Module 3: Nutrition

How does gut physiology reflect diet?

Gut physiology reflects how animals extract energy from their diet. In carnivores that consume mostly animal products, microbial fermentation is reduced. This is reflected in their long small intestines and reduced ceca (the plural of cecum). In herbivores consuming a high quantity of plant matter, microbial fermentation helps them maximize energy gain from their diet and their guts provide space for that fermentation. This is reflected in either large ceca and sacculated large intestines (like a horse) or multi chambered stomachs with a rumen and long small intestine for SCFA absorption (like a ruminant animal).

The appendix was long thought to be vestigial organ. What is the potential benefit of having an appendix?

The appendix can serve as a reservoir for gut microbes, helping to re-colonize the gut after a severe environmental perturbation, like diarrheal disease.

Whaet do all mammalian infants have in common?

They have evolved to consume milk

Define weaning

Weaning is the process of cessation of consumption of mother’s milk.

Define complementary foods

Complementary foods are foods that supplement breastfeeding, introduced during infancy to provide extra energy in addition to mother’s milk. These foods help to meet the infant’s increasing caloric needs.

Compare & contrast the timing of complementary food introduction and weaning for industrialized populations, hunter-gatherer populations, and chimps

Introduction of complementary foods occurs at roughly the same time across industrialized populations, hunter-gather populations, and chimpanzees: 5-6 months. Weaning occurs earliest in industrialized populations at 12-18 months. Weaning occurs later in hunter-gatherer
populations at 2-3 years. Chimpanzees take even longer, weaning at 4-5 years

What is the breakdown of the nutrient consumption in human milk?

Human milk contains carbohydrates, fat, and proteins. The major nutrient component breakdown of human milk is 52% lactose, 31% fat, 10% HMO, and 7% protein.

In addition to macronutrients & HMO, human milk has many other important components. List 3

any from: growth factors, enzymes, minerals, vitamins, antibodies, live cells, hormones

How can breastfeeding potentially protect the infant from some diseases

Human milk contains maternal antibodies against certain diseases, immunoglobins A & G, and live immune cells like macrophages, leukocytes, neutrophils, and lymphocytes. All of these cells & proteins can help protect the infant from infection

Compare & contrast human milk & infant formula

The macronutrient and water content of human milk and infant formula are largely the same. There are more vitamins and minerals in infant formula. However, formula is missing the bioactive components of human milk. Some infant formulas include one type of HMO, 2’FL, but it is unclear what benefits that supplementation might have because humans produce a wide variety of HMO in their milk and 2’FL is just one kind of HMO. This does not appropriately mimic the profile of HMO in human milk

Define & describe colostrum

Colostrum is the low-volume, viscous substance produced in the first 2 to 4 days of breastfeeding. It is low in lactose and high in antibodies, growth factors, protein, fat, and HMOs

What is foremilk? What does it do?

Foremilk is the milk produced at the beginning of a nursing bout. It is low in fat and high in water and lactose. It hydrates the infant and helps encourage them to settle when they have strong hunger cues (via the quick energy from the sugar).

What is hindmilk? What does it do?

Hindmilk is the milk produced as the nursing bout continues. It is high in fat, protein, and HMOs and helps to truly satiate the infant.

Why don’t complementary foods look like the food they come from?

In industrialized societies, complementary foods are highly processed into purees. In non-industrialized societies, it is common for adults to pre-masticate food and then provide that to infants. Both of these (processing and pre-mastication) serves as ways to pre-digest food to make it easier for infants to metabolize.

How does pre-mastication make it easier for infants to digest food?

Pre-mastication performs mechanical digestion for infants that have no teeth because the pre-masticator’s teeth break down the food. It also starts chemical digestion because of enzymes like salivary amylase produced in the mouth of the pre-masticator. The mechanical and chemical digestion in the mouth of the pre-masticator gives infants a jumpstart on their digestion.

What is the benefit of high-quality weaning foods?

They enable early weaning, which reduces interbirth intervals (the time between two consecutive births).

How does early weaning reduce interbirth intervals (IBIs)?

Prolactin, the hormone that stimulates milk production, also suppresses ovulation, causing lactational amenorrhea. If offspring are weaned earlier, prolaction decreases and cycling can resume faster, allowing for the next pregnancy to occur.

How do human IBIs compare to other primates? Why is this advantageous?

