It is crazy really. I was talking to my mum a while ago, she was trying to remember why she had all these vitamins but could not. “I know I am taking them for something, but I cannot remember what. Maybe I will stop”. She did stop. Still healthy. Probably healthier if those recent reports on vitamins shortening lifespan are at all true.

Suppose for a moment that increased expenditure of mechanical energy caused the body to alter its biochemical processes such that the greater the mechanical energy output the less heat was produced. Obviously our subjective experience is that during exercise we get hot, but it’s entirely feasible that afterwards our temperature drops below the long-term average for long enough to offset the energy used during the exercise. In that way it is possible that exercise would not cause a net increase in chemical energy consumed from food.

I have no clue whether this is a real phenomenon but I would like to know.

The human body gets its energy from food.

An idealised perfect combustion system, running at 100% efficiency, will still lose mass as it burns energy according to the mass-energy equivalence relation. Human muscle tissue is fairly efficient (17-26%, Stephen Steiler) but nowhere near perfection. Exercise requires lots of mechanical energy. More fats and sugars will be burned by an exercising body than a sedentary one.

Unless more food is eaten, environmental temperature changes or some other efficiency-altering parameter is tweaked, exercise will reduce the weight of a human body as certainly as driving a car will reduce the weight of the fuel in its tank.

This is a simplified and sort of pedantic argument, but it at least shows that it’s a physical impossibility for an exercising body to lose less weight than a lazy one, if all other energy-related parameters are fixed.

A lot of experience (including my own) is very much tied up with circumstances and environment and a myriad of confounding factors. At best it provides some information about what happens to a specific individual in a specific environment who is subject to a specific set of interventions. This is far from useless but equally it is far from telling a coherent and complete story.

Clearly there is a relationship between energy intake and fat storage and energy expenditure. At the limiting case if your intake is reduced to zero you will eventually die and it is likely that you will become very thin first. However the idea that from this we can imply some sort of linear or even regular relationship between the variables seems to me to be extremely simplistic.

As this is one of the most significant public health issues in the developed world it seems to me that we, as a community, should be devising ways to research the problem effectively rather than issuing “government guidelines” that are at best based on guesswork.

I think that this is the most important take away from the Taubes book and I am very much looking froward to seeing David Colquhoun’s review.

Suw’s criticism is more valid though – an examination of athletes is self selecting.

Hence if you were ideally replacing fat with muscle, you would put on weight – no-one could say you were thereby “getting fat” – ask the Governator !

The article to which the press release is referring is rather interesting and is accompanied by a well considered editorial that examines among other things the plausibility of such an association:
www.bmj.com/cgi/content/abstract/339/sep03_2/b3292

Neither article nor editorial stray anywhere near making the sort of claim alluded to in the press release.

Clearly such catchy headlines attract the attention of editors in the media, but BMJ are shooting themselves in the foot with this sort double standard.

Erm, isn’t that exactly the logic that proponents of alternative medicine use?

Others in these parts will know more about how to make such a trial statistically valid (I’m afraid I slept though most of my stats lectures 35 years ago).

It would be really great to see it done though…..

I’ll quite happily issue a challenge to the ‘exercise doesn’t shift weight’ lobby. You maintain a monitored replacement calorie intake and do the old professional sprint circuit training – starting with 5 reps each of pressup, squat jump, ab curls and alternate leg shifts (leg shoots in a pressup position) – with only changeover rest. On day 2 you do 6 reps of each and so on daily until you get to 20 when you split to 3 sets of 10, then on to 3 sets of 20, 4 sets of 20 and so on building the volume. You could get to the 100 rep per set state like Alan Wells did prior to his Olympic 100m Gold in 1980. If you get to daily volumes of 10 sets of 20 (remember the monitored calorie intake?) and have not lost a kilo, then I’ll accept your contention. But until that kind of very gentle and gradual, but eventually brutal, progression is incorporated into studies, I stick with forty-plus years of doing weight manipulation and seeing the evidence in others.

I think BMI is still useful for most people. It’s not very useful for people with very high muscle mass (such as sportsmen) or people with very low muscle mass (such as very old people). But those two groups are a small proportion of the total population.

Its weight categories are also not universally accepted, but you’d need to ask an expert about that.

I believe most health professionals now also use waist size as a criterion for weight-related risk factors.

Just a thought on use of BMI as an indicator which features on the page. BMI uses height squared as its denominator. Since we live in a 3-D universe there should really be a third power in there somewhere. The effect of not doing so is that average BMI will tend to increase with increasing average height in the population regardless of actual changes in bodily composition. Has the WHO corrected for this in assessing the extent of the obesity “epidemic”?

Just for clarity – I do not doubt that obesity has increased in recent years but I do think that reliance on BMI as the main or only indicator has exaggerated the numbers somewhat.

1. study finds people with skinny thighs have more heart/cardiovasc problems;

2. media reports this as “Having large thighs is good for you”;

3. people everywhere go “Woohoo, pass the doughnuts! Aren’t scientists stupid with their mixed messages?”

So what’s the link, and how important is it? If stress can in some people increase appetite and preference for sweet foods (as some of the abstracts I’ve just looked at conclude), is that enough to counteract the effects of exercise? Does lowering stress improve weightloss?

Willpower has to come into it too. Is willpower affected by stress (I’d guess it’s decreased)? If stress does decrease willpower and increases appetite, it would be harder for stressed people to stick to a diet and exercise regime. That would indicate that people looking at reducing their weight should address stress problems too.

I base my hypothesis on sources such as the WHO who look at incidence of overweight and obesity worldwide. When countries develop to the point where work becomes more sedentary and convenience foods become more common, their populations become more obese. Details can be found here.

www.who.int/dietphysicalactivity/publications/facts/obesity/en/

As long as someone lives in a society that has created situations that make maintaining a healthy weight so difficult, individual diet and exercise interventions are swimming against the tide.

I applaud the work of Wilbert and others who are seeking medical solutions to lifestyle diseases. But I do hope governments start waking up to the idea of more societal solutions.