Macronutrients: Complete Guide to Dietary Fats
Comprehensive tutorial on dietary fats - saturated, unsaturated, trans fats, omega-3 and omega-6 fatty acids, cholesterol, digestion, metabolism, food sources, and cardiovascular health. From the NIH, AHA, and USDA.
This content is for informational purposes only. Always consult a healthcare professional.
Overview
Dietary fats (lipids) are the most energy-dense macronutrient, providing 9 kcal per gram. They serve essential structural, hormonal, and metabolic functions. Fats are composed primarily of triglycerides (three fatty acids esterified to a glycerol backbone).
Function
Description
Energy provision
9 kcal/g (primary energy reserve)
Energy storage
Adipose tissue (triglycerides)
Cell membrane structure
Phospholipid bilayer (phospholipids, cholesterol)
Hormone precursors
Steroid hormones from cholesterol
Fat-soluble vitamin transport
Vitamins A, D, E, K absorption
Insulation
Thermal (subcutaneous fat) and electrical (myelin)
Organ protection
Visceral fat cushions organs
Satiety
Delays gastric emptying, stimulates CCK release
Flavor and texture
Contributes to food palatability
Chemical Classification of Fatty Acids
Saturation
Type
Carbon Bonds
Structure
Physical State
Examples
Saturated
All single bonds (C-C)
Straight chain, packs tightly
Solid at room temp
Butter, coconut oil, animal fat
Monounsaturated (MUFA)
One double bond (C=C)
Bent chain, packs loosely
Liquid at room temp
Olive oil, avocado, nuts
Polyunsaturated (PUFA)
Two or more double bonds
Highly bent
Liquid at room temp
Vegetable oils, fish oil
Chain Length
Chain Length
Carbon Atoms
Food Sources
Short-chain (SCFA)
2-4
Produced by gut fermentation of fiber (butyrate, acetate, propionate)
Medium-chain (MCFA)
6-12
Coconut oil (lauric acid C12), palm kernel oil
Long-chain (LCFA)
14-20
Most dietary fats (palmitic C16, stearic C18, oleic C18:1)
Very long-chain (VLCFA)
22+
Fish oil (EPA C20:5, DHA C22:6), brain tissue
Saturated Fatty Acids
Name
Carbon Atoms
Food Sources
Butyric acid
4:0
Butter (4% of fat), produced by gut bacteria
Caproic acid
6:0
Butter, coconut oil (trace)
Caprylic acid
8:0
Coconut oil (6%), palm kernel oil
Capric acid
10:0
Coconut oil (6%), palm kernel oil
Lauric acid
12:0
Coconut oil (47%), palm kernel oil
Myristic acid
14:0
Butter (11%), coconut oil (18%)
Palmitic acid
16:0
Palm oil (44%), butter (26%), animal fat (25-30%)
Stearic acid
18:0
Cocoa butter (34%), animal fat (15-20%)
Arachidic acid
20:0
Peanut oil (1-2%)
Monounsaturated Fatty Acids (MUFA)
Name
Carbon Atoms
Double Bond Position
Food Sources
Palmitoleic acid
16:1
n-7
Macadamia oil, sea buckthorn, some animal fats
Oleic acid
18:1
n-9
Olive oil (55-83%), avocado (70%), almonds (70%), canola oil (60%)
Gondoleic acid
20:1
n-11
Jojoba oil, mustard oil
Erucic acid
22:1
n-9
Rapeseed (old varieties), mustard (limited in canola by regulation)
Nervonic acid
24:1
n-9
Brain tissue, myelin
Polyunsaturated Fatty Acids (PUFA)
Name
Carbon Atoms
Double Bond Position
Food Sources
Linoleic acid (LA)
18:2
n-6 (Omega-6)
Vegetable oils (soybean, corn, sunflower), nuts, seeds
Alpha-linolenic acid (ALA)
18:3
n-3 (Omega-3)
Flaxseed, chia seeds, walnuts, canola oil
Gamma-linolenic acid (GLA)
18:3
n-6
Evening primrose oil, borage oil
Arachidonic acid (AA)
20:4
n-6
Meat, eggs, synthesized from LA
Eicosapentaenoic acid (EPA)
20:5
n-3
Fish oil (salmon, mackerel, sardines), algae
Docosahexaenoic acid (DHA)
22:6
n-3
Fish oil, algae, brain/retina
Omega-3 and Omega-6 Fatty Acids
Omega-3 Family
Fatty Acid
Chain
Conversion Efficiency
Key Sources
Alpha-linolenic acid (ALA)
18:3 n-3
(Parent)
Flaxseed, chia seeds, walnuts, hemp seeds
Stearidonic acid (SDA)
18:4 n-3
~30% to EPA
Ahiflower oil, genetically modified soybean
Eicosapentaenoic acid (EPA)
20:5 n-3
(Direct from source)
Fatty fish (salmon, mackerel, herring, sardines)
Docosahexaenoic acid (DHA)
22:6 n-3
(Direct from source)
Fatty fish, algae, fish oil supplements
Conversion of ALA to EPA/DHA: In humans, approximately 5-10% of ALA converts to EPA, and 2-5% converts to DHA. Conversion is inhibited by high omega-6 intake and activated by insulin.