Human IBIs are much shorter than other primates, due to our ability to wean early. This allows us to have a unique pattern of a slow life history but a very fast pace of reproduction. Each birth increases reproductive success, so shortening IBI increases fitness.

Compare and contrast the diets of industrialized, hunter-gatherer, and pastoralist populations and chimpanzees.

• Industrialized populations are consuming high quantities of simple sugars, like sugar and honey, and animal foods, like meat and dairy. They have very low intake of ripe fruit and fibrous plants.
  

• Hunter-gatherer populations have a more balanced diet with about half of their food from
  plants (ripe fruit and fibrous plants) and half from animals. Their intake of simple sugars is highly
  variable and primarily from honey.
  

• Pastoralist populations rely almost exclusively on animal foods, like milk, blood, meat, with very
  little plant intake and essentially no simple sugars. They do consume some berries and medicinal
  plants.
  

• Chimpanzees rely primarily on ripe fruit. They also consume a moderate amount of fibrous
  plants and some meat. They consume very little simple sugars that mostly come from honey.
  Overall, chimpanzees get more fiber than human populations, whereas humans prioritize
  energy-rich, easily digestible foods

How does the ripe fruit in the chimpanzee diet differ from the ripe fruit you find in the dining hall? Why does it differ?

Ripe fruit consumed by chimpanzees is roughly as sweet as an unripe banana. The fruit chimps eat are high in resistant starch or fiber. The fruit in the dining hall is much sweeter and contains less fiber because humans have selectively bred fruits to be sweeter.

Why are chimpanzees more reliant on their gut microbiome than we are?

Chimpanzees consume much more fiber, which they cannot break down with their own enzymes, so they rely on their microbiome to digest that fiber and produce SCFA they can absorb for energy. We consume a high-quality, easily digestible diet that we can metabolize with our own enzymes in the small intestine, requiring less fermentation by the gut microbiome.

What are non-thermal methods of food processing?

These are methods that don’t use heat. They include methods like crushing/pounding, grinding/milling, and blending.

Compared to chimpanzees, what human features indicate we have a higher daily energy budget?

Increased body mass: Human males are 34% larger than chimpanzee males and human females are 56% larger than chimpanzees. Increased brain size: Human brains are more than three times larger than chimpanzee brains. Human brains are roughly 1350 cm³ and chimpanzee brains are roughly 400 cm 3.
Increased activity: Chimps walk around 3-5km per day, while hunter-gatherers walk roughly 10- 20km per day.

How do the human features indicative of higher daily energy budget relate to increased energy budgets?

Increased body mass requires more energy to maintain and support body tissues. Brains are very energetically expensive, so larger brains also require more energy to support. Increased activity means more energy is being used by muscles. Each of these features is energetically
costly, so human males expend 44% more energy than chimpanzee males and human females expend 17% more energy than chimpanzee females on a daily basis.

Briefly describe the chewing adaptations that differ between humans and chimpanzees.

Humans have a smaller mouth, reduced chewing muscles and bite forces, and spend less time chewing than chimpanzees. Humans have small chewing surfaces on their teeth than chimpanzees. The temporalis muscle, a muscle of mastication, is greatly reduced in humans
compared to chimpanzees and the zygomatic arch, where the temporalis passes through to insert on the mandible, is also reduced. A mutation in the myosin of human jaw muscles reduces bite force. Chimpanzees spend five to six hours a day chewing, while humans spend less than
one hour per day chewing.

Briefly describe the anatomical differences between chimpanzees and humans that relate to the gut.

Humans have reduced guts compared to chimpanzees, relative to body size. Chimpanzees have an upside-down funnel shaped rib cage with a wide pelvis to contain their large guts. Humans have a tapered thoracic cavity that creates a waist. The large intestine and cecum is larger in
chimpanzees, while humans have larger small intestines. The large intestine in chimpanzees is also much more sacculated than in humans.

Taken together, what do human high energy budgets and chewing and gut adaptations suggest about diet? Explain your reasoning

They suggest we require foods that are 1) rich in calories and 2) easy to digest. We need foods with high calories per gram to meet our high energy demands. Our decreased chewing muscles/force/time indicates we need foods that are easier to chew. The decreased size of the large intestine/cecum and increased size of our small intestine indicates that we rely less on microbial fermentation and more on our own enzymatic digestion and absorption so we need foods that our enzymes can easily breakdown.

Where do we first see this whole suite of dietary adaptations in human evolutionary history?

At the transition from Australopithecus to Homo ergaster/erectus, around 2 million years ago.

