Initial Body Fat and Body
Composition Changes |
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Initial Body Fat and Body Composition Changes
by Lyle McDonald
http://www.bodyrecomposition.com
For many years (decades?) a common suggestion was that one should attempt to
gain some muscle mass mass (through resistance training and possibly overeating)
prior to beginning a diet. Well meaning individuals would suggest you spent 3-4
weeks or more training hard and eating well to gain muscle mass. The goal was to
raise metabolism so that the diet would go more effectively.
In that current data indicates that each pound of muscle might burn an
additional 6 calories (as opposed to older values of 25-40 cal/lb or even
higher) (1), this argument is no longer tenable; to significantly affect
metabolic rate would require a monstrous gain of muscle mass, far more than you
could gain in 3-4 weeks.
Even if you gained 10 pounds of muscle, that would only add up to an
additional 60 calories burned per day, hardly enough to worry about and
certainly not enough to affect the following diet. Which isn't to say that diets
don't work better after short or even medium periods of overfeeding, mind you,
it's simply not because of gains in muscle mass.
A more recent idea making the rounds in bodybuilding nutrition is that, prior to
trying to gain lean body mass, people should diet down first. This reasoning is
based on a variety of data that has examined the changes in body composition
that occur when you overfeed either thin or fat individuals (see for example,
reference 2 or just about anything Gilbert Forbes has written).
A Primer on the P-ratio
The above recommendation is based on a lot of data on something called the
P-ratio (which stands for partitioning ratio) which essentially represents the
proportion of protein (LBM) you gain relative to the total weight you gain (this
isn't the technical definition of P-ratio, by the way, I'm just trying to
simplify it a bit).
Now, a lot of factors control P-ratio including genetics, hormones, diet and
training (to a smaller degree than you'd expect) and probably some I'm
forgetting (3). But by and large, the primary predictor of P-ratio is starting
body fat percentage. Basically, your starting body fat percentage predicts the
great majority of what you will lose/gain when you diet/overfeed (4).
So, when you diet, the fatter you are, the less LBM (and more fat) you will
lose. Conversely, the leaner you are, the more LBM and less fat you will tend to
lose when you diet. This makes sense in evolutionary terms, the more fat you
have to lose, the more your body can lose without having to burn off muscle
tissue; the leaner you get, the less fat you have and the more muscle you end up
losing. Anyone who's dieted naturally to sub 10% body fat levels knows this to
be true: the leaner you get, the more muscle mass you tend to lose
So what about overfeeding and gaining weight? Well, in general, the same holds
but in reverse: leaner individuals will tend to gain more LBM and less fat and
fatter individuals will tend to gain more fat and less LBM. This actually makes
sense when you think about it. The fat individual loses a lot of fat/a little
LBM when they diet and gains a lot of fat and little LBM when they overfeed
while the leaner individual does the opposite. P-ratio appears to be constant
going in both directions. That is, P-ratio appears to be constant for a given
individual (5).
So, typically, when overfed, thin/lean individual will gain 60-70% lean body
mass (LBM) while fat individuals may gain only 30-40% LBM. Note that these
percentage gains are without exercise, simply with overfeeding from a starting
body fat level. Although research hasn't examined overfeeding nearly as much as
underfeeding, we might expect intensive weight training to skew these numbers to
an even better point.
So far, so good right; it sure seems like the leaner you are, the better your
body composition changes will be during overfeeding? So get lean and then train
and eat and you should gain piles of muscle back, right?
The Problem: Naturally Lean People vs. Dieted Down People
The problem with the above analysis, exciting as it sounds, is that there are
significant differences between folks who are naturally lean (on whom the
original overfeeding research was done) and subjects who have been dieted to
leanness.
Let's consider, for a second the likely physiology of those folks who stay
naturally lean. Based on the Geneticcs Hypothesis (3), we'd expect them to have
pretty good hormonal status in terms of thyroid levels, low or normal cortisol,
maybe decent levels of testosterone, GH and IGF-1. They probably also show a
normal nervous system output and an ability to increase fat oxidation when
calories are raised as well.
We'd probably expect them to exhibit a spendthrift metabolism (6), one that
cranks up in response to overfeeding to burn off excess calories. It wouldn't be
surprising if they were the ones who showed a great deal of Non-Exercise
Activity Thermogenesis (NEAT, 7) which is what allows them to burn off excess
calories without getting fat. All of this, almost certainly with other factors
would all contribute to their general lack of fat gain during overfeeding. Of
course, if fat gain is limited during overfeeding, that would tend to mean that
any weight gain will tend to be LBM, as the P-ratio data described above
indicates.
The problem is that the above physiological profile in no way describes
individuals who have dieted down to a low body fat percentage. Rather, dieted
individuals typically show a biology that is absolutely not geared towards
anything except packing the body fat back on. Typically, the metabolic
consequences of dieting include a lowered metabolism, decreased fat oxidation,
decreased HSL activity, increased LPL activity impaired hormonal status
(including lowered testosterone and raised cortisol), decreased thermogenesis
from a reduction in both thyroid levels and nervous system output and a host of
other metabolic defects. All of these serve to both slow fat loss during the
diet and ensure rapid fat regain when food is reintroduced.
For example, in the classic starvation study (the Minnesota Semi-Starvation
study) men were dieted for 6 solid months reaching 4-5% body fat at the end of
the study. Then they were refed and body composition was tracked. By the theory
being advocated, they should have gained lots of LBM and little fat during
refeeding, they were clearly super lean to start out with. But this is
absolutely not what happened.
As would be expected based on the metabolic adaptations to dieting, their
bodies were mainly primed to replenish fat stores. Reductions in metabolic rate,
fat oxidation and thermogenesis all contributed to a preferential gain of body
fat and these systems didn't reset themselves until all of the body fat lost had
been regained (8). Quite in fact, signals from body fat (i.e. leptin and the
rest) are the mechanism behind this physiology (9).
The bottom line is that, in dieted down individuals, the body is primed to
gain body fat at the expense of LBM to replenish what was lost during the diet.
Again, this is fundamentally different than looking at genetically lean
individuals (for whom a low body fat percentage is their normal level) in terms
of what happens when they are overfed.
And even without this research available, anybody who's dieted to a low body
fat percentage can attest to the above. Regardless of the theories being
advocated by the individuals looking just at Forbes' data on P-ratio, the end of
the diet is a time when you gain body fat the most easily. Even a brief look at
the real world should have pointed out why the theory was incorrect in the first
place.
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Now watch me packpedal
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