What do green tea, black tea, chili peppers, coffee, pure caffeine, calcium, conjugated linoleic acid, fish oil, flax oil and drinking cold water have in common? They all are sold as or said to be weight loss aids, that supposedly increase your metabolism, burn more calories and let you lose weight almost effortlessly. What does science say about them?
Green tea in the last years has been connected with all possible kinds of health benefits, among them helping against multiple sclerosis, reducing the effects of the "bad" LDL cholesterol, preventing cancer, and, not the least of the claims, aiding weight loss. Dr. Nicholas Perricone, a popular weight loss and health book author goes as far as claiming that simply drinking green tea instead of coffee for six weeks will let you lose ten pounds (4.5 kg).
Despite these claims, the scientific evidence is rather slim: In one study, green tea slightly increased fat burning and thermogenesis (the process of heat production in organisms), but the study was not designed to assess weight loss. Another study found no effect at all.
What you experience as "hot" when you eat a chili pepper is due to capsaicin, a chemical substance that naturally occurs in these fruits and causes a burning sensation when coming into contact with human tissue.
A 1985 study found that in rats capsaicin increases adrenaline production, which raises heart rate and should therefore burn more calories, while in 1986 a study concluded that capsaicin caused a reaction in the brain thought to suppress appetite.
While all this sounds promising and "weight loss experts" tell you to eat chilis or sell products containing capsaicin, it already ends here. Further research repeatedly found no effect on metabolism, for example here and here. If an effect exists, it most likely is so small that it won't make a big difference in weight control.
Coffee, and therefore caffeine, is almost everyone's favorite stimulant and its effects are very well documented: It raises alertness and can lead to increased performances in both endurance and strength sports. As it also raises metabolic rate for up to 24h after consumption, it didn't take long for caffeine to be sold as yet another weight loss aid.
Most studies reporting an effect of caffeine on weight control examined it combined with other substances. This study for example, which looked at caffeine taken together with ephedrine, a chemical substance with a stimulating effect similar to amphetamine. Only one study looked at caffeine alone and that one reported no more effect for caffeine than a placebo had.
Some of the effect in studies where caffeine was used in combination with another substance may have been due to the caffeine or they may have enhanced each other, but scientific evidence is once more slim and we may again assume that any effect will be negligible.
Before you now stop reading and conclude "ephredrine and caffeine is where it's at" and buy an ephedrine supplement, let us mention that the above study also showed that ephredrine alone was ineffective as well. And using ephedrine in combination with caffeine can have some hazardous effects.
Each alone can cause insomnia, tachycardia, nervousness, euphoria and tremors. Combining them can make these effects stronger, while the achieved weight loss will still be rather small: One study reports an average fat loss of 3.3 kg (7 lbs) over six months, compared to 2.8 kg (6 lbs) for participants on a placebo - a mere 0.5 kg (1 lb) difference.
Calcium is a chemical element that occurs in most, if not all, dairy products and plays an important role in many cellular processes, for example the building of bones. It became a contender in the fight against obesity when research showed that adults with calcium levels below normal had bigger waistlines and more body weight.
Numerous websites and advertisements took this as a chance to sell calcium supplements as a fatbusting wonder. But what they usually leave out is that the scientists behind above studies explicitly noted that calcium's positive effect only takes place in people whose nutrition doesn't provide enough calcium. Angelo Temblay, one of the scientists behind them, said:
Our hypothesis is that the brain can detect the lack of calcium and seeks to compensate by spurring food intake, which obviously works against the goals of any weight loss program. Sufficient calcium intake seems to stifle the desire to eat more.
The use of calcium supplements will therefore make no difference for you, if you want to lose weight, but have enough calcium in your diet.
Conjugated Linoleic Acid
Conjugated linoleic acid, often abbreviated as "CLA", is a fatty acid found in most meats and many dairy products. The idea behind using it for weight loss is that it enhances the use of fat as energy source, therefore preserving fat-free mass and changing body composition.
And indeed, a wide variety of studies found that CLA has a positive effect on weight management, but a meta-analysis of these revealed that the measurable fat loss due to CLA was rather small and amounted to 82 g per week at a daily dosage of 3.2 g.
The above meta-analysis also notes that CLA may increase insulin resistance, which can cause diabetes, a condition overweight people already have a greater risk for.
Flaxseed And Fish Oil (Omega-3 Fatty Acids)
While both have very different sources, one a plant, the other fish, their supposed weight loss effect comes from a component they share: omega-3 fatty acids. Science considers them essential to human health, as the body can't produce Omega-3s on its own and them playing a crucial role in normal brain function and during growth and development.
In animal studies omega-3 fatty acids had a positive influence on weight management, but the effect couldn't be replicated in humans. In a 2010 study people on a placebo lost 5.8 kg (13 lbs), while the fish oil group lost 5.2 kg (11 lbs).
I am convinced omega-3 fatty acids have a positive effect on human health and you need them, but a benefit on weight management remains dubious.
Drinking Cold Water
The theory here is that when you drink cold water, the body will have to heat it up, expending energy in the process.
Once more we can conclude that if there is an effect at all, it's very small. You are better advised to swim in water than drink it when hoping for weight loss; a 155 lbs person burns about 455 kcal when leisurely swimming for an hour.
The scientific evidence for weight loss effects of these supplements is rather shaky. If there was an effect, it was rather small or only applied to special populations.
You could of course go now and combine all of them. It probably would be a rather interesting, yet possibly fatal self-experiment, when you try to find out what high doses of caffeine, ephedrine and capsacain taken together will do to your body. A much healthier alternative is to change your eating habits and include some fitness activities into your lifestyle.
Last but not least, it simply is common sense telling us that if all you had to do to lose weight was drink green tea or swallow a pill, then there would be no one suffering from obesity.