Tuesday, May 31, 2011

Calories Density Causes Obesity?

Obesity is a complex issue involving nutrition, metabolism, food choices, economics, and even physchological factors. I am sure that there is more than one factor for obesity for each individual or groups of individuals. The thing gets more complex as we try to examine the cause or causes at the societal level.

There are a few hypotheses around about the cause of obesity in people. For example, Stephan Guyenet is proposing food reward as a main factor for people getting obese. You can read about this hypothesis in a series of articles published on Stephan blog (here, here, here, and here).

Guyenet hypothesis is very interesting.But what about a simpler hypothesis: the increase of calories density is what is causing people to become obese. Now, I know this is not a new idea (as it is not Guyenet food reward hypothesis).  But let me try to explain.

In terms of caloric density it is not the same to eat 100 grams of wheat than to eat 100 grams of lettuce. A simple look at the macronutrient content of both wheat and lettuce reveals significant diferences. Wheat has about 80% of starch which will give about 4 calories per gram while lettuce has almost no starch at all but has a lot of lignin and other fiber components which in theory have no calories.

A search on the USDA database give us the exact numbers. One-hundred grams of wheat (hard red spring) give us 329 of calories while 100 grams of lettuce will give us only 15 calories. So you can see that wheat is more nutrient dense (and hence calorie dense) than lettuce.

In terms of quantity there is a limit of how much food a person can ingest. Even obese people have a limit, and there may be individual variance, but the truth is that you and me and any other person can eat no more than a certain quantity (by weight). I am not sure if this amount has been determined but I would venture that you could not eat more than 3-4 pounds of food at any meal.

Industrialized societies have been shifting what they eat from low calories dense food to high calories dense foods. We, humans, have shifted from meat and vegetables to highly processed foods such as breads, pastas, etc. This shift can be proved by examining archeological evidence of what humans ate so many years ago.

Please take a look a the table shown bellow. You can see how the foods eaten by our ancestors (the first 8 on the table, except for nuts) have energy nutrient density. 

So, if society has shifted from eating low nutrient dense food to high density foods and even if the amount of food ingested has remained fixed then people are simply eating too many calories and this may explain, in part, the increase of body weight. I know it sounds too simple but sometimes simplicity is the key to understand certain things.

Of course this idea needs more tetsing and I am trying to look at the literature.

There may be also an influence of the state of the food, that is, if the food is solid or liquid. Liquid food (beverages) are more dense (they are packed with sugars) which may be an additional factor in increasing the overall nutrient density of the daily food intake. Also, how it is cooked may be an additional factor.


  1. Rafael, did you listen to Stephan's podcast with Chris Kresser? He mentions energy imbalance which certainly is related to calorie density.

    As "professionally designed industrial foods" are both ultra high reward *and* calorie dense, it's a big problem either way!

  2. I am going to listen to that. thanks