2/11 - Caffeine & Such
Early Research Hypothesis
Caffeine is widely studied as a performance-enhancing supplement
Endurance exercise research focus on caffeine effects on fat metabolism, glycogen sparing + central nervous system (CNS) activation
78% of studies show ergogenic effects of caffeine on endurance performance
Increases free fatty acids release from adipose tissue
Spares muscle glycogen prolonging endurance
Conflicting Evidence on Fuel Utilization
No metabolic shift after caffeine ingestion
Current Understanding - CNS activation
Primary ergogenic mechanism = CNS stimulation NOT fuel utilization
Adenosine receptor blockade leads to:
Reduced perception of fatigue
Increased alertness + endurance performance
Majority of studies support caffeine’s ergogenic benefits in endurance exercise
CNS activation = key mechanism behind caffeine performance-enhancing effects
Recommended dose 3-6 mg/kg for endurance benefits
Death do we part?
FDA recommends limit of 400 mg or 0.4 g
4-5 cups of coffee
Estimate of dangerous effects w consumption around 1,200 mg of caffeine
Average caffeine intake for a American = 165-230 mg
Caffeine sound in energy drinks ranges - 40-250 mg per 8 fl oz.
Caffeine Mechanisms of Action - Adenosine Receptor Blockade
Rapidly Absorbed + 99% bioavailable within 45 min
Peak plasma concentration = 15-120 min (post ingestion)
Caffeine binds to adenosine receptors prevents adenosine from inducing fatigue
Results = increased levels
Norepinephrine
Dopamine
Acetylcholine
Serotonin
Glutamate
Leads to enhanced alertness + cog function
Absorption + Metabolism
No hepatic first pass effect - directly enters circulation
Metabolized mainly in the liver into paraxanthine (70-80%)
Factors that affect metabolism
Pregnancy
Obesity
Smoking
Altitude
Oral contraceptives
Effects on Lipid Metabolism
Mechanisms = increases lipolysis via beta adrenergic stimulation
Mobilizes free fatty acid for energy
Increased cAMP - stimulates neurotransmitter + hormone release
Inhibits phosphodiesterase - prevents cAMP breakdown
Research
Previous studies suggest >300 mg of caffeine may induce acute diuresis
In contrast - excessive + impractical doses of caffeine 6 mg/kg or >500 mg may facilitate acute diuresis
Popular Trend - Delaying Morning Caffeine
Tik tok suggests waiting 90-120 min after waking to drink coffee
Claims
Prevents prologing morning cortisol peak
Avoids an afternoon energy crash
Cortisol Natural Circadian Rhythm
Cortisol peaks within 1 hr of waking + declines throughout the day
Additional to small peaks occur around meals
Key - caffeine does not disrupt the natural rhythm
Caffeine + Cortisol Response
Caffeine increases cortisol + ACTH secretion
Effects occurs regardless of when caffeine is consumed
Conclusion = delaying caffeine does not prevent cortisol related effects
Adenosine + Sleep-Wake Cycle
LOOK AR SLIDE
Afternoon Crash
No evidence links to morning caffeine intake to an afternoon energy crash
Possible causes of fatigue
Poor sleep
Blood sugar fluctuation
Natural circadian rhythm dips
Solution - small afternoon caffeine does - not delayed morning intake
Benefits to Delaying Caffeine
Effectiveness - no cortical or adenosine decline should guide timing
Pregnant Women Avoid Caffeine - Risks
Caffeine freely crosses the placenta -
Fetus or placenta can metabolize it
May accumulate in oviducts + uterine fluids - can affect embryonic development
Can contribute adult onset disease
Around 80% pregnant ladies consume caffeine daily
Research - suggest caffeine intake during pregnancy = linked to adverse gestational outcomes
Increase risks
Intrauterine growth retardation/ low birth weight
Subfertility + spontaneous abortion
Fetal growth restrictions + cognitive impairments
Obesity + metabolic rates
Potential epigenetic changes across generations
Individual Variability + Caffeine Metabolism
Effects vary -
