Lec 4: Fats Flashcards
What are fatty acids and types (3)
-building blocks of lipids
-hydrocarbon chain attached to carboxyl group
-saturated (all C bonded to H+), monounsaturated (1 double carbon bond) or polyunsaturated (2+ carbon bonds). More double carbon bonds= bends and easier to digest
-triglyceride= glycerol molecule (head) and 3 fatty acid molecules (tail)
Essential fatty acids (+2 types)
-Essential fatty acids are fatty acids that cannot be synthesized by our bodies and so must be obtained through our diet
-Linoleic acid (LA- an omega-6 fatty acid) and alpha-linolenic acid (ALA- an omega-3 fatty acid) are considered essential fatty acids because they cannot be synthesized by humans
Sources of Omega-6s vs Omega-3s
Omega-6 fatty acids:
-LA (vegetable and safflower oil) -> GLA -> DGLA -> AA (meat, poultry, eggs)
*Most important= LA (vegetable oils) and AA (eggs and meat)
Omega-3 fatty acids:
-ALA (green leafy vegetables, flax and chia seeds, canola, walnut and soybean oils) -> SDA -> ETA -> EPA (oily fish, krill oil, algae oil) -> DPA -> DHA (fish and krill oils)
*Most important= ALA (plant sources), EPA and DHA (fish sources)
What are Omega-3s?
Polyunsaturated fatty acids where the first double bond is between the 3rd and 4th carbon atom from the methyl/omega end of the fatty acid
-EPA= 20:5 n-3 (20 carbons, 5 double carbon bonds, first double bond occurs at #3)
-DHA= 22:6 n-3
-ALA= 18:3 n-3
What are omega-6s?
Polyunsaturated fatty acids where the first double bond is located between the 6th and 7th
carbon atom from the methyl end of the fatty acid.
-LA= 18:2 n-6 (18 carbons, 2 double bonds, first double bond at 6th carbon)
-AA= 20:4 n-6
Desaturation and elongation of essential fatty acids
Humans can synthesize longer omega-6 and omega-3 fatty acids from the essential fatty acids through a series of desaturation and elongation reactions
-Desaturation= addition of a double bond between 2 carbon atoms
-Elongation= addition of two carbon atoms
Roles of Omega-3s (3)
-Components of phospholipids (Membrane order)
-Precursors for anti-inflammatory molecules (Resolvins, protectins, maresins)
-Cardiovascular benefits
Recommended intake of Omega-3s
-There is no RDA
-Adequate Intake/DRI (so for most of healthy population) for ALA
Adults: men= 1.6g/day, women= 1.1g/day
Children: 0-12 months= 0.5g, 1-3 years= 0.7g, 4-8 years= 0.9g, then differences between girls and boys up to adult AI
-AHA= 2 servings of oily fish per week for healthy individuals
History of omega-3 literature
-Cross-sectional studies (comparing different groups- Danish eskimo= highest LA, Greenland eskimo highest EPA)
-Case-control studies (comparing group to control- found higher serving fish= lower risk compared to control)
-First major prospective trial DART 1989, found decreased risk of mortality with fish in diet
Omega-3 Index (3 studies pre-2018)
-Level of EPA and DHA in erythrocyte phospholipids to determine risk for coronary heart disease
<4%: High risk
4-8%: Moderate risk
>8%: Lowest risk
-Low level evidence
* Mainly case-control studies (correlative)
* Risk categories may not generalize to other populations
*higher % EPA and DHA = lower risk
Primary vs Secondary prevention
Primary= usual risk population (don’t have disease of interest, preventing from occurring in risk population)
Secondary= known CVD/CHD, previous MI, stroke, etc. (has disease, preventing from worsening)
VITAL 2019- Primary Prevention Trial
-compared 1g/day of omega-3 vs. placebo
-found less than 1.5 servings of fish/week= greater risk reduction
REDUCE-IT 2019- Primary and Secondary Prevention
-double blind RCT
-2nd prevention= >45 years old and established CVD
-1st prevention= >50 with T2D and 1+ CV risk factor
-Given concentrated form of EPA (4g/day) compared to placebo, ~5 year follow up
-Found greater reduction in secondary-prevention cohort
Post-2018 Major Trials
-Updated meta-analysis by Hu et al.= risk reduction, but more significant when Reduce-It study added
-Cochrane review= gold standard, most recent meta-analysis (2020), found no change in recommendations regarding supplementation (slightly reduces risk)
Omega-3 Literature Limitations (4)
- Support for omega-3 benefit comes from low quality studies
-Pre-2018= case-control and cross-sectional
-Post-2018= RCTs and meta-analyses - Issues with control pills (fishy taste, control oil composition)
- Analyses not controlled for all variables (protein consumption, SES/education)
- Generalizability limitations (secondary prevention populations- hard to generalize to broader population- no standardized dose)
Omega-3 affects in skeletal muscle (6)
- Omega-3 supplementation increases EPA and DHA composition of skeletal muscle
-after 2 weeks first shown in cows
-In humans evidence it affects skeletal muscle; 1.9g/day EPA + 1.5g/day DHA, 4 weeks - Fish oil supplementation increases muscle protein synthesis (after 8 weeks in study) in response to amino acid/insulin infusion
*maybe omega-3s affect amino acids and helps in skeletal muscle protein synthesis - Omega-3 fatty acid intake promotes skeletal muscle mass and strength in older adults
- Omega-3 fatty acids enhance exercise-induced increases in muscle quality in older women not men (force per unit of muscle mass)
*older women most impact - Meta-analyses support efficacy of omega-3 fatty acid intake to promote muscle anabolism
- Omega-3 fatty acid intake reduces muscle disuse atrophy
Take home points
- Omega-3 fatty acid intake appears to have a beneficial effect on cardiovascular health
- Beware of study design limitations and conclusions
- Omega-3 fatty acids may enhance muscle anabolism and protect against muscle loss during disuse
