Human Nutrition

Flashcards about Human Nutrition

Fiber

Generic recommendation for adults is 25-40g daily.

Fiber recommendations

Can be met by ingesting daily whole-grain products, vegetables, fruits, and legumes.

Lipids

Main types are fatty acids, TG, phospholipids, and sterols.

Lipids participate in

Energy production (fatty acid oxidation) and storage (TG accumulation), insulation and padding (TG stored in the adipose tissue), cell signaling (diacylglycerol, DAG), structural support (cell membrane formation), inflammatory responses (eicosanoids), hormonal production (steroids), etc.

Fatty Acids

Simplest of the lipids, containing methyl (non-polar) and carboxyl (polar) ends that do not cyclize.

Fatty acids classification according to chain size

Short-chain (2-4 carbons), medium-chain (6-12 carbons), and long-chain (14-26 carbons).

Fatty acids classification according to double bonds

With one double bond are called monounsaturated (MUFA, e.g. oleic and palmitoleic acids) and those having 2 or more double bonds are called polyunsaturated (PUFAs, e.g. linoleic and arachidonic acids).

Delta (A) system

Counting carbons from carboxyl end.

Omega (w) system

Counting carbons starts from the methyl end and identifies only the position of the first carbon where the initial double bond is located.

Shorter fatty acids

Tend to be more water-soluble than longer ones.

Fatty acids and polarity

The greater the number of double bonds the greater the polarity of a fatty acid and so its solubility in water.

Fatty acids and melting point

The greater the chain length and the more saturated a fatty acid is, the higher its melting point.

Essential fatty acids

Those not synthesized by our body, so they need to be obtained through the diet. Linoleic and a-linolenic acids are essential because humans lack A2 and A15 desaturases, enzymes that are crucial to incorporate double bonds at such positions.

w-3 fatty acids

Regular consumption has been associated with reduced blood pressure and blood clots, reduced risks of heart disease and stroke, and improved defense against inflammatory diseases.

w-6 fatty acids

Have been associated with a pro-inflammatory effect and can be harmful.

Cis-fatty acids

Most unsaturated fatty acids in nature have the hydrogens located next to the double bond on the same side of the carbon chain.

Trans-Fatty acids

Have hydrogens next to the double bonds on the opposite side of the carbon chain.

Hydrogenation

The industry uses a process to add hydrogens to unsaturated fatty acids.

Triglycerides (TG)

Composed of three fatty acids esterified to one glycerol molecule.

Visceral adipose tissue

Located in the intra-abdominal area provides mechanical support for internal organs.

Triglycerides (TG)

Stored in the white adipose tissue can be mobilized for energy production under conditions of food restriction and/or increased energy expenditure.

Hydrolysis of TGs

Yields glycerol and three fatty acids.

Phospholipids

Composed of glycerol, two fatty acids, and a phosphate group (PO4).

Phospholipids

Are amphiphilic molecules because they can attract both water- and fat-soluble substances, which makes them ideal structural components for cellular membranes and lipoprotein shells.

Sterols

Are characterized by a four-ring core structure (cyclopentanoperhydrophenanthrene) or steroid nucleus.

Cholesterol

Most common sterol in animals, which also serves as a precursor for the formation of other steroid molecules that exert major physiological functions.

Cholesterol synthesis pathway occurs in three phases

Conversion of Acetyl-CoA into mevalonate, mevalonate into squalene, and squalene into cholesterol.

Rate-limiting enzyme

Hydroxymethylglutaril-CoA (HMG-CoA) reductase that catalyzes the conversion of HMG-CoA to mevalonate is inhibited by cholesterol as the levels of this sterol rises in the cytoplasm

Salivation and mastication at the oral cavity

Allow lingual lipase to start the process of TG hydrolysis that cleaves FA esterified at the sn-3 position of the glycerol moiety.

Bile

Released by the gallbladder and has amphipathic properties (possess both hydrophilic and hydrophobic "ends").

Enterohepatic circulation

A system by which bile salts are reabsorbed in the gut.

The diet-heart hypothesis

States that dietary saturated fat elevated circulating cholesterol levels leading to the development of CAD.

Vegetable/seed oils

Release toxic chemicals during cooking that might increase the risk of cancer.

Lipids in the blood

Transported in the bloodstream as constituents of lipoproteins.

Chylomicrons

Contain ApoB-48 that originates from the intestine.

VLDL and LDL

Enriched with ApoB-100 that originates in the liver.

Apo-E

Exist in three isoforms and is present in almost all lipoproteins; functions as a receptor ligand, particularly the LDL receptor.

Chylomicrons role

Deliver dietary lipids to tissues other than the liver.

VLDLs role

Similar to that of chylomicrons, except that they deliver endogenous rather than dietary TG to peripheral tissues.

Lipoprotein lipase (LPL)

Hydrolyzes TG molecules present in lipoproteins passing through the capillary bed of tissues such as adipose, skeletal muscles, and heart.

LDL function

To deliver cholesterol to tissues where it may be used for membrane construction, as well as to produce steroid hormones.

HDL

A particle that removes unesterified cholesterol from cells and other lipoproteins and transports them to the liver (reverse cholesterol transport) to be excreted in the bile.

Scavenger receptors (SR-B1)

Receptors that remove "debris" by phagocytosis.

Loss of one functional PCSK9 allele

Prevented 88% of CVD events.

Lp(a)

A lipoprotein that consists of a unique protein homologous to plasminogen named apolipoprotein (a), which is covalently bound to the apoB-100 moiety of an LDL particle.

Main driver/predictor of metabolic dysfunction and heart disease

Hyperinsulinemia

Proteins

Essential nutrients because they are critical components of all cells and tissues in our body.

Proteins properties

Contribute to cell growth, repair and maintenance, regulate fluid and electrolyte balance, transport nutrients and other substances, act as enzymes and hormones, and even serve as energy source.

Protein recommended dietary allowance (RDA)

0.8 g per kg of body weight per day.

The 9 amino acids our body cannot either synthesize at all or in sufficient amounts

Essential/indispensable amino acids

Sources of high-quality protein

Foods that contain all 9 essential amino acids.

Those not containing all essential amino acids

Low quality proteins.

HCl

Parietal cells of the stomach secrete a fluid rich, which is important to maintain an acidic environment in which specific proteolytic enzymes operate optimally.

Pepsin

Pepsin, an enzyme initially secreted in an inactive form (pepsinogen, a pro-enzyme also called a zymogen), which in the presence of HCl loses a portion of its NH2 terminus and becomes activated.

Secretin and CCK

Hormones that stimulate the release of alkaline pancreatic juice, bicarbonate, electrolytes, water, and zymogens (inactive enzymes).

Enteropeptidase

Activates trypsinogen.

Aminopeptidases

Aminopeptidases are responsible for cleaving amino acids from the amino (N)-terminal end of oligopeptides.

The hydrocarbon side chain and net electrical charge of amino acids

Affect the affinity of the carrier; the bigger the side chain the higher the affinity.

The transport of peptides

This involves the movement of peptides across the brush border membrane of enterocytes along with protons (H+).

Liver

Monitor the absorbed amino acids and adjust the rate of their metabolism (catabolism and anabolism) according to the needs of the body.

BCAA

Spared by the liver; they stay in the circulation and tend to be used to a greater extent by other tissues such as skeletal muscles, kidneys, and heart.

Regular exercise, particularly resistance training, causes an anabolic response in skeletal muscles

That lead to increased muscle mass.

Inhibitors of CETP

Prevent the flux of cholesterol from HDL towards VLDL and potentially reduces the formation of LDL particles (also known as "bad cholesterol" particles).