The Truth about Fat

March 24, 2012 § Leave a comment

Surgeon Gabriel Weston claims that we are in the middle of a fat epidemic. In this week’s Horizon documentary she seeks to explain a “mystery”, why she asks when we are all surrounded with ample food do some people pile on the pounds while others do not?

Weston’s documentary makes an appropriate companion piece to last week’s The Truth about Exercise. The focus this week is on appetite and individual differences. Weston tells us that there is a hunger hormone (Ghrelin) and a fullness hormone (PYY). Dr Carel Le Roux says that the gut talks to the brain and influences how hungry or full we feel.

Using a functional MRI scan Weston’s brain is shown to be normal, with limited activation in response to calorie-rich food. By comparison a scan of an obese person’s brain reveals considerable activation in areas of the brain associated with “reward-centres”, addiction and emotional responses to food. Psychiatrist Dr Samantha Scholtz says that gastric bypass surgery can change the way the brain responds to food. 21 stone Marylin Walsh underwent a stomach bypass operation at Dr Le Roux’s hospital; within weeks she had lost four stones. More interestingly she reports that she no longer desires sweet or fatty foods. Weston is shown before and after brain scans of an obese person who had a stomach bypass and while the before image demonstrated great activity in response to high calorie foods, the post-operation scan shows minimal activity just like Weston’s own scan.

Discussion

The Truth about Fat is an interesting documentary but while I found Gabriel Weston’s narrative compelling I kept wondering if there were alternative explanations that were not offered. I felt that time given over to dissections of pigs to show us visceral fat might have been better dedicated to providing stronger evidence to support the theories advanced.

At the start of the programme  Weston explains that the human brain evolved at a time when food was scarce and therefore is attuned to storing energy, however in today’s world with plentiful food available 24/7, behaviour that was once useful to human survival is maladjusted to modern life. An interesting theory, but why I wondered has the fat epidemic that Weston talks about only taken hold (outside of the US) in the last 2o years when for most of the 20th century food has been cheaper and more plentiful than any other time in our history. While I find Weston’s explanations quite persuasive I felt she need to go a little further to make her case completely convincing.

Another example is the former shot putter who tells us that despite being very motivated he found it impossible to increase his weight beyond a certain point. This is an interesting change of tack from the usual case studies of people trying to lose weight; however this was only one person and therefor it is impossible to say whether this individual is a one-off or representative of the wider population.

3500 kcal equals 1 pound of body weight: fact or myth?

March 18, 2012 § Leave a comment

In the article ‘What’s a few billion neurons between friends?‘ I expressed surprise that the figure of 100 billion neurons in the human brain was often repeated despite no one seeming to know where the figure came from. It reminded me of a claim I heard regarding the usual answer to a common dieting question: ‘how many calories do I need to burn to lose 1lb of weight’. There are different variations to this question but the answer is almost invariably the same – 3,500 calories.

By chance I caught the end of a radio interview with a lady who was questioning the provenance of this figure, which like the number of neurons in the brain, had gained general acceptance. I didn’t hear the name of the interviewee and was unable to follow up the claim that the 3,500 calories figure is a myth, but I now believe the person involved was Zoë Harcombe.

In her article ‘1 lb does not equal 3,500 calories‘ Zoe says that she asked several organisations (the National Health Service (NHS); the National Institute for Clinical Excellence (NICE); the Department of Health; the National Obesity Forum; the Association for the Study of Obesity; the British Dietetic Association and Dieticians in Obesity Management) where the 3,500 figure came from but none of them were able to provide a satisfactory answer. This is an interesting line of investigation which I will comment on later but first I want to focus on her claim that ‘you will struggle to find anyone demonstrate the precise calculation behind this’.

True, I did struggle at first but only because attempts to Google the answer only brought up page after page of links to forums, blogs and articles asking how many calories are in a pound of weight. However, searching more academic sources I found articles referencing the work of Max Wishnofsky. Wishnofsky’s 1958 article ‘Caloric Equivalents of Gained or Lost Weight‘ provides the following explanation:

“… the average fat content of human adipose tissue taken from various parts of the bodies of well-nounished subjects is 87 per cent. One pound (454 g) of human adipose tissue, therefore, contains 395 g of fat. The caloric value of one g of animal fat is 9.5 ; consequently, the caloric equivalent of one pound of human adipose tissue may be considered to be about 3,750 cal.”

My research also produced several references to Dr Gilbert B Forbes. Forbes observed that body weight changes involves both body fat and fat-free body mass and devised a formula to reflect this. As Forbes states in ‘Body fat content influences the body composition response to nutrition and exercise‘:

“In most situations involving a significant change in body weight, both fat-free body mass (FFM) and body fat participate, but the relative contribution of FFM and fat to the total weight change is influenced by the initial body fat content.”

