Metabolic enhancers: hype or hope?
The market of dietary supplements is big and continuously growing. Given the diverse range of available products, it is quite unsurprising that manufacturers are also marketing some supplements developed to upregulate metabolism. After all, taking a pill or some powder to make your body burn calories faster with no side effects will sound tempting to everyone who has ever tried dieting. Do such dietary supplements actually boost the metabolic rate and should you learn more about them or is it all just a marketing trick? The answer is: “It depends...”
Metabolic boosters are available in a variety of forms – from the most popular capsules, through powder to be dissolved in water, to single shots. Their goal is to increase the intensity of metabolic reactions, thus prompting the body to burn more calories.
Most often, such metabolic stimulants are supposed to work by triggering a thermogenic effect, causing the body to burn more calories. Some additional reactions caused by the substances include enhanced lipolysis (fat tissue breakdown), easier digestion or reduced appetite.
While some substances may really be effective in this sense, this is not a universal rule. Let’s have a look at some popular substances used in metabolic boosters and consider the evidence of their efficacy.
Metabolic boosters – an overview of popular substances
Many metabolic enhancers consist of a mixture of various substances with varying levels of proven efficacy. Each product should be analysed separately and its makeup should be thoroughly studied, although many share similar ingredients in varying proportions. Here are some of the most common compounds found in metabolic boosters.
Caffeine – the best studied metabolic booster
Caffeine is one of the best studied and most effective substances that genuinely affect the metabolic rate.
It boasts a multi-faceted mode of action:
- it intensifies thermogenesis (burning of calories) by stimulating the mitochondria to work more efficiently;
- it promotes the oxygenation of fat and its use as a source of energy;
- it activates the sympathetic system that regulates the energy balance and stimulates the burning of calories;
- taken 1-4 hours before a meal, it may reduce appetite.
The effective doses used in studies ranged between 3 and 4 mg of caffeine per kilogram of body weight (i.e. an 80 kg individual should ingest ca. 320 mg). The doses may be close to the maximum safe daily intake (400 mg of caffeine per day), so it is important to use them with caution (e.g. do not drink coffee if you are also taking caffeine supplements). People who metabolize caffeine slowly may experience unpleasant side effects, such as heart palpitations, shaking hands or a feeling similar to stress.
Green tea extracts (EGCGs) boost fat burning
Green tea is among the most popular foods famous for its weight reduction properties. The metabolic rate-boosting properties of green tea extracts have been quite well proven scientifically. Epigallocatechin gallate (EGCG) has the strongest metabolic effect. This potent antioxidant accounts for up to 1/3 of the dry mass of green tea.
You can read more about the six different types of tea and their properties HERE.
Scientists claim that ingesting green tea extracts or pure EGCG as a supplement may help to increase the metabolic rate by another 3-4%. One study found that up to 8% was possible. For a person with a BMR or 1500 kcals, this would represent an additional energy expenditure of 45-90 kcals.
The doses used in research to obtain such results ranged between 200 and 500 mg of EGCG in various forms, including as supplements or tea infusions with a controlled EGCG content. Good quality green tea contains ca. 100-150 mg of EGCG per cup (200 ml).
One study reported that ingesting 400 mg of EGCG per day during three months resulted in the loss of 1.31 kg of fat tissue.
It is worth adding that although EGCG seems a safe metabolic booster (because of its natural origin), caution is advised with its use. EGCG doses exceeding 800 mg per day may be hepatotoxic.
Capsaicin, piperine and hot spice extracts to boost your metabolism
Hot spices or, more specifically, their extracts, are also typical ingredients often used by supplement manufacturers to enhance thermogenesis. The most effective substances in this groups include:
- capsaicin, found in hot peppers,
- piperine, found in black pepper,
- gingerol, found in ginger,
- allyl isothiocyanate (AITC), found in horseradish and mustard seeds.
Capsaicin and piperine have the strongest thermogenic effect and their potency is further enhanced if they are combined to take advantage of their synergy effect. They work by activating the sympathetic system, which accelerates the metabolic rate.
The recommended dose of capsaicin which may be effective without causing side effects is 2-6 mg per day. For piperine, it is 5-20 mg per day.
Although the thermogenic effect caused by hot spices is undeniable and quite well known, researchers advise against excessive enthusiasm when it comes to supplements based on these substances. While they do promote the breakdown of fats and boost thermogenesis, the scale of these processes is quite limited in the body, so they will not be able to replace physical exercise or a balanced diet.
Synephrine from bitter oranges – used, but poorly effective
As a thermogenic substance, synephrine intensifies calorie burning processes and additionally also promotes lipolysis (the breaking down of fats). However, it is relatively less potent than other known thermogenic substances.
