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Obesity, Diabetes, and Lactose-Tolerance: A Summary of Human Nutritional Evolution

will-leonard3

The Author of this chapter, William R. Leonard, is currently a professor of anthropology at Northwestern University. He holds the title at this university as the Abraham Harris Professor of Anthropology. He He received his PhD from the University of Michigan in 1987. His research interests include biological anthropology, adaptability, growth and development, and nutrition focusing on populations in South America, Asia, and the United States. His most recent publication was on the topic of precursors to over-nutrition and the effects of household market food expenditures on body composition among the Tsimane in Bolivia.

The ecological variation of available food has been an important factor throughout the history of human evolution and continues to shape the biology of traditional human populations today. The relationship that humans share with their environments (i.e., acquisition and expenditure of energy) has adaptive consequences for both survival and reproduction. Humans are similar to other primates in that we are omnivorous (i.e., we eat both plants and animals) and we have nutritional requirements (e.g., the inability to synthesize vitamin C) that has caused us to adapt diets that include large quantities of fruit and vegetable material. However, what is unique to humans is our highly diverse diet (i.e., dietary plasticity) that evolved because of cultural and technological innovations that developed for processing various resources. This has allowed humans to expand into the many different ecosystems that we inhabit today.

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In order tomaintain our health, humans require six classes of nutrients:

(1)   Carbohydrates are the largest source of dietary energy for most human groups. For example, carbs account for about 40-50% of the daily calories of U.S. adults. There are three type of carbohydrates including monosaccharides (i.e., simple sugars), disaccharides (i.e., sugars formed by two monosaccharides), and polysaccharides (i.e., complex sugars made up of three or more monosaccharides).

(2)   Fats are the most calorically dense source of dietary energy and provide the largest store of potential energy for the body to do biological work. Fats are divided into three groups. The first, simple fats, is mostly made up of triglycerides (i.e., glycerol and fatty acid). Fatty acids can be further divided into saturated (i.e., found in animal products) and unsaturated fats (i.e., monounsaturated and polyunsaturated mostly found in vegetable oil). Compound fats are the second type of fat that consist of a simple fat in combination with another type of chemical compound, such as a sugar or a protein. Compound fats are important for blood clotting and insulating nerve fibers. The third category of fats is known as derived fats, which are a combination of simple and compound fats (e.g., cholesterol). Cholesterol is important for normal development and function. It is also a precursor in the synthesis of vitamin D and hormones like estradiol, progesterone, and testosterone.

(3)   Proteins are an important energy source, but they are also crucial for the growth and replacement of living tissues. In order to get theadequate nutrition per day a person needs a sufficient quantity and quality of protein. The digestibility and amino acid composition determine the quality of a protein. Complete proteins have the necessary amino acids in the quantity and proportions that are needed to maintain healthy tissue repair and growth. Good sources of complete proteins come from animal foods including eggs, milk, meat, fish, and poultry. Incomplete proteins are those that lack one or more essential amino acids. Incomplete proteins are found inplant foods, such as grains, legumes, seeds, and nuts. So if you want to be a vegetarian it will require combining different sources of plant foods in order to get all of the essential amino acids you need.

(4)   Vitamins are not a source of energy, because they just help the body use energy and carry out other metabolic activities. There are two categories of vitamins: water-soluble vitamins (i.e., B vitamins and vitamins C are needed on a daily basis because they are not stored in the body) and fat-soluble vitamins (i.e., vitamins A, D, E, and K are stored in the body so they don’t have to be taken every day). Be careful because if you take too many fat-soluble vitamins over a long period of time it can be toxic.

(5)   Minerals, such as iron, are inorganic elements that are needed in many biological molecules (e.g., hemoglobin) and are vital formaintaining various physiological functions.  

(6)   Water makes up a large portion of our body weight at 40-60% for adults. Humans get water from liquid intake, food, and “metabolic water” that is produced as the result of energy-yielding reactions.

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Recent research has focused on developing and refining energy and nutrient requirements for the various human populations around the world. Many factors must be considered in order to efficiently estimate a person’s daily energy needs including diet, daily activities and exercise, energy costs for reproduction, sex and age. According to the World Health Organization (WHO), women who are pregnant need an extra 85 kcal/day during the first trimester, an extra 285 kcal/day during the second trimester, and an extra 475 kcal/day during the final trimester. Children’s and adolescents’ energy requirements are measured differently from adults, because they have extra energy costs that are associated with growth. Pregnant women, children and adolescents also require more protein than the average adult.

