Archive for the ‘Obesity’ Category

Obesity Policy

March 6, 2018
BBC Story Extract

Extract from BBC news story. The annotations in red are mine!

Today the BBC are reporting that:

Britain needs to go on a diet, says top health official

The article states that people should allow:

  • 400 kilo-calories for breakfast
  • 600 kilo-calories for lunch
  • 600 kilo-calories for dinner

which adds up to 1600 kilo-calories a day. With this dietary intake, most adults in sedentary occupations will lose weight or maintain a healthy weight.

However, the article then goes on to say:

It is recommended that women should eat no more than 2,000 kilo-calories a day, while men should limit their intake to 2,500 kilo-calories.

No! As I pointed out previously, this is just too many calories for both men and women with sedentary lifestyles.

Any government campaign based on these figures is bound to fail.

Calories versus Age

For someone of my height and weight, the government’s recommend dietary intake is about 30% too high.

Who is going to die in 2048?

April 9, 2014
Age Standardised UK Mortality

Graph showing Age-Standardised UK Mortality per 100,000 of population per year. In 2010 mortality was around 1100 per 100,000, so for the UK population of 60 million we would expect around 660,000 deaths per year. However if the trend continues, no one will die in 2048!

While investigating causes of death in the United Kingdom, I came across the data above. The graph shows that the age-standardised mortality in the UK has been falling since at least 1980 – and shows no signs of stopping.

Indeed, if the trend continues, then sometime around the 14th March 2048, mortality will reach zero and no one will die in the UK!

Now of course, although this data is real and correct, the trend can’t possibly continue indefinitely. But the data is nonetheless fascinating for at least three reasons.

Firstly, in the face of seemingly endless stories telling us all how unhealthy we are – it seems that the trend to lower mortality is continuing unabated, despite the obesity ‘crisis’.

Secondly, although the linear trend in the data is striking, we have no justification for extrapolating the trend into the future. Why? Because its the future! And we don’t know what is going to happen in the future.

And finally, these numbers give us a scale for considering the relative seriousness of different causes of death: that was the reason I looked up the data in the first place.

I read that air pollution causes 30,000 deaths a year in the UK and that seemed a surprisingly large number. From the graph we can estimate that mortality in 2014 is approximately 1000 deaths per 100,000 of population per annum. So that that for the UK population of 60 million, this is about 5% of deaths – which still seems shockingly high, but is a smidgeon closer to believability.

So good news all round: especially if you, like me, are a man. The mortality of men and women is shown separately below.

If the trend continues, then after millennia of ‘excess male mortality’, the mortality of men should fall below that of women in approximately 2027 and reach zero in 2042 – before the women – who will not attain immortality until 2060!

Age Standardised UK Mortality by sex

Graph showing Age-Standardised UK Mortality per 100,000 of population per year for men and women. If trends continue, male mortality will fall below female mortality in 2027 and no men will die at all after 2042!


Dave asked: Are you sure age standardised mortality means what you think it does? Age standardised mortality might drop to zero. But that is not mortality. If the plot showed mortality that would suggest life expectancy has doubled since 1980, from 50 to nearly 100.

And I replied: The calculation is this:

  • How many people died in a particular year aged (say) 69.
  • This number is then expressed as a fraction of the actual UK population who were aged 69.
  • This is then expressed as an actual number who would have died in a ‘standard population’ called the European Standard Population.

This procedure allows the relative mortality in different countries to be compared

So, if for example, the UK has a high absolute mortality for 69 year-olds, but not many 69 year olds – then this will produce a larger number when ‘age standardised’.

I have obtained one or two sets of actual death data – but I don’t know the equivalent population to divide by to get the absolute mortality per 100,000. However this data shows a similar trend with roughly the same intercept.

What does it mean? I don’t know! I think it means that we are living longer (Is that news?). I was just struck by how straight the line was and how it begged to be extrapolated!

Float or Sink: Don’t believe everything you see on the internet

January 15, 2014
Wow! A can of Diet Coke floats and a can of regular Coca Cola sinks! Mmm. Don't believe everything you see on the internet.

Wow! A can of Diet Coke floats and a can of regular Coca Cola sinks! Really? Well No. Like so many things you see on the internet, it is not so simple.

While discussing recent news stories on the dietary ‘value’ of sugar, a colleague told me he had seen a surprising video on the internet.

