HNF 150 (Intro To Human Nutrition) exam 2
study guide (COMPLETE SOLUTION NEW
VESRION) Michigan State University
Week 6
Lipids = A lipid is a water-insoluble, fat-soluble molecule that provides
energy, supports cell structure, aids in vitamin absorption, and includes
fats, oils, phospholipids, and cholesterol.
The soluble/insoluble part matters because it affects how lipids behave in the
body and in digestion:
● Since lipids are insoluble in water, they don’t mix with blood (which is
mostly water)
—this is why the body needs special transport structures like lipoproteins
(e.g., LDL, HDL) to move fats through the bloodstream.
● Their fat solubility is also what allows lipids to carry and store fat-
soluble vitamins (A, D, E, K) and to form cell membranes, which need
both water-loving and fat-loving parts to function.
● In digestion, their water-insolubility means they must be emulsified by
bile before enzymes like lipase can break them down.
So in short: it affects how lipids are digested, absorbed, transported, and
used in the body.
🥑 Why Moderate Lipid Intake Is Essential + Energy vs. Nutrient Density
○ Provide 9 kcal/g (most energy-dense)
○ Needed for:
■ Cell membranes (phospholipids)
■ Fat-soluble vitamin absorption (A, D, E, K)
■ Hormone synthesis (cholesterol → steroid hormones)
■ Satiety (help feel full, slow digestion)
■ Cushioning for organs and body temperature regulation
■ Source of essential fatty acids
● Energy Density = calories per
gram
○ Lipids are very energy-dense
○ Ex: oil, butter
,● Nutrient Density = nutrients per calorie
, ○ Nutrient-dense foods provide lots of vitamins/minerals
○ Ex: avocado (both nutrient- and energy-dense)
○ Ex: soda = high energy density, low nutrient density
🧈 Triglycerides
● What they are: The most abundant form of lipid in both food and the
human body— about 95% of dietary fat is in this form.
● Structure: Made up of one glycerol molecule and three fatty acids. The
type of fatty acid (saturated, monounsaturated, polyunsaturated) affects the
physical properties of the fat.
● What they do:
○ Energy storage: Triglycerides are stored in adipose (fat) tissue
and used as a long-term energy source.
○ Insulation: Fat under the skin helps maintain body temperature.
○ Protection: Cushions organs like the kidneys and heart.
○ Fat-soluble vitamin transport: Helps absorb vitamins A, D, E, and K.
● Sources: Oils, butter, lard, full-fat dairy, fatty meats, nuts, and seeds.
🧬 Phospholipids
● Structure: Similar to triglycerides, but with 2 fatty acids and 1 phosphate
group
attached to glycerol.
● This gives them a dual nature: the fatty acid "tails" are hydrophobic
(water-repelling), while the phosphate "head" is hydrophilic (water-
attracting).
● What they do:
○ Form cell membranes: Phospholipids form the lipid bilayer of all
cells. The dual nature allows them to form a semi-permeable barrier
between the cell and its environment.
○ Emulsifiers: Because they can interact with both fat and water,
phospholipids help mix substances that normally don’t blend (e.g.,
oil and water). This is
, important for digestion and is also used in food products like salad
dressings.
○ Cell signaling: Phospholipids are involved in sending signals
within and between cells.
● Sources: Egg yolks, soybeans (lecithin), and also made by the body.
🌀 Sterols (e.g., Cholesterol)
● Structure: Sterols are different from triglycerides and phospholipids—they
have a multi- ring structure and no fatty acid chains.
● What they do:
○ Hormone production: Cholesterol is the building block for steroid
hormones, such as estrogen, testosterone, and cortisol.
○ Vitamin D synthesis: The body makes vitamin D from cholesterol
when the skin is exposed to sunlight.
○ Bile production: Cholesterol is used to make bile acids, which help
digest fats in the small intestine.
○ Cell membrane structure: Cholesterol is found in every cell
membrane, helping maintain fluidity and structure.
● Sources: Only found in animal products (meat, eggs, dairy, shellfish).
● Note: The body makes its own cholesterol in the liver, so it is not
considered an essential nutrient. Dietary cholesterol intake has less impact
on blood cholesterol levels than previously believed—saturated and trans
fats are more influential.
