Thermogenic Fat Burners for Weight Loss (Feeling the Burn)

Conjugated linoleic acid (CLA), an unsaturated omega-6 fatty acid mainly found in dairy products and meat, has been shown to reduce body fat and prevent weight gain. The International Journal of Obesity published a study in 2001 that found a four-week supplementation of CLA (as Tonalin® CLA, from Cognis Nutrition and Health) in obese men with metabolic syndrome may decrease abdominal fat, without simultaneous effects on overall obesity or other cardiovascular risk factors.⁹ The researchers added due to the limited sample size, the effects of CLA in abdominal obesity need to be further investigated in larger trials with longer duration. A Scandinavian study demonstrated a significantly higher reduction in body fat mass for groups who ingested CLA (P=0.03), compared to the placebo group; however, there was no effect on body fat mass with CLA doses higher than 3.4 g/d.¹⁰

Interestingly, one French study showed CLA supplementation did not affect adipose weight or the components of energy expenditure despite a theoretically higher capacity of red muscle to burn fat; but it did prevent the body from increasing levels of triglycerides, a type of fat.¹¹ However, a 2007 study reported supplementation with 4 g/d of 78 percent active CLA isomers (as Tonalin) increased fat utilization, fat burning and energy expenditure during sleep in healthy adults.¹²

Stress can also induce thermogenesis, according to an Australian study indicating psychological stress causes activation of 5-HT2A receptors, a member of the serotonin receptor family, in neural pathways that control thermogenesis in the BAT and facilitate the narrowing of blood vessels in the skin.¹³

Botanical Ingredients

Botanicals also contribute to thermogenesis. Bitter orange (Citrus aurantium) was one of the high-profile ingredients formulators turned to when ephedra (Ma huang) was taken off the market. Studies have supported its efficacy and safety. One double blind, placebo-controlled study at Greenwich Hospital in Connecticut involved subjects given Citrus aurantium extract (as Advantra Z®, from Nutratech), caffeine and St. John’s wort while on a strict diet and exercise plan.¹⁴ At the end of six weeks, subjects in the treatment group lost significantly more body weight and fat than those in the placebo or control group. There were no significant changes in blood pressure, heart rate, electrocardiographic findings, serum chemistrics or urinalysis, suggesting the combination of Citrus aurantium extract, caffeine and St. John’s wort is safe and effective when combined with mild caloric restriction and exercise for promoting both body weight and fat loss in healthy overweight adults.

A Canadian study conducted in 2005 stated the thermogenic effect of food in men, when given Citrus aurantium as a supplement, was much higher than in women; however, when both male and female subjects were administered Citrus aurantium in their meal, it increased the thermic effect of food of only women to values no longer different from men.¹⁵Citrus aurantium had no effect on blood pressure and pulse rate but it increased epinephrine excretion by 2.4 fold.

In an unpublished study supported by Nutratech Inc. at the University of Colorado, Colorado Springs, researchers found ingestion of Advantra Z in an herbal blend increased the RMR without affecting heart rate and blood pressure.

Green tea and green bean coffee extract are popular mainly for their high antioxidant content; however, they also appear to play a role in fat burning. A Japanese study conducted in 2006 found green bean coffee extract “is possibly effective against weight gain and fat accumulation by inhibition of fat absorption and activation of fat metabolism in the liver.”¹⁶

Green tea, meanwhile, was found in a study out of the University of Geneva to significantly increase 24-hour energy expenditure and significantly decrease 24-hour respiratory quotient without any change in urinary nitrogen.¹⁷ The researchers concluded green tea extract has thermogenic fat burning properties and promotes fat oxidation beyond that explained by its caffeine content per se and it may play a role in the control of body composition through sympathetic activation of thermogenesis, fat oxidation or both.

Another study involved 14 subjects given a placebo or a capsule of 200 mg of caffeine and epigallocatechin-3-gallate (EGCG), a catechin found in green tea, three times daily 30 minutes before meals.¹⁸ The results showed a significant increase in 24-hour energy expenditure with all EGCG-caffeine mixtures compared with the placebo. There was no effect observed for lipid oxidation with the EGCG-caffeine mixture.