fats chapter 6. functions of fat fuel for cells organ padding and protection transport fat-soluble...

Fats

Chapter 6

Functions of Fat

• Fuel for cells

• Organ padding and protection

• transport fat-soluble vitamins

• Constituents of cell membranes

• Constituents of hormones

Categorization of Fats

• Degree of Saturation– Saturated– Monounsaturated– Polyunsatrated

• Chain Length– Short– Medium– Long

Saturated Fat

• Lacks C-C double bonds

• Saturated with H• Animal fat & tropical

oils• Most unhealthy• Hydrogenated oils

Monounsaturated Fat

• Contains single C-C double bond

• Most healthy• Most common

– Olive oil– Canola oil– Peanut(s) oil– Walnuts– Almonds

Polyunsaturated Fat

• Two or more C-C double bond

• Omega 3– Flax oil, Fish oil -linolenic acid

• Omega 6– Corn, soyben,

safflower, sunflower– Linoleic acid

Hydrogenated Fats

• Process used to convert unsaturated oils into saturated oils– Increases temp at which oil burns– Increases shelf life– Stays in mixture better

• Health impact is same as saturated fats

Trans Fatty Acids

• Formed from hydrogenation process

• May have worst health impact of all fats

TABLE 5.1 Fatty Acids in fats and oils

Oil/Fat Saturated Mono-unsat Polyunsat

Beef 50 43 4

Chicken 30 46 22

Tuna 27 26 37

Olive 14 74 9

Canola 6 62 30

Tuna 27 26 37

Coconut 87 6 2

Fatty Acids by Chain Lengths

• Short Chains– 6 or less carbon atoms– Found in butter, coconut oil, palm kernel oil

• Medium Chain– 8 or 10 carbons– Absorbed into blood more quickly

• Long Chain – 12 or more carbons, most are 16 and 18– Most common in the diet

Key Terms

• Lipolysis

• Triglycerides (triacylglycerols)

• Glycerol

• Gluconeogenesis– Lactate– Glycerol– Alanine

• 3500 kcal = 1 lb fat

Sources of Triglycerides/Fatty Acids for Fuel

• Adipose tissue– 140 lb @ 3% fat = 20,000 kcal– 280 lbs @15% fat = 170,000 kcal

• Muscle Triglycerides– 2,000 - 3,000 kcal– Supplies energy at 1/3 rate of CHO

• Plasma triglycerides– Minimal contribution (40 kcals)

Characteristics of Fat That Make It Preferential to CHO as a Fuel

Substrate Reserve

• 2+ X as much energy per gram

• Not hydrated when stored– 3 g H2O per g glycogen

– Equivalent energy as glycogen would increase body weight by 50% or more

Figure 1. Storage and mobilization of stored triglycerides.

HSL

EPI

Glycerol-3-phosphate

FFA Availability

• At rest, 70% of all FFA released during lipolysis are re-esterified.

• During exercise, re-esterification is suppressed by 50% which increases FFA avaiability.

• Exercise increases lipolysis (300%) which contributes to the plasma FFA.

• Blood flow to adipose tissue and to muscle is increased increasing overall delivery of FFA

FFA Transport into Muscle

• Protein carrier mediated process

• Carriers become saturated at high plasma FFA levels (1.5 mmol/liter)

• Muscle contraction increases the activity of the carriers which increases the transport of FFA into the cell.

Intramuscular Triglycerides (IMTG)

• Type I muscle fibers have higher concentrations.

• Endurance training translocates the IMTG next to the mitochondria

• Lipolysis of IMTG mediated by HSL and inhibited by insulin, just like in adipose tissue.

Training

Fig. 2. Contribution of the four major fuel substrates to energy after 30 min of exercise at 25%, 65%, and 85% of VO2max in fasted subjects.

Figure 3. Expanded view of the sources of fat for oxidation during exercise at 25%, 65% and 85% of VO2max in fasted subjects.

