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It would be great if even half the things you see about fat loss supplements were true, but the vast bulk of these claims come from sources that make, sell or advertise supplement – or they're funded by these companies. Too often these claims cling to old or tiny studies that often never involved humans, or the people plugging them twist or edit one aspect of a study to suit their sales pitch. In the end, fat loss mostly comes down to diet and exercise.
Here we chew the fat on some of the talked-up 'fat-burners', with thanks to the findings of an Obesity Reviews meta-analysis of 'nutrition supplements that increase fat metabolism'.
The hot new thing weight-loss supplements is hydroxycitric acid (HCA), which is often made from fruits of the garcinia family. However, HCA from garcinia can affect your body's ability to metabolise sugar, which is why diabetics are often warned off it.
HCA appears to block the process of converting simple sugars into fats. It is also claimed to suppress appetite by increasing serotonin levels, and some say it stimulates your body to oxidize ('burn') stored fat for energy during long-duration exercise. There is very little scientific evidence to support either of these points.
People often point out that mangosteen has been used medicinally in Southeast Asia for centuries. This is true – but it has been used as a tea for conditions such as diarrhea, bladder infections and gonorrhea. Not weight loss.
L-carnitine is found in red meats and dairy, but it's also produced in the body. Healthy people can synthesize enough carnitine in the liver and kidneys to survive, even when dietary carnitine is considered insufficient.
It's true that L-carnitine has an important role in fat metabolism, especially if you're doing low to moderate intensity exercise on an empty stomach. Advocates of L-carnitine believe that ingesting more L-carnitine will increase muscle carnitine concentration and therefore increase fat oxidation. However, carefully conducted studies have proven that eating extra carnitine does not produce greater muscle carnitine concentration. Obesity Reviews declares claims about supplementation with L-carnitine for fat loss are 'not only unfounded, but theoretically impossible'.
Taurine is an amino sulfonic acid in protein-rich food foods such as meat, fish, and breast milk, but it's also often pumped into energy drinks. There's concern that scientists know little about how high levels of taurine affect your body in the long term, and this has resulted in warnings against having more than 3000mg a day.
Obesity Reviews looked at some studies that are often-quoted in support of taurine, and the verdict was that they were flawed or insubstantial. For example, in Amino Acids and Proteins for the Athlete, author Mauro Di Pasquale claims that taurine can keep you from losing muscle mass during periods of rapid weight loss as it increases your body's sensitivity to insulin and boosts your protein synthesis – two factors that aid in muscle development. However, this is based on one study on mice, and another on 30 Japanese students who lost weight and body fat with taurine supplementation. Obesity Reviews declared that there was 'insufficient evidence that taurine has a stimulating effect on fat metabolism'.
The conditional amino acid L-tyrosine is often claimed to help you lose weight by boosting metabolism, but the University of Maryland Medical Center and others have stated that there's no proof to support this. It appears this claim has its roots in a study on rats that suggested that L-tyrosine may enhance a sense of wellbeing when calories are cut back. L-tyrosine helps your brain create neurotransmitters such as dopamine, so the idea is that your appetite may then go down because your body's not looking for food to create dopamine. Another claim is that it works well when 'stacked' (used with) with products containing caffeine, ephedrine or phenylpropanolamine – but it's the other products doing all the work. Caffeine is a proven fat burner, but phenylpropanolamine has been pulled from sale in the USA and ephedrine is heavily restricted (and banned from sale in many parts of the world).
CLA has had positive results getting mice all buff, but results in humans have been inconsistent. CLA supplements have been shown to increase calorie burning and help reduce food intake, but Obesity Reviews concluded that you'd need a lot – about 3g per day long term – to achieve even a 'modest fat loss'. There was also a safety concern after one study found a three-month daily dose of CLA significantly lowered insulin sensitivity.
Fiber supplements aren't exactly “fat burners” but they are an effective way to suppress hunger, make you feel more satisfied with smaller food portions, and reduce absorption of other foods you eat. All up, they make for a safe and easy way to lower your calorie input enough to achieve some fat loss. It really is that simple.
Green tea is a well-researched substance that contains compounds called catechins. One of these, epigallocatechin gallate (EGCG), can hold back an enzyme that breaks down norepinephrine, a neurotransmitter that helps regulate metabolic rate and the breakdown of fat. When this happens, the metabolism and rate of fat oxidization is elevated for longer, especially when there's extra caffeine on board to help free up fat from fat cells (see 'Caffeine').
Obesity Reviews notes that both at rest and during exercise, green tea has an effect on fat oxidation and fat loss, but these effects are 'relatively small'. Drinking a standard green tea isn't really enough, either – for best results an extract is better, as the ECGC concentration should be high.
Caffeine's effects on fat oxidation are relatively small, but they are well established. Caffeine also has proven short-term thermogenic effects (you burn more calories at rest) even at low doses (100mg – a weak cup of instant coffee). A high dose (8mg per kg – a double or triple espresso) can significantly increase the rate of calorie burning at rest for three hours afterwards, as long as you're not a habitual high-caffeine consumer. Caffeine also helps free up fatty acids for oxidation, most notably during low-intensity exercise – the effects are less obvious during moderate or high-intensity exercise.
In foods, caffeine is bound in compounds, and the differences in these compounds change how the caffeine acts. For example, coffee reaches peak strength about 30-90 minutes after ingestion, but guarana takes longer to reach peak effectiveness (how long depends on its form) and 'the kick' last longer, whereas caffeine anhydrous (used in pills and supplements) reaches peak strength more instantly.