Omega-6 Family
Fatty Acid
Chain
Key Sources
Linoleic acid (LA)
18:2 n-6
Soybean oil, corn oil, sunflower oil, nuts, seeds
Gamma-linolenic acid (GLA)
18:3 n-6
Evening primrose oil, borage oil, black currant seed oil
Dihomo-gamma-linolenic acid (DGLA)
20:3 n-6
Synthesized from GLA (minor dietary)
Arachidonic acid (AA)
20:4 n-6
Meat, poultry, eggs (synthesized from LA)
Omega-6:Omega-3 Ratio
Diet Type
Omega-6:Omega-3 Ratio
Ancestral/hunter-gatherer
~1:1 to 4:1
Standard Western diet
~15:1 to 20:1
Mediterranean diet
~4:1 to 6:1
Current recommendations
4:1 to 5:1
A high omega-6:omega-3 ratio promotes pro-inflammatory states, while a lower ratio is associated with reduced risk of cardiovascular disease, inflammation, and autoimmune conditions.
Trans Fats
Natural vs. Industrial Trans Fats
Type
Source
Formation
Health Effect
Natural (ruminant)
Dairy, beef
Biohydrogenation in ruminant stomach
No adverse effects at typical intake; some may be neutral/beneficial
Industrial (partially hydrogenated oils)
Processed foods, fried foods, baked goods
Partial hydrogenation of vegetable oils
Clearly harmful — increases LDL, decreases HDL, promotes inflammation
Vaccenic acid (natural)
Dairy fat (trans-11 18:1)
Ruminant biohydrogenation
Neutral to beneficial (precursor to CLA)
Conjugated linoleic acid (CLA, natural)
Dairy, beef
Ruminant biohydrogenation
Mixed effects — may have anti-cancer properties in animal models
Elaidic acid (industrial)
PHOs, margarine, shortening
Partial hydrogenation
Clear CVD risk factor
Regulatory Status of Industrial Trans Fats
Jurisdiction
Status
United States (FDA)
Generally Not Recognized as Safe (GRAS) — phased out by 2020 (with limited exceptions)
European Union
Limit of 2 g per 100 g of fat (2021)
Canada
Banned in PHOs (2018)
Denmark
Effectively zero (first country to ban, 2003)
WHO (REPLACE initiative)
Goal: global elimination by 2023
Cholesterol
Types
Lipoprotein Class
Composition
Apolipoprotein
Function
Chylomicrons
90% triglycerides
B-48
Transport dietary fat from intestine to tissues
VLDL (Very Low Density)
55% triglycerides
B-100
Transport endogenous triglycerides from liver
IDL (Intermediate Density)
30% triglycerides, 25% cholesterol
B-100, E
VLDL remnant, taken up by liver or converted to LDL
LDL (Low Density)
50% cholesterol
B-100
Transport cholesterol to peripheral tissues
HDL (High Density)
50% protein, 20% cholesterol
A-I, A-II
Reverse cholesterol transport (from tissues to liver)
Lipoprotein(a) [Lp(a)]
LDL-like + apo(a)
B-100, apo(a)
Genetic cardiovascular risk factor
Dietary Cholesterol vs. Blood Cholesterol
Aspect
Evidence
Dietary cholesterol effect on blood cholesterol
Modest — increases both LDL and HDL; individual variability significant
Hyper-responders
~25% of population — dietary cholesterol significantly raises blood LDL
Hypo-responders
~75% — dietary cholesterol has minimal effect (compensatory downregulation of endogenous synthesis)
Saturated fat effect
Much stronger determinant of blood LDL than dietary cholesterol
Eggs and CVD risk
Current evidence: no significant association with CVD in most populations (up to 1 egg/day)
2020-2025 USDA Dietary Guidelines
No specific limit on dietary cholesterol (removed 300 mg/day limit from 2015 guidelines)
Recommended Lipid Levels
Parameter
Desirable
Borderline
High/Risk
Total cholesterol
<200 mg/dL
200-239 mg/dL
≥240 mg/dL
LDL cholesterol
<100 mg/dL
130-159 mg/dL
≥160 mg/dL (≥190 mg/dL very high)
HDL cholesterol
≥60 mg/dL
40-59 mg/dL (men)
<40 mg/dL (men), <50 mg/dL (women)
Triglycerides
<150 mg/dL
150-199 mg/dL
