by Aditi Majumdar and Len Kravitz, PhD on Jan 01, 2008


Women’s weight loss breakthrough or bust?

Ahrens, J.N., et al. 2007. The physiological effects of caffeine in women during treadmill walking. Journal of Strength and Conditioning Research, 21 (1), 164–68.

Caffeine is one of the world’s most popularly consumed substances. In the U.S., a typical coffee-drinking adult consumes 200–400 milligrams (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 sidebars for more details on caffeine).

For decades, researchers have investigated caffeine’s ergogenic potential for enhancing athletic performance. Results of numerous studies (predominantly involving trained male athletes) have consistently suggested that caffeine, recognized as a mild stimulant, is an ergogenic aid for cardiovascular activities (lasting ~30–60 minutes) and that 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 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 delay fatigue in exercise.

Athletes are not the only people consuming caffeine for athletic performance and body composition reasons. To date, there has been a definite lack of research examining the ergogenic effects of caffeine on recreationally active individuals, particularly females. Debate also exists as to whether caffeine directly affects weight loss (Graham 2001).

The Study

The purpose of this study was to investigate caffeine’s potential as an ergogenic aid by determining differences in metabolic and cardiovascular responses to treadmill walking in physically active females given either caffeine or a placebo. The study investigated caffeine’s influence on oxygen uptake (V02); 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 (%V02R). An additional aim was to clarify caffeine’s potential contribution to weight loss efforts.

Twenty-six young women (ages 19–28 years and weighing 129–213 pounds) began the study, but six withdrew for personal or health reasons. None of the subjects were regular users of caffeine, meaning (as defined by the authors) that they consumed < 80 mg of caffeine per day (< 1 cup of coffee). All subjects exhibited poor to good fitness levels, according to a maximal aerobic capacity (V02max) test, with the average V02max being 32.9 milliliters per kilogram (kg) per minute. 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, 2–7 days apart. During the initial visit, researchers recorded subjects’ descriptive characteristics (height, weight, age) and subjects performed a V02max test. The caffeine supplement used in the trials was an anhydrous (dry) caffeine powder, dispensed into capsules. The experiment was placebo-controlled, with dextrose capsules used for the control trial. Originally the caffeine doses for the trials were 3 mg/kg (of body weight/BW), 6 mg/kg (of BW) and 9 mg/kg (of BW)—amounts 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 and to follow the same food and beverage intake for 24 hours prior to each trial.

At the start of each trial, subjects were given either a caffeine or a placebo capsule with 8 ounces of water. There was a 60-minute gap between capsule intake and treadmill walking. Each trial involved the subjects walking on the treadmill at a pace of 3.5 miles per hour (mph) for 8 minutes. The study researchers noted that, according to previous research, the ergogenic effects of caffeine could show up within 5 minutes during aerobic exercise.

The 3 mg/kg dose of caffeine did not have any significant effects on physiological performance. The 6 mg/kg dose of caffeine correlated to an increase in V02 (4% increase), REE (5% increase) and %V02R (5% increase). However, the 6 mg/kg dose of caffeine did not affect RPE, HR or RER. The fact that there was no change in HR even though V02 increased is interesting; 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 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 intensity of treadmill walking at 3.5 mph was too low for caffeine to have a measurable effect. Participants did not rate the task of treadmill walking as 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 increase the total energy expenditure by only 7 kilocalories, a value incapable of impacting weight loss.

Practical Application

Caffeine supplementation does not provide recreationally active women a viable pathway to weight loss or any meaningful ergogenic performance benefits. Rather than encouraging caffeine consumption, personal trainers and fitness instructors are better off designing an effective aerobic and resistance training program, while simultaneously encouraging basic nutrition strategies that specifically address clients’ needs for weight management. Regular aerobic exercise, resistance training and proper nutrition habits are always going to have the most beneficial effect on overall health.

SIDEBAR: What Is Caffeine?

Caffeine is a bitter-tasting chemical substance that possesses the qualities of a mild stimulant. It acts directly on the central nervous system (CNS) and skeletal muscles (Spriet 1995). As a CNS stimulant, caffeine triggers an increase in blood circulation, heart rate, urine output and gastric secretions and causes a decrease in glucose metabolism (Armstrong 2002). Caffeine is most commonly associated with coffee and tea but is found in numerous plants. That’s because many plants naturally produce caffeine as a pesticide.

SIDEBAR: 10 Frequently Asked Questions 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 acts as 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 nonusers of caffeine.

6. Does decaffeinated coffee have any caffeine?
Yes. In order for decaf to qualify as such, at least 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. Also, caffeine does not lead to an increase in blood pressure or hypertension.

8. Is it safe to drink caffeinated 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 that expectant mothers limit themselves to 2 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.

SIDEBAR: 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 by controlling body temperature. Coffee and/or caffeine are regularly described as diuretics, suggesting that ingestion may lower hydration levels before and during exercise. However, the present literature does not support this acute diuretic effect. In fact, during exercise, caffeinated beverages hydrate almost identically to noncaffeinated beverages (Armstrong 2002).

Aditi Majumdar is enrolled in her third year of the exercise science program at the University of New Mexico at Albuquerque (UNMA). She is a UNMA Regents’ Scholar, as well as a pole vaulter for the UNMA track and field team. She plans to attend medical school to pursue a career as an orthopedic surgeon.

Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at UNMA, where he recently won the Outstanding Teacher of the Year Award. In 2006 he was also honored as the Can-Fit-Pro Specialty Presenter of the Year and as the ACE Fitness Educator of the Year.

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.


Want more from Len Kravitz?

Fitness Journal, Volume 5, Issue 1

Find the Perfect Job

More jobs, more applicants and more visits than any other fitness industry job board.

© 2008 by IDEA Health & Fitness Inc. All rights reserved. Reproduction without permission is strictly prohibited.

About the Authors

Aditi Majumdar

Aditi Majumdar IDEA Author/Presenter

Len Kravitz, PhD

Len Kravitz, PhD IDEA Author/Presenter

Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico in Albuquerque, where he recently won the Outstanding Teacher of the Year award. Len was also honored as the 2006 Fitness Educator of the Year by the American Council on Exercise.