Monday, August 1, 2011

Notes: Diet and Obesity: down a road less travelled

I'm interested in food in lots of ways.  I like knowing where I can eat great meals, I enjoy understanding the science behind how dishes are made (though not enough to purchase a copy of Nathan Myrvold's 5+ volumes of Modernist Cuisine), and I also care about the effect of food on my body (not that it stops me from indulging in fries far too often).  In the first lecture of the 2011 Vice Chancellor's Lecture Series: Good Food, Good Health held last Thursday, Professor Mike Gibney, Professor of Food and Health at University College Dublin, explored issues around obesity which are not often discussed.  I thought I'd put a summary here, in case anyone else was interested.

1) People are putting on more and more weight, but this increase is not linear
Two groups of people were studied over two different periods in time.  In both cases, their average Body Mass Index (BMI) increased over time, but this was not in a straight line.  Rather, it plateaued before increasing again, as shown below. I'm not too sure what the significance of this is, and it was not explained why this happened, so I will skip over this one.

2) Fidgeting can improve your cardiovascular fitness and help with weight loss
I don't know about you, but the only time I've gone to a gym was when I bought membership for a semester while at university, and I never managed to work out.  I looked around, decided it was all too hard, and never made it back again.

It's important to be fit though. Fat people who exercise have better cardiovascular fitness than thin people who just sit around.  And apparently, the risk of mortality is the same for fit people, regardless of whether they are overweight or not, while the risk of type 2 diabetes increases for sedentary people.

Fortunately, we don't necessarily need to go to the gym.  Minor activity that we don't consider exercise, such as walking to the water cooler, can also be beneficial.  Dr. James Levine of the Mayo Clinic investigated the role of this incidental activity, or NEAT (non-exercise activity thermogenesis), in reducing fat gain.

Even when we are not doing what we consider physical activity, we are expending energy.  It takes energy to digest and absorb food.  Resting energy makes up about 85% of where our calories go, while physical activity accounts for only 12 - 15%.  The rest is consumed by non-exercise activity that we can call fidgeting.

ActivityEnergy expended (kJ/min)
Sitting motionless5.6
Sitting fidgeting8.2
Standing motionless6.1
Standing fidgeting10.3
Walking (stop/start)13.7
Walking (stroll)16.4

A study found that fat people who were slimmed down sat still more than naturally lean people.  In another study, non-obese subjects were overfed 1000 kcal/day for 8 weeks, with restrictions on what they could do.  Those who gained more weight were those who did less non-exercise activity.

Over the past 50 years, people have shifted away from work in production and agriculture, towards service jobs, which have become more and more sedentary.  Maybe we can address this by encouraging ourselves to move more, even in minor ways.  (Another great idea which wasn't discussed in the lecture, but which I have read elsewhere, is making sure you get enough sleep, since you are still burning calories, while not being tempted by food, when you are sleeping.)

3) Nature vs. nurture: your genes interact with your environment in influencing your weight
There isn't one gene for obesity, but multiple risk alleles.  Some researchers narrowed these down to looking at 5 genes, and tested 101 Caucasian women for 3 genotypes after randomly assigning them diets over a year:
  • low CHO responsive genotype
  • low fat genotype
  • balanced diet genotype
They were able to predict weight loss for those who had been assigned the right diet for their genotype.

In another study, children were followed from the age of 4 to the age of 11.  In the children of non-obese parents, the environmental factors seemed to make little difference.  They were lean whether they belonged to a poor family or not.  However, children of obese parents were much more likely to be obese if they also had a lower social economic status.

The take-home message is that we shouldn't blame our weight on our genes, and give up on eating well, though genetics certainly play a role.  Rather, we can apply science to target an optimal diet for the genes that we have.

4) The Pinocchio factor: food intake is often under-reported to researchers, adding complexity to any study
In dietary surveys, energy under-reporting ranges from 30% - 50%.  This applies not just to "bad" foods, but anything the subjects have been eating.  Females are more likely to under-report, overweight females more so, and smoking overweight females even more so.

Misrepresentation can occur in three different ways:
  • Denial, e.g. "I never eat chocolate"
  • Frequency, e.g. "I only eat chocolate at Easter"
  • Portion, e.g. " I only have a small square of chocolate"
It is diffiicult to know which foods have been lied about, and which form of falsehood has been used.

5) Reflections and projections
There are four challenges in the fight against obesity:
  • Prevention of initial weight gain
  • Prevention of progressive weight gain
  • Managing the metabolic syndrome
  • Maintaining weight loss

Obesity is often politicised.  For instance, if 20% of professionals and 30% of unskilled workers are obese, this would be reported as "obesity rate 50% higher in unskilled workers".  These statistics are much less dramatic if you look at them from the opposite view: 80% of professionals and 70% of unskilled workers are not obese.

People will make sweeping statements against fast food giants like McDonald's.  But why? Is it because chips are bad for you?  If so, shouldn't the corner cafe or local fish and chip store, which also sell chips, also be banned?

Any public policy to address obesity will require long term planning, not random rules based on irrational fears.

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