The dietary patterns and metabolism of humans has been shaped by the energy demands of our relatively large brain. The energy demands of humans are usually divided into maintenance energy (i.e., needed for day-to-day survival) and productive energy (i.e., needed for growth and reproduction). Humans spend a larger portion of their daily energy budget on brain metabolism when compared to other organs in the body. We use 20-25% of our BMR (basal metabolic rate) on brain metabolism compared to the 8-10% used by primates and only 3-5% used by other mammals. It has been hypothesized that because of the high metabolic costs of our brains we require high-quality diets. Animal foods contribute to about 45-65% of the diet amonghunter-gatherers, which is much higher quality than expected for primates of our body size. Humans also have small gut volumes for our size, because most large-bodiedprimates have large intestines for digesting fibrous, low-quality diets. So, we probably evolved to have smaller intestines and a reduced colon because of our high-quality diets.  

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Throughout the evolution of the different hominin species there has been changes in brain and body size. The australopithecines had smaller brains relative to their body size, but with the emergence of the genus Homo there was a dramatic increase in brain size. The body size of Homo erectusalso increased, but the changes of the brain size were much larger than those that occurred with body mass. Homo erectus had a larger brain and body but smaller teeth, which suggests that this species relied on a different subsistence source than the australopithecines that was probably easier to digest (i.e., less fibrous plant foods) and richer in calories. The greater nutritional stability of the genus Homo provided the fuel for the energy demands of their larger brains.   

While Humans do have a diverse range of diets across the world, environmental pressures have contributed to adaptations such as lactose tolerance and the ability to digest starch. Some adaptations have become maladaptive in modern society, such as increased fat storage, which has lead to increasing rates of obesity. The amount of animal foods (meat, eggs, milk, etc.) varies across cultures and geographic location. Contemporary foraging groups consume animal foods for approximately 45-65% of their diets. However in the US our animal foods consumption is approximately 26% of our diet. Macronutrient consumption also varies across populations. Americans derive 15% from protein, 34% from fat, and a very high 51% of their energy from carbohydrates. This carbohydrate % is higher than every other population except for small-scale farmers. Another interesting statistic is the estimated consumption percentages estimated for modern foragers: 20-31% protein, 38-49% fat, and 31% carbohydrates. What do you think about these forager percentage estimates in comparison to American percentages?  

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Carbohydrates consumed in subsistence-level societies are typically more complex with a small percentage of their carb consumption coming from simple carbs. American carbohydrates however come mostly from simple carbs and processed grains. These simple and processed carbs are absorbed faster into the blood stream than more complex varieties. A high glycemic level in the blood stream may lead to insulin resistance, which may lead to obesity, type II diabetes, hypertension, hyperlipidemia, and coronary heart disease. In comparison to subsistence-level populations, industrialized men weigh approximately 26.5 lbs more and require 150-200 kcal less. Industrialized women weigh 17.7 lbs more and demand approximately 90kcals. The US Department of Health and Human Services has also released guidelines that adults do approximately 150min/week of moderate physical activity. Another recommendation by IOM set the bar higher at 1 hour/day.

Another interesting fact from later on in the chapter is associated with the enzyme amylase. Carbohydrate digestionbeings in the mouth with amylase (enzyme found in saliva). Populations with high-carb diets have more copies of the AMY1 gene and therefore more amylase. So differences in dietin recent human evolution have exerted strong selection at the AMY1 locus. Also humans have three times as many AMY1 genes as chimps and bonobos. This implies that there was strong evolutionary selection on this gene during the early divergence of hominins from apes.

Food processing techniques are developed to fit the needs of the subsistence-level society that grows that particular crop. Corn, a major crop in the Americas, is high in protein but low in the amino acids lysine and tryptophan as well as the B vitamin niacin. To solve this problem, corn is processed in the presence of alkaliproducts (e.g., ash, lime, and lye) adding back these key nutrients. Andean populations processed potatoes in a way that removes the hazardous glycoalkaloids. Also, Asian populations processed the antitrypsin factor out of soybeans.