≥200 mg/dL (≥500 mg/dL very high)
Non-HDL cholesterol
<130 mg/dL
130-159 mg/dL
≥160 mg/dL
Fat Digestion and Absorption
Digestive Pathway
Site
Enzyme/Agent
Substrate
Product
Mouth
Lingual lipase (minor)
Short/medium-chain triglycerides
Free fatty acids, diglycerides
Stomach
Gastric lipase (minor, active at pH 3-6)
Triglycerides (especially MCT)
Free fatty acids, diglycerides
Small intestine (lumen)
Bile salts (from liver/gallbladder)
Fat globules
Emulsified fat droplets (micelles)
Small intestine (lumen)
Pancreatic lipase
Triglycerides
2-monoglyceride + 2 free fatty acids
Small intestine (lumen)
Colipase (pancreatic, activates lipase in presence of bile)
—
Facilitates lipase activity
Small intestine (lumen)
Phospholipase A₂
Phospholipids
Lysophospholipid + free fatty acid
Small intestine (lumen)
Cholesterol esterase
Cholesteryl esters
Cholesterol + free fatty acid
Small intestine (brush border)
Micelles deliver to enterocyte
—
Cellular uptake
Absorption and Transport
Step
Location
Process
Micelle formation
Duodenum/jejunum lumen
Bile acids surround fat digestion products, forming water-soluble micelles
Uptake into enterocyte
Brush border of jejunum
Diffusion of free fatty acids, monoglycerides, cholesterol, and fat-soluble vitamins
Resynthesis of triglycerides
Smooth ER of enterocyte
2-monoglyceride + 2 fatty acyl-CoA → Triglyceride
Chylomicron formation
Golgi apparatus
Triglycerides + cholesterol + phospholipids + apolipoprotein B-48
Lymphatic transport
Lacteals → Lymphatic system
Chylomicrons enter lacteals (not directly into portal blood)
Thoracic duct → Bloodstream
Thoracic duct → Subclavian vein
Chylomicrons enter systemic circulation
Lipoprotein lipase
Capillary endothelium
Hydrolyzes chylomicron triglycerides → FFA taken up by tissues
Chylomicron remnant
Liver
Taken up by liver via apoE receptor
Dietary Recommendations
Fat Intake Recommendations
Organization
Total Fat
Saturated Fat
Unsaturated Fat
USDA/DGA (2020-2025)
20-35% of total calories
<10% of total calories
Majority from unsaturated
AHA
20-35% of total calories
<7% of total calories (or <5-6% for CVD patients)
Replace saturated with unsaturated
WHO
15-30% of total calories
<10% of total calories (<7% for additional benefit)
(Not specified)
IOM (AMDR)
20-35% (adults), 25-40% (children)
As low as possible
As needed to meet total fat
EFSA
20-35% of total calories
<10% of total calories
(Not specified)
Specific Fatty Acid Recommendations
Fatty Acid
Recommendation Source
Recommendation
Total omega-3 (ALA)
IOM RDA
1.6 g/day (men), 1.1 g/day (women)
Total omega-3 (EPA + DHA)
AHA
≥2 servings fatty fish/week (~500 mg/day EPA+DHA)
Total omega-3 (EPA + DHA)
FDA
≤2 g/day from supplements (safety)
Total omega-6 (LA)
IOM AI
17 g/day (men), 12 g/day (women)
Trans fat
WHO, FDA
As low as possible (<1% of total calories)
Industrial trans fat
FDA
Eliminated from food supply
Dietary cholesterol
USDA/DGA 2020-2025
No specific limit (eat as little as possible while maintaining healthy diet)
Food Sources
Saturated Fat Content by Food
Food
Serving
Total Fat (g)
Saturated Fat (g)
SFA as % of Total
Coconut oil
1 tbsp (14 g)
14
12
86%
Butter
1 tbsp (14 g)
12
7.5
63%
Palm oil
1 tbsp (14 g)
14
6.7
48%
Heavy cream
1 tbsp (15 g)
5.5
3.5
64%
Cheddar cheese
30 g
9
6
67%
Bacon (cooked)
3 slices (35 g)
13
4.5
35%
Beef (80/20, cooked)
100 g
16
6
38%
Chicken thigh (skin-on)
100 g
16
4.5
28%
Salmon (farm-raised)
100 g
13
3
23%
Avocado
100 g
15
2.1
14%
Egg (whole)
1 large (50 g)
5
1.6
32%
MUFA Content by Food
Food
Serving
Total Fat (g)
MUFA (g)
Olive oil
1 tbsp (14 g)
14
10
