Lecture 4 - Lipids and Nutrition

Digestion

Breaking down large food molecules into water-soluble ones to be absorbed

Ways to Digest

1. Acid

2. High temperature (not for humans)

3. Enzymatic (protein biocatalysts)

Why don’t high temperatures work for humans?

The body functions at a specific temperature, or humans would die

Proteins as Enzymes

Biocatalysts that speed up reaction; named with ‘ase’

Mechanism of Enzymes

Binding to active site on substrate to form enzyme-substrate complex, release broken-down products

Enzyme Specificity

• Enzymes often only react with 1 molecule

  • Different active site shapes

Factors that affect Enzymes

1. Temperature

2. pH

Path of food through GI Tract

1. Stomach

2. Small Intestine

3. Large Intestine

4. Rectum

Accessory organs of GI system

1. Pancreas

2. Liver

3. Gallbladder

4. Sphincters

Stomach Function

Production of HCl, acidic digestion of foods

Small Intestine Function

Absorption of nutrients

Large Intestine Function

Absorption of water

Rectum Function

Excretion of food wastes

Sphincter Functions

• Muscles that open/close between GI passages

• Autonomic control except for anal sphincter (controlled by us)

Liver Function

Production of bile

Gallbladder Function

Storage of bile

Pancreas Function

Secretion of digestive enzymes

Enzymes in Digestive Tract

1. Lingual lipase in saliva breaks down food first

2. Gastric lipase in the stomach hydrolyzes lipids

   1. Both digest short and medium fatty acids

pH of Small Intestine

• Want to be stabilized at neutral 7

  • Hormone secretin stimulates bicarbonate secretion from pancreas to neutralize HCl from stomach

Cholecystokinin (CCK) Function

• Secreted by small intestine cells

  • Stimulate bile release by gallbladder

  • Stimulate pancreas to secrete pancreatic juice containing lipase

Pancreatic Juice

Juice secreted by pancreas containing all digestive enzymes; catalyzing cleavage of molecules

Cholesterol Esterase

• Secreted by the pancreas

  • Breaks down esters, tri/monoglycerides, phospholipids, Vitamin A and D

• “Phospholipases”

Bile Secretion

By CCK in liver, containing polar and nonpolar sides

Bile Function

Attach to fat globules for emulsification, forming micelles

Concentration Gradient

Digestion products flow from high to low concentration due to rapid re-esterification inside cells

Chylomicron Location

Small Intestine

Chylomicron Structure

Phospholipid outer layer, triglyceride inner layer containing embedded lipoproteins

Lipoprotein Lipase Function

Digest triglycerides to allow into blood

Essential Nutrients

Nutrients we need but can’t make

Is cholesterol an essential nutrient?

No, it is made in the liver.

HDL (High Density Lipoprotein) Cholesterol

• “Good” cholesterol because it regulates LDL and promoted its excretion

• Made mostly of lipoproteins (high density)

LDL and VLDL Cholesterol (Low-density)

Stored in the blood and made mostly of triglycerides

Essential Fatty Acids

Linoleic and Linolenic (Omega 3 and 6); enzymes can’t place double bonds in positions 3 and 6

Where do we get Omega 3 and 6 from?

Oils/seafood oil

Are EPA and DHA essential?

No, we make them and also consume them in seafood

Omega-3 Benefits

• Reduce triglycerides

  • Raise HDL

• Lower BP, prevent clots, prevent plaque

• Prevent blindness

• Promote brain health and prevent mental disorders

  • Schizophrenia, BPD, etc.

• Fight Alzheimers

• Help with diabetes, obesity, and autoimmune disorder

• Prevent cancer by promoting apoptosis

• Boost calcium to strength bones

• Fight inflammation

DHA Location

Retinal cell membranes

Normal Functions of DHA

Development and function of eyes; recycled when low

Function of DHA during pregnancy

• More intelligent, better communication, less behavior issues

• Decrease developmental issues, ADHD, autism, cerebral palsy

Lipid Functions

• Provide and store energy (1 g = 9 kcal)

• Insulation

• Transport fat-soluble vitamins in chylomicrons

• Cell membranes

Saturated Fatty acids do this to cholesterol:

Decrease HDL, increase LDL

Polyunsaturated fatty acids do this to cholesterol:

Decrease HDL and LDL

Monounsaturated fatty acids do this to cholesterol:

Decrease LDL, increase HDL

Diabetes and Lipids

Insulin increases cholesterol synthesis in liver; indication of CVD

Non-modifiable factors for atherosclerosis:

• Genes

• Age

  • Vessels narrow and stiffen automatically

• Gender

  • Women lower risk due to high estrogen, reducing plaque

Modifiable Factors of atherosclerosis

• Smoking

• Stress (cytokines inflame vessels)

• Diet (increase LDL)

• Exercise

• Obesity and diabetes

Plant Stanols/Sterols

• Reduce cholesterol absorption in small intestine

• Phytosterols

• Abundant in seeds and nuts

  • Stanols = wood pulp

  • Sterols = soybeans