It showed Steven Spengler putting cans of Coca Cola and Diet Coke into a tank and the can of Diet Coke floated while the can of Coca Cola sank. The celebrity scientist then related this to the amount of the sugar in the drink. See what you think:

I told my colleague that I didn’t believe anything I saw on the internet, but that the demo was convincing: it seemed as though nature itself was voting on the evils of sugar. A sort of ‘Witch Trial’ for harmful additives.

However being the person I am, I thought I would just check. I bought a can of each drink at lunchtime, went to the lab and did the test. This is what I saw:

This is what I saw when I put the two cans into water: they both floated.

This is what I saw when I put the two cans into water: they both floated.

Yes, that’s right: both cans floated. If you look closely you can see that the Coca Cola is lower in the water, but it did not sink. So how did I get the picture at the top of the page? Simple: I heated the water.

The density of water falls slightly with increasing temperature (See the graph at the bottom of this article) and when the water was around 36 °C at the top and 32 °C at the bottom, the Coca Cola sank. But when the water cooled to between 33 °C at the top and 30 °C at the bottom, the Coca Cola floated.

I made measurements of the mass of the cans, full and empty and found that the 330 ml of Coca Cola weighed 340.2 g while 330 ml of Diet Coke weighed 330.8 g. And hence I made an estimate for the density of the two fluids, and yes, Coca Cola appears to be 2.8% denser that Diet Coke.

But then the label tells you that 330 ml of Coca Cola contains 15.9 g of sugar, whereas Diet Coke contains Aspartame which is weight-for-weight 200 times sweeter. So there is only about  0.07 g of Aspartame in a can of Diet Coke. So this isn’t really ‘news’ of any kind.

I couldn’t understand the exact 9.4 g difference in mass because the density of the fluids is affected by all the other components ingredients which could differ between products.

However both fluids were denser than water (0.5% and 3.3.% respectively) . And whether a can floats or sinks depends only partially on the density  of the liquid in the container.

It also depends on the ‘air’ gap, and the weight of the can. So Steven Spengler’s demo just relies on a simple coincidence between the average density of the US-size cans and the density of water at about room temperature.

For larger containers, the mass of the container will make less difference and so I thought that for a 2 litre PET bottle, both fluids would probably sink. Was I right? No.

The Coca Cola weighed in at 2.129 kg and the Diet Coke was 85 g lighter at 2.044 kg. But in fact these bottles have a larger air gap and so – even when heated to 48  °C – both bottles floated.

2 litre bottles of Coca Cola and Diet Coke both float in water - even when heated to 48 Celsius.

Two 2 litre bottles of Coca Cola and Diet Coke floating in water – even when heated to 48 Celsius. The blue lines scrawled on the photograph show the water level around each bottle and the value on the thermometer.


The density of water plotted as a function of temperature and fitted with a quadratic polynomial.

The density of pure water plotted as a function of temperature and fitted with a quadratic polynomial. The entire vertical range represents just 1% change of the density.

Are you sure you want to lose weight?

January 4, 2013
The relative risk of having a Body Mass Index in different ranges. Being overweight or being obese (Class I) results in a lower risk of death than being 'normal'.

The relative risk of having a Body Mass Index in different ranges. Being overweight or being obese (Class I) results in a lower risk of death than being ‘normal’. The error bars represent a 95% confidence interval.

Welcome to 2013! It may be that you – like me – are considering losing a little weight. But if you are considering a diet or exercise regime, then you should be aware that a new study confirms that although you may feel better, you will also be increasing your risk of an early death.

I have written about this before (here), but this new study by Flegal et al (available free here) confirms this result a fortiori . The work is a ‘meta’ study covering more than 2.8 million people on several continents – mainly Europe and the US – and has recorded more than 270, 000 deaths. Thus the relative risks of being overweight can be isolated from many other causes. The results (see the Figure above) confirm that being ‘overweight’ reduces the relative risk of death (the Hazard Ratio) compared with being ‘normal’. They even confirm that being Class I obese still offers a protective effect. Higher levels of obesity increase the risk the of death significantly.

This result is important in a social context where right-wing think tanks suggest that the benefits of overweight unemployed people should be cut if they fail to exercise (Guardian, BBC). Their aim – no doubt laudable – is to reduce the burden of obesity-related disease on the National Health Service. However the data here indicate that the consequence would be to increase the risk that these people would die. This is not a morally defendable position. Indeed, this work seems to me to call into question every piece of government advice on the topic of obesity.