🔁 Summary
● Triglycerides = storage fat and energy
● Phospholipids = structural role in cells + emulsification
● Sterols (Cholesterol) = hormones, bile, vitamin D, membranes
study guide (COMPLETE SOLUTION NEW
VESRION) Michigan State University
Week 6
Lipids = A lipid is a water-insoluble, fat-soluble molecule that provides
energy, supports cell structure, aids in vitamin absorption, and includes
fats, oils, phospholipids, and cholesterol.
The soluble/insoluble part matters because it affects how lipids behave in the
body and in digestion:
● Since lipids are insoluble in water, they don’t mix with blood (which is
mostly water)
—this is why the body needs special transport structures like lipoproteins
(e.g., LDL, HDL) to move fats through the bloodstream.
● Their fat solubility is also what allows lipids to carry and store fat-
soluble vitamins (A, D, E, K) and to form cell membranes, which need
both water-loving and fat-loving parts to function.
● In digestion, their water-insolubility means they must be emulsified by
bile before enzymes like lipase can break them down.
So in short: it affects how lipids are digested, absorbed, transported, and
used in the body.
🥑 Why Moderate Lipid Intake Is Essential + Energy vs. Nutrient Density
○ Provide 9 kcal/g (most energy-dense)
○ Needed for:
■ Cell membranes (phospholipids)
■ Fat-soluble vitamin absorption (A, D, E, K)
■ Hormone synthesis (cholesterol → steroid hormones)
■ Satiety (help feel full, slow digestion)
■ Cushioning for organs and body temperature regulation
■ Source of essential fatty acids
● Energy Density = calories per
gram
○ Lipids are very energy-dense
○ Ex: oil, butter
,● Nutrient Density = nutrients per calorie
, ○ Nutrient-dense foods provide lots of vitamins/minerals
○ Ex: avocado (both nutrient- and energy-dense)
○ Ex: soda = high energy density, low nutrient density
🧈 Triglycerides
● What they are: The most abundant form of lipid in both food and the
human body— about 95% of dietary fat is in this form.
● Structure: Made up of one glycerol molecule and three fatty acids. The
type of fatty acid (saturated, monounsaturated, polyunsaturated) affects the
physical properties of the fat.
● What they do:
○ Energy storage: Triglycerides are stored in adipose (fat) tissue
and used as a long-term energy source.
○ Insulation: Fat under the skin helps maintain body temperature.
○ Protection: Cushions organs like the kidneys and heart.
○ Fat-soluble vitamin transport: Helps absorb vitamins A, D, E, and K.
● Sources: Oils, butter, lard, full-fat dairy, fatty meats, nuts, and seeds.
🧬 Phospholipids
● Structure: Similar to triglycerides, but with 2 fatty acids and 1 phosphate
group
attached to glycerol.
● This gives them a dual nature: the fatty acid "tails" are hydrophobic
(water-repelling), while the phosphate "head" is hydrophilic (water-
attracting).
● What they do:
○ Form cell membranes: Phospholipids form the lipid bilayer of all
cells. The dual nature allows them to form a semi-permeable barrier
between the cell and its environment.
○ Emulsifiers: Because they can interact with both fat and water,
phospholipids help mix substances that normally don’t blend (e.g.,
oil and water). This is
, important for digestion and is also used in food products like salad
dressings.
○ Cell signaling: Phospholipids are involved in sending signals
within and between cells.
● Sources: Egg yolks, soybeans (lecithin), and also made by the body.
🌀 Sterols (e.g., Cholesterol)
● Structure: Sterols are different from triglycerides and phospholipids—they
have a multi- ring structure and no fatty acid chains.
● What they do:
○ Hormone production: Cholesterol is the building block for steroid
hormones, such as estrogen, testosterone, and cortisol.
○ Vitamin D synthesis: The body makes vitamin D from cholesterol
when the skin is exposed to sunlight.
○ Bile production: Cholesterol is used to make bile acids, which help
digest fats in the small intestine.
○ Cell membrane structure: Cholesterol is found in every cell
membrane, helping maintain fluidity and structure.
● Sources: Only found in animal products (meat, eggs, dairy, shellfish).
● Note: The body makes its own cholesterol in the liver, so it is not
considered an essential nutrient. Dietary cholesterol intake has less impact
on blood cholesterol levels than previously believed—saturated and trans
fats are more influential.
🔁 Summary
● Triglycerides = storage fat and energy
● Phospholipids = structural role in cells + emulsification
● Sterols (Cholesterol) = hormones, bile, vitamin D, membranes
