Fat burners are one of the most popular supplements. They have been linked to a number of benefits such as health and performance improvements and of course weight loss. Commercially available fat burners often claim to increase fat metabolism, weight loss and fat oxidation (the rate at which the body use fat as a fuel), as well as reduce fat absorption. The supplements available on the market are made out of a combination of ingredients, each with its own unique mechanisms of action, which lead to these proposed benefits. Here we outline some of the key ingredients found in popular fat burners and weight loss aids, their effects, and the efficacy of each.
Caffeine
Caffeine is naturally found, and added to, a vast range of food and drinks. Studies have shown that consuming coffee or pure caffeine before exercising increases fat oxidation, performance and switches muscle energy metabolism from carbohydrates to fat, leading to weight loss.
Caffeine has also been shown to indirectly increase adrenaline levels, making fat more available as energy for muscles. It has also been demonstrated that even low doses of caffeine increases resting metabolic rate 3 hours after consumption. However, it has been shown that consuming caffeine supplements may not be potent enough alone to induce weight loss, particularly if consumed over long periods of time or in habitual high-caffeine consumers.
In summary, research to date has demonstrated that in some cases, caffeine can increase metabolism at rest and during low-intensity exercise and that these effects are likely to be short term. It is therefore suggested that if using caffeine-based supplements, cycling these in periods of 2-4 weeks will give the best results, allowing the body to ‘reset’ tolerance and gain more continual fat loss benefits.
L-carnitine
L-carnitine helps transport fat to the mitochondria, the powerhouse of muscle cells. This is where fat is used as an energy source during overnight fasted low to moderate exercise.
L-carnitine supplements theoretically would increase this fat metabolism. A few studies have shown that carnitine may have an effect on fat metabolism if in combination with the consumption of a large amount of carbohydrates as this increases its uptake into muscle, though this seems counterproductive for weight loss purposes. however for weight maintenance after fat loss, it may be of some benefit.
As it stands, there is not enough evidence to recommend L-carnitine for weight loss or highly increased fat metabolism, but some athletes may see small improvements in these areas.
Green tea
Green Tea Extract (GTE) ingestion, has been reported successful for gradual weight loss, in combination with food energy restriction and exercise. It has also been shown that GTE supplements can help weight maintenance after weight loss. It is important to note that routine caffeine consumption can surpass these weight loss effects of GTE, and so a higher dose of GTE may be required.
It has been reported that using mixtures of green tea catechins and caffeine improves weight loss and weight maintenance over the long-term. Other studies have shown weight maintenance occurs after weight loss through a calorie restricted diet, while ingestion of green tea catechins and caffeine mixtures suggesting that green tea has appetite regulating effects more so than direct fat burning properties.
Green tea catechins with caffeine have also been shown to decrease weight, body mass index (BMI), and waist circumference when compared with consumption of caffeine supplements alone. It has been found that not only high habitual caffeine consumption, but also certain foods influence green tea’s actions on energy metabolism.
In conclusion, the effects of caffeine and GTE on fat metabolism and weight loss have been studied through many decades and there is more available data to support their fat metabolising properties. Other supplements have also been studied, such as chromium and conjugated linoleic acid (CLA), but there is a lack of evidence on their efficacy. There is an increasing list of fat burners being promoted in the industry, and research around them is likely to grow, but, as it stands, caffeine and GTE are the ‘safest bet’ to support weight loss from both a metabolic and appetite suppressing perspective.