Is there strong archaeological evidence for cooking being directly responsible for this transition? Explain

No. This transition occurred roughly 2 mya and the earliest archaeological evidence for control of fire was 1 mya. We also don’t know that control of fire necessarily means cooking was occurring

What drove these dietary adaptations in human diet?

1) increased access to protein and fat (which came with increased reliance on animal foods)
2) food processing (initially non-thermal, then cooking)

List the evidence for increased reliance on animal foods and describe one.

Physical cut marks on bones: cut marks on bones indicate butchering of animals by species capable of tool use, likely human ancestors.

Genetic evolution in tapeworms: Taenia tapeworms that infect humans are most closely related to the Taenia tapeworms that infect lions and hyenas. Since these tapeworms require an herbivore host and then a predator host, it suggests humans and lions/hyenas were consuming
the same herbivore prey.

Anatomical adaptations for running and throwing: These adaptations appear with Homo erectus. Changes to the shoulder that allow for precise and accurate throwing suggest the ability to throw rocks or spears for hunting. Running would also allow Homo to run down animal prey.

Physiological loss of taurine synthesis: Unlike our closest living primate relatives, humans cannot synthesize taurine. This amino acid is found in meat and we likely lost the ability to synthesize it due to meeting our taurine requirements via meat consumption.

Cultural consumption of animals: In most non-industrialized societies, cultural practices include
eating meat

Despite the evidence of reliance on animals for food, increased reliance on animal foods likely wasn’t the only driver of this change. Why?

Even modern hunter-gatherers only have a successful hunt every 10 hunts or so, indicating that other foods would have been necessary to buffer the consequences of hunting failure. We are unlikely to have been able to utilize scavenged meat, as pathogenic organisms quickly invade
meat after the death of the animal and our immune system would not have adequately protected us from that pathogen load. Human teeth have flat cusp molars that are good for
crushing, but not good for slicing or tearing raw meat. Our large brains have an energy requirement of 170g per day of glucose which could not be sustained by ketogenesis alone (now is a good time to review ketones), suggesting a substantial carbohydrate source was also required in our diet. Finally, vegans and vegetarians do not demonstrate differences in body mass, ovarian function, or age at menarche compared to omnivorous humans, indicating
humans do not require a diet that includes animal foods

What supplements are required for vegan children? Why are these important?

Vitamin B12 and DHA need to be supplemented during childhood in vegans, because requirements for these compounds are usually met through meat consumption. Vitamin B12 and DHA are important for brain development

How does non-thermal food processing increase digestibility?

Non-thermal food processing ruptures cells and breaks down particle sizes, increasing the surface area to volume ratio. This increases enzymatic exposure to the surface of the particles, allowing them to be broken down faster.

Explain why raw fine-milled flour more digestible than raw course-milled flour.

Fine-milling reduces particle size even more than course-milling so there is even more surface area available for enzymes to break down the flour.

Do thermal and non-thermal processing increase digestibility to the same extent? Why?

No. Non-thermal processing does not increase digestibility as much as thermal processing, because it can only physically change foods. Thermal processing also chemically transforms food particles.

Briefly describe the effects of heat on starch.

Starches are long chains of glucose that exist in semi-crystalline granules in their raw form. When starch is heated, those chains take up water and gelatinize.

How does this increase digestibility of starch?

In the semi-crystalline form, amylase, the main enzyme we use to break down complex carbohydates, cannot penetrate the granules. When starch is gelatinized, the chemical structure has changed in a way that allows amylase to bind to it and break it down.

Describe the effects of heat on protein and how this increases digestibility.

When protein is heated, it becomes denatured. The protein structure is lost and becomes a polypeptide chain. Once the protein is unravelled, proteases can cleave off amino acids

How does cooking meat impact the ability to chew it?

Cooking makes meat easier to masticate, because the muscle fibers stiffen and shrink along the grain. However, the collagen matrix surrounding the fibers gelatinizes and becomes squishy. So tough fibers are between parts that are easy to chew, which helps the piece of meat break apart
faster when it’s chewed

What evidence indicates that humans are adapted to require some amount of cooked foods in their diet?

Raw foodists in Germany demonstrated decreased body mass and increased amenorrhea as their proportion of raw food intake increased, which indicates negative energy balance. This means raw foodists are energy limited, despite having access to extensive non-thermal processing and (for the omnivores) animal products. The inability to meet our energetic demands with raw foods suggests cooking is an important part of meeting our dietary niche requirements of calorie-rich, easily digestible foods.

