others. However, keep in mind that this is not purely genetic, as weight is a polytypic trait. Therefore, variation arises only due to genetic and environmental interactions. Human nutrition and nutritional adaptation is a complicated component of variation to assess. Due to our evolutionary history and the fact that our subsistence patterns have changed
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throughout evolution, our adaptions to these changes are impacted by genetics and environment. Another factor that contributes to the assessment of nutritional adaptations is that there are clear differences between populations in their diet, nutritional requirements, and physical activities. All of these factors work together to contribute to nutritional variation. Don’t forget to read through the assigned article for the week.
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For this week’s article, you are going to read more about the genetic component of nutritional variation. It is a little heavy in the technical language, but I hope you can apply much of what we have discussed in lecture to the article.
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