Supplement research


Thermogenics

What are thermogenics?

Thermogenics are agents that are used to increase metabolic rate and thus increase overall energy expenditure. Examples of thermogenic substances are synephrine, ginger root, caffeine, and cayenne powder.

Proposed Benefits of thermogenics

Thermogenics are used to enhance weight loss.

Mechanism of Action of thermogenics

It is proposed that by increasing metabolic rate and thus overall energy expenditure, thermogenics will result in weight loss.

Other components of thermogenics are said to decrease lipogenesis (the formation of fat) and suppress appetite e.g. Garcinia cambogia. The active ingredient of Garcinia cambogia is hydroxycitric acid. Hydroxycitric acid competitively inhibits the extramitochondrial enzyme adenosine triphosphate-citrate (pro-3S)-lyase. It is thought that hydroxycitric acid, because it is a citrate cleavage enzyme, may play an essential role in the inhibition of de novo lipogenesis (the formation from fat from sources such as carbohydrate).

Research on thermogenics

One unpublished study reported that synephrine plus caffeine increased metabolic rate, which may result in body fat loss (1). Blood pressure increased in this study, but not as high as is seen with ephedrine. It has been suggested that synephrine should not be ingested by individuals with severe hypertension, tachyarrhythmias, and narrow-angle glaucoma and monoamine oxidase inhibitor recipients and those taking decongestant-containing cold preparations (2).

Another component of some thermogenic supplements is Garcina cambogia (hydroxycitric acid). This is purported to promote weight loss, in part by suppressing hunger. The research on hydroxycitric acid has produced mixed results. Problems with study design include, small subject numbers (3,4), lack of a placebo or double-blinding (5) and inappropriate methods to measure body composition (4). Several studies did not solely use hydroxycitric acid, but also other compounds such as chromium and caffeine, this making it difficult to interpret which compound might elicit an effect (3,5-7). Also a lot of the research is presented in abstract form and not in peer reviewed journals (4,5,7). A recent 12-week randomised placebo-controlled clinical trial failed to show any benefit of hydroxycitric acid over placebo in terms of weight loss in a group of overweight males and females (8). Body composition was measured by the accurate method of DXA. The subjects in this study were also asked to follow a low-energy high fibre diet (5045KJ, 50% carbohydrate, 20% fat, 30% protein). It could be argued that such a diet may not have allowed for the optimal lipid synthesis-inhibition properties of hydroxycitric acid. These properties may be maximised with the consumption of a higher carbohydrate diet where hydroxycitric acid would prevent the conversion of excess carbohydrate to storage fat.

One study which investigated the effects of hydroxycitric acid (HCA) on appetite control showed no effects on appetite variables, although those taking HCA did lose more weight that the placebo group (9).

Obviously better controlled studies are required to provide more consistent results.

Rating of Efficacy for thermogenics

Some of the components of thermogenic supplements appear to enhance the metabolic rate, although all components have not being investigated specifically in terms of weight loss.

6 1/2/10

 

References

  1. Shugarman A. Effect of thermogenic dietary supplements on resting metabolic rate in healthy male and female volunteers. Master's Thesis. University of Utah, Salt Lake City, 1998.
  2. Penzak S.R., Jann M.W., Cold J.A., Hon Y.Y., Desai H.D. and Gurley B.J. Seville (sour) orange juice: synephrine content and cardiovascular effects in normotensive adults. J Clin Pharmac. 41:1059-1063, 2001.
  3. Conte A.A. A non-prescription alternative on weight reduction therapy. Am J Bariatr Med. Summer:17-19, 1993.
  4. Thom E. Hydroxycitrate (HCA) in the treatment of obesity. Int J Obes. 20 (suppl 4):48, 1996.
  5.  Badmaev V. and Majeed M. Open field, physician controlled, clinical evaluation of botanical weight loss formula citrin. Presented at: Nutracon 1995. Abstract, 1995.
  6. Girola M., De Barnardi M. and Contos S. Dose effect in lipid-lowering activity of a new dietary intetrator (chitosan, Garcinia cambogia extract, and chrome). Acta Toxicol Ther. 17:25-40, 1996.
  7. Rothacker D.Q. and Waitman B.E. Effectiveness of a Garcinia cambogia and natural caffeine combination in weight loss: a double-blind placebo-controlled pilot study. Int J Obes. 21:53, 1997.
  8.  Heymsfield S.B., Allison D.B., Vasselli J.R., Pietrobelli A., Greenfield D. and Nunez C. Garcinia cambogia (hydroxycitric acid) as a potential antiobesity agent. JAMA. 280:1596-1600, 1998.
  9. Mattes R.D. and Bormann L. Effects of (-)-hydroxycitric acid on appetite variables. Physiol & Behav. 71:87-94, 2000.