Is weight homeostasis possible?

I am slightly obsessed with my weight. Forgive me: I am 58 and have spent many decades repeatedly putting on weight slowly, and then losing it rapidly.

For many years I have wondered why can’t I just eat modestly and trust my body to “sort itself out!”

My recent discovery of the Mifflin St Joer equations (link) has allowed me to  simulate my weight over time, and my calculations are allowing me to understanding my own experience.

But my calculations have also raised a profound question:

  • Is homeostasis of weight even possible?


Homeostasis (or Homoeostasis) is the term given to physiological systems which conspire to keep something constant.

For example, we have systems that maintain our body temperature without any conscious effort. I don’t have to berate myself for being too hot and promise myself that in the future I will try to be cooler.

No. Our bodies sort out their internal temperature. I understand the system consists of temperature sensitive cells and nervous system reflexes that control blood flow, sweat glands, shiver reflexes, and our desire to undertake activity.


And I have generally imagined that in a more perfect world, a similar kind of system would underpin my desire to eat.

In this ideal world, I would naturally maintain my weight without any obvious effort on my part – stopping eating when I had eaten ‘enough’.

I had thought such a system actually existed. One part of the system is supposed to arise from the competing actions of hormones such as ghrelin – which makes us experience hunger – and leptin – which makes us feel satiated.

Together, ghrelin and leptin are supposed to act as part of a system of energy homeostasis.

However, having run many simulations of my own weight versus time (see below) and reflected on this, I am sceptical.

“But I know a bloke who…”

We all know people who seem to be able to eat at their ease and not put on weight.

I have no explanation for that, but then I have never experienced that myself.

My experience is that my weight either increases or decreases over time. What I have never observed it to do in all my 58 years on Earth is to stay the same! (I have written about this before: story 1 or story 2.)

What’s the problem?

I programmed the Mifflin St Joer equations into a spreadsheet to see the predicted effect on my weight of various dietary and exercise choices.

You can download the spreadsheet here and perform calculations about yourself in the privacy of your own computer. 

I entered my current age (58.2 years) and weight (74 kg), and I used the MSJ equations to predict what would happen to my weight if I ate 1800 kiloCalories (kCal) a day.

The results are shown below together with the effect of eating 50 kCal/day more or less

Weight versus Age Projection

  • The red line suggests that if I eat 1800 kCal/day then my weight will gradually decline over the next couple of years stabilising at about 71 kg. That would be dandy.
  • However, the dotted green lines show what would happen if I got my calorific intake wrong by ± 50 kCal per day. This is plus or minus half of a small glass of wine, or a half a biscuit either eaten, or not eaten.

These ‘alternate realities’ predict that my weight in three years time might be anywhere between 64 kg and 77 kg – a range of 13 kg!

To be within a kilogram of the predicted weight, my average energy intake would need to match 1800 kCal/day within 10 kCal a day. That is less than a single mouthful of food!

I don’t believe that any autonomic system can achieve that level of control. 

Weight versus Age Projection 2

So what?

Reflecting on these simulations, I don’t believe that the systems within our bodies that mediate ‘energy homoeostasis’ operate well over many years.

At least they don’t operate well in an environment where calories are so easy to obtain.

So I think my experience of slow weight gain over time is not a fault with my autonomic nervous system, or a moral failing on my part. It is just the way things are.

Asking the thinerati

Asking several slim individuals around the coffee machine this morning confirmed my view. They all were either (a) young (b) self-conscious about fitting into clothes or (c) weighed themselves regularly.

Personally I have resolved to keep weighing myself and using this to provide manual feedback.

How is my weight doing? Thank you for asking. It’s been just about stable since Christmas and I intend to keep it that way!

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4 Responses to “Is weight homeostasis possible?”

  1. edhui Says:

    Wow. And do you think there is any hysteresis in the system? Does that wagon wheel you eat now add 1mm to your waist the next day?

    I think the best argument for your non-homeostasis hypothesis is that there is no real reason for the body to know exactly how much it weighs at any time. Biology does odd things, though- your limbs grow almost exactly the same length over a period of years, without any obvious way of comparing their lengths.

    This is one of two homeostatic problems that intrigue me. The other is whether it’s possible to make a paper aeroplane stable to straight line flight. It’s trivial to make a stable paper aeroplane, and if you make it accurately it will approximate a straight line in an average room. But a glider really only has one reference- the direction of gravity. And that is at right angles to any tendency to turn. Obviously I don’t mean stable to a compass direction- that needs a gyro or something. I mean a paper aeroplane that is geometrically stable to flying in a straight line when not perturbed- to have some aspect of its geometry that makes it tend towards straight flight rather than an arc. My instinct is that it can’t be done, and my instinct is also that you are right in that there is very little homeostasis in our weights too.

  2. Victor Venema Says:

    Exactly, there needs to be a feedback mechanism, but it will not work to do this by monitoring how much you eat. Feeling full is such a feedback for the short term, but clearly not enough.

    There needs to be a feedback mechanism that uses something like body fat percentage, but no longer works well for our modern life style. A lion is able to keep his weight stable without scale and caring about the fitting is its clothes.

    Replacing this internal feedback with a scale does sometimes work, I did it as a PhD student. But to be honest I felt horrible and nowadays wonder whether part of my cells were getting too little energy, while my fat cells were still doing quite okay.

    We need to understand the feedback to get a real solution. This will be hard as long as overweight people are portrayed as sloths and the general advice is to “just” eat less and move more.

    • protonsforbreakfast Says:

      Victor. I do not know the secret of the lion or of animals in general. What I suspect is that for animals food is generally much harder to come by than it is for humans. And I can imagine that in a situation where if a human is working physically hard – perhaps requiring an additional one thousand kilo-calories per day – that a feedback system does operate but perhaps in the other way – stopping one from working too hard rather than eating too much.

      Also, perhaps there is an analogy with feedbacks in weather and climate. Feedback systems operate over a whole range of timescales from the short-term leptin-ghrelin system controlling hunger and appetite, to longer term effects associated with ageing and (in nature) famine.

      I seem to recall that even in old English literature such as the Canterbury Tales dating from ~ 1400 AD, some characters (e.g. the monk) were described as ‘fat’. So presumably being overweight is not an entirely modern phenomenon. So could it also be that a population as a whole contains individuals with a range of feedback settings that generate a range of weight responses to different environments.

      Anyway I have struggled with this my whole life and it seems that actually my experience is very normal. And I expect I will have to keep struggling at least until my stress levels subside. (94 months to go until pension day!).

      • Victor Venema Says:

        As far as I know lions hunt about twice a week. The rest of the time they just enjoy life in the shade of a tree. Like your calculation showed they would only have to hunt 1% more to look like an elephant after some time.

        Also hunter gatherers have quite a bit of free time, they should be able to gather or hunt a few percent more food and look like a wine-enjoying monk.

        Given that there are strong variations in the environment and you also have to survive a bad year (at least our ancestors did), it should be easy to eat a few percent more in an average year.

        I am also struggling with my weight. Clearly the feedback mechanism that once work no longer works for many of us. I would love to understand why. Chronic stress could be one option. If our bodies are in fight or flight mode it prioritises short-term survival and gives less resources to processes that are important for long-term health.

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