Thermogenic supplements, which are often used by people wanting to lose weight, can potentially boost the metabolism and burn body fat, as well as suppress appetite.
However, according to some studies and experts, thermogenic supplements can also have negative side effects, including inflammatory bowel changes and liver damage.
This article takes a look at thermogenic supplements, including what they are, how they work and whether or not they’re safe.
Additionally, we’ve included the findings of two studies published by the National Institutes of Health that present both good and bad outcomes, so you can discern whether or not to take them yourself.
Keep in mind that this article is not intended as medical advice. While some findings show that thermogenic supplements may be effective, the potential outcomes can be dangerous. So before you try them, talk to your medical provider, first.
Thermogenic supplements are supplements that produce heat, thereby potentially boosting your fat-burning capabilities and boosting your metabolism, explained Dr. Monica Flora, who is board certified in family medicine with a special interest in obesity medicine, and works at Adventist Health Simi Valley.
The most used thermogenic supplements are caffeine, green tea and capsaicin, which is a chili pepper extract, noted Dr. Flora, who added that thermogenic supplements may also reduce your appetite.
Thermogenic supplements are often used by people seeking to decrease their body weight, according to the National Institutes of Health, which noted that stimulants such as caffeine and green tea extract are often combined to achieve these effects.
Many of these supplements are formulated with multiple ingredients, and are purported to do the following:
- Increase energy expenditure
- Maximize fat loss (increase fat oxidation)
- Suppress appetite
When it comes to thermogenics, “think of energy, or calories being burned,” said Robert Ferguson, CEO of Diet Free Life who is a certified nutritionist, author, and speaker known as America's Fat Loss Coach. There are a few ways the body does this, including “naturally being alive, movement or activity – and even when you eat, your body burns calories.”
In the course of a day, “anything that stimulates your metabolism – that’s a thermogenic effect,” Ferguson explained.
A natural thermogenic is caffeine or caffeinated tea, because “if you consume any caffeine you will burn more calories opposed to if you don’t.”
That means if thermogenic supplements “are laced with some form of caffeine…it works as an appetite suppressant, so you have no desire to eat and you’re burning more calories.”
To that end, supplements that can potentially create a thermogenic effect are the ones that are caffeine-based, Ferguson noted, as well as ones that contain yohimbine, which comes from an evergreen tree found in parts of central and western Africa.
According to the National Institutes of Health, yohimbine supplementation “appears to be suitable” as a fat loss strategy in elite athletes, according to a study on yohimbine and its effects on body composition and exercise performance in soccer players, which showed that fat mass “was significantly lower” in the yohimbine versus placebo trial.
Eating protein can also have a thermogenic effect, Ferguson said, because “it stimulates your metabolism a little more than carbohydrates or fat.”
Additionally, “soluble fiber could be a thermogenic because your body requires more energy to break it down – this is arguable, but it still falls into the category of thermogenics.”
Soluble dietary fiber improves energy homeostasis, and prevents obesity, by increasing the diversity of the gut microbiota and the colonization of beneficial bacteria, according to the National Institutes of Health, which conducted a study that treated a high fat diet-induced obese mouse with soluble dietary fiber.
The results showed that soluble dietary fiber reduced body weight gain and the excessive accumulation of white fat tissue in diet-induced obese mice.
Being fully hydrated by drinking lots of water can also have a thermogenic effect, Ferguson added, “because the more water you drink, the easier the blood flows, carrying nutrients throughout the cells – everything is operating more efficiently.”
Dr. Flora offered her insight into the most popular thermogenic supplements, caffeine, green tea, and capsaicin:
Caffeine has a small effect on metabolism. It does not make much of an impact on weight loss.
Green tea is said to increase your metabolism but has minimal effect on weight loss.
Capsaicin is said to speed up your metabolism, causing you to burn more calories. “Studies show that these effects ideally should be significant but the effects are minimal,” Dr. Flora noted.
However, according to the National Institutes of Health, these three ingredients can potentially do the following:
Caffeine is a sympathetic nervous system stimulant known to increase energy expenditure and fat oxidation following acute ingestion.
Green tea extract, in long-term studies, has been suggested to aid weight loss and weight management following weight loss.
Capsaicin, a bioactive compound found in hot red peppers, has been shown to suppress appetite and energy intake.
Caffeine and green tea are “definitely effective,” according to Ferguson. For instance, “a person who drinks a cup of caffeinated coffee compared to someone who doesn’t will burn 75 calories or more that day to a person who doesn’t drink caffeinated coffee.”
Things like caffeine and green tea are considered safe, according to Ferguson, “but everyone’s unique, and people will respond differently.”
“If you drink a cup of coffee and you’re not really bothered, you could probably take some type of supplement laced with caffeine or green tea extract,” Ferguson noted.
“But where people blow it is, they’ll drink a cup of coffee at the same time they’re taking a thermogenic supplement – it’s almost like drinking two cups at the same time.”
Generally, thermogenic supplements are not considered safe, Dr. Flora warned. “They do have side effects that can be minimal, while others can cause inflammatory bowel changes and liver damage.”
Some of the most efficacious thermogenic supplement ingredients “have been deemed unsafe” for consumption, and subsequently removed from the market by the Food and Drug Administration, according to the National Institutes of Health, which further noted it’s prudent to verify the safety and potential side effects of thermogenic supplements currently on the market.
One study published by the National Institutes of Health reported the case of a 30-year-old woman with toxic leukoencephalopathy (a rare condition characterized by progressive damage to white matter in the brain) and hyponatremia (low level of sodium in the blood) associated with oral consumption of a thermogenic dietary supplement and essential oils.
This study, entitled “A Callosal Catastrophe: Toxic Leukoencephalopathy Associated with Thermogenic Weight Loss Supplement Use,” noted she was taking a thermogenic dietary supplement daily for six months, as well as a number of essential oils.
An examination revealed mild right-sided ataxia (a degenerative disease of the nervous system) and diffuse hyperreflexia (overactive or over-responsive reflexes which can include twitching or spastic tendencies.)
While the study indicated that the pathophysiology of this patient's hyponatremia and toxic leukoencephalopathy is unknown, “physicians must be aware of the association between thermogenic dietary supplements and toxic leukoencephalopathy.”
Thermogenic Ingredients Can Increase Resting Metabolic Rate
In another study published by the National Institutes of Health, it was noted that thermogenic dietary supplementation “may increase” overall energy expenditure, potentially leading to reductions in fat mass over time.
The purpose of the study – which involved healthy women in a randomized, double-blind, placebo-controlled, cross-over trial – was to look at the effects of a single-dose thermogenic supplement on resting metabolic rate and hemodynamic variables.
The conclusions of the study noted that the thermogenic dietary supplement treatment “experienced greater elevations” in resting metabolic rate as compared to baseline. The study also indicated that due to the slight elevations in blood pressure, “caution should be taken for those with increased risk for hypertension or pre-hypertension.”
Due to the potential side effects of thermogenic supplements, Dr. Flora does not recommend their use for anyone.
Instead, “I would recommend lifestyle modifications and possible consultation with a dietitian to help educate on how to lead a healthy lifestyle and achieve specific goals.”
Ferguson also does not recommend the use of thermogenic supplements. “I concur it’s one of those things where people are looking for that little pinch of hope – they think it will work and they’ll do it.”
For those who decide to take them anyway, “always make sure you read the ingredients and become knowledgeable of any potential side effects,” Ferguson advised. “Before using any product like this, at least talk to your doctor first.”
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