Adenosine receptor activity
CYP1A2 enzyme activity - responsible for caffeine metabolism
Some women can be more vulnerable to adverse effects than others
Conclusions + Rec
Maternal caffeine consumption linked to neg pregnancy outcomes
Rec = pregnant women or those considering - should limit or abstain from caffeine
More research needed
Supplements
Nutritional weight loss supplements = purported to work by increasing energy expenditure, modulating carbs or fat metabolism, increasing satiety or blocking fat or carb absorption
2/13
Ephedrine = the primary active ingredient of herbal ephedra - has been studied both alone or in combo with caffeine
Placebo controlled studies have demonstrated the ephedrine w caff
DNP - Dinitrophenol
Chemical compound historically used in explosives, dyes + pesticides
Later marketed as a weight loss aid
Extremely dangerous with severe side effects + high fatality risk
Mechanism of Action
increases basal metabolic rate (BMR) - rapid fat + carb burning
Thermogenic effect - body temperature rises dangerously
Average metabolic rate increase = 11 % per 100 mg dose
Loss up to 1.5 kg per week reported
Uncoupling of Oxidative Phosphorylation
With DNP: ATP synthase func = disrupted
ATP production = stopped
Energy dissipates as a heat instead of being stored
DNP Mechanism of Action
Prevents ATP formation by blocking inorganic phosphate uptake
Increases oxygen consumption
Causes proton (H+) leakage across mitochondrial membrane
Risk
Carb consumption markedly increase - allows for rapid weight loss with small doses
Pyruvic acid is aerobically metabolised to H2O and CO2
Results in production of lactic acids when metabolized anaerobically
Discrepancy between stimulation of glycolysis + inhibition of oxidative phosphorylation = rapid production of pyruvic acid - leading to increase production of lactic acid
Failure of Thermoregulation
Excess proton leakage = heat generation
Increased metabolic rate - uncontrolled cal burings
Hyperthermia
Rapid heart rate, sweating, shortness of breath
Death
Capsaicin
Important compound in chili peppers
Animal studies - can reduce prevalence of obesity by suppressing inflammatory responses + enhancing fatty acid oxidation in adipose tissue + liver
Human studies - controversial
Some research - can help control body weight (BW) + reduce risk of developing obesity
Perception of Spicy Foods
Eating spicy food - increases appetite but reduces appetite + increases satiety
Mechanism = unclear
Acute lunches containing capsaicin = shown to increase + decrease auxin-releasing peptide - can affect hunger
Release of catecholamines caused by capsaicin affects appetite
Results of Capsaicin
Potential intake to reduce BMI, BW, and WC but no effect on WHR
Potential to promote lipid oxidation reduce appetite + accelerate energy metabolism - impacts weight loss
Mechanism of increasing liquid oxidation + energy consumption due to the activation of transient receptor potential vanilloid subtype 1
Large Scale Chinese Study Findings
The increase in body size may be linked to these added ingredients rather than capsaicin
Thermogenic
Caffeine
Proposed mechanism- CNS stimulation, lipolysis
Dosage - 100-400 mg
Green Tea
Proposed mechanism - norepinephrine enhancement
Dosage - 250-500 mg
Capsaicin
Proposed mechanism - TRPV1 receptor activation
Dosage - 2-10 mg/day
Yohimbine
Proposed mechanism - Alpha-2 receptor blockade
Dosage - 5-20 mg
Synephrine
Proposed mechanisms - beta adrenergic agonist
Dosage - 10-50 mg
L-Carnitine
Proposed mechanism - fatty acid transport
Dosage -1-3 g
5-HTP
Proposed mechanism - serotonin increase (appetite control)
Dosage - 100-300 mg
Forskolin
Proposed mechanism - cAMP activation (fat breakdown)
Dosage - 25-50 mg
Raspberry Ketones
Proposed mechanism - norepinephrine induced lipolysis
Dosage - 100-200 mg
CLA
Fat metabolism alteration
Dosage - 3-6 g