Hall revisited Forbes’s work and devised a new formula. This formula produces results that ‘… compared favorably with data from human under-feeding and over-feeding experiments and accounted for previously unexplained trends in the data’. In another journal article Hall asks the question “under what conditions is it appropriate to use this rule of thumb and what are the factors that determine the cumulative energy deficit required per unit weight loss?” The rule of thumb Hall refers to is the need to create a calorie deficit of 3,500 calories in order to lose one pound of weight. Hall comes to the conclusion:

“The rule of thumb approximately matches the predicted energy density of lost weight in obese subjects with an initial body fat above 30 kg but overestimates the cumulative energy deficit required per unit weight loss for people with lower initial body fat.”

Returning to the point raised by Zoe Harcombe, several organisations she questioned were unable to say where the 3,500 calorie figure came from. It is a figure repeated by “government literature, in just about every diet book, in private health booklets and all over the internet’. Zoe’s investigations show that too often received wisdom is accepted without looking deeper and checking sources. Since my first draft of this article I have looked deeper and after checking Zoe’s sources I realise that not only did she know about Wishnofsky’s work she even referenced his 1958 article in her book The Obesity Epidemic.

Other than the point about the need for trusted organisations to be more careful about the provenance of the information repeated to the public, an interesting point to arise from this investigation is that the truth about how many calories are in a pound of body weight is more complex than is commonly recognized.

My investigations show that 3,500 figure is not wrong per se and is certainly not a myth, but rather it is a rule of thumb that cannot be applied blindly. So do 3,500 kcal equals 1 pound of body weight? The answer is ‘sometimes’.

What’s a few billion neurons between friends?

March 14, 2012 § Leave a comment

Reading through various articles linked by Anil Seth’s piece in the Guardian that I reviewed yesterday one in particular caught my attention. The article, ‘How many neurons make a human brain? Billions fewer than we thought‘, reports on the research of Dr Suzana Herculano-Houzel that indicates that the healthy human brain contains about 86 billion neurons; this is 14 billion less than widely quoted figure of 100 billion.

Dr Herculano-Houzel’s methodology has attracted attention.  She took the brains of four adult males and reduced them to a “brain soup” then counted the number of cell nuclei belonging to neurons from a sample of the “soup”. From this she was able to estimate that the total number of neurons in the brain. The advantage of this method over taking a count of neurons from a sample of a specific brain region is that it is not affected by the differing density of neurons found in different areas of the brain.

However, it was not the methodology that I was most interested in. What surprised me is that the previous estimate of 100 billion neurons has been widely quoted despite no one seeming to know where the figure came from. It seems strange that science, a field of inquiry that should be rigorous and reliable, should accept a figure that cannot be verified. Which reminds me of a figure often repeated in relation to dieting and weight loss – but that’s for another day.

That aside how important is this research? 14 billion neurons are we are told roughly that of a baboon brain or half that of a gorilla brain. This gives some idea of the large number of neurons that the human brain contains in comparison to other primates. The human brain is typical for a primate except for the number of neurons; it would seem that for brains at least it is size that matters.

Consciousness: Eight questions science must answer (Review)

March 13, 2012 § Leave a comment

Anil Seth, who took part in a debate about the nature of consciousness at the Royal Institution last week, wrote ‘Consciousness: Eight questions science must answer‘. This is the third of the the Guardian’s series ‘Consciousness: The hard problem‘; the other two ‘Neuroscience and philosophy must work together‘ by Barry Smith and ‘Consciousness: why bother?‘ by Chris Frith were reviewed previously. Unlike the other two which are essays this article after a short introduction goes point-by-point through the eight questions.

Although the format does not allow Anil to select one or two main themes and to develop them in greater detail, it does make for a very accessible article and allows the reader to get an overview of some important issues very quickly.

The eight questions are:

  1. What are the critical brain regions for consciousness?
  2. What are the mechanisms of general anaesthesia?
  3. What is the self?
  4. What determines experiences of volition and ‘will’?
  5. What is the function of consciousness? What are experiences for?
  6. How rich is consciousness?
  7. Are other animals conscious?
  8. Are vegetative patients conscious?

Some of these questions, such as ‘what is the self?’ are probably as old as philosophy itself. However, modern science is providing some fresh insights into some of these questions and promises to provide future insights into others. For example one approach to answering the question, ‘what are the critical brain regions for consciousness?’, is to try to identify the neural basis of consciousness. Essentially, this means identifying what brain activity at a neural level correlates to specific experiences of consciousness; these are referred to the Neural Correlates of Consciousness.

