Myth: Eat frequently to "stoke the metabolic fire"

Each time you eat, metabolic rate increases slightly for a few hours. Paradoxically, it takes energy to break down and absorb energy. This is the Thermic Effect of Food (TEF). The amount of energy expended is directly proportional to the amount of calories and nutrients consumed in the meal.

Let's assume that we are measuring TEF during 24 hours in a diet of 2700 kcal with 40% protein, 40% carbohydrate and 20% fat. We run three different trials where the only thing we change is the the meal frequency.

A) Three meals: 900 kcal per meal.

Six meals: 450 kcal per meal.

C) Nine meals: 300 kcal per meal.

What we'd find is a different pattern in regards to TEF. Example "A" would yield a larger and long lasting boost in metabolic rate that would gradually taper off until the next meal came around; TEF would show a "peak and valley"-pattern. "C" would yield a very weak but consistent boost in metabolic rate; an even pattern. "B" would be somewhere in between.

However, at the end of the 24-hour period, or as long as it would take to assimilate the nutrients, there would be no difference in TEF. The total amount of energy expended by TEF would be identical in each scenario. Meal frequency does not affect total TEF. You cannot "trick" the body in to burning more or less calories by manipulating meal frequency.


The most extensive review (http://www.ncbi.nlm.nih.gov/pubmed/9155494) of studies on various meal frequencies and TEF was published in 1997. It looked at many different studies that compared TEF during meal frequencies ranging from 1-17 meals and concluded:

"Studies using whole-body calorimetry and doubly-labelled water to assess total 24 h energy expenditure find no difference between nibbling and gorging".

Since then, no studies have refuted this. For a summary of the above cited study, read this research review by Lyle McDonald. http://www.bodyrecomposition.com/research-review/meal-frequency-and-energy-balance-research-review.html#more-1389

Earlier this year, a new study was published on the topic. As expected, no differences were found between a lower (3 meals) and higher meal (6 meals) frequency. Read this post for my summary of the study. This study garnered some attention in the mass media and it was nice to see the meal frequency myth being debunked in The New York Times.
http://www.ncbi.nlm.nih.gov/pubmed/19943985
http://www.leangains.com/2009/12/new-meal-frequency-study.html


Origin

Seeing how conclusive and clear research is on the topic of meal frequency, you might wonder why it is that some people, quite often RDs in fact, keep repeating the myth of "stoking the metabolic fire" by eating small meals on a frequent basis. My best guess is that they've somehow misunderstood TEF. After all, they're technically right to say you keep your metabolism humming along by eating frequently. They just missed that critical part where it was explained that TEF is proportional to the calories consumed in each meal.

Another guess is that they base the advice on some epidemiological studies that found an inverse correlation between high meal frequency and body weight in the population. What that means is that researchers may look at the dietary pattern of thousands individuals and find that those who eat more frequently tend to weigh less than those who eat less frequently. It's important to point out that these studies are uncontrolled in terms of calorie intake and are done on Average Joes (i.e. normal people who do not count calories and just eat spontaneously like most people).

There's a saying that goes "correlation does not imply causation" and this warrants further explanation since it explains many other dietary myths and fallacies. Just because there's a connection between low meal frequencies and higher body weights, doesn't mean that low meal frequencies cause weight gain. Those studies likely show that people who tend to eat less frequently have:

* Dysregulated eating patterns; the personality type that skips breakfast in favor of a donut in the car on the way to work, undereat during the day, and overeat in the evening. They tend to be less concerned with health and diet than those who eat more frequently.

* Another feasible explanation for the association between low meal frequencies and higher body weight is that meal skipping is often used as a weight loss strategy. People who are overweight are more likely to be on a diet and eat fewer meals.

The connection between lower meal frequency and higher body weight in the general population, and vice versa, is connected to behavioral patterns - not metabolism.