Fig. 4. Substances providing energy during exercise at a given absolute intensity of 65% VO2max before and after 12 weeks of training.

Fat Oxidation and Exercise Duration

• Fat oxidation increases as duration increases

• Maximal oxidation rates are approximately 1.5 g/min.

• Fat oxidation increases probably because glycogen goes down.

Fat Oxidation and Intensity

• Fat oxidation rates peaks at ~ 60-65% VO2max and then declines

• At low intensities (25% VO2max), most fat is from adipose tissue

• At 65% VO2max, most is from IMTGs

• At high intensities, fat oxidation is suppressed

Why is Fat Oxidation Suppressed at Higher Exercise Intensities?

• Reduced blood flow to adipose tissue due to sympathetic constriction of vessels

• Lactate increases re-esterification of FAs

• Transport into mitochondria is reduced

Muscle Adaptations Which Enhance Fat Use

• Increase in enzymes of beta-oxidation

• Increase of ETS capacity

• Increase sensitivity of SNS stimulation

• Increase in transport mechanism across sarcolemma and within muscle

Systemic Adaptations Which Enhance Fat Use

• Decrease in insulin

• Decrease in lactate

• Increase delivery of substrate– Cardiovascular– Capillarization

Recommended Consumption of Dietary Fat

• Essential fatty acids must be supplied in the diet– Linoleic acid (omega-6 fatty acid)

• 3-6 grams per day• Supplied if 5-10% of calories are from fat

– Sources• 1 tablespoon of corn oil• 2 tablespoons of sunflower oil• 2.5 tablespoons of canola oil• 5 tablespoons of olive oil

• Alpha-linolenic Acid (omega-3 fatty acid)– 1-2% of kcal consumption– 2-3 grams for 2000 kcal diet– Sources

• 1.5 teaspoons Flaxseed oil• 1.5 tablespoon canola oil• 3 tablespoons soybean oil• 12 oz cod, flounder, haddock, halibut, tuna• 6 oz salmon• 3.5 oz herring, mackerel, sardines

Daily Recommendation for Fats

• Less than 30% of total calories for most

• Less than 10% of calories as saturated fat

• Adequate essential fats

• Most fat should be monounsaturated with polyunsaturated as second choice

Fat Supplementation During Exercise

• Cannot consume FFA because they are too acidic and require protein carrier for absorption

• LCT are slowly absorbed and rate of uptake by muscle is slow

• MCT are directly absorbed and easily transported into muscle– 30 g is limit of tolerance– Practically can contribute no more than 10%

of total energy

Short-Term Dietary Fat Supplementation Before Exercise

• Consuming high fat diet increases fat utilization but reduces exercise intensity that can be tolerated

• Consuming high GI CHO just prior to exercise will inhibit fat utilization during first 50 min of exercise and increase use of blood glucose

Long-Term High-Fat Diet and Exercise Tolerance

• Exercise duration may be increased at intensities <65% VO2max

• Durations at competitive intensities are not improved

Combined Fat and CHO Loading

• No demonstrated beneficial effect of combining high fat diet in days before exercise and CHO loading immediately before exercise.

Fat Intake During Recovery

• Requires 2gm/kg to resynthesize IMTG

• Take ~ 22 hrs to resysnthesize

• Optimizing IMTG may compromise CHO

Carnitine Supplementation

• Facilitates transport of LCT into mitochondria

• Found primarily in animal products, especially meat

• Consensus is that carnitine is not ergogenic

Caffeine

• Likely will produce a glycogen sparing effect and direct effect on CNS resulting in reduced fatigue

• Increases plasma FFA levels but not necessarily fat metabolism

• Effect is greatest in naïve caffeine users• Effective dosage begins @ 100-300 mg

– Coffee : 100 to 150 mg per cup– Cola: 35-55 mg per 12 oz– Tea: 20-50 mg per cup– Vivarin: 100-300 mg