The questions cover a broad range of subjects within the field of consciousness; most people with an interest in consciousness should find something of interest in this article. I thought the question ‘What is the function of consciousness’ particularly interesting. The best answer appears to be that consciousness integrates information. Conversely it might be expected that a lack of consciousness could reflect a breakdown in how the brain integrates information. Anil points to increasing evidence to suggest that disintegration of how different parts of the brain work together that underlies how anaesthesia works.

Anil has backed up each of the eight points with at least one link which enables the reader to look deeper into the subject. It also allows the reader to get a better understanding of the evidence on which Anil bases his writing.

Of the three articles I found this one to be the most interesting and useful, and Anil has highlighted several strands of research in the neuroscience of consciousness highlighted here that are worth following the progress of.

The Truth About Exercise – Synopsis (part 2)

March 9, 2012 § Leave a comment

“Exercise, I know I should do it …… but I hate it”

Like Michael Mosley 80% of us do not take regular exercise. Earlier in ‘The Truth About Exercise‘ Mosley established that taking a 90 minute walk reduced the amount of fat in blood following a fat-laden breakfast the next day by about a third. But as Mosley’s quote above makes clear, the problem isn’t that we are not aware that exercise is good for us, the problem is that for many of us keeping up regular exercise is too difficult.

It might have occurred to you that if there was an exercise regimen less onerous than the recommended 150 minutes of moderately intensive aerobic activity the chances that more people would comply with it must be greatly enhanced. If so you would be glad to know that research by Prof. Jamie Timmons among others is beginning to indicate that such a regimen is indeed possible. Prof. Timmons told Mosley about the benefits of the HIT (High Intensity Training) protocol. Under this regimen an exercise session consists of three sets of 20 seconds of very intensive activity interspersed with periods of rest. Mosley agreed to follow HIT 3 times a week for a month after which his progress would be assessed.

So Mosley is filmed taking away an exercise bike in readiness for his 12 minutes of exercise over the following 4 weeks. During this period Mosley took the opportunity to investigated another regimen and to introduce us to another acronym – NEAT (Non-Exercise Activity Thermogenesis)’; this is, as a rather excited Dr. James Levine tells us everything we do that is not exercise. The sedentary lifestyle is very bad for us (“the chair is a killer” says Dr. Levine). Standing up only raises the metabolism by about a third; better is walking which can double or treble the metabolic rate. Michael Mosley and two volunteers he enlisted wore special pants, ‘fidget pants’, for a day; these pants, monitor and record the subjects activity. The measurements showed that Mosley was mostly sedentary throughout the day. So he wore the fidget pant for another day, this time being more active without exercising (by walking where possible, standing instead of sitting, taking the stairs instead of the lift etc). This attempt to raise his NEAT proved very successful and Dr. Levine revealed that Mosley had used an extra 500 calories in a single day. By increasing our NEAT we can, without exercise or radically changing our lifestyle, significantly increase our calorie expenditure.

Having completed his 12 minutes of exercise Mosley returned to Prof. Timmons to find out how much benefit, if any, he had derived from the HIT protocol. First, he was told about the insulin sensitivity results which had increased by 23% (consistent with experimental findings). There is evidence to suggest that improving insulin responsiveness is associated with improving fat metabolism and weight loss. This is thought to be as a result of glycogen reserves being broken down. Mosley was very impressed and pleased with these results – his father suffered from diabetes and he is keen to not suffer the same fate.

Mosley was less please to discover that his exercise had made absolutely no difference to his aerobic fitness. He is among the 20% of the population are non-responders i.e. their aerobic fitness does not improve with exercise. On the other hand 15% of people are super-responders and their aerobic fitness in response to exercise far exceeds that of most other people. Eleven genes appear to be responsible for individuals aerobic responsiveness and how well different people will respond can be predicted from gene tests. Prof. Timmons revealed that Mosley’s test had predicted that he would be a non-responder. In future science may be able to guide people towards finding the most effective exercise for them as individuals.

Despite the disappointment of being told he was a non-responder Mosley vowed to continue following HIT for the improvements in insulin sensitivity, and NEAT for the benefits of increasing calorie expenditure.

I found ‘The Truth About Exercise’ to be both interesting and informative. The presenter Michael Mosley is personable and a good communicator. Yet a review of the considerable response from reviewers and the public alike shows that there is a great deal of misunderstanding and/or mistrust of the messages in this documentary. I found the response to be very revealing with regards to how information about health and the scientific investigation into exercise is ‘consumed’ by the public. It is for this reason I shall be revisiting this subject again.

