Key Topic

The common consensus in the evidence-based nutrition and fitness community is that fat burners don’t work. But is it that simple? This episode takes a deeper look at the mechanisms behind fat burners and whether they translate into meaningful fat loss outcomes.

Mechanisms For How They Could Work

  • Increased metabolic rate or energy expenditure (increase caloric output)
  • Reduced appetite (decreased input)
  • Increased fat oxidation (but as we know, fat oxidation doesn’t necessarily = fat loss)
  • Better muscle preservation (and therefore more fat loss in the same circumstances)

Quick Analysis of Those Mechanisms

  • The reduced appetite aspect is obviously relevant. But I’ve spoken previously about how a lot of these tools often have a finite lifespan before it becomes the “new normal”
  • An increase in energy expenditure can make it easier to stay in a deficit. Although it’s also worth noting that over time appetite and desire to eat often adjust based on this stuff e.g. a good example is people gaining weight while training for a marathon
  • Increased fat oxidation sounds promising, but we know there is a difference between fat burning and fat loss. When you go deep down the rabbit-hole, you see that in the majority of cases, even if you “hacked the system” to favour fat oxidation HEAPS, it would lead to a problem of glycogen storage eventually maxing out… and at some stage that has to balance out
  • Better muscle preservation would obviously help. But how much is a fat burner really doing here?

Individual Ingredients

  • Caffeine increases energy expenditure, suppresses appetite, and might increase fat oxidation. So this is why it’s often high in fat-burning supplements.
    • One example of this is a study where 90mg of caffeine compared to placebo daily for 2 weeks led to 25 calories extra burned per day.
    • I mean that’s still more calorie burn, but it’s not a huge difference.
  • L-Carnitine is an ingredient that is technically used in the body for fat transportation. But supplementing it doesn’t seem to make much difference. For starters, absorption of the supplement is poor if consumed orally. But outcomes also don’t show much difference for fat loss anyway.
  • Green Tea Extract has the same mechanisms related to promoting fat oxidation, but outcomes haven’t been very promising in research
  • Capsaicin is often added to increase metabolic rate through the thermic effect, and it has small appetite suppressing effect. This increase in calorie expenditure is genuine and has been documented at around 50-75 calories per day if higher dosages are used (which also has a risk for GI upset). But once again, how that plays out in the longer term matters more.
  • We could keep going, but this becomes an endless list, so instead we will look at the outcomes.

Meta-Analysis Findings

  • A 2021 meta-analysis looked at all the research on fat burners that went over 8 weeks
  • It basically found no difference in outcomes vs placebo
  • So that’s a pretty clear piece of evidence that either they basically do nothing, or the difference is so small it’s not really worth looking at.
  • I also think the >8 week duration aspect is relevant for certain things that can balance out with more time, such as the impact of appetite.

Summary

  • Fat burners either have no effect, or a very small effect.
  • In the cases of the small effect, you need to ask yourself is it worth it?
  • Like would it be worth taking a noticeably different intake of caffeine to what you would want for other reasons for the potential small effect that might not even exist longer term?

Relevant Blogs/Research

Relevant Studies:

Relevant Blog Posts: