It has been a long-held belief in bodybuilding and health/fitness circles that eating more frequently throughout the day leads to an increase in metabolic rate and fat-loss.
This is colloquially coined, “stoking the metabolic fire.” In fact, this very concept has been disproved about 15 years ago , and still remains accurate to this day, with the most recent research showing no differences in 24hr energy expenditure, respiratory quotient (RQ), or fat oxidation . For those of you who are less attuned to the popular bodybuilding and fitness dogma that I just mentioned, it usually goes something like this:
- Gym-goer: “I want to lose weight. What’s the best way to go about doing so?”
- Trainer: “Well, first off, you need to eat at least 6 meals per day, spaced 2-3 hours apart. That will ignite the metabolic furnace and enhance fat loss.”
It is here that the person recommending such strict, dogmatic claims shows his lack of knowledge in basic human physiology and biochemistry, not to mention a complete lack of respect for the person’s personal preferences when it comes to dieting.
Breaking it down
There are essentially four factors that affect a person’s overall energy expenditure (EE) throughout the course of a day (24EE). Those factors are basal metabolic rate (BMR; also termed resting metabolic rate [RMR]), diet induced thermogenesis of food (DIT; also known as the thermic effect of food [TEF]), exercise thermogenesis (EEx), and spontaneous movement, termed non-exercise activity thermogenesis (NEAT). Mathematically it looks something like this:
24EE = BMR + TEF + EEx + NEAT
Now, if increasing meal frequency in fact does lead to an increase in metabolic rate and fat loss, through whatever means, it would have to affect one of the above factors.
Obviously increasing meal frequency will not directly alter EEx or NEAT, so we can cross those off the list immediately, leaving us with BMR and TEF as potential modifiable factors.
Let’s take a step back
Before we analyze the two remaining variables, let us consider what energy actually is and what food provides in the context of the body deriving energy from it and then using it. Simply put, energy is the capacity to do work. It can neither be created nor destroyed; only transformed. This work can be biological (cellular function, transport of ions, etc.), chemical (breaking or building of bonds between atoms), mechanical (muscle contraction), osmotic, or electrical. Food is essentially potential energy that, when ingested, is oxidized and yields ATP for us to do some form of work. It can also be stored (as glycogen, triacylglyceride, and muscle protein [although not a “true” storage form]) and subsequently released during times when food is not present in order to provide us with an endogenous, readily available fuel source.
So the question remains; does a simple manipulation of food intake (i.e. frequency of ingesting potential energy) promote a beneficial effect on energy expenditure (i.e. our ability to use that food to do work) such that we burn more calories, specifically those derived from our fat stores?
Basal metabolic rate (BMR)
The primary driving force behind 24EE, assuming that your EEx isn’t through the roof, is fat-free mass (FFM) . Taking this one step further, FFM is the primary driving force behind BMR . Therefore, a majority of the energy expended over the course of a day is dictated by BMR (i.e. how much FFM someone has). Knowing this, how can increasing meal frequency alter someone’s BMR? Plain and simple, it can’t. If anything, it would have to indirectly increase BMR through increases in FFM, but this is irrelevant given that there is no indication that eating smaller more frequent meals increases FFM to a greater extent than does eating an isocaloric diet with fewer, larger meals. In a related vein, there is some equivocal research suggesting increases in BMR and TEF following exercise [5, 6]. However, most of the research was done in previously untrained men and women.
So if anything, the increase in an athletic individual is likely to be negligible at best. Now all we are left with is the thermic effect of food.
Thermic effect of food (TEF)
Quite simply, TEF is averaged out to ~10% of someone’s total caloric intake. So, if a given person ingests 3,000kcals over the course of the day, ~300kcals will be lost as heat through obligatory processes like absorption, digestion, and storage . Also, as a point of interest, there has been some early research showing that obese individuals actually have reduced values of TEF (i.e. <10%), possibly increasing their risk for weight gain . Nevertheless, will increasing meal frequency have any effect on TEF? Again, the answer is no . In fact, in the acute studies showing non-significant increases in TEF based on meal frequency, it was shown that lower meal frequencies actually yielded the higher values of TEF [1, 9].
This is diametrically opposite of what many bodybuilders and fitness enthusiasts believe! Bottom line: increasing meal frequency doesn’t affect TEF to any significant degree.
Other factors to consider with meal frequency
From a practical standpoint, increasing meal frequency is a great way to increase an athlete’s caloric intake or reduce a dieter’s feelings of hunger on a hypocaloric diet. Furthermore, there is research to suggest that the body anticipates meals times based on fixed meal patterns . This is manifested in ghrelin (a hormone that causes sensations of hunger) signaling the brain that you are hungry because it is ‘expecting’ a meal. Therefore, those who might be considering dropping the number of meals they eat per day may experience an initial increase in hunger due to the ‘entrainment’ of ghrelin on your previous feeding pattern.
This will eventually subside after the body adapts your new feeding routine.
In closing, there is no strong evidence to suggest an increase in metabolic rate and body fat oxidation by way of increased meal frequency. So whether you eat three times per day, or six or more, the effects on metabolism will essentially be the same. As I mentioned before, BMR is dictated by FFM and TEF is essentially unchanged by how or when you eat your meals. Therefore, the only two logical modifiable factors when it comes to meal frequency are essentially non-modifiable to any significant degree. On the other side of the coin, things to consider when it comes to meal frequency are increased feelings of hunger with fewer meals during a hypocaloric diet and the possible increase in feelings of hunger with a shift in feeding pattern (from higher frequency to lower). Nevertheless, at the end of the day it comes down to personal preference and the person’s individual fitness/performance goals.
If you find that eating more frequently throughout the day is tedious and difficult to follow, perhaps fewer, larger meals may be the way to go. There is no difference.