The Journal of the American Medical Association has an accompanying editorial discussing the work:

“The optimal BMI linked with lowest mortality in patients with chronic disease may be within the overweight and obesity range. Even in the absence of chronic disease, small excess amounts of adipose tissue may provide needed energy reserves during acute catabolic illnesses, have beneficial mechanical effects with some types of traumatic injuries, and convey other salutary effects that need to be investigated in light of the studies by Flegal et al and others.”

Not all patients classified as being overweight or having grade 1 obesity, particularly those with chronic diseases, can be assumed to require weight loss treatment. Establishing BMI is only the first step toward a more comprehensive risk evaluation.

In other words being marginally overweight is a good thing if you fall ill – because you can draw on the energy in the fat if you are not eating. However its also states that there are “other salutary effects that need to be investigated in light of the studies by Flegal et al and others.” In other words “We don’t understand this, but its real”.

My body mass index is around 27 kg/m2, close to the UK average so I am technically overweight. I also feel overweight. And I understand that this increases my risk of disease (morbidity). However, it also reduces the risk that I will die from it (mortality). Nothing in life is as simple as we would like it to be!

Happy New Year.

The incredible lightness of being wrong

July 18, 2012
BBC GLobal Fat Scale

Where I lie on the BBC Global Fat Scale. Under average for the UK – over average for the world. But the text in the ‘info’ box (shown enlarged in the figure below) has  been changed. Click for larger image.

One of the most interesting features of modern media is that if one makes a mistake, it can be corrected quickly and the original error then disappears. Anyone who accidentally witnessed the transient error is then left with a feeling of bewilderment when they try to show the mistake to their friends. They may even experience a feeling of paranoia. I take advantage of this feature regularly on this blog, and the more august BBC took advantage this week when it erred in an article on Body Mass Index (BMI).

Both myself and one of my international network of informants noticed that the ‘hover over’ information text stated that having an above ‘normal’ BMI caused increased mortality – an increased risk of death. As I mentioned in a previous article, this appears to be not true. In fact being ‘overweight’ (BMI 25 to 30) appears to reduce mortality. Even being ‘obese’ (BMI 30 to 35) appears to give a reduced risk of death. Before I could write to the BBC about this, they removed the offending text, leaving me and my informant scratching our heads.

BBC GLobal Fat Scale

Detail from the image at the head of the article.

This matters. If the BBC, or the government, or a health authority, encourages people to move from the ‘obese’ or ‘overweight’ categories to the ‘normal’ category, then they are encouraging them to die earlier. Generally we consider ‘dying younger’ to be a ‘bad thing’. But that is what the statistical evidence indicates and that presumably is why the BBC chose to remove this reference.

There are two lessons to learn from this episode.

Firstly, reputable media, such as the LA Times, make a note on a page to record the fact that it has been updated since publication. This should be routine in a public organisation such as the BBC. They should not try to re-write history.

Secondly, the article in itself is profoundly flawed. It ranks a large number of countries but fails to note that the bottom half of the list are countries in which the populace is profoundly and tragically undernourished. The mortality data indicate that the ‘normal’ BMI categories may well have been drawn up in a time when our population was malnourished. Being overweight may not the most beautiful condition, but the data tells us that in terms of living longer, its the best condition to be in. And that is something this chubby 52 old (BMI = 27) feels pretty good about.


Published first at 12:09 a.m. on the 19th July 2012


July 1, 2012
BMI Mortality

The upper curve shows the relationship between body mass index (BMI) and mortality expressed as relative risk of death compared to those with a BMI in the range 22.5 to 25. The data indicates quite robustly that being in the overweight category is ‘protective’. The data point at BMI=18 includes data for all people with lower BMI and the data point at BMI=35 includes data for all people with higher BMI. The lower curve shows the distribution of BMI in the population used for the study.

Friends, I am concerned about my weight. In particular I am concerned about whether being overweight (i.e. with a body mass index or (BMI) in the range 25 to 30) is genuinely bad for me, or whether it just makes me feel bad.

I have looked at this issue before and expressed my puzzlement at how ‘normal’ ever came to be defined as having a BMI in the range 20 to 25, when as far as I could tell, it has never coincided with the central range in the population.

My puzzlement appears to be vindicated by research which shows that the relative risk of death – mortality – is lower for people who are overweight compared with people in the ‘normal range’. These conclusions are backed up by other studies. But even so, it is important to understand how the research was done in order to appreciate what it really tells us.

The research followed 11,834 individuals in Canada from 1994/5 to 2006/7, and saw how mortality was affected by their BMI at the start of the study in 1994/95. Let me stress this. It saw how the BMI statistic in 1994/5 affected the rate at which they died in the subsequent 12 years. This large population included men and women, smokers and people who never smoked, and people in all age groups.

