Do Fat Burners Work? An Honest Guide to Thermogenics, CLA and Carnitine

Most fat burners are built around caffeine, often with green tea extract, and the evidence says they might help you lose a little weight at most. The US National Institutes of Health Office of Dietary Supplements (ODS) says there is little scientific evidence that weight-loss supplements work, and that the proven ways to lose weight are eating healthful foods, cutting calories and being physically active (ODS). Here is what is in a typical fat burner, how much caffeine is too much, who should avoid stimulants, and how to read a label.

What is in most fat burners?

The same ingredients turn up on most labels:

• Caffeine. The main active, as caffeine anhydrous or from guarana, green coffee, yerba mate or kola nut (ODS).
• Green tea extract. Often standardised for EGCG.
• Carnitine, CLA and garcinia cambogia. Common in stim-free formulas.
• Extras. Chilli extracts, L-tyrosine and B vitamins.

"Thermogenic" means it aims to raise the heat your body produces, which is mostly the caffeine at work.

Do fat burners work? What the evidence shows

ODS has reviewed the common ingredients:

So what are the real fat burner benefits? Caffeine raises energy use slightly: ODS notes 100 mg increased it by about 9 Calories (38 kJ) an hour, and regular use blunts the effect. The thermogenic benefit most people notice is feeling more alert before training, and the Australian Institute of Sport (AIS) lists caffeine as a performance supplement at about 200 mg (AIS). As an appetite suppressant, the evidence is weak: ODS rates glucomannan and garcinia as having little to no effect.

Is there a best fat burner in Australia? Not in any research sense. The best thermogenic for you is one whose caffeine fits your daily total.

Why diet and training matter most

The International Society of Sports Nutrition (ISSN) says fat loss is driven by a sustained calorie deficit, and many diet styles work if you stick with them (Aragon and colleagues, 2017). Resistance training and protein help you keep muscle: ISSN suggests 1.4 to 2.0 g of protein per kg of body weight a day for most exercising people, and possibly 2.3 to 3.1 g per kg for resistance-trained people while dieting (Jäger and colleagues, 2017).

So protein for weight loss is a practical tool, not a magic one: a shake simply helps you reach your target. Weight loss shakes sold in Australia as formulated meal replacements must give at least 12 g of protein, 850 kJ and 25% of the RDI for set vitamins and minerals per serve under the Food Standards Code (Standard 2.9.3); a plain protein powder is not a meal. Compare our lean protein range or our whey protein isolate guide.

The best supplements for weight loss and fat loss protect your training: protein powder, creatine if you already use it, and sensible caffeine before sessions. See our guide to supplements for cutting.

Fat burner caffeine content and safe limits

AIS and healthdirect say healthy adults can have about 400 mg of caffeine a day from all sources, and AIS suggests no more than 200 mg at any one time. healthdirect advises no more than 200 mg a day if you are pregnant or breastfeeding, and less than 2.5 mg per kg of body weight a day for under 18s (healthdirect). Caffeine has a half-life of about 5 hours, so an afternoon thermogenic can still affect your sleep (AIS).

Stacking a burner with a pre-workout adds up fast; our guide to pre-workout caffeine and the Australian rules explains the limits.

Who should avoid stimulants?

• Anyone under 18, pregnant or breastfeeding.
• People with high blood pressure, heart disease, diabetes or liver disease, who ODS says should talk to their doctor first.
• Anyone prone to anxiety or poor sleep.
• People on regular medicines, as caffeine can interact with some of them (healthdirect).
• Drug-tested athletes: a Sport Integrity Australia survey found 35% of 200 supplements bought online contained a prohibited substance, with fat burners among the most likely (Sport Integrity Australia).

Stim-free options, CLA and L-carnitine

Stim-free fat burners suit evening trainers and caffeine-sensitive people, but their evidence is no stronger. R1 Lean 5 lists 1.5 g of L-carnitine tartrate, 300 mg of garcinia and 100 mg of decaf green tea extract per scoop. OxyShred Non-Stim is caffeine-free but contains theacrine, which EHP Labs calls a mild stimulant.

CLA benefits and side effects

Conjugated linoleic acid (CLA) is a fatty acid found in meat and dairy. In the trials ODS describes, weight and body fat fell only slightly more than with placebo. Trials have included women, and ODS describes no separate benefit for them, though CLA may affect breast milk fat. There is no best CLA supplement in Australia in a research sense: compare the actual CLA per softgel, not the oil weight.