Consciousness: why bother? (Review)

March 8, 2012 § Leave a comment

The second article in the Guardian’s series about consciousness comes from Professor Chris Frith, professor emeritus at the Wellcome Trust Centre for Neuroimaging at University College London.

Professor Frith cites some useful examples of phenomenon that clarify the relationship between mind and brain. For example, he tells us about how damage to visual areas of the brain resulting in “visual agnosia” can lead to the paradoxical situation of people who are unable to recognise an object from its shape but can nonetheless adjust their hands to grasp the object when picking it up.

Much of the article, while interesting, did not offer a great deal of insight into recent developments in our understanding of the brain. Indeed, many of the examples were strongly reminiscent of Oliver Sacks’ book ‘The Man Who Mistook His Wife for a Hat‘ that was first published in 1985.

Perhaps I was expecting too much from a professor in a neuroimaging centre, however I would have liked Professor Firth to have focused more on experiments such as those into “change blindness”. These are experiments in which the subject is unable to detect a change in stimuli, for example two similar pictures that are rapidly presented to the subject. Yet the brain scanner is able to detect distinct brain activity that indicates the change has been detected even if the subject is not aware of it.

Also interesting was Professor Firth’s own area of research into the value of sharing conscious experiences. Professor Firth’s research group found that as a result of this sharing it was possible on the experimental task for two individuals to reach more accurate results than either individual on their own.

Although not the article I was hoping for it is nonetheless very interesting and informative. It also ends with a helpful list of links for further reading.

Neuroscience and philosophy must work together (Review)

March 6, 2012 § Leave a comment

Tomorrow the Royal Institution holds a debate on the nature of consciousness entitled ‘Consciousness: The hard problem‘.  Dr Anil Seth, Professor Chris Frith and Professor Barry Smith will take part in the debate. They have also contributed thought provoking articles for the Guardian in the run up to the event.

The latest of these articles comes from Professor Barry Smith, director of the Institute of Philosophy at the School of Advanced Study, University of London. The article ‘Neuroscience and philosophy must work together‘ is a readable overview of what could be a dry and difficult area. However, I found that while he does indicate how philosophy can benefit from new evidence arising from neuroscience, the article failed to explain why he believes neuroscience and philosophy must work together. Any philosophy of consciousness must take account of  new information about what is going on in the brain which neuroscience is providing.

“Now we are also learning more and more from neuroscience and neurobiology about how much of what we do is the result of unconscious processes and mechanisms.”

Professor Smith doesn’t explain what neuroscience has to gain from philosophy or how the two working together would be beneficial. Perhaps part of the answer is that philosophy has something to offer where science comes up short.

“… it must be the brain that gives rise to consciousness and decision-making. So how does consciousness arise in the brain? Science still has no answer.”

Maybe, but this would be to relegate philosophy to the role of to a sort of stand-in science, there as a place-holder until the real science is ready to step in.

This I would object to not least because there is one branch of moral philosophy that I believe should always have a role in any field of science – ethics. As we learn more about what make us who we are, and about the neuroscience that underpins our identity, the more important it is that a firm grasp of the ethical issues involved in investigating and using this information becomes.

More fundamentally I believe it is a mistake to view philosophy and science as two completely separate (and as seems apparent from some responses to the article – incompatible) phenomenon. Both philosophy and science are ways of knowing, in this case knowing about consciousness. Neurobiology can investigate consciousness at a biological level, whereas philosophy seeks to understand knowledge and the nature of knowledge.

Philosophy therefore has a role to play in two ways. First, philosophy of science is necessary to make sense of scientific findings. While the philosophy of science may not be made explicit it is always there, for example when scientists use inductive reasoning formulate theories  or derive conclusions  from their experiments using deductive reasoning.

Second, because philosophy operates at a higher level than the hard sciences it is able to provide a context in which findings from different fields of science can be understood. Not that I am suggesting that every multi-disciplinary team requires a philosopher to act as interpreter between scientist operating in different specialisms but rather that they are probably applying philosophy on some level even if they are not, dare I say, conscious of it. For example, doctors with observations about the behaviour of patients with different brain injuries talking with scientists who carry out brain-imaging on subjects undergoing different activities, can each benefit from the knowledge of the other. This benefit will be operating at a level of abstraction higher than discussions of lesions to specific brain regions or the actions of specific neurotransmitters.

Moreover, it is unnecessary to operate some sort of league table for the usefulness of different fields of inquiry. Philosophy has a role in investigating and explaining consciousness I am sure, however, I feel Professor Smith’s article is a missed opportunity for making this role clear. Hopefully, once the debate has taken place follow-up articles will explain more clearly how and why neuroscience and philosophy must work together.

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