In the world of weight loss supplements, there are essentially three mechanisms by which a supplement can help you lose weight. We've talked about them before, but it's worth going over them in more detail.
The three types of weight loss supplements are characterized by how they affect the body.
- One type, known as appetite suppressants, work to fill you up. When you're full and stay full longer, you have less desire to eat, and thus you intake fewer calories and can lose weight.
- One type, known as thermogenics, stimulate your body to convert stored fat into energy. This energy is most often presented as body heat, hence the "thermo" name.
- One type, known as inhibitors, work to prevent your body from absorbing all of the nutrients in a given meal. Fewer nutrients absorbed means less energy that can be stored as fat.
All three of these can be roughly classified as fat burners. For the most part, there's no difference between the products listed as fat burners and the products listed as thermogenics. It's largely a marketing thing; the fancy word thermogenic makes a product sound more scientific, which tricks people into thinking the product has been tested, proved, or approved by science, when it's really just another supplement.
We have often seen the same products listed as both fat burners and thermogenics on different storefronts. Really, it all depends on how much effort the store puts into keyword selection to attract people looking for one or the other.
How Thermogenics Work
Thermogenics are some of the most dangerous weight loss supplements, because of their potential side effects and the kinds of ingredients often included in them.
A thermogenic is a stimulant. It's a chemical that interacts with your body to convince it to burn its stored energy. Caffeine is one such example: it gives you energy and makes you more alert, but can often have negative side effects, especially when taken regularly or in high doses.
Any stimulant that causes an increase in energy production is going to count as a thermogenic, simply because of the way the body produces energy. Burning fat for energy isn't just a euphemism; you're literally burning that fat, and that reaction produces heat. The increase in body heat is what gives thermogenics their name.
Thermogenics are tricky supplements. All supplements are unregulated drugs, basically, but thermogenics are one of the more dangerous categories. The reason is that stimulants, in high doses, can be very dangerous. If you overdose on fish oil, nothing really harmful is going to happen to you. If you overdose on a thermogenic, you could die.
Common Ingredients in Thermogenics
We've mentioned caffeine a few times, and indeed, it's the most common thermogenic out there. Pretty much any thermogenic is going to have caffeine in it, or another ingredient that contains caffeine itself.
Did you know that caffeine is often hidden in ingredients lists? Any supplement that includes ingredients like Mate, Guarana, Cola, Tea Leaf Extract, or Coffee Extract in it is going to have caffeine in it. In fact, the "extract" from those products is caffeine. They simply don't want to label it as caffeine because so many people are wary of the stuff.
Caffeine is only modestly effective at helping you lose weight. Studies have shown that caffeine helps burn roughly 1 calorie for every 10 milligrams you consume. For reference, here are some common sources of caffeine and the amount of caffeine in them:
- A Venti Starbucks coffee has around 200-400 milligrams of caffeine.
- 8 oz. Of brewed black tea tends to have around 50 milligrams of caffeine.
- A 20 oz. bottle of soda has around 60-70 milligrams of caffeine.
- A single 5-Hour Energy shot has 200 milligrams of caffeine.
So as you can see, unless your caffeine intake is extremely high, you're not going to be burning all that much with them.
Caffeine is best used as a stimulant to help wake you up and make you more alert, to help you go about your day or hit the gym more effectively.
Another common thermogenic compound is called EGCG. EGCG stands for Epigallocatechin gallate, and it's a compound found in green tea leaves. Thus, anything that includes green tea extract likely includes this chemical as its primary ingredient, with caffeine on the side.
EGCG is a compound with some anti-inflammatory properties, and it works as an antioxidant, protecting your body against free radicals that would otherwise circulate and cause damage within your body. Research into the efficacy of EGCG is ongoing, of course, so there's not a ton of information about what it specifically does.
Some people think that EGCG can help protect against various diseases, up to and including diabetes, heart disease, and some cancers. Does it actually do so? We don't know, not yet. It needs a significant amount of study before any such benefits can be confirmed.
Whole EGCG is most commonly found in green tea, it can also be found in other kinds of tea, including oolong and black teas. It's also present in some fruits, such as cranberries, blackberries, cherries, apples, and avocados. It can be found in some concentration in pecans, pistachios, and hazelnuts as well.
As far as fat burning or thermogenic properties are concerned, EGCG is difficult to analyze because it is often accompanied by caffeine. Taking it alone doesn't seem to have much effect, but it can enhance the efficacy of caffeine when the two are taken together.
Another common thermogenic ingredient is capsaicin. While you might think "that's the stuff that makes hot peppers burn, of course it will burn fat", you're not quite correct. The burn of capsaicin as a flavor is different from the chemical reaction that burns fat. However, capsaicin does have thermogenic properties.
Primarily, capsaicin triggers the body to release adrenaline, similar to caffeine. This adrenaline gets your heart pumping and your metabolism running, which makes you more likely to put more energy into exercise. Additionally, capsaicin can help reduce appetite, which helps you complete the cycle by not eating as much while burning more. It is, however, still pretty minor; capsaicin supplements have been shown to boost metabolism by around 50 calories a day. That's not a whole lot in the grand scheme of things.
Unfortunately, there is emerging evidence that suggests your body builds up a tolerance to capsaicin over time, making it less effective the longer you take it. If you're using it for a short-term supplement, fine; if you're trying to take a supplement every day, it will gradually lose its potency.
One of the more recent thermogenic ingredients is called yohimbine, which is an extract from the African yohimbe tree. Like other thermogenics, it works by stimulating the production of hormones in the body, primarily adrenaline, but also noradrenaline and dopamine. 
There is thus far very little research into the efficacy of yohimbine. It's relatively new and relatively untested, which means it's gold for supplement sellers; they can make claims about it that aren't backed by anything, and just claim it works in an unregulated market.
One of the formerly-common thermogenics that is no longer in circulation is ephedrine. Ephedrine is a stimulant like caffeine, but much stronger. It was very popular in the 90s and early 2000s, but it dropped off when the Food and Drug Administration banned it as a supplement.
Why was ephedrine banned? It killed people. Ephedrine was effective at short-term weight loss, but the products that included it often encouraged longer-term usage or simply lacked any sort of warning. Additionally, high doses of ephedrine lead to stress on the cardiovascular system. Ephedrine had a range of negative side effects, including nausea, vomiting, and psychiatric issues, as well as the potential to cause heart attacks or strokes.
It doesn't help that ephedrine was also a common precursor ingredient in the production of methamphetamine, a very illegal drug. Taking it off the market was considered a benefit to public health.
Of course, most modern thermogenic supplements include more than one of the above ingredients, along with additional ingredients like vitamins, minerals, and fiber. Everyone is trying to find a proprietary blend they can use to generate the best weight loss effects with the fewest side effects.
Thermogenic Side Effects
Speaking of side effects, what might you encounter when you're using thermogenics? The list is pretty common for a lot of different supplements.
Thermogenics can, for some people and in some dosage levels, cause nausea, constipation, abdominal pain, and headaches. They can also lead to high blood pressure. Some people find that thermogenics also lead to jitters, restlessness, and even dizziness. 
In extreme doses, or for long-term use, or for people who are sensitive to the ingredients, thermogenics can lead to inflammation of the intestines, hepatitis, liver damage, or even liver failure.
There's also a range of possible side effects that come from the fact that thermogenics are not well regulated. You have to trust what the label says, but you never know how accurate it is. When a lot of these ingredients are manufactured in third world countries, there can be all sorts of contamination.
How to Use Thermogenics Properly
If you're interested in using a thermogenic or fat burner in your weight loss plan, you can do so, and you can do so safely. The key is to know what you're doing, and pay attention to your body.
First, carefully research the ingredients in any thermogenic compound or mixture you want to use. Make note of any ingredients you're not sure you want to take. For example, many people want to avoid caffeine, because it gives them headaches. You will then want to avoid any thermogenic that includes that ingredient.
Second, make sure you're doing more than just taking a thermogenic. On its own, a thermogenic will only burn a few dozen calories a day. You need to combine it with two things: dietary improvements and exercise.
Dietary improvements typically means cutting back on calories consumed, though you may have a different goal with different specific desires. Cut out harmful sugars and processed carbs, replace them with whole grains and produce, and you're on your way.
Exercise, of course, simply means getting more activity. Depending on your goals, this might be anything from going on a long walk every day to spending several hours at the gym with a personal trainer on a regular basis.
Third, make sure to monitor your body for any signs of side effects that might be dangerous. Weight loss is a common side effect, though often minor on its own. You want to watch for headaches, particularly daily or frequent headaches. Keep an eye out for abdominal discomfort, as it can be a sign of more serious issues. Also, while it's rare, familiarize yourself with the signs of liver failure, to catch it if it happens.
If you encounter any of the negative side effects of thermogenics, discontinue their use and talk to your doctor. In most cases, simply stopping the supplements will be enough, but in extreme cases you may need other treatment to help reverse the effects of high blood pressure or liver damage.
Finally, keep in mind that thermogenics aren't meant for a long-term use. Use them for a few months while you strive to decrease your weight, and then focus your energy on a maintenance diet and exercise program. After all, losing weight isn't as hard as keeping it off.
