Hey,

It's time for another instalment of the Vitamin––the weekly fitness newsletter that helps you be healthier, stronger, and leaner while navigating fitness bullshit.

Do fat burners work?

Despite the myriad of supplements available on the market, very few offer strong evidence for a positive effect on body composition or training performance (e.g., whey protein, creatine, and caffeine). [1]

Among these are fat burners. Fat burners are proposed to enhance thermogenesis, accelerate fat loss, and improve exercise performance. They're typically sold as multi-ingredient supplements, with some of the more common ingredients including caffeine, l-carnitine, conjugated linoleic acid, and green tea extract [2].

There may be some mechanistic rationale for how these ingredients could influence thermogenesis. For example, caffeine ingestion acutely increases energy expenditure by 3-4% (i.e., in the hours following ingestion) [3].

However, whether these thermogenic effects are of practical relevance over the longer term (weeks to months) needs to be decided in human trials with relevant outcomes (e.g., body fat and fat-free mass).

To investigate, a recent study assessed the effect of taking a fat burner with whey protein compared with whey protein only or no supplement use on outcomes related to body composition and energy expenditure. [4]

Let’s look at what they did.

What did the researchers do?

• This trial recruited 52 healthy, trained participants (50% female).
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• The participants were grouped by sex, body fat, and training status and then randomised to one of three groups (2:2:1 ratio) for 4 weeks:
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  • Protein only (33 – 100g/day based on body weight).
  • Protein with fat burner (EHP Labs OxyShred Thermogenic Fat Burner).
  • No supplement (placebo powder).
• Before and after the intervention, resting metabolic rate (indirect calorimetry), body composition (DEXA), abdominal fat (ultrasound), physical activity (IPAQ), mood (MFQ), sleep (PSQI), and dietary intake (TFEQ) were measured.
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• Hemodynamic measures (heart rate and blood pressure) were also taken.
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• Participants were instructed to maintain their normal supplement regimen while restricting their caffeine intake to no more than 100mg/day.

What did the researchers find?

• There were no significant differences in body composition variables (i.e., body mass, fat mass, fat-free mass) between groups.
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• Resting energy expenditure significantly decreased in the control group but not the protein or fat burner groups.
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• The fat burner group had significantly higher resting energy expenditures than the placebo (a difference of about 111 kcals/day).
  ​
• However, the difference between the protein-plus fat burner group and the protein-only group (about 69 calories per day) was not significant.
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• Sleep quality, cognitive restraint, and mood were similar between groups.
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• There were no differences in heart rate and blood pressure between groups.
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What does this all mean?

The key finding from this study is that protein supplementation or protein supplementation with a fat burner didn't induce appreciable changes in body composition when compared to a control.

This was despite the fat burner significantly increasing participants' resting metabolic rate compared to the placebo. Given that there were no differences in body composition between groups, the increase in resting metabolic rate in the fat burner group could be interpreted as of little practical significance.

Additionally, fat burners had no effect on outcomes related to sleep, mood, cognitive restraint, heart rate, or blood pressure.

Overall, the main takeaway from this study runs counter to the marketing claims––fat burners don't accelerate fat burning or weight loss.

The present study's findings are in line with a previous systematic review and meta-analysis that investigated the effectiveness of fat burners and thermogenic supplements on weight loss, with researchers concluding: [5]

The same study also found that combining diet with exercise significantly outperforms dietary supplements for weight and fat loss.

Key takeaways

• Save your money on fat burners. The evidence so far isn't promising, and they likely won't lead to any meaningful body composition changes.
  ​
• Few supplements have strong evidence behind them, like creatine and caffeine.
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• More effective fat loss strategies involve creating a sustainable calorie deficit, eating enough protein, and being more active.

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–Aa

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