Nutrition

By the end of this class you should understand:

• The major nutrients the body requires for life and their roles in the body

• The essential concept of calories and metabolic rate

• The major risks associated with excess and deficiencies of key nutrients

Vital Nutrients• The small intestine absorbs all

the nutrients required for life• Some nutrients are required for

energy and for building blocks for more cells and cell parts– Carbohydrates– Proteins– Lipids

• Other nutrients are required for homeostasis but not energy– Water– Vitamins– Minerals

Carbohydrates• A single carbohydrate molecule

is called a simple carbohydrate (such as glucose)– Starches are made of many bound

together and are called complex carbohydrates

– Some are more complex than others, and the more complex the branching, the longer the digestion takes

• “White” starches such as white rice and pasta contain simpler chains

Glycemic Index• The faster a food breaks

down into glucose molecules, the higher the glycemic index– Pure glucose has a

glycemic index of 100• People with diabetes and

pre-diabetes must eat only foods with lower glycemic indices so as to not spike the blood sugar– People with a family

history of diabetes should probably do so as well…

Insulin Spike

• Insulin is released in response to glucose– Insulin stimulates the

liver and fat cells to absorb glucose

• A rapid release of glucose followed by an insulin spike can cause the blood sugar to crash

Proteins• Proteins must be broken down to

the individual amino acids• The human body can synthesize

many of the amino acids from other amino acids (so they are nonessential), but there are certain ones that cannot be synthesized– These are called essential amino

acids• If even one of the essential amino

acids is missing, the diet is incomplete and no new protein can be made

Lipids• There are many classes of lipids– Some vitamins and cholesterol are

both lipids, but cannot be burned for energy

• The energy-storing lipids are fatty acids, and these fats can be saturated or unsaturated– Saturated fats have no double bonds

and so pack together more tightly than unsaturated fats

– Treating unsaturated fats with hydrogenation can create trans fats, which are very difficult to metabolize and therefore very unhealthy

Vitamins and Minerals• Vitamins are organic

compounds that serve key purposes in cell mechanisms but only in small amounts– Example: vitamin A used to

make retinal• Minerals are inorganic

elements and compounds, such as sodium, potassium, calcium, iron, and iodine– Also necessary for life

Calories

• A Calorie is a unit of energy– Measures how much heat could

be released by completely burning a given amount of material

• The average adult requires around 2000 Calories a day– The exact rate at which we

burn calories is called the metabolic rate and includes exercise, etc

Calories in Food

• Carbohydrates and Proteins have 4 Calories per gram

• Fats have 9 Calories per gram– This is why our body uses fat as a

long-term energy storage material

– This is also why fat tastes delicious: it’s a very calorie-rich food!

• Fun fact: alcohol has 7 Calories per gram!

Alcohol Dehydrogenase• The liver must metabolize

alcohol into acetic acid using an enzyme called alcohol dehydrogenase– This requires energy and uses

some of the liver’s resources– Most women and some ethnic

groups such as East Asians have less enzyme, making them have a lower tolerance for alcohol

• Acetic acid is then converted into Acetyl CoA, which can be converted into fat or metabolized by the mitochondria

Dietary Proportion

• Opinions vary wildly on the “optimal” dietary proportions of carbs, proteins and fats

• A major reason for this is the different efficiencies of enzymes in different people– Genetics in action!

• What is healthy for one person may be unhealthy for another!

Essential Macronutrients• New cells must be formed

every day– Mostly epithelial cells (skin, GI

tract, etc) and blood cells• All cells require fat (cell

membrane) and protein (for cell structures)– Carbohydrates are also used

structurally for skin glycoproteins

– Carbohydrates are also used as the energy source for mitosis

Excess Nutrition• An excess of nutrients above

what is needed to make more cells and perform cellular respiration causes the body to store extra materials– Excess glucose stored as glycogen– Excess glucose and fat also stored

as far– Protein cannot be stored

Nutrient Storage• People have genetic differences

in how they form and store fat– Some people form fat more

easily– Fat is also stored in different

places in the body• Due to its high calorie density,

storing fat is vital for life– Pictured is Lizzie Velasquez, who

has a genetic condition where her body literally cannot form fat

– If she were to stop eating for more than a few hours she will die (once her glycogen runs out)

Nutrient Deficiencies• If insufficient carbohydrates or

lipids are eaten, the body digs into its reserves

• The body also lowers the metabolic rate to try and slow the loss of nutrients– Prevents starvation

• Insufficient protein poses serious health risks because protein cannot be made from fat or sugar, so protein is taken out of the muscles

Nutrients and Dieting• Due to sociocultural forces, being

“thin” is currently conflated with being “attractive” by many people– This has led to fats and “carbs”

having a negative connotation since they may result in fat buildup

– Please note that having a high metabolic rate is a better indicator of health than body weight or BMI

• Ironically an increasing proportion of people in the US are also obese due to high-sugar diets

Hunger Effect• Hunger is a rather complex effect in the body

mediated by the hypothalamus but it is dominated by two hormones:– Leptin: produced by fat, suppresses hunger– Ghrelin: produced by stomach, stimulates hunger• Fun fact: the molecule THC acts on the brain similarly

to ghrelin, causing the “munchies”

• Swelling of the stomach and small intestine suppress hunger

Hunger and Stress

• Stress (Sympathetic nervous system and cortisol) both block hunger

• Ghrelin is released by the parasympathetic nervous system in response to food stimuli (even thoughts)– This allows you to eat even

when you’re stressed– Also, mmm, donuts…

Who’s Hungry?

• Next week: last week of new material!– Monday: Kidneys– Wednesday: Reproductive Systems