According to some studies, taking synephrine could increase metabolism by ca. 2-5%, i.e. for a person with a BMR or 1500 kcals, this would represent an additional energy expenditure of 30-75 kcals. In this case, synephrine was dosed at 50 mg once daily or at 10-20 mg divided into three doses throughout the day.
More recent studies, however, completely undermine the efficacy of synephrine as a metabolic booster. According to a 2022 metanalysis, synephrine supplementation during 8 weeks had no significant impact on body composition or weight, but caused some undesirable effects, such as high blood pressure and an increased heart rate.
Protein – an unlikely metabolic booster
A protein-rich diet is one of the best nutritional strategies to increase the metabolic rate. Protein is the best thermogenic agent among all macronutrients, while at the same time protecting muscle tissue from breaking down. An adequate amount of protein in a reduction diet is key for the success of the weight loss process and more.
Therefore, protein supplements can be safely recognized as having a real impact on the metabolic rate. However, protein has an entirely different kind of impact on the burning of calories when compared to the substances described above. Protein supplements supply energy and make your daily diet more complete. They do not directly stimulate thermogenesis and do not increase the amount of calories burnt. They are far from being “fat burners”. They can simply be a valuable component of your varied eating plan, promoting a faster metabolic rate. However, be careful when incorporating them into your menu. They will work well with meals which contain few other natural sources of protein or may offer a vital protein option at times when it would be challenging for you to prepare a wholesome balanced meal.
Try also: “3 Protein Meal Ideas”.
Other metabolic boosters with limited evidence of efficacy
The market of dietary supplements offers plenty of metabolic boosters. Some of them are supported by only limited or inconclusive evidence of efficacy, while others have not been extensively studied or are associated with more adverse reactions. It is worth keeping an eye on them because as more research and scientific evidence emerges, they might either make it into the list of the top most effective metabolic boosters or they may drop out if it entirely.
- Pyruvate – most frequently used as calcium pyruvate at 20-50 g daily. It can proportionally replace some of the carbohydrates ingested with food. Besides other uses (especially in athletes) it is also claimed to accelerate fat burning by ramping up the metabolic rate. There is limited evidence of its efficacy.
- Yohimbine – marketed as a metabolism enhancer and a substance effective in supporting men’s sexual functioning. It stimulates lipolysis and may be especially effective in burning “stubborn fat” in the final stages of the weight reduction process. The recommended dose is 0.2 mg per kg of body weight. It is often combined with caffeine in supplements. It may cause side effects such as nausea and stress-like physiological symptoms.
- L-carnitine – it occurs naturally in the human body and is also present in animal-derived products (such as meat). It is involved in the transport of fatty acids into the mitochondria, where they are used to produce energy. However, there is limited evidence to support the efficacy of L-carnitine in boosting metabolism. It is commonly dosed at 500-2000 mg per day.
- Garcinia cambogia or brindle berry – although used as a dietary supplement promoting the burning of fat, evidence of its efficacy is limited to animal studies. Human trial results are ambiguous and do not attest to the efficacy of the substance enough for it to be recommended.
Read also: “5 Supplements for Athletes That Don’t Deliver What They Promise”.
The risks associated with metabolic boosters
When considering the use of any dietary supplements, you need to be aware of the potential risks. Metabolic boosters which claim to promote weight loss are especially prone to contamination. According to a study of 634 samples of dietary supplements, even 14.8% of them contained prohibited substances (e.g. performance-enhancing substances or steroids). It is estimated that the contamination of dietary supplements may be the reason behind up to 8.8% of positive anti-doping test results! This should be borne in mind.
Other risks associated with metabolic boosters consist in the likelihood of side effects. In many cases, the doses necessary to achieve real benefits in the form of thermogenesis are often close to the maximum permitted doses and may cause adverse reactions, such as nausea, an accelerated heart rate or elevated blood pressure. The exact side effects depend heavily of the type of substance used.
Metabolic boosters – a practical approach
The above analysis shows that there are a few substances which can actually go a long way to improving your metabolic rate. However, their effects are often overestimated. The maximum extra energy expenditure you can expect when ingesting such substances at safe doses is around 100-200 kcals per day. Judge for yourself if this result is worth your money.
Before you decide, consider the risk of contaminants. The dietary supplements market in Poland is poorly regulated. Formally, they are classified as foodstuffs and not medicinal products. Studies of their ingredients are not as restrictive as those required for medicines. The list of ingredients and the labels only include the manufacturer’s claims, which leaves ample room for negligence.
Also remember that if you want to enjoy the benefits of the substances which offer an actual thermogenic effect, you do not need to take supplements. You can achieve similar results if you simply have some coffee (especially before a workout) or green tea, or use hot spices.
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