What nutrients are most prized by hunter-gatherer groups? Why?

Simple sugars and fats. fat provides the highest energy per gram so it is the most efficient source of energy. Simple sugars, like honey, provide a fast energy source as they are easy to digest and absorb and raise blood glucose quickly

What does this relationship btwn hunter-gatherers & honeyguides suggest about the human history of honey consumption?

This mutualistic relationship where the honeyguide and the hunter-gatherers both benefit suggests a long evolutionary history of human consumption of honey, which allowed this
relationship to develop

When did agriculture first emerge in human history?

~12,000 years ago

List the areas where agriculture emerged and the primary crop for each area.

The Americas—maize

The Middle East/Fertile Crescent—wheat

China—rice

What plants form most of the human diet today?

60% of global energy intake from plants comes from corn, wheat, and rice.

How is agriculture linked to domestication of animals?

Ancient populations realized animals could be used for labor to help with agricultural work, like pulling plows and hauling crops. Domestication of animals allowed us to maximize our plant- based intake through farming. It also led to an increase in dairy consumption as people realized
animals could offer nutritional resources

Explain two examples of strong positive selection on digestive enzymes, including what caused these adaptations.

1) Increase in AMY1 copy number: AMY1 is the gene that leads to production of salivary amylase, a key enzyme for breakdown of starch. More copies of the gene means more
production of salivary amylase. Agriculture increased the availability of starch, due to the high starch content of agricultural foods (corn, wheat, and rice). Populations with long histories of agriculture have been exposed to high-starch diets for a long time and have a greater copy number of AMY1 to help them digest those high-starch diets.

2) The evolution of lactase persistence: All mammals are exposed to lactose in mother’s milk during infancy. Most mammals stop producing lactase at the end of weaning because they stop consuming milk. Lactase persistence, or the ability to continue to produce lactase after weaning,
has evolved independently in multiple human populations. Lactase persistence allows humans to exploit milk as a caloric source, since it is digested and absorbed in the small intestine, instead of making it to the colon to be fermented by microbes. There is a tight correlation between pastoralists and agriculturalists who use farm animals for dairy and lactase persistence because those populations had access to milk from their animals and incorporated it into their diet

What features characterize the industrial diet?

Increased processing, sugar, fat, salt, and additives, and decreased fiber.

How does the industrialized diet relate to the human dietary niche of our evolutionary past?

The human dietary niche is high-calorie, easy to digest foods. The industrialized diet is characterized by features that define the human dietary niche, but it has taken it to the extreme. Now, he ultra-processing of foods, including increased fat and sugar content and decreased fiber, has increased energy gain from food which can lead to obesity.

Compare and contrast soluble and insoluble fiber

Soluble fiber, like pectin found in the body of an apple, dissolves in water, forming a gel. It slows emptying of the stomach, promoting satiety, and sequesters sugar and fatty acids, reducing absorption. It is fermentable by the gut microbiome. On the other hand, insoluble fiber, like cellulose found in the peel of an apple, forms a lattice and traps water, which softens stool. This lattice helps speed passage of stool through the intestine and only some forms of insoluble fiber can be fermented by the gut microbiome. So not all insoluble fiber can be converted to energy in the large intestine.

How does soluble fiber impact satiety food and nutrient intake?

By slowing the emptying of the stomach, soluble fiber promotes satiety, making you feel fuller for longer, reducing food intake. Soluble fiber also forms a gel that traps sugar and fat, making it difficult for enzymes to break down those nutrients. This means less sugar and fat is digested and absorbed in the small intestine, reducing energy uptake from these nutrients.

Define glycemic index (GI).

GI is how quickly a given food raises blood sugar compared to pure glucose, which is assigned a GI value of 100. Low GI foods are less than or equal to 55, high GI foods are greater than or equal to 70.

Define glycemic load (GL)

GL is the impact on blood sugar considering both GI and carbohydrate content, so the formula is GL= [GI * Carbcontent(g)]/ 100

How do high GL foods promote fat storage?

High GL foods cause blood glucose to increase rapidly and to higher levels than low GL foods. The higher the blood glucose, the more insulin is released. High insulin levels promote fat storage. When high insulin levels come down, insulin overshoots, causing blood sugar to drop too low, promoting hunger and sugar cravings, which can lead to eating more high GL foods and this cycle continues