Could the ‘BMI effect’ have been protective in young people, but harmful in older people? This might make sense, since young people are less likely to die in any case. This might have masked the effect that I would have expected to see: that being overweight was harmful. The researchers controlled for that and looked at how the relative risk of death varied with BMI categories for various sub-populations within the group. Surprisingly – to me at least – the effect was seen in all categories.

BMI Mortality versus age

BMI Mortality versus age for different subpopulations within the study. The risk of death is relative to those with BMI in the ‘normal’ range. The lowest and highest BMI points include data for all individuals at lower or higher BMI. I have missed out the confidence indicators (error bars) because they make the graph too confusing.

Mortality and Morbidity. This report recorded the BMI of a population at a point in time, and studied correlations between the BMI and the rate at which people died in the following 12 years: This is called the risk of mortality. It did not record whether the individuals concerned became ill or unwell, and did not study how their BMI affected their chance of becoming unwell – that is called the risk of morbidity. I do not have data to hand but I would be pretty sure that being in the ‘overweight’ category (as defined by a BMI in the range 25 to 30) would be a significant risk factor for diseases such as cardio-vascular disease and type II diabetes.

This data was taken amongst a population which, for possibly the first time in human history, has enjoyed essentially unrestricted access to food for several generations. This is an astonishing cultural achievement. If the data really does fall in this way for other populations – including that in the UK – it will be very interesting to understand why that occurs. It will also be interesting to hear doctors argue that ‘chubby’ people like me should lose weight – something which will increase my risk of death!

What am “I” ?

May 9, 2012
A portrait of the artist as a young man.

A portrait of the artist as a young man. This is a photograph of the collection of atoms which went by the name Michael de Podesta circa 1980. In the same way that Manchester United still exists, but no longer has any players from the 1980’s, so Michael de Podesta ‘exists’ but retains none of these particular atoms or cells. What does that mean?

I remember being an undergraduate.  And at about the time the image above was captured, I recall imagining being very tiny – smaller than an atom – and moving through the atoms of ‘my body’. I remember asking: How would I identify the edge of ‘me’?

On this tiny scale, the nuclei of atoms would be far apart, and so I would barely be able to tell whether I was inside an atom, or in-between atoms. The edge of ‘me’ would be very hard to detect: it would correspond to nothing more than a relative decrease in the frequency with which I came across a nucleus. And also to changes in the types of nucleus I encountered – with many fewer carbon nuclei in the bits that were not ‘me’.

The upshot of my imaginings was that I decided that the concept of an ‘individual’ was one that only made sense when viewed on a large scale. On a small scale, all one would see would be essentially chaotic variations. This was a pivotal moment for me,

From this journey of my imagination I understood (pace any high energy physicists out there) that in same way that a microscopic explorer would never deduce the existence of the phenomenon I called ‘me’, so looking at the components of matter would never – even in principle – result in a ‘theory of everything‘.

I was reminded of this insight today while reading an article in the Scientific American on bacteria. First I was shocked to find that: In the human body, bacterial cells outnumber human cells 10 to one. The article then explained that many dis-eases were not caused by ‘foreign’ bacteria, as had at first been imagined. Instead many dis-eases arose from a disturbance of the ”social’ balance between the vast populations of bacteria that live on (and within) our bodies.

For example, the microbe Heliobacter Pylori is associated with ‘causing’ stomach ulcers, but in normal life Heliobacter Pylori lives happily in our stomach. And it helps us by producing the hormone ‘ghrelin‘ which produces a sensation of ‘satiation’ after eating. Similarly, the bacterium Bacteriodes fragilis stops inflammatory T cells from damaging our bodies, and ts absence could be associated with auto-immune diseases.

And so biology brought me back to same question that physics had raised 30 years ago. What do I mean when I use the word ‘I’? Physics told me that ‘I’ was only blearily separated from the atoms around ‘me’. And now biology tells me that ‘I’ am a combination of my genetically unique cells, and a vast army of bacterial ‘hangers on’ that have come to live with ‘me’ essentially by chance.

The concept that dis-eases were not caused by individual poisonous foreigners, but instead resulted from an imbalance in a diverse social network resonated strongly with me. And so I thought I would share that with you. Goodnight.

See and links within for further details.

Body Weight Simulator

January 13, 2012
Body Weight Simulator

Screenshot of the Body Weight Simulator. At last a piece of software that explains why its hard to keep the weight off - and uses realistic numbers. Click for larger image: See text for link.

