Debbie J., MS, RD contributed this article –

Without giving a blanket response (as all products vary) let me explain how thermogenics work. Caffeine [or its herbal counterparts guarana, kola, yerba mate] and epinephrine replacements, such as synephrine, activate the sympathetic nervous system (which regulates organs and mediates stress response) — raising metabolic rate, increasing energy expenditure and releasing stored fat.  Caffeine is known to enhance fat burning. When combined into supplement form, these compounds may improve exercise performance or enhance fat loss. Yeah!

After looking into research studies* for a couple of popular thermogenics, I found the results to be promising but not convincing… meaning results shouldn’t be directly applied to the population at large. This is because a small group of college students at rest for 3 hours is very different than older active men and women using a product routinely. The effectiveness of a supplement is also clouded when use among sedentary adults is combined with a new exercise program, since the exercise itself produces physiological changes.

Here’s what the research says about these potential effects:

Metabolic Rate

One study showed a range of 7-15% rise in energy expenditure over three. Whereas another showed a near 30% rise in energy expenditure at rest over three hours for a single dose. Daily use prompted a 100 Calorie rise in metabolic rate.

Fat Loss

Greater stored fat was used as an energy source for a single dose. Daily use affected a modest 1.3 pound loss over a month. A longer 10 week period averaged 5.5 pounds loss for sedentary men with a concurrent exercise program, equating to a 2% reduction in body fat percentage.

Muscle Gain

A few studies showed greater muscle mass gains with thermogenic use compared to controls. One study indicated a 3.3 pound gain for sedentary men over 10 weeks with a concurrent exercise program. An increase in muscle mass was also observed in overweight women with a concurrent exercise program.

Exercise Performance

For high intensity exercise, thermogenics may improve muscle endurance, not power output. That translates into more muscle contractions, not stronger ones. It follows in theory that more repetitions would create enhanced muscle growth.

For endurance work, the improvement is in aerobic exercise performance. An observed increase in VO₂ (volume of oxygen consumed) and increased time to exhaustion may mean improved cardio respiratory fitness.

Other Effects

Stimulating the central nervous system is like going into “fight or flight” mode, readying your body for action. Being in panic mode ongoing is stressful to your system.

A couple studies suggest cholesterol and other blood lipids may reduce marginally while serum glucose (blood sugar) may rise. These are simply observed outcomes, not definitive cause-and-effect situations.

It’s not proven whether physical benefits are maintained once use of the product is ceased. So continued administration may be necessary to reap benefits, while safety is not determined for chronic use.

Now for my professional opinion:  I wouldn’t call them a “waste of money” as there is some effectiveness. The pay-off may be limited though, especially for a recreationally active adult with little weight to lose. So it is only worth it if you feel that a loss of less than a half-pound per week justifies the cost of thermogenic supplements. For sedentary adults just starting exercise, the outcomes may be greater. For athletes, using a thermogenics as an ergogenic aid is an option for a cutting edge.

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Debbie James is a registered dietitian. Any views or opinions presented in this article are solely those of the author and do not necessarily represent the opinions or recommendations of Fitness International, LLC.

*References

Thermogenic effect of an acute ingestion of a weight loss supplement. Jay R Hoffman, Jie Kang, Nicholas A Ratamess, Stefanie L Rashti, Christopher P Tranchina and Avery D Faigenbaum. Journal of the International Society of Sports Nutrition 2009, 6:1  doi:10.1186/1550-2783-6-1

Dietary supplement increases plasma norepinephrine, lipolysis, and metabolic rate in resistance trained men. Richard J Bloomer, Kelsey H Fisher-Wellman, Kelley G Hammond, Brian K Schilling, Adrianna A Weber and Bradford J Cole.  Journal of the International Society of Sports Nutrition 2009, 6:4 doi:10.1186/1550-2783-6-4

The acute effects of the thermogenic supplement Meltdown on energy expenditure, fat oxidation, and hemodynamic responses in young, healthy males.  Jean Jitomir, Erika Nassar, Julie Culbertson, Jen Moreillon, Thomas Buford, Geoffrey Hudson, Matt Cooke, Richard Kreider and Darryn S Willoughby. Journal of the International Society of Sports Nutrition 2008, 5:23

Metabolic responses to the acute ingestion of two commercially available carbonated beverages: A pilot study. Ron W Mendel and Jennifer E Hofheins. Journal of the International Society of Sports Nutrition 2007, 4:7 doi:10.1186/1550-2783-4-

Acute effects of ingesting a commercial thermogenic drink on changes in energy expenditure and markers of lipolysis. Vincent J Dalbo^†, Michael D Roberts^†, Jeffrey R Stout^† and Chad M Kerksick

Journal of the International Society of Sports Nutrition 2008, 5:6 doi:10.1186/1550-2783-5-6

Efficacy and safety of a popular thermogenic drink after 28 days of ingestion. Michael D Roberts, Vincent J Dalbo, Scott E Hassell, Jeffrey R Stout and Chad M Kerksick. Journal of the International Society of Sports Nutrition 2008, 5:19 doi:10.1186/1550-2783-5-19

Pre-workout consumption of Celsius® enhances the benefits of chronic exercise on body composition and cardiorespiratory fitness.  Jeffrey R Stout*, Jordan R Moon, Sarah E Tobkin, Christopher M Lockwood,

Abbie E Smith, Jennifer L Graef, Kristina L Kendall, Travis W Beck and Joel T Cramer. Journal of the International Society of Sports Nutrition 2008, 5(Suppl 1):P8 doi:10.1186/1550-2783-5-S1-P8

Low-calorie thermogenic beverage and exercise improves composition and lipid profile in overweight and obese women. Abbie E. Smith, Jordan R. Moon, Chris M. Lockwood,, Kristina L. Kendall, David H.

Fukuda, Joel T. Cramer and Jeffrey R. Stout.  Unpublished, University of Oklahoma 2009

Low-Calorie energy drink improves physiological response to exercise in previously sedentary men: A placebo controlled efficacy and safety study.  Christopher M. Lockwood, Jordan R. Moon, Abbie E. Smith, Sarah E. Tobkin, Kristina L. Kendall, Jennifer L. Graef, Joel T. Cramer, and Jeffrey R. Stout.  Journal of Strength and Conditioning Research 2010 Aug;24(8):2227-38. doi: 10.1519/JSC.0b013e3181aeb0cf