Key Topic

  • Metabolic adaptation is a process where in response to a calorie deficit, the body down regulates certain processes to conserve energy.
  • When you lose weight, your metabolic rate naturally decreases due to the reduction in size requiring less energy.
  • Metabolic adaptation is measured by how much LARGER the reduction in metabolic rate is compared to what would be predicted by weight change alone.
  • It’s a real process. And it sounds scary. But today we are going to talk about HOW much it matters. Both in terms of the severity and duration.
  • This will be done through a combination of theory, research and practical findings.
man running up a hill

Metabolic Adaptation Information

2 extra general points I would like to add would be:

  1. We call it metabolic ADAPTATION rather than damage because it goes in both directions. When you increase calorie intake, the opposite also happens and that is a fact that is often left out of this conversation online 
  2. Technically metabolic adaptation refers specifically to your metabolic rate. But some definitions can include incidental movement too. However, we will focus on research looking at metabolic rate, and then will broaden the discussion after.

Research

  • A large super broad look at the research on the topic found AVERAGE reductions of ~30-120 calories due to metabolic adaptation in the groups they looked at. 
  • Note that this is based on a variety of durations and losses etc.
  • Larger weight losses led to more metabolic adaptation. Looking at people averaging ~58kg weight loss, they found 200-400kcal as the average reduction.

Issue With Simply Looking At Practical Outcomes

  • Talking a little bit about the issue, simply looking at practical outcomes in regards to weight loss.
  • We have tons of experience working with people and have seen a huge variety of cases.
  • But in these cases we never know exactly how many calories people are consuming. 
  • We can make a plan and assess outcomes – but we aren’t physically there all the time.
  • This means that if somebody has numbers that are wildly different than expected either:
  1. They are doing exactly what they have said and are genuinely a big outlier
  2. They aren’t doing exactly what they have said
  • We know underreporting is very common statistically. But I point to this because it would be silly to make too strong conclusions based on just our experience working with people if it was COUNTER to data where all variables were actually controlled. 

Measuring RMR In Our Clinic

ideal nutrition DEXA clinic
  • We actually do measure RMR in our clinic. This does allow us to see some very helpful data.
  • It still isn’t perfect though because:
    1) In many cases we don’t know what they were doing leading up to the test. They will give us a summary, but once again, we aren’t actually there the whole time monitoring.

2) The test can be skewed by variables such as stress. The machine is literally measuring energy expenditure for a 10 minute period. That’s accurate. But what if somebody happened to be anxious during that 10 minutes? It wouldn’t accurately reflect their normal RMR. That’s just one of many examples.

An Attempt at a Practical Interpretation That Is Useful

  • My practical interpretation is that for a 12-week moderate deficit, I’d expect ~50-150kcal of metabolic adaptation.
  • That’s not intended to be perfect, it’s just to highlight that it’s a small change that is relevant, but often not large.

Duration

  • In terms of how long metabolic adaptation is relevant, research typically finds that if you try to measure it after 4 weeks at maintenance, it is usually no longer even relevant. 
  • Longer and more severe deficits would take longer to recover from.
  • The body seems to care more about what you have done recently in this regard, rather than stuff you did a while ago though.

Adding Incidental Movement Into This

lady walking up stairs on her phone
  • The numbers we have referred to have been about resting metabolic rate. 
  • When you are in a deficit, there is a tendency for incidental movement to decrease too. That can also reduce energy expenditure further.
  • This is harder to put practical advice around because
    1) There is individual response. And this seems to vary even more than metabolic adaptation.

2) Sometimes it is more than offset by intentional changes e.g. adding more to your planned step count. 

Summary

  • Metabolic adaptation by itself typically isn’t a big deal. 
  • The bigger the loss the more significant this drop in metabolic rate can be, but even in those cases, on average the numbers are not large. 
  • Adding the incidental movement aspect into it makes it a larger thing. So it’s often worth taking steps to try to offset that, or at least account for it. 
  • We also know that appetite and desire to eat often increase the longer a deficit goes on. This isn’t relevant to today’s podcast, but I like to highlight it when talking about plateaus.
  • When there is a plateau, it is almost never just one thing. It’s not caused by metabolic adaptation in isolation. But metabolic adaptation could be a small contributing factor. 

Relevant Blogs/Research

Relevant Studies: 

Relevant Podcasts:


Relevant Blog Posts: