Friday, May 29, 2009

The 1 Really Important Thing We Didn't Tell You About Losing Weight

The most interesting part of 10 Things You Need to Know about Losing Weight was the segment which focussed on an overweight actor. This lady revealed that she had always been large and that she felt that she had a 'slow metabolic rate'. She also stated that she had given up worrying up about her weight or trying to diet and just concentrated on eating a healthy diet and being active. Clearly, neither was helping her to lose weight.

This idea that you are overweight because you have a body that burns food off more slowly is, of course, a common belief, but it isn't the case. Indeed, as Gary Taubes explains in his book Good Calories, Bad Calories [Alfred A. Knopf, NY, 2007] in the chapter Paradoxes (p. 278):

The most obvious difficulty with the notion that a retarded metabolism ... is that it never had any evidence to support it. ... Magnus-Levy had reported that the metabolism of fat patients seemed to run as fast if not faster than anyone else's. .... The obese tend to expend more energy than lean people of comparable height, sex, and bone structure, which means their metabolism is typically burning off more calories rather than less. When people grow fat, their lean body mass also increases. They put on muscle and connective tissue and fat, and these will increase total metabolism...

For example, from Fitday, I, at 5'4" and 8 stone 3lbs, with a sedentary type of job require 2050 calories per day, whereas if I was 12 stone, I would need 2432 calories. As predicted, the metabolic rate for the subject of this segment came up perfectly normal.

Next came an investigation into how much she was eating. Looking at the lady in question, I guesstimated 3000 calories per day for her. She thought she was eating 1900 calories or less. As most people really have no idea about calories and portion sizes, I don't find this surprising and I don't think it's a deliberate or even an unwitting self-deception. It's just understandable, because humans didn't evolve doing complicated calorie counts before putting food into their mouths.

The test involved a 9-day diet record. Some of this was a video food diary plus a written food diary. The food that we saw looked perfectly reasonable: chicken and vegetables (though, my goodness - a whole head of broccoli?), (a very large) fruit salad, something dipped into a cup of coffee or tea. The guinea pig also drank doubly-labelled water so that the team could monitor her caloric intake. The result given to us was that she had underreported her food intake by 43% and that her actual intake was 3000 calories per day (score one me!)

Two things need commenting on here. Firstly, the underreporting. So what? It is fiendishly difficult to estimate portion sizes. I should know, I do it quite a lot to use Fitday. I try to be quite accurate, occasionally weighing or measuring to try and learn to 'eyeball' - say 30g of cheese or 1 oz of ham. On the other hand, there is a temptation to cheat. In my case, if I see the carbs going too high, there is a definite urge to downsize my estimates, even if this is silly because I'm only denying reality.

Secondly, what we weren't told. We weren't told what her energy expenditure was. We were told that the doubly-labelled water technique told the team that her caloric intake was 43% higher than her food diary records showed. The implied conclusion was that she was overeating - here we go, she thinks she's eating 2000 calories a day and she's actually eating 3000 calories a day and so she's fat. Whereas in fact that's probably not the case. She would probably be in energy balance - most people are, even fat people - they plateau at a certain weight, they don't all keep on getting fatter and fatter and fatter....

Now I thought this at the time, but I didn't know how right I was because then, to write this post I looked up the doubly-labelled water technique to see how it worked and found this :
the term doubly-labeled water test refers to a particular type of test of metabolic rate, in which average metabolic rate of an organism is measured over a period of time.
Energy expenditure measurements are easier to perform since the development and application of the doubly-labelled water technique.*
In other words, to work out that she was eating more calories than she said, they proved that she was using that many calories because the test itself measures energy expenditure not actual energy intake! But they didn't tell us that and they didn't draw the obvious conclusion that she was in energy balance! Certainly, if she ate less than 3000 calories a day she could draw on the stored fat and not starve. But, as she had pointed out herself at the start of the segment, she was not trying to diet and just trying to 'eat healthily'. Possibly to a dietician or nutritionist 'eating healthily' for an overweight person, by definition ought to mean dieting. However, the point is that just eating normally, she was not overeating, she was just eating as much as she needed to maintain her body - including all the extra fat - without discomfort or hunger.

Clearly, if she could only mobilise that fat and burn it up, she could eat less, so what is stopping that? The reason the fat mass isn't simply used as fuel as soon as we restrict calories is to do with the interplay of hormones in the body. In the simplest terms, if you have too much circulating insulin, then it promotes storage of fat in fat tissue and glucose burning in muscle. It does this because its job is to get excess glucose out of your blood because high blood sugar is damaging. Only if your insulin level is low, can your fat tissue release fat into the bloodstream and your muscles burn fatty acids.

The carbohydrate hypothesis of obesity basically says that carbohydrate intake promotes insulin release which promotes fat storage and the conversion of excess glucose (all starch breaks down into glucose) into fat for storage. So a person who eats a 'healthy diet' that would be 50-60% 'healthy' carbohydrates - 6-11 servings a day of cereals anyone? plus lots of fruit but is quite sensitive to this effect of insulin would convert all the excess to fat and store it. If they are unlucky their insulin stays relatively high preventing their body accessing this stored fat. Now they are 'growing' (but outwards) and as long as enough carbohydrates are consumed to keep insulin 'too high' for fat burning, their appetite tells them they need to eat more and so on it goes.

And that is why all nutritionists and dieticians and doctors should read Gary Taubes' book Good Calories, Bad Calories - published as The Diet Delusion in many countries.

*from Invited Commentary, Energy requirements assessed using the doubly-labelled water method, Klaas R. Westerterp, British Journal of Nutrition (1998), 80, 217–218. Available here.

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