The Nutrition Debate #52: The Thermic Effect of Food

Thermogenesis is the process of heat production in organisms, and heat is a form of expended energy. The unit of measurement is a calorie. Human metabolism is comprised of three components of energy expenditure: 1) the energy expended by the basal metabolic rate (to keep the resting organism “going,” i.e. alive), 2) the energy expended through exercise (motion), and 3) the energy expended due to the “cost” of processing food for storage and use. This last component is known as the thermic effect of food.  It is also sometimes called Diet-Induced Thermogenesis (DIT).

It is estimated that the thermic effect of food is about 10% of the caloric intake of any given meal, “though the effect varies substantially for different food components,” according to Wikipedia. Of the three food components (called macronutrients), fat has minimal thermic effect. Carbohydrates, especially simple sugars and carbs in highly processed, manufactured foods, are very easy to process and have very little thermic effect. Proteins, on the other hand (and whole food, complex carbohydrates to a lesser extent) are harder to process and have a much larger thermic effect. The ratio of protein to carb energy expenditure is generally between 2:1 and 3:1, depending on how “simple” the carb is.

So, for total daily energy expenditure there's a resting metabolic rate component (60-70% of total), the physical activity component (15-30% of total), and the thermic effect of food component (~10%). While 10% is a small percentage, if the energy expended to digest, absorb and eliminate protein is two or more times the amount required for carbs and fat, wouldn’t replacing carbs with protein in an isocaloric diet thus increase the metabolic rate and help to burn more calories including stored fat? And if the difference in the burn rate was even greater for the simple sugars and processed carbs made easier to digest by manufacturing, couldn’t that account for why our metabolisms burn less on today’s modern processed-food diets? Thus, to naturally increase our metabolic rate, we should 1) increase the amount of protein in our diet and 2) replace simple sugars and processed-foods in the diet with whole foods, that is, unprocessed, complex carbohydrates. Note that 2) above assumes that you don’t already have insulin resistance (IR), pre-diabetes, or full-blown Type 2 diabetes, or are obese. It you are, you should severely restrict/limit the carbohydrates in your diet.

The typical American (or for my international readers, Western) diet currently gets about 15% of calories from protein. The Standard American Diet (SAD for short), espoused by the FDA and promoted on food packages in the Nutrition Facts Panel, is 10% protein. (On a 2,000 calorie diet, 50g/day x 4 cal/g = 200 cal.) I get about 25% of my calories from protein.

So, who’s looking at this? Barr SB and Wright JC, that’s who, in their paper, “Postprandial energy expenditure in whole-food and processed-food meals: implications for daily energy expenditure,” published online July 2010 in The Journal of Food and Nutrition Research. The abstract on PubMed explains: “Empirical evidence has shown that rising obesity rates closely parallel the increased consumption of processed foods (PF)… in the USA. Differences in postprandial thermogenic responses to a whole-food (WF) meal vs. a PF meal may be a key factor in explaining obesity trends, but currently there is limited research exploring this potential link.” And their conclusion: “Ingestion of the particular PF meal tested in this study decreases postprandial energy expenditure by nearly 50% compared with the isoenergetic WF meal. This reduction in daily energy expenditure has potential implications for diets comprised heavily of PFs and their associations with obesity” (Italics added by me).

The processed food meal decreased energy expenditure by nearly 50%. Wow! That’s a big difference in thermic effect. And the meals they were comparing were “either ‘whole’ or ‘processed’ cheese sandwiches; multi-grain bread and cheddar cheese were deemed whole, while white bread and processed cheese product were considered processed.” Imagine if they had chosen a real whole food instead of ‘multigrain bread’ which is a far, far cry from a real whole food as readers here know. And what if it had been a protein food instead? The authors explained, “A more strict WF would be one devoid of any processing, such as a specific fruit, vegetable, or meat. However, for the present study, we sought to compare two meals that were familiar to the Western diet, and could be easily interchangeable.”And while the much higher thermic effect of protein is probably too small to have a noticeable effect on weight loss in the short term, over a period of months or years this difference becomes significant. Have I discovered another cause for the obesity epidemic? Just joking, folks. I am just your humble commentator bringing you the insights of the cognoscenti.                   

© Dan Brown 5/13/12