Fat burners in a bottle?

A few years ago billboards announced the arrival of "negative calorie" food. Drinking three 12-oz. cans a day of Enviga, the Coca Cola and Nestle carbonated tea drink, will burn an extra 60-100 calories daily, claimed the products' packaging.

The Center for Science in the Public Interest (CSPI) filed a lawsuit against Coke for Enviga's false weight-loss claims. Coke and Nestlé agreed to add language to the labels and marketing materials stating that the product will not promote weight loss without diet and exercise and Enviga is slowly vanishing from shelves. But supplements and foods claiming to slim you down have not - they are alive and thriving.

A new paper in Obesity Reviews looks at the dynamic market of nutritional supplements claimed to increase fat metabolism, and explores how much evidence - or lack of it - is behind some of these popular supplements.

What is a 'fat burner'?

A fat burner is a substance that is claimed to increase energy expenditure, make you lose weight, or somehow promote fat breakdown. Many fat-burning supplements combine several ingredients, claimed to work in concert. Is there such a thing as a fat burner? The article examines some of the most popular such miracles, and I'll discuss just a few of those.

Fat burners on the market


The ultimate functional ingredient, caffeine appears naturally in coffee, tea and cocoa and is also added to many foods and drinks. Anyone who drinks coffee knows that coffee does have active ingredients that increase alertness - that's why I love my morning cup. It makes loose dreamy words stick into lucid sentences. But does it increase energy expenditure and promote weight loss?

A few studies showed that high doses of caffeine increased metabolic rate, however, longer-term studies tracking dieters taking caffeine or placebo showed caffeine performing no better than the dummy pill. Overall, the authors conclude:

"Caffeine on its own has not been shown to be effective in reducing body weight and if caffeine increases fat metabolism, the effects are generally small"


Carnitine, which occurs naturally in meat, and is produced by our own liver and kidneys, is claimed to improve fat metabolism and increase muscle mass.

Most of the carnitine in our body is in our muscles, and our muscle takes up carnitine from our blood against a huge concentration gradient (sorry for the flashback to high school chemistry, but it's needed in order to understand how little sense this makes). Studies have shown that the enzyme that is responsible for transferring carnitine into the muscle is at maximum capacity, and therefore ingesting extra carnitine doesn't raise muscle carnitine at all.

The only way in which muscle carnitine could be elevated was by increasing blood levels of both carnitine and insulin at the same time - by insulin intravenous drip or very large amounts of ingested sugar. This impractical scenario is quite counterproductive from the weight-loss point of view.

Carnitine supplementation for weight-loss just doesn't make sense!


Tea contains catechins, which are thought to stimulate fat metabolism. Green tea, which is non-oxidized and non-fermented tea leaves, has especially high levels of catechins, the most interesting of which is EGCG (epigallocatechin 3-gallate). The authors review the green-tea weight burning studies and find them inconclusive:

"Green tea has the potential to increase fat metabolism at rest, also during exercise, and may help to lose body fat and body weight. As with caffeine, the effects appear to be relatively small…"


Chromium is added to many "functional" foods and drinks (Vitamin Water, Fuze) and is sold as part of many supplements as a fat burner and muscle builder. Chromium occurs naturally in broccoli, red wine, mushrooms, brewer's yeast, wheat germ and other foods, and was reported to increase lean body mass during exercise.

The excitement was dampened by further, better studies that found chromium had no effect - overall, the majority of studies find it useless - and the authors also caution that a few studies on cell cultures found chromium can cause chromosomal damage.

Want to burn calories?

The authors, A. E. Jeukendrup and R. Randell, conclude with an overall impression that most of the supplements marketed as fat burners have little or no science to support their claims, and that among the group, caffeine and green tea have some effect, but it is small, and more consistent in habitual caffeine users. They write:

"The ever increasing list of fat-burning supplements is industry driven, and is likely to grow at a rate that is not and cannot be matched by similar increase in scientific underpinning"

In other words, marketers are quick to announce miracle solutions based of the flimsiest of evidence collected on a few lab mice or a cell culture; if and when the science manages to amass enough research that more often than not doubts the substance's merit, sellers are already quick to market with the next new fat-burning sensation.

How can we end this? Silly and optimistic as I am, I'm hoping for an end to health claims on foods and supplements. Health claims were introduced in 1994, have been so miserably abused and have become so utterly misleading that it's just time to say goodbye.

The other more realistic way is that consumers will start rejecting the hype and express their skepticism with their wallets.

Let's end with the age-old solution to fat burning. We know it works. It's healthy and inexpensive, too. It's called exercise.

Dr. Ayala

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