As I mentioned back in November 2011 (The Mass of Sisyphus) I don’t seem to be able to keep my weight stable at a level with which I am comfortable. Since I wrote that, I have lost around 6 kg but I seem to be stuck at about 80 kg. Now I have at last found an explanation based on physiology and physics.

The Body Weight Simulator is available is a piece of ‘java’ software from the US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The software runs directly from your web browser and requires various inputs (mainly initial weight, height, age and level of activity) that allows it to estimate how many food calories you require each day. Significantly this number differs from the standard numbers for adults (e.g. 2500 calories for an adult male).

One of the insights embodied in the software is that heavier people have a higher calorific requirement. So if you restrict your diet by 500 calories per day, your weight will not fall indefinitely, but stabilise at a new lower value. This is what I have observed previously, but never really understood.

For example it tells me to that get from 80 kg to 75 kg in 50 days I need to restrict my diet by around 713 calories per day (if I don’t do any extra exercise). Additionally it tells me that in order to maintain a weight of 75kg, I need to restrict my calorie intake permanently by 87 calories a day compared to what I am doing now.

It’s possible to cut and paste the predicted weight data and so I can compare theory and experiment – see below – and the numbers are sort of plausible.

Dieting Graph

I have been on a diet since 16th October 2011 and the graph below shows my weight versus the prediction of the body weight simulator for a 700 calorie restriction in my diet which stopped after 70 days. The agreement is plausible.

So now I will sit at my computer for even longer and consider strategies which will allow me to reach – and maintain – a body weight of 75 kg. Mmmm. Or maybe I should just go for a run…

My Weight 1995 to 2011: The mass of Sisyphus

November 14, 2011
My weight from 1995 to 2010

My weight from 1995 to 2010

My weight having tipped 86 kg, (BMI 28) and my belly having inched past the limits of 34″ waist trousers, I have begun a diet. Again. The first couple of weeks have been fine with my weight falling by roughly 1 kilogram a week (my target is 0.1 kilograms per day).

Plotting my weight on a spreadsheet I see that this is my fourth diet in 16 years and with each diet I seem to go over the same weight range. And at the end of each diet I am eating happily, I feel much better, my BMI is back to 25, and  I can’t think of any reason why that should change. But it does.

Somehow – all that weight creeps back on. Between 2006 and 2009 (≈1000 days) I put on roughly 10 kilograms – or about 10 grams per day – equivalent to an calorific imbalance of around 85 ± 15 calories per day. This is a single biscuit a day – or the difference between a slice of buttered bread or non-buttered bread.

Is this my fate? Am I condemned to an antiSisyphean cycle: endlessly pushing my weight down the hill only to have it roll back up? Oh! the Gods are cruel!

The mystery of sleep

November 7, 2011

The talk above is by Giulio Tononi, of the University of Wisconsin on “Sleep function and synaptic homeostasis” – stop yawning at the back! Its about 20 minutes long and is comprehensible for around the first 5 minutes.

I have been dieting lately, restricting my calorie intake to somewhere around 1500 calories* per day. I am using the H-plan® diet – where the H stands for hunger: basically the idea is to avoid panic when I feel hungry and just get used to the feeling. Well I am losing weight (of which more later), but the diet has had a side-effect: I don’t need as much sleep. I know that after eating a big meal I would feel especially sleepy, and I wonder if this is just a re-bound from having previously eaten too many large meals?

Normally I sleep for just under 8 hours but crave for more. Currently I am sleeping for 7 and waking refreshed.  I have looked on-line for explanations, or corroboration that this is a genuine effect and found nothing. Why I should feel the need for corroboration of something I am experiencing is something else I don’t understand! But even though it appears to be just me, it certainly lifts my mood.

With my current surfeit of wakefulness, I came across a discussion on Quora about sleep, linked to a talk on YouTube (see top of the page) addressing the fundamental question: What is sleep for? Hearing the basic facts of sleep read out (about 1 minute into the talk) it seemed amazing that we don’t have an answer to the question. Sleep is central to our lives – both personally and as part of of our symbiotic relationship with our spinning planet – and essential to our health. And yet we not know the answer to something so basic as ‘What is it for?’. Wow.

I was reminded of the role of the Sun in our lives. Our lives and cultures are based around the action of sunlight on the Earth, and yet we never look at the Sun directly – it would damage us if we did so. Similarly with sleep, because we lose consciousness during sleep – it evades our gaze.

*1 calorie is a dietary unit of energy approximately equal to 4200 joules.

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