Climate may also have an effect on metabolic rates. Studies show that populations living in warmer climates have a lower metabolic rate than those living in colder environments. This attributes to a variation in dietary needs in different climates. It is being questioned whether these population differences are genetic or part of acclimatization.

lactose-intolerance

The ability to digest lactase disappears after weaning for most mammals, however some human populations have developed the ability to digest lactose and are thus lactose-tolerant. This change is a relatively recent evolutionary event occurring within the last 10,000 years. Genetic analysis shows that selection for the lactase persistence appeared about 7500 years ago. The allele spread across Europe in association with dairy/farming subsistence. It also appears to have evolved independently in some African populations approximately 6000-7000 years ago. However, some malabsorbers (genetically intolerant) people are able to digest lactose, and some genetically tolerant people are unable to digest milk. This suggests that dietary habits during development may contribute to lactose tolerance. In the malabsorbers this is due to an increased tolerance in the colon instead of an increase in lactase (enzyme that digests lactose. Life tip:If it ends in –ase it is an enzyme).

African-Americans have an increased risk of cardiovascular diseases. One model says that the problem is a consequence of genetic adaptation for efficient sodium (Na+) storage. Na+ is readily lost in sweat and was rare in many tropical societies. These groups have lower sweat rates and lower sodium concentrations in their sweat than European control groups. Now with salt being readily available to people who have genetically evolved to retain it, these people have higher bloodpressure. In relation to this model, the same scientist says that slaves brought over on slave ships would have been exposed to severe dehydration, and those with salt-retention would have been more likely to survive. So dependents of slaves have a high probability of having this recently selected for trait. (This study focuses on the West Indies and thereforemay not be representative of the US). Some argue that the slavery hypothesis is overly simplistic and a modern representation of racism in science. Still others argue that this increased risk is related to socioeconomic stress. Increased stress leads to increasedsympathic nervous system activity. The release of norepinephrine and adrenocorticotropic hormone elevate blood pressure by increasing sodium retention.  Do you think the slavery hypothesis is racist? Which of these models makes more sense to you?

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Type 2 diabetes is when your cells reduce the number of insulin receptors and then become insensitive to insulin (your insulin levels are not necessarily affected). “Thrifty Genotype” is the current hypothesis for why we evolved to be sensitive to insulin. Hunter gather societies were faced with seasonal and year-to-year fluctuations in availability of nutrients and therefore would have developed a “thrifty genotype” that would have allowed for a quick release of insulin and an increase in glucose storage during times of plenty. Nowadays we live in a constant state of plenty, and this “thrifty genotype” is now maladaptive and a contributor to diabetes and obesity. Native Americans have a very high rate of diabetes which could beassociated with the fact that they were part of a population with many “thrifty genotype” traits due to their old lifestyle, and due to the recent change in diet they are especially at risk. In addition to the ancestry view of “thrifty genotype”, recent studies also show that babies with poor nutritional conditions in early life select for “thrifty phenotype” which can also lead to increased rates of diabetes and obesity in adulthood. Could thrifty phenotype be epigenetic and passed on to offspring?

obesity_trends_20092

The obesity epidemic is a combination of all the above traits, and is associated with the transition from subsistence-level nutrition to modern-day industrial nutrition styles (processed foods, growth hormones, etc.). Thrifty genotype and phenotype are playing a huge role in populationsthat are just now gaining access to stable food supplies. Urbanization and rising incomes throughout the developing world have increased rates of overweight and obesity. Trends in US food use patterns the global trends. Energy consumed from soft drinks has increased 70% since the mid-1970’s. Available energy from vegetable oils has increased by 30% over that same time period. Other factors include the increase in eating away from home and snacking. Sugars, processed grains, and added fats are some of the cheapest food options, and with today’s bad economy poorer people are consuming more of these bad nutrients. Our modern environment has been characterized as “obseogenic”—that is, providing abundant food energy, while requiring little work or activity to produce that energy. What do you think about the obesity epidemic? Is genetics an excuse?

obesity-and-fastfood-nations

 

 

11 thoughts on “Obesity, Diabetes, and Lactose-Tolerance: A Summary of Human Nutritional Evolution

  1. Andrea Morris

    I think the percentage of carbs that we consume compared to foragers is incredible. Then again, I am not all that surprised because our lifestyle has changed and people now rely on fast food, frozen dinners, and packed foods all which contain a lot of carbs. Although, I did expect the percentage of animal foods to be higher considering the amount of people that proclaim their love for bacon in this country. The percentages foragers and their diets makes more sense to me because they rely off of what they can find. This would mean more natural foods which would include animal foods and less carbs.