Canola oil
1 tbsp (14 g)
14
9
Avocado
100 g
15
10
Almonds
30 g (23 nuts)
15
9.5
Cashews
30 g (18 nuts)
12
7
Peanuts
30 g
14
7
Pecans
30 g (19 halves)
20
12
Macadamia nuts
30 g (10-12 nuts)
22
17
Lard
1 tbsp (13 g)
13
6
Pork tenderloin (cooked)
100 g
4
1.5
PUFA Content by Food
Food
Serving
Total Fat (g)
PUFA (g)
Omega-3 (g)
Omega-6 (g)
Salmon (wild, cooked)
100 g
11
3.5
1.8 EPA+DHA
0.3
Sardines (canned)
100 g
11
4
1.8 EPA+DHA
0.3
Mackerel (cooked)
100 g
14
4
1.6 EPA+DHA
0.2
Herring (pickled)
100 g
10
3
1.5 EPA+DHA
0.2
Flaxseed (ground)
1 tbsp (7 g)
4
3
2.3 ALA
0.6
Chia seeds
1 tbsp (12 g)
5
4
2.5 ALA
1.2
Walnuts
30 g (14 halves)
18
14
2.7 ALA
10.5
Soybean oil
1 tbsp (14 g)
14
8
0.9 ALA
6.7
Corn oil
1 tbsp (14 g)
14
8
0.1 ALA
7.5
Sunflower oil
1 tbsp (14 g)
14
5
0
5
Hemp seeds
3 tbsp (30 g)
15
11
2.5 ALA
8.5
Fats and Health
Cardiovascular Disease
Dietary Factor
Effect on LDL
Effect on HDL
Effect on Triglycerides
Net CVD Risk
Saturated fat (C12:0-C16:0)
↑↑
↑
↓→
↑ (moderate)
Stearic acid (C18:0)
→
→
→
Neutral
MUFA (oleic acid)
↓
↑
↓
↓
PUFA omega-6 (LA)
↓↓
↓→
↓
↓
PUFA omega-3 (EPA+DHA)
↑ (mild, sometimes)
↑
↓↓↓
↓↓
Industrial trans fat
↑↑↑
↓↓
—
↑↑↑
Dietary cholesterol
↑ (modest, variable)
↑ (modest)
—
Neutral in most
Omega-3 Health Effects
Condition
Effect
Evidence Level
Hypertriglyceridemia
↓ Triglycerides 20-50% (dose-dependent)
Strong (FDA-approved)
Cardiovascular mortality
↓ Risk, especially sudden cardiac death
Strong
Heart failure
↓ Risk (moderate intake)
Moderate
Atrial fibrillation
Mixed (may ↓ risk at moderate intake, possible ↑ at very high intake)
Mixed
Rheumatoid arthritis
↓ Joint pain, morning stiffness
Strong
Depression
↓ Symptoms (adjunctive therapy)
Moderate
Dementia / cognitive decline
↓ Risk (observational), mixed (RCT)
Moderate
Age-related macular degeneration
↓ Risk
Moderate
Asthma
↓ Inflammation, mixed clinical outcomes
Weak-Moderate
Insulin sensitivity
Minimal effect (high dose may slightly improve)
Weak
Inflammation and Eicosanoids
Fatty Acid
Eicosanoid Effect
Inflammatory Potential
Omega-6 (AA)
Pro-inflammatory series 2 prostaglandins, series 4 leukotrienes
Pro-inflammatory (balanced with omega-3)
Omega-3 (EPA)
Anti-inflammatory series 3 prostaglandins, series 5 leukotrienes, resolvins
Anti-inflammatory
Omega-3 (DHA)
Resolvins, protectins, maresins
Pro-resolving (actively resolves inflammation)
Medium-Chain Triglycerides (MCTs)
Property
MCTs
LCTs
Chain length
6-12 carbons
14-22 carbons
Digestion
Rapid (no bile/pancreatic lipase needed)
Requires bile and pancreatic lipase
Absorption
Direct to portal vein
Via chylomicrons → lymph
Energy density
8.3 kcal/g
9 kcal/g
Ketogenic potential
High
Low
Common sources
Coconut oil, palm kernel oil
Most dietary fats
Key Takeaways
Fats provide 9 kcal/g and are essential for cell membranes, hormones, and vitamin absorption
Saturated fat should be <10% of total calories; replace with unsaturated fats for cardiovascular benefit
Industrial trans fats should be effectively zero (banned in US, EU, and many countries)
Omega-3 fatty acids (EPA/DHA) from fatty fish (≥2 servings/week) reduce CVD risk
Omega-6 fatty acids are essential but Western diets have an imbalanced omega-6:omega-3 ratio (~15:1 vs. recommended 4:1)
Dietary cholesterol has modest effects on blood cholesterol in most people; eggs are not associated with CVD risk
Total fat should comprise 20-35% of total calories, with the majority from unsaturated sources
Fat digestion involves emulsification (bile), hydrolysis (lipases), micelle formation, and chylomicron transport via lymphatics