Has anyone ever told you that if you eat too little that your metabolism will slow?
Maybe you yourself have gone on a diet in an effort to lose body fat and started out strong only to stall out for no apparent reason despite not changing the way you are eating.
Naturally you turn to Dr. Google to try and figure out why and you see a bunch of articles saying that when you eat in a caloric deficit for too long that your metabolism slows down and you are suffering from what is called metabolic adaptation.
In a fat loss scenario this could mean that the caloric intake that was working so well for your fat loss goals no longer works and you either fail to lose weight, or even worse being to gain weight.
You may even come across articles that say that metabolic adaptation is permanent, and once you slow your metabolism you are stuck at this new slower metabolism forever.
Now you are really scared!!!!
Is this true?
Can your metabolism slow?
Are you stuck with this new slower metabolism forever?
Luckily we have some research to answer many of these questions. No only does it help answer these questions but it can help us put in perspective how it impacts your goals.
So, does metabolic adaptation occur when you drop your calories?
In one study, researchers found that participants had a difference of 92 calories between predicted metabolic rate and actual metabolic rate after 9 weeks of eating 1000 calories a day. From weeks 9 to 13 the same participants ate at maintenance calories and researchers saw a difference of 38 calories from predicted to actual metabolic rate.
During weeks 9-13 some participants happened to regain some of the weight they lost. Researchers followed these participants for an additional 9 months having them continue to eat at maintenance calories. After the 9 months they measured their metabolic rate one final time and it showed only a difference of 7 calories between predicted and actual metabolic rate. During this 9 month period of eating at maintenance calories the participants gained 4.1 kg, around 9 lbs. However since their metabolic rate had pretty much returned to baseline, researchers concluded that the weight regain was not due to metabolic adaptation.
What can we take away from this study?
Clearly if you consume less calories than you need, which is a requirement for fat loss, your metabolism will slow. However, as the study above shows, once you start consuming maintenance calories again, your metabolism will likely return to normal.
The real question is what should you do about metabolic adaptation if you are trying to lose fat?
In the overall scheme of things, 90 calories is really a small amount. A tablespoon of peanut butter has about 100 calories in it, cutting out a little peanut butter in your diet could account for the difference. In practice the difference in metabolic rate is probably contributing very little to any kind of weight or fat loss struggles.
What then does contribute to the struggles people encounter as they try to lose fat?
Some of what contributes to metabolic adaptation is unavoidable. As you lose body fat your body is going to burn less calories purely because it has less fat A reduction of body weight is inevitably going to burn less calories.
The other thing that typically happens is people tend to move less when they are in a prolonged caloric deficit. One study showed that a reduction in non-resting energy expenditure, aka calories burn via movement, accounted for 85-95% in total energy expenditure.
This means that the majority of the reason why we people struggle with fat loss over the long term is because they are just moving less. The other 15-5% of energy reduction could be due to purely weighing less and/or other bodily functions becoming more efficient such as a lower heart rate and/or reduced kidney function.
There is nothing we can do about our heart rate slowing or our kidneys becoming more efficient, but we can control our movement and to some degree our body weight.
By developing good movement and exercise habits!
It pays to develop good movement and exercise habits before going into any kind of fat loss period. If you develop the habits of taking two 20 minute walks a day and working out 3-5 days a week before dropping your calories, you will mitigate movement related caloric expenditure reductions.
In addition if some or all of those exercise sessions are devoted to strength training, you will not only mitigate a reduction in movement related caloric expenditure but you can also build more lean muscle mass. By adding lean muscle mass you will avoid the drop in metabolic rate due to weighing less. Remember your goal is fat loss, not weight loss. If you lose 5lbs of fat but gain 3lbs of muscle, you may only be 2lbs lighter but you replaced that fat with muscle which is much more metabolically healthy and also avoided the metabolic adaptation of being 5 lbs lighter!
Once you have movement and exercise habits in place you are very likely to maintain them in a caloric deficit. The other advantage of developing these habits beforehand is that it reduces your overall stress load. When you throw a bunch of new movement goals plus a caloric reduction at someone at the same time they are more likely to break under the stress load, either from a nutritional perspective or a movement perspective….or both! If the movement and exercise habits are engrained before the caloric reduction you can avoid the unnecessary stress.
Yes metabolic adaptation is a thing, it will happen when you lose weight, however, it is not permanent, and it is not related to why people stall or gain weight when they try to lose fat. A majority of the reason why people tend to stall or gain weight is because they start to move less.
To mitigate the chances of stalling or gaining weight, it is important to establish good movement and exercise habits before heading into a fat loss phase in order to lessen the overall stress of achieving your fat loss goals. Walking twice a day, preferably outside, and strength training 3-5 days a week should be a good framework for most people.
It may sound easy enough, but establishing habits can be hard. My newsletter is full of ideas for you to use to develop healthy habits that last a lifetime. To jump on the newsletter fill out the form below. If you need a more custom approach to developing lifelonghabits I am happy to talk to you about establishing a coaching relationship. Fill out the form here and we can set up a time to talk.
If you need a more custom approach to developing lifelong habits I am happy to talk to you about establishing a coaching relationship. Fill out the form here and we can set up a time to talk.
- (2020, November 11). Metabolic adaptation is an illusion, only present … – PubMed. Retrieved December 2, 2020, from https://pubmed.ncbi.nlm.nih.gov/32844188/ ↑
- (n.d.). Adaptive thermogenesis in humans – NCBI – NIH. Retrieved December 2, 2020, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3673773/ ↑
- (n.d.). Metabolic adaptation to caloric restriction and … – PubMed. Retrieved December 2, 2020, from https://pubmed.ncbi.nlm.nih.gov/26399868/ ↑