|Caffeine: Women's Weight Loss Breakthrough or Bust?
Aditi Majumdar and Len Kravitz, Ph.D.
Ahrens, J.N., Crixell, S.H., Lloyd, L.K., and Walker, J.L. (2007). The physiological effects of caffeine in women during treadmill walking. Journal of Strength and Conditioning Research. Vol. 21(1), 164-168.
Caffeine is one of the world's most popularly consumed substances. In the U.S. a typical coffee-drinking adult consumes 200-400 mg of caffeine (2-4 cups of coffee) each day (Armstrong, 2002). Although caffeine consumption is not a necessary component of a regular, healthy diet, its prevalence in everyday foods and beverages depicts its true influence on society (see Side Bars 1, 2, and 3 for more on caffeine).
For decades, researchers have investigated caffeine's ergogenic potential for enhancing athletic performance. Caffeine, classified and recognized as a mild stimulant, is consumed by many athletes for the purpose of boosting athleticism. Results of numerous studies (predominantly in trained male athletes) have consistently suggested that caffeine is an ergogenic aid for cardiovascular activities (~30 - 60 minutes), and its effects are less impressive in the performance of short-term, high intensity exercises (Graham, 2001, Armstrong, 2002).
One popular theory underlying caffeine's ergogenic endurance effect is that caffeine inhibits the breakdown of muscle glycogen (stored carbohydrate in the muscles) (Armstrong, 2002). Further, it is suggested, but not clearly established in the literature, that caffeine enhances endurance performance by increasing the release of epinephrine into the blood, thus stimulating the release of free fatty acids (disassembled molecules of triglycerides) from fat tissue and/or skeletal muscle (Spriet, 1995). The working muscles use this extra fat early in exercise, reducing the need to use muscle carbohydrate (glycogen). The sparing of muscle glycogen may help to delay fatigue in exercise.
Of course, athletes are not the only people consuming caffeine for athletic performance and body composition reasons. Yet, there is a definite lack of research examining the ergogenic effects of caffeine with the recreationally active individual, particularly females. Debate also exists whether or not caffeine has a direct effect on weight loss (Graham, 2001).
The purpose of this study was to investigate the potential of caffeine as an ergogenic aid, by determining differences in metabolic and cardiovascular responses for treadmill walking after caffeine intake in physically active females. This study investigated caffeine's influence on an individual's oxygen uptake (VO2), rate of perceived exertion (RPE), heart rate (HR), respiratory exchange ratio (RER) [which determines what fuel source is being used], rate of energy expenditure (REE), and percentage of maximal oxygen uptake reserve (%VO2R). An additional aim of this study was to clarify caffeine's potential contribution towards weight loss efforts.
Twenty-six young women (ages 19-28 yrs and 129-213 lbs) began the study, but 6 subjects withdrew due to personal or health reasons. None of the subjects were regular users of caffeine, as defined (by the authors) as consuming < 80 mg of caffeine per day (&Mac178; one cup of coffee). All subjects exhibited poor to good fitness levels, according to a VO2 max test, with the average VO2 max = 32.9 ml/kg/min. In addition, a 3-day dietary inventory indicated that subjects consumed 53%, 14%, and 33% of calories from carbohydrate, protein and fat, respectively.
Testing procedures involved four independent laboratory visits (separated by 2 to 7 days between visits). The initial visit included the attainment of descriptive characteristics (height, weight, age) and the performance of a maximal aerobic capacity test (VO2max). The caffeine supplement used in the trials was an anhydrous (dry) caffeine powder, dispensed into capsules. The experiment was placebo-controlled, with use of dextrose capsules for the control trial. Originally the caffeine doses for the trials in this study were 3 mg/ kg (of BW), 6 mg/kg (of BW), and 9 mg/kg (of BW), which are the equivalent to 2-6 cups of coffee. However, the 9 mg/kg protocol was eliminated because early testing showed that it caused several women to experience adverse reactions such as body tremors, sweating, dizziness, and vomiting.
Preparation for each trial was identical. Subjects were instructed to abstain from any caffeine intake 12 hours prior to each trial, as well as follow the same food and beverage intake for 24 hours prior to each trial.
At the start of each trial subjects were administered a caffeine or placebo capsule with 8 ounces of water. There was a 60-minute gap between capsule intake and treadmill walking. Each trial involved the subject walking at a pace of 3.5 mph on the treadmill for duration of 8 minutes. The study researchers note that the ergogenic effects of caffeine have been demonstrated to exhibit in as little as 5 minutes of aerobic exercise.
The 3 mg/ kg dose of caffeine supplement did not have any significant effects on physiological performance. The 6 mg/ kg dose of caffeine correlated to an increase in VO2 (4% increase), REE (5% increase), and %VO2R (5% increase). However, the 6 mg/kg dose of caffeine did not effect RPE, HR, or RER. Interestingly, although there was an increase in VO2 there was no change in HR. Typically HR increases when oxygen uptake increases. Thus, this experimental result suggests caffeine may have enhanced cardiovascular efficiency.
In general, the values of HR and RPE help to define the range of exercise intensity. In this experiment, the exercise intensity was moderate, and the values of HR and RPE reflected a light intensity. It is possible that the exercise stimulus of treadmill walking at 3.5 mph was too low of an intensity for caffeine to have a measurable effect. However, in the results of the subjects' subjective perception, the task of treadmill walking was not assessed to be any easier with caffeine supplementation.
The increase in REE was encouraging because it implied an increase in caloric expenditure. However, the authors calculated that a moderate caffeine dose of 6 mg/kg consumed prior to a 30-minute walk would only increase the total energy expenditure by 7 kilocalories, a value incapable of impacting weight loss.
Caffeine supplementation does not provide recreationally active women a viable pathway to weight loss or any meaningful ergogenic performance benefits. As a personal trainer and fitness professional, it is best to design an effective aerobic and resistance training program, while simultaneously encouraging nutritional strategies that specifically address an individual's needs for weight management. Regular aerobic exercise, resistance training and proper nutrition habits are always going to have the most beneficial effect on an individual's overall health as well.
Side Bar 1. What is Caffeine?
Caffeine is a bitter-tasting chemical substance that possesses qualities of a mild stimulant. It acts directly on the central nervous system (CNS) and skeletal muscles (Spriet 1995). As a stimulant of the CNS, caffeine triggers an increase in blood circulation, heart rate, urine output, gastric secretions and causes a decrease in glucose metabolism (Armstrong, 2002). Caffeine is most commonly associated with coffee and tea and found in numerous plants. The reason for such availability is that many plants naturally produce caffeine as a pesticide towards insects.
Side Bar 2. Ten Common Questions and Answers about Caffeine
1. Is caffeine addictive?
Yes, but the effects are much milder than the effects of other drugs. Caffeine increases the body's natural level of dopamine (a pleasure-enhancing neurotransmitter).
2. Does caffeine improve memory?
Yes, and No. Caffeine intensifies the level of brain activity. This results in faster reaction times and better short-term memory (by increasing the amount of acetylcholine, a neurotransmitter that improves short-term memory), but not long-term memory.
3. Does caffeine provide energy?
No. Caffeine is a chemical, not a macronutrient. However, it has actions of a mild stimulant, and thus may cause an individual to perceive less fatigue.
4. Will caffeine make you smarter?
No. Caffeine effects memory retention, not acquisition or ability to process information.
5. Can people become immune to the effects of caffeine?
Yes. The stimulatory and ergogenic effects of caffeine are often more apparent in caffeine nonusers.
6. Does decaffeinated coffee have any caffeine?
Yes. In order for decaf to be considered decaf, 97% of the caffeine must be removed, which means the brew still contains miniscule amounts of caffeine.
7. Is caffeine associated with heart disease?
No. Any evidence linking caffeine consumption to coronary heart disease is very weak. As well, caffeine does not lead to an increase in blood pressure or hypertension.
8. Is it safe to drink caffeine containing beverages during pregnancy?
In moderation. Although up-to-date research has not established a direct correlation between caffeine intake and spontaneous abortions or birth defects, most health experts recommend expecting mothers to limit themselves to two cups of coffee per day.
9. Will caffeine consumption contribute to breast cancer?
No. Caffeine itself does not trigger the development of breast cancer.
10. Is caffeine a risk factor for osteoporosis?
No. Most studies have shown that caffeine intake is not a risk factor for osteoporosis, particularly in women who consume sufficient calcium.
Side Bar 3. Does Caffeine cause Dehydration?
Water facilitates every metabolic function in a cell. From a workout perspective, proper hydration helps to achieve optimal athletic performance by aiding in efficient cell respiration and controlling body temperature. Coffee and/or caffeine are regularly described as diuretics, proposing that ingestion may lead to reduced hydration status prior to and during exercise. However, the present literature does not support this acute diuretic effect. In fact, during exercise, caffeinated beverages hydrate almost identical to non-caffeinated beverages (Armstrong, 2002).
Armstrong, L.E. (2002). Caffeine, body fluid-electrolyte balance, and exercise performance. International Journal of Sport Nutrition and Exercise Metabolism, 12, 189-206.
Graham, T.E. (2001). Caffeine and exercise: Metabolism, endurance and performance. Sports Medicine, 31(11): 785-807.
Spriet, L.L. (1995). Caffeine and performance. International Journal of Sport Nutrition, 5: S84-S99.
Aditi Majumdar is enrolled in her third year of the Exercise Science
program at the University of New Mexico (Albuquerque). She is a UNM Regent's Scholar, as well as a pole vaulter for the UNM Track & Field team. She plans to
attend medical school after her undergraduate studies to pursue a
career as an orthopaedic surgeon.
Len Kravitz, Ph.D., is the Program Coordinator of Exercise Science and Researcher at the UNMA where he recently won the "Outstanding Teacher of the Year" award. Len was honored with the 1999 Canadian Fitness Professional International Presenter of the Year and the 2006 Canadian Fitness Professional Specialty Presenter of the Year awards and chosen as the American Council on Exercise 2006 "Fitness Educator of the Year.