Not Just a Man's World

Weight loss – part 2

Last week I wrote about why women become obsessed with needing to lose weight.  This is a series of articles about all aspects of weight loss including diet, exercise, measuring your success and keeping the weight off when you stop.

This week we’re going to delve into the science of calorie deficits, thermodynamics and the thermic effect of food.

Calorie deficit doesn't have to mean no food at all

Calorie deficits

The idea behind calorie deficits relies on the rules of thermodynamics.  Energy in equals energy out.

We all have a basic energy output required to exist as human beings.  This energy goes into keeping our heart beating, our brains (and neurons) firing, our lungs sucking in air and processing oxygen into the bloodstream and enabling us to undertake basic movements that take place in day-to-day life.  On top of this we can increase our energy consumption through increased levels of exercise – whether through general NEPA (non-exercise physical activity such as taking the stairs in the office or giving the kitchen a thorough clean) or through more focused cardio or resistance training.

We source this energy primarily from our food and this is why “calories”, while most often associated with being a measure of food, is in fact a simple measure of energy.

If we believe that the laws of thermodynamics apply then putting in fewer calories of fuel than we require in a day should result in a calorie deficit.  Therefore maintaining a calorie deficit should result in weight loss.  We’ll have to find our energy from somewhere else and this should force the body to burn its own fat for fuel.

Is a calorie deficit enough?

Considering the principle of calorie deficits we could expect that we can lose weight simply by reducing our calorie intake, increasing our calorie expenditure and subsequently creating a calorie deficit.

Unfortunately, it’s not so simple.  Scientists in Oregon found that rhesus monkeys, who are often used as test subjects for human-related studies since they are so similar to us in genetic make-up, did not lose weight when their caloric intake was significantly reduced but their physical output (exercise levels) was not increased.

You would have expected that the reduced calories would create a calorie deficit yet despite this the body worked hard to conserve energy.  Studies have shown that a calorie deficit diet may result in energy preservation elsewhere, like reduced body temperature and this is one of many ways that the body can use to conserve energy without us reducing our actual apparent energy output through reduced exercise.

For this reason, increasing energy expenditure at the same time as reducing exercise becomes critical and I will, later in this series, look at some aspects of exercise for weight loss.

The thermic effect of food

The thermic effect of food takes the idea of calorie deficit a step further by claiming that foods, in themselves, take a certain amount of energy to digest and process. 

This is true but it is also vastly overrated.  Yes, it takes energy to digest food, but not as much energy as you take in with that food.

Negative calorie foods

It we follow the principles of thermodynamics and the thermic effect of food to their logical conclusion we find ourselves looking for negative calorie foods.  I’m sure you know the ones I’m referring to without even stopping to think about it.  Celery, lettuce, cucumber.  Foods that supposedly take more energy to consume that they provide. 

Brian St Pierre wrote an excellent article recently about the myth of negative calorie foods. 

Brian seems to take great joy in exploding the myth, although I would heartily agree with him that just because they are not negative calorie doesn’t mean you shouldn’t use them as part of a nutritious weight loss diet plan.  I certainly used lettuce with superb results when I was trying to lose some excess body fat in January.

Does a calorie really mean a calorie

Another subject that I’ve taken great interest in recently is whether a calorie really means a calorie.  A study of rats being fed on diets of sucrose or high-fructose corn syrup, those rats consuming the high-fructose corn syrup gained more weight than those on the sucrose solution, despite the high-fructose corn syrup group consuming fewer calories.  (I’ll go into more detail on this study in part 3.)

So we need to scrap the notion that a calorie is a calorie and that the laws of thermodynamics simply require us to take in fewer calories than we use.  It seems that we need to ensure we get the right composition of calories too.

Having written that, I strongly suspect that if your body is accustomed to burning fat for fuel and has mastered a nutrient partitioning that is believed to be closer to that which we evolved with, then we return closer to the principle that a calorie is a calorie.  However, it is still necessary to bear in mind that carbs and fat are energy sources and restriction of these should force your body to find energy elsewhere.

I have very little basis for this idea, other than my own observations of our weight loss efforts at home as our standard diet has shifted from a “normal” western diet to a clean, low carb, paleo diet and we have become efficient fat-burners, rather than placing reliance on carbs for our main fuel source.

So that’s it – the core of the science behind weight loss diets explained.  Next week I’ll drill down into a few specific foods that you may want to avoid to perfect your weight loss diet.

If there is anything in particular you would like me to explore as I work through this series, please let me know and I’ll build it into my research.

Related posts:

1. Alternative approaches to weight loss diets
2. Fat strip January 2010: the diet
3. Foods to avoid to lose weight
4. Low carbohydrate diets