  2. Emily Barron

    I think animal product consumption would be higher, since many people consider it the main part of the meal. You can hardly get a salad in the south without some sort of meat on it. I follow a vegetarian diet, and people always ask me if I get enough protein or will even insist that there is no possible way to get enough protein. I always have to remind them that protein does not only come from meat and the whole grains I eat do actually contain some protein. The carbohydrates doesn't surprise me, especially since many of us growing up were taught to follow the food pyramid which makes it seem like we should be eating tons of carbs.

    I do not think genetics is an excuse for obesity or diabetes in most cases. Of course there are people with predispositions, thyroid issues etc., but with the majority of people I just think they don't take care of themselves well enough. I think how a person is raised and the culture they live in is partially responsible for their obesity, but I do think there is something to be said for self-discipline and considering your family history.

    If everyone understood nutrition better than your average Joe does now (like my friend who though white bread was really healthy... what?) I think people would be healthier. There is just not enough education about what's healthy and why in our school system. Of course, I do agree that unhealthy foods are often cheaper, but that's a whole separate issue to tackle.

  3. Madeleine Cheatham

    I do not think genetics is an excuse for obesity (in most cases)
    So in the U.S the average adults diet is 40-50% carb....why is that percentage so high? Why do we eat so many carbs? Do people in other parts of the world consume this many carbs? Is this a normal percent compared to everyone else?

  4. mrhill2

    I think that “obseogenic” is now a relivent factor in today's society. I think this because there are so many additives in foods now that weren't in foods back in the 50s and 60s when our parents were born. But were introduced while they were growing up. So it only makes sence for our parents to have developt genes to process those additives and pass it on to us. Just like we will deplove a genes to process the new additives in the food now (i.e. Monsanto products). There are now additives that make foods like watermelons and tomatoes square so that more can be packed for transport all over the worldwide.

    But on the other hand, I believe that people will use this concept as an excuse for being overweight. As a way to not take ownership of their part in being overweight.

  5. Jonathan Belanich

    According to the data, compared to foragers we eat 20% more carbohydrates and 5-15% less protein. Honestly, I found these numbers to be surprising as I would expect the foragers to eat less protein and more carbohydrates, as it would seem to be easier to find carbs rather than protein. But I suppose by factoring in insects and the like the scales are probably tipped in favor of the protein.

    In looking at our carbohydrate intake, it isn't too surprising that it is roughly 50% of our energy. Carbs are found in almost everything, from energy drinks to salad dressing, and comprise a large part of 'fast food'. It seems our original 'programming' to desire sugars for energy in a food scarce environment, has remained and not been entirely helpful.

  6. rebeccaleon

    The Author of this chapter, William R. Leonard, is currently a professor of anthropology at Northwestern University. He holds the title at this university as the Abraham Harris Professor of Anthropology. He He received his PhD from the University of Michigan in 1987. His research interests include biological anthropology, adaptability, growth and development, and nutrition focusing on populations in South America, Asia, and the United States. His most recent publication was on the topic of precursors to over-nutrition and the effects of household market food expenditures on body composition among the Tsimane in Bolivia.

    1. Christopher Lynn

      Please edit & include as the main part of the post w/ a nice photo of him. Guarantee he'll see this 😉

  7. Taylor Burbach

    Late comment... oops

    I actually just took my nutrition midterm on macronutrients, so we talked about basically the same stuff. I think it's amazing how few people are taught anything about nutrition and how much misinformation is out there, too. One of the things we talked about earlier this semester is most medical doctors only receive about 25 hours total (think time hours, not credit hours) of nutrition training in medical school. Think about that the next time you visit your doctor and they give you nutrition advice...

  8. Brittany Fuller

    I do not believe that genetics plays a complete role in our society for obesity. In the United States there are abundant amount of unhealthy choices to eat. Most of our food has a lot of unnecessary additives and hormones. These hormones that they add to almost everything now is not good for our weight. If you want to have a good diet it is extremely hard (at least for me) because of all the unhealthy food that is here to temp me. I have gone to the nutritionist on campus and gotten the ideal calorie intake I should have and learned a lot about what I should, and should not, be eating.

  9. Sophia Fazal

    Adding onto Taylor's late comment, doctors are also given maybe one course in evolutionary studies, maybe. They have elective choices that include genetics, epidemiology and other in depth studies within biomedical fields, but none that basis that of any evolutionary model.

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