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.

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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’.

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.

The Truth About Exercise – Synopsis (part 1)

March 5, 2012 § Leave a comment

The main benefits of exercise is not the amount of calories that you expend directly undertaking exercise – Michael Mosley was told that to work off the calories he gain consuming a modest snack of a cappuccino, muffin and banana would require him to run for 55 minutes.

However, as Mosley discovered, there are other benefits. He is, he revealed, a TOFI (Thin Outside, Fat Inside); this means that despite appearing to be fairly lean he has a lot of internal fat around his organs (visceral fat). Visceral fat is more dangerous than subcutaneous fat (fat which resides primarily under the skin). Fat levels in Mosley’s blood were measured before and after a cooked breakfast. He then went for a 90 minute walk. The next day he had the same cooked breakfast and again fat levels were measured. This time the level of fat was found to be 30% less than the day before. Exercise has a marked impact on the way our bodies metabolise fat.

However, realistically many of us are unlikely to  undertake this level of activity regularly enough to benefit. So Mosley then investigated a less imposing exercise regimen. The protocol requires as little as 3 minutes 3 times a week on an exercise bike. In fact the amount of physical exertion is shorter than this – just three bursts of 20 seconds in each session, or 3 minutes in total over the week. This is called HIT (High Intensity Training, although many people maintain that the proper acronym is HiiT or High Intensity Interval Training). The idea is that what is really important is the intensity of the activity not the length of the activity.

After following this regimen for four weeks Mosley was tested for insulin responsiveness and for aerobic fitness. These results will be discussed in more detail in part 2.

The Truth About Exercise

March 4, 2012 § Leave a comment

Michael Mosely exercisingThe most interesting programme of the week was Horzon’s “The Truth About Exercise”. As is the case with TV documentaries these days the presenter, Michael Mosley, put himself through the trials and tribulations required to provide the programme with empirical evidence, and the viewer with voyeuristic entertainment.

As one of the more informative documentaries I have seen recently I shall devote a greater than usual level of attention to this programme starting with “The Truth About Exercise – Synopsis (part 1)“.

Of particular interest is the  HIT (High Intensity Training) and NEAT (Non-Exercise Activity Thermogenesis); both of these are explained in more detail in “The Truth About Exercise – Synopsis (part 2)“.

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