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Fats & Lipids — what they are, where they’re from, and what they do
How the body digests & absorbs fats (quick path)
Mouth & stomach
Lingual/gastric lipases start clipping triglycerides (TGs), esp. in infants and with high-fat meals.
Small intestine (main event)
Fat in the duodenum → CCK released → gallbladder squeezes bile into the gut.
Bile salts emulsify large fat droplets → tiny droplets (↑ surface area).
Pancreatic lipase + colipase hydrolyze TGs → free fatty acids (FFAs) + 2-monoacylglycerol; phospholipase A₂ works on phospholipids; cholesterol esterase frees cholesterol.
Micelles → enterocyte
Bile salts form micelles that ferry lipids to the intestinal wall; contents diffuse into enterocytes.
Re-assembly & export
Inside enterocytes: re-esterify to TGs, pack with cholesterol & phospholipids into chylomicrons (apoB-48).
Chylomicrons enter lymph → blood. Lipoprotein lipase (LPL) on capillaries releases FFAs to muscle/adipose; remnants go to liver.
Short/medium-chain FAs (≤C12) skip chylomicrons and go portal vein → liver bound to albumin.
Nutritional sources of fats
Monounsaturated (MUFA): olive oil, avocado, almonds, peanuts.
Polyunsaturated (PUFA):
Omega-3: fatty fish (salmon, sardines), flax/chia/walnuts; algae (DHA).
Omega-6: safflower, sunflower, corn, soybean oils; nuts, seeds.
Saturated: dairy fat, butter, ghee, coconut oil, palm oil, marbled meats.
Trans: industrial partially hydrogenated oils (avoid); small natural amounts in ruminant dairy/meat.
Phospholipids: egg yolk, soy, meats.
Cholesterol: eggs, shellfish, meats (note: dietary cholesterol ≠ blood cholesterol 1:1).
Types of fats & major functions
Triglycerides (TGs): storage/transport form; dense energy (9 kcal/g).
Saturated FAs: straight chains; stable at heat; excessive intake can raise LDL in many people.
Monounsaturated FAs (MUFA): heart-friendly; support insulin sensitivity and favorable lipid profiles.
Polyunsaturated FAs (PUFA):
Omega-3 (ALA, EPA, DHA): anti-inflammatory signaling, membranes (DHA in brain/retina), ↓TG, vascular health.
Omega-6 (LA → AA): growth, skin barrier; precursors to eicosanoids involved in immune/inflammatory responses.
Trans FAs (industrial): raise LDL, lower HDL; increase CVD risk—avoid.
Phospholipids: membrane bilayers; emulsifiers (e.g., lecithin); lipoprotein structure.
Sterols (e.g., cholesterol): membrane fluidity; precursor to steroid hormones (cortisol, estrogen, testosterone), vitamin D, and bile acids.
Roles of lipids in the body (why they matter)
Energy & fuel partitioning
Resting/low-intensity fuel; β-oxidation yields ATP. During fasting/low-carb, liver makes ketone bodies.
Cell structure & function
Phospholipids + cholesterol build membranes; DHA keeps neural/retinal membranes flexible.
Hormones & signaling
Steroid hormone synthesis; eicosanoids (prostaglandins, leukotrienes, resolvins) regulate inflammation, clotting, vasodilation.
Nutrient transport
Lipoproteins (chylomicrons, VLDL/LDL/HDL) move lipids in blood; fats enable absorption/transport of fat-soluble vitamins A, D, E, K.
Protection & insulation
Adipose cushions organs; subcutaneous fat conserves heat; myelin (lipid-rich) speeds nerve conduction.
Gene regulation
Fatty acids bind nuclear receptors (e.g., PPARs) altering metabolism and inflammation genes.
Satiety & taste
Slows gastric emptying, enhances flavor, supports appetite control.
Practical coaching notes
Daily intake: most adults do well around 20–35% of calories from fat, emphasizing MUFAs and omega-3 PUFAs.
Balance PUFAs: include fish 2–3×/week or ~1–2 g/day EPA+DHA via food/supplement if intake is low.
Cooking: use olive or avocado oil for most tasks; save saturated fats or high-PUFA oils for specific needs.
Label check: avoid “partially hydrogenated” (trans).
Athlete cut/bulk: keep essential fats in; adjust mostly carbs for training load.
