Posts Tagged ‘Overweight’

Is weight homeostasis possible?

February 28, 2018

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!

The effect of excess BMI

February 14, 2011

Dave Lowe is one of those colleagues who makes working at NPL such a pleasure. Having read my blog about the excess mortality associated with BMIs greater than 25 , he dropped me a line to let me know of a paper in the Lancet. The paper (Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies) presents its result in quite a technical way but their ‘interpretation’ section reads thus:

Although other anthropometric measures (eg, waist circumference, waist-to-hip ratio) could well add extra information to BMI, and BMI to them, BMI is in itself a strong predictor of overall mortality both above and below the apparent optimum of about 22·5—25 kg/m2. The progressive excess mortality above this range is due mainly to vascular disease and is probably largely causal. At 30—35 kg/m2, median survival is reduced by 2—4 years; at 40—45 kg/m2, it is reduced by 8—10 years (which is comparable with the effects of smoking). The definite excess mortality below 22·5 kg/m2 is due mainly to smoking-related diseases, and is not fully explained.

As I understand it, this is the link between premature death and the BMI at the time of death . So according to this, if I maintain a BMI of 27 ish for the coming years, I appear to be set to cut my life short by about a year. So I can reasonably hope to live to the age of seventy-ish (and so enjoy three years of my pension :-)). But what happens if I shift my BMI back to 25 in 5 years time? Do I then negate the excess risk to which I had exposed myself. The question to which I would like an answer is this.

  • What is excess hazard to which I am exposing myself NOW, by having a BMI of 27 at my current age (51) ?

Weight and Obesity: updated

January 20, 2011
The normal distribution of Body mass Index and what I think one would rationally expect to call normal, and overweight

The normal distribution of Body mass Index and what I think one would rationally expect to call normal, and overweight

It’s that happy time of month when Scientific American lands on my doorstep and allows me to consume something relatively highbrow, but accessible. And this month they featured an article on Obesity. I am a 51 year old male, 1.75 metres in height (5′ 9” for you oldies out there) and weighing 82 kg. So my  body mass index – my weight (in kilograms) divided by my height (in metres) squared (=82/1.75 x 1.75) is 26.8.  So I am officially overweight. So as I venture into heart attack territory, the issue of obesity is a matter of personal interest. The article is easy to summarise – to loose weight you need to change your habits – gimmicks or willpower based diets aren’t sustainable. But the article featured one extraordinary graph that shocked me profoundly. It is a graph of the distribution of the BMIs of americans from 1976 to 1980. The question is this –  what would you call ‘normal’?


The curve representing the distribution of Body Mass Index amongst the American population measured from 1976 to 1980 is shown in the figure at the head of this article. This kind of curve represents the distribution of many properties of a population, such as height. I think most scientists would  say that if you were within the band middle band of the above graph – your BMI would be ‘normal’ and it would be perverse to class people within this central band as ‘overweight’. But that is exactly what the usual medical classification of overweight does. The medical classification looks like this:

Medical classification of terms 'normal' 'overweight' and 'obese' in terms of Body Mass Index

Medical classification of terms 'normal' 'overweight' and 'obese' in terms of Body Mass Index

Now this seems to me to be perverse. This distribution is the ‘natural’ distribution of weight amongst a population. This classification defines nearly 50% of people to be overweight! Saying this is a problem and implying that those who are overweight or obese by this classification should loose weight and thus move into the ‘normal’ zone is bizarre. It’s like insisting that everyone should be above average intelligence. I find this curve really shocking. There could only be one possible justification for it: if having a Body Mass Index even slightly above average caused a pronounced increase in liklihood of health problems, then this could make sense. Does it? No.

Health : UPDATED

When I wrote this article I resorted to Wikipedia, and used data from the article on obesity which I thought had just the data I wanted. The data is sadly complex but is summarised in the graph below and shows essentially that there is a slight excess mortality in the ‘overweight’ group – BMI between 25 and 30 – but only just above the statistical significant levels.

Data on relative mortality as a function of Body Mass Index for white american males

Data on relative mortality as a function of Body Mass Index for white american males

Please note that the data are taken from this reference and were derived by examination of 1.4 million americans whose ages ranged from 19 to 84 with a median age of 58. They were re-visited after 10 years and it was seen whether or not they were dead! Note that the abstract does not describe how the general trend for more elderly people to be heavier was accounted for – clearly a critical correction since the elderly are overwhelmingly more likely to die. Note also that the Wikipedia figure curtails the y-axis so that the tiny changes look larger, and neglects to plot the confidence intervals of each data point.

However on reflection I realise that this is not the data I want. What I want are answers to two questions

  • Firstly: Was the definition of ‘normal’ (BMI in the range 19 to 25) derived from a previous time when this reflected the normal distribution of weights?
  • Secondly: What I want to know is the impact of being overweight NOW – aged 51. I doubt very much that this has much effect on my current mortality, but I could believe that it could affect me in years to come. So there is probably a risk factor – or excess mortality – which grows the longer I spend overweight. As an illustration, an overweight 25 year old probably has no excess mortality in their twenties or thirties, but if he or she lives to be 60 and stays overweight, then it is possible that all those years of overweightness could have some consequence.
  • Try as I might – and I have looked for hours –  I have not yet found the data I want.  I will be sure to let you know when I do.

Summary: UPDATED

From what I have read and seen so far, there is not a jot of evidence only marginal evidence for ascribing any negative health outcomes to men (actually white american men) in the overweight category of BMI between 25 and 30. Indeed the classification of people with BMI in this range as being ‘overweight’ or in any way abnormal is bizarre. I have not considered diseases associated with overweight, most notably diabetes, but I am looking for the data on that as well!

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