A Little Bit About Metabolic Adaptation

Why your liver is more important than you think

Dieting sucks. It turns out sauces, deserts, and snacks all have Calories in them and if you want to lose weight all the advice tells you to avoid them. Now your only eating boring food, you’re hungry all the time and you’re and losing weight. It’s hard, but it’s working. Then, after a few weeks or months, you’re weight stabilizes. Your still hungry, your still only eating boring food, your doing everything the same, but you stopped losing weight. What happened?

Your body adjusted. It found ways to burn fewer Calories so it didn’t have to keep burning extra tissue. There are a lot of ways to do this, you can fidget less, you can walk around the house less¹, you can lower your body temperature a degree or two, you can adjust how you move around so it’s more efficient², and your body can burn tissue that’s more metabolically active than fat. This whole process is called Metabolic Adaptation and it’s a major reason that weight loss dieting is hard.

How do you fight it?

Metabolic adaptation is a very useful survival process for most of human history when food shortages were an occasional fact of life. This doesn’t apply to modern American life, and it doesn’t apply to me. I can get a cake at the grocery store across the street at any time, any Calorie deficit I have is a life choice and I want my body to respect my choices³. So I fight it. What do I do?

• I go for long walks so that my activity is high enough that even if I’m a total lump for the rest of the day I’ve still burned enough Calories to keep my NEAT where I want it to be.

• I drink coffee and other caffeinated beverages which raise my body temperature.

• I lift weights to produce an anabolic stimulus, telling my body to grow muscle. Since my body needs to burn something, that means it prioritizes fat tissue and my weight loss is confined to fat instead of being fat plus muscle.

• I still lose the fight with metabolic adaptation, so after 8-12 weeks I call a truce and regroup. It’s an uneasy truce, but if I’m able to maintain the new weight for those 12 weeks, I can go back into the fight fresh but with a new, lower, baseline.

None of this saves my liver.

Your Liver?

Not just your liver, your entire fat free mass. If you’re like me and spend most of your hours in front of a screen every day, most of your daily Calorie burn is determined by your Basil Metabolic Rate (BMR)⁴. Your BMR is determined by the metabolic activity of all your cells, the more cells you have the higher your BMR. But it also depends on the type of cells, every cell has it’s own metabolic rate. Fat cells have one of the lowest metabolic rates, around 6 Calories per kg compared to skeletal muscle’s 13 Calories per kg. But both of those are dwarfed by kidney tissue, heart tissue, liver tissue, and brain tissue.

I’ve posted this chart before, but I can’t stop thinking about it. Your liver, your brain, and your skeletal muscle make up ~60% of your BMR. What if your liver gets smaller during metabolic adaptation?

Here’s the story I keep seeing in my head: A guy who’s 5’10” never exercises growing up and hits adulthood weighing 300lbs, decides this is terrible and diets down to 160lbs with 20% bodyfat⁵. Every day he goes to lunch with his best friend who is the same height, weight, and bodyfat percentage, but never got fat. If he eats the same amount of food as his always skinny friend, the formerly overfat guy will gain weight and his friend won’t. This is crazy.

What’s going on here? People online talk about “bodyweight set points” but that’s just a label, there’s no mechanism proposed. But the metabolic adaptation framework does propose a mechanism and a solution, increase your fat free mass.

My guess is that some “metabolically unlucky people” or “people with a slow metabolism,” who are otherwise doing everything right, have lower than expected metabolic activity. I think this is caused by their fat free mass being lower than expected and this is causing huge problems for them. If you’re short half a kg of muscle, that’s only a loss 6 Calories from your BMR but if you’re short half a kg of liver tissue that’s 100 Calories. Add in similarly modest shrinking of your heart, kidneys and other organs and you really have a problem.

But Why The Liver?

The chart above suggests that increasing your fat free mass with the goal of increasing your BMR means either increasing your muscle tissue, your brain tissue, or your liver tissue. We know how to increase muscle tissue, lift weights and eat protein⁶. You can’t increase your brain tissue, there’s not enough room in your skull for 50% more brain. But what about your liver?⁷

I don’t know the answer to that, and I don’t think anyone else does either. You can check your liver size with an abdominal ultrasound scan⁸ but basically no one does this. Even if you do have a small liver, what do you do? Fat free mass can be increased lifting weights, but does that cause you to regrow lost liver while building muscle? I haven’t been able to find a good answer. People with severe metabolic adaptation post diet just aren’t studied enough.

I do plan on writing up a more comprehensive discussion on Metabolic Adaptation, the work of Erik Trexler, and Ponzer's Paradox. It’s taking a while.

I Want A Bigger Liver, And Maybe You Do Too

There are two types of people who might want a bigger liver, those wanting to undo metabolic adaptation they suspect happened to them at some point and those who want to eat more food without getting fat⁹. We’re going to want to test any solution against both groups, because things that work for one group might not work for the other.

A muscle growth plan (i.e. lifting weights and eating protein) seems to work to a limited extent for both groups. Adding fat free mass can mitigate other symptoms of metabolic adaptation from extreme dieting, like hyperphagia, so it is probably having some effect there. And athletes who put on fat free mass during college increase their organ size and BMRs. The problem is the effect size is small. Unless your clearing some key breakpoint or getting as big as a college football player you’re not going to feel it¹⁰.

What else might work? DRUGS! The liver is incredibly regenerative and stops growing due to complicated biochemical processes. It is possible to modify those processes to cause your liver to grow back to, or above it's original size.

THIS IS VERY DANGEROUS. WE HAVE A NAME FOR TISSUES IN YOUR BODY GROWING OUT OF CONTROL. ITS CANCER.

The risks seem pretty big, which is why I’m not taking anything for this and I’m not planning to. I was really curious so I asked the smartest medical research I know¹¹ to look into this. She tells me she’s working on it right now and will write a blog post of her own soon. (It took me too long to finish this, so her post is up and you should read it, I’ll react to it next week.)

1. Fidgeting and idle walking are two forms of NEAT, non exercise activity thermogenesis. It’s stuff your body does to keep your Calorie intake and output balanced.

2. This was only discovered recently, but the amount of Calories you can burn can very by a factor of three depending on your activity level and Calorie balance. (check this)

3. My body seems to be incapable of respecting simple verbal requests, much worse than even my two year old.

4. There’s a few other names for this, your “resting metabolic rate”, your “sleeping metabolic rate”, and I’m sure I’ve said base metabolic rate.” They’re all basically the same thing, how many Calories do you burn doing nothing all day.

5. This is a far cry from impressive, but no one would call this guy fat. It’s a very normal body.

6. And maybe stretch your muscles out to a painful degree several times a week, I’m not sure. More research is needed.

7. This is why I keep talking about livers

8. Very similar to what pregnant women get.

9. Some people are in both categories.

10. The exception is if you become active enough to become an athlete. Fat free mass predicts BMR very well, but for some reason it’s a different prediction for athletes and for non-athletes. I have no idea why, but the finding has been repeated many times. The bar for athlete isn’t that high, regular attendees of CrossFit gyms count, but I can’t pinpoint it better than that.

11. It’s Sarah Constantin, my wife.