Not all of them are created equal. Here's what each type can and can't do.
The fat burning supplements category is quite broad. Tons of different products are being sold with the claim of helping you lose fat faster and more easily. Fat loss supplements are formulated to do one of the following:
- Increase metabolic rate or energy expenditure via increased beta adrenergic (adrenaline) activity
- Increase metabolic rate or energy expenditure via a higher T3 (thyroid hormone) production
- Increase fat mobilization via inhibition of the alpha-adrenergic receptors
- Increase fatty acid transport and/or utilization of fat for fuel
- Improve insulin sensitivity
- Activate the mitochondrial uncoupling protein 1 (UCP1)
There might be other mechanisms (like reducing fat absorption) but these are the main ones. So let's break each of these down.
Increased Metabolic Rate Via Beta Adrenergic Stimulation
This is done with products often labeled "stimulants" so think ephedrine, synephrine, and the like. Caffeine can even be included here, indirectly.
These work, and they do increase energy expenditure which leads to fat loss. But their effect is fairly small. An old study looked at the effect of the ephedrine/caffeine stack. It improved metabolic rate/energy expenditure by 5%. That's maybe an extra 100 calories per day.
It can still have an affect and help get that last bit of fat off when you're dieting down for a contest, but it's no miracle.
The main reasons stimulants "work" is that they blunt appetite, which makes you eat less and makes it easier to follow a diet. It also gives you more energy when you're tired from dieting down. If you have more energy, you'll move more and train harder which will also help you lose fat.
But overusing stimulants come at a price. First they lead to an increase in cortisol, and most of us already have too much of that. But more importantly, when you chronically overstimulate, the beta adrenergic receptors can easily become desensitized (they don't respond well to adrenaline anymore). When that happens it'll actually become harder to lose fat and you'll also have less energy and motivation. Ultimately, you'll start to feel worse and worse.
This category of product is best left for losing the last few pounds. I only recommend using them for a few weeks, which is why they need to be the very last thing to add in a regimen.
Increased Metabolic Rate/Energy Expenditure Via Higher T3 Production
The T3 thyroid hormone is in large part responsible for elevating your metabolic rate. The body produces mostly T4 which is then converted to T3. To boost T3 levels you can either increase overall thyroid hormone production or increase T4 to T3 conversion.
To boost overall thyroid production the best thing to do is to provide the body with enough raw material to make these hormones. Specifically iodine and tyrosine. As such, supplements containing both can help a bit with thyroid production.
As for T4 to T3 conversion, one of the best things you can do is decrease stress levels. Chronically elevated cortisol can impair that conversion. Zinc deficiency will also be problematic because zinc is required for the conversion to take place. Rhodiola and raspberry ketones, which are in Hot-Rox® Extreme, can indirectly increase that conversion too.
Increased Fat Mobilization Via Inhibition of the Alpha-Adrenergic Receptors
We have two main types of adrenergic (adrenaline) receptors: the beta and alpha receptors. The beta receptors are the "on" switch. When activated they increase heart rate, CNS activation, energy mobilization (including fat) and muscle strength. These are the receptors being targeted by most stimulants.
The alpha receptors are the "off" switch. When activated, they shut down energy/fat mobilization, slow heart rate, decrease CNS activation, etc.
Some supplements are antagonists of the alpha adrenergic receptors. This simply means that these supplements block the alpha receptors. If you block them, your body continues mobilizing energy for longer.
There's a theory that stubborn body fat sites (where you have problems losing fat the most) have more alpha and less beta adrenergic receptors, making it much harder to mobilize fat there.
Yohimbe HCL/yohimbine, which is also found in Hot-Rox® Extreme, is an antagonist of the alpha receptors. For that reason it can work for increasing fat mobilization, especially in stubborn regions.
Just be aware that if you're overly stressed or planning to do a monster CrossFit-like workout, yohimbe might not be a great idea: even without stimulants these kind of workouts will increase adrenaline so much that you can run into trouble. The best use for a yohimbe-containing product is before steady-state cardio.
It's not a magic pill, but it can help get rid of the stubborn body fat when that's all you have left. It works WITH exercise – it'll make the exercise more efficient at mobilizing fat. By itself it will have a small impact, and it'll be a lot more effective with cardio than weight training.
Increased Fatty Acid Transport and/or Utilization of Fat for Fuel
Some supplements improve fatty acid transport to the mitochondria or they increase the enzymes involved in energy production from fat. Some supplements only claim to do this, but don't.
For example Acetyl-L-Carnitine can help use fat more efficiently for fuel. However, that effect is fairly small. The main benefits of ALCAR are mostly on brain function, for which it's actually quite effective. (It's one of the ingredients in Brain Candy®.) Now, some bodybuilders use the injectable version of ALCAR and it seems to work a bit better for fat loss, but it's still pretty minor.
Raspberry ketones can help by increasing the enzyme responsible for breaking down fatty acids so that they can be used for fuel by the mitochondria.
Improved Insulin Sensitivity
This is where most people should focus. Besides helping with body composition, improving insulin sensitivity is very healthy. There's not really any drawback from improving insulin sensitivity.
How is being insulin sensitive good for losing fat? Insulin is a storage hormone, as long as it's elevated significantly above baseline, fat mobilization is less effective. If you're insulin-resistant your cells don't respond well to insulin, and as a result you must produce a lot more of it when eating a meal (especially a carb-containing meal).
If you produce more insulin it takes longer for it to go back down to normal levels. So you spend less time in "efficient fat mobilization mode" which makes it harder to lose fat. Being insulin resistant doesn't necessarily make you store more fat, but it makes it harder to mobilize it.
If you become more sensitive to insulin, you produce less of it when you eat, and it comes back down to normal levels much faster, giving you more time in the fat mobilizing state. It just makes it easier to lose fat.
Many supplements are effective at improving insulin sensitivity. The two best ingredients are cyanidin-3-glucoside (Indigo-3G®) and berberine.
Other effective supplements include r-ALA, omega 3 fatty acids, and chromium has a small effect. There are others too but nothing spectacular. Apple cider vinegar and cinnamon also have a positive impact on insulin sensitivity.
Supplements that improve insulin sensitivity won't lead to a dramatically increased rate of fat loss, however they will make the fat loss process much easier and will make you a lot healthier in the process.
Activating the Mitochondrial Uncoupling Protein 1 (UCP1)
This leads to more heat and less energy production, which means you need to burn more fat for the same amount of required energy production.
The most well known "uncoupler" is the dangerous drug DNP. It was, at one point, popular in bodybuilding circles, but it directly led to a few deaths. Basically, uncouplers work by making the energy production very inefficient. Instead of being turned mostly into ATP (energy), glucose and fatty acids are turned into heat. This means you need a lot more fatty acids/glucose to produce enough ATP to function. This dramatically increases energy expenditure.
A few supplements can have a small effect on UCP1 but nothing spectacular. If something has a large impact on UCP1 then it'll come with many potential side effects.
The Bottom Line On Fat Burners
Not all fat loss products are BS. In fact, a lot of ingredients are backed by science.
The best supplementation strategy to help with fat loss is targeting insulin sensitivity. Stimulants and antagonists of the alpha-adrenergic receptors are effective, but not magic. They should be used carefully, only when truly needed (for that last little bit of fat), and for a brief period.