L-carnitine

Carnitine helps your cells burn fatty acids for energy, and ODS says healthy people make enough (ODS carnitine). AIS places L-carnitine in Group B (emerging evidence) and says there is a lack of evidence that it further enhances fat loss (AIS). ODS notes gut bacteria can turn it into TMAO, which might raise heart disease risk. Compare options in our L-carnitine guide.

How to read a fat burner label

• Find the caffeine per serve and maximum serves a day, then add your other caffeine.
• Hidden caffeine: guarana, green coffee, yerba mate, kola nut and di-caffeine malate all count.
• Be wary of blends that hide individual doses.
• Green tea extract may appear as Camellia sinensis. The TGA links it to rare liver harm: stop and see your doctor if you get stomach pain, dark urine, pale stools or yellow skin or eyes (TGA).
• Bitter orange (Citrus aurantium) is a stimulant ODS says might not be safe with other stimulants.
• Follow start-low directions where the label gives them.
• Drug tested? Look for HASTA or Informed Sport batch testing.

Products to look at

• Hydroxycut Original: 200 mg caffeine per 2 capsules, with a start-low schedule.
• AfterDark Pyrodex Burn: about 340 mg caffeine per scoop, for experienced caffeine users only.
• R1 Lean 5: stim-free, with L-carnitine and decaf green tea.
• OxyShred Non-Stim: caffeine-free, with carnitine and theacrine.
• Nutrex Liquid Carnitine 3000: 3,000 mg L-carnitine per 15 mL, no stimulants.
• Condemned Labz CLA 1000 mg: 1 g of CLA oil, providing 80% CLA, per softgel.
• Nutrex Lipo-6 CLA: 1,000 mg CLA blend per softgel, twice a day with meals.

Browse our fat burner and weight loss range, CLA range and L-carnitine range.

FAQs

Where can I buy fat burners in Melbourne or online?

You can buy fat burners, thermogenics, CLA and other weight loss supplements online at Supps247 with Australia-wide delivery. To compare labels in person, Supps247 has 18 stores, 17 in Victoria including many Melbourne suburbs, plus Richlands in Queensland. Use the store locator to find a store near you, and check stock on the product page or call before you travel.

Can I take a fat burner and pre-workout together?

Usually not, because most of both contain caffeine. The AIS suggests no more than 400 mg a day from all sources and 200 mg at one time, and one scoop of a high-stimulant burner can pass that single-dose figure alone. If you want both, make one of them stim-free, such as a stim-free pre-workout, and count your coffee too.

Is there a good fat burner for men or for beginners?

Fat burners work the same way for men and women, and adult caffeine limits are the same for both. Beginners to weight loss supplements should start with the basics: a calorie deficit, resistance training and enough protein. If you still want one, pick a stim-free formula or the lowest caffeine dose, and skip other caffeine until you know how you react.

Does CLA work, and is it safe?

The effect is small. ODS describes a review of seven trials using 2.4 to 6 g a day for 6 to 12 months, where the authors called the benefit small and its clinical relevance uncertain. CLA seems safe at up to 6 g a day for a year; gut upsets are the most common side effect, and some forms might lower HDL cholesterol. Ask your GP first if you are pregnant or breastfeeding.

Are weight loss supplements safe?

Weight loss supplements can have side effects and can interact with medicines, so ODS advises telling your doctor what you take. The common thermogenic side effects come from caffeine: jitters, anxiety, a faster heart rate and poor sleep. Green tea extract has rare links to liver harm, and carnitine can upset your stomach. Check with your GP first if you have a medical condition.

Do protein shakes help with weight loss?

Protein shakes do not burn fat, but they can make a calorie deficit easier. ISSN notes protein is filling and, with resistance training, helps you keep muscle while dieting. To replace a meal, choose a formulated meal replacement with added vitamins and minerals, such as those in our meal replacement range.

Sources: NIH ODS weight loss (consumer); NIH ODS weight loss (health professional); NIH ODS carnitine; AIS caffeine; AIS Group B; healthdirect caffeine; TGA green tea extract; Sport Integrity Australia; ISSN diets and body composition; ISSN protein and exercise; FSANZ Standard 2.9.3; product labels.

Order online with Australia-wide delivery, free on orders of $99.99 or more, or visit a Supps247 store in Melbourne, regional Victoria or Brisbane to compare products in person before you buy. Members can use our member price match on full-priced items.

Always read the label and follow the directions for use. If you have a medical condition, are pregnant or take regular medication, check with your doctor first.