The notion of dramatic changes in metabolism is routinely used by fat people
to explain why they "cannot" lose weight.  The reality is that you will always
lose weight if you eat less than you burn, and your metabolism changes very
little in the process.  The laws of thermodynamics cannot be set aside, and
you need a certain amount of energy for certain things; if you don't consume
enough to provide the energy, you burn fat to make up the difference.  There
are no exceptions, period.

No.  The truth hurts, but you can't lose weight unless you accept the truth.

Yes.  Everyone can, but many obese people do not.

A pound of body fat represents about 3500 kcal, not 32.

Hypothesis = speculation

No.  You can lose it as soon as you burn it, practically.  If you exercise and
burn 5500 kcal per day, and you consume only 2000, you'll lose a pound of fat
per day.

The deficit has to come from somewhere, and if it doesn't come from fat, it
has to come from destruction of lean body mass, glycogen, etc.  There isn't
enough of these to fill the deficit for more than a short period, so
ultimately you have to burn fat, or you die.  Rest assured, your body will
very willingly burn fat to find those extra calories needed.  There are no
exceptions to this rule.

If things were really as some people claim, people in Third World countries
during famines would die fat.  But they don't.  They are always skin and bones
when they die.  If they have fat, they stay alive.

People who starve become "fat free," with essentially no significant fat
anywhere.

That's a rocking good paper but a pain to read; I personally prefer
the translation by Lyle MacDonald (and note that by using the formula
he discusses + bodyfat measurements (calipers) I've noted that it
tracks as predicted, i.e., if I 'underfeed' by more than a 100 caloris
AND do aerobics I bonk quickly).

*********************************************************************************************
Determining the Maximum Dietary Deficit for Fat Loss
by Lyle McDonald

The Question

A long-standing question in my mind has been, “What is the optimal (or
maximal) deficit for a fat loss diet?” Yes, I know I’m not the first
to address the issue but I’ve always wondered if we couldn’t figure
out exactly what an optimal deficit might be on a diet, rather than
relying on annoying trial and error.

I’m sure readers are familiar with previous approaches but let’s run
through them quickly. The simplest (read: totally retarded) method of
setting calories on a diet is to give everyone some fixed amount.
Usually women get 1200, men get 1500. How such an intake can magically
be correct regardless of bodyweight or activity, I have no idea. But
apparently a 300 lb man and a 150 lb man should both eat an identical
amount and that amount is 1500 calories/day when they diet. Amazingly,
in 2006, that kind of moronic stuff is still out there.

The second approach is along the lines of, “To lose one pound of fat
per week, eat 500 calories/day less than your maintenance; to lose 2
pounds, eat 1000 calories less per day.” Simple math, although not
entirely correct for a variety of reasons I don’t want to get into. I
addressed problems with both approaches in the big Ketogenic Diet
book.

In Bodyopus, Dan Duchaine (who was writing for lean folks, remember)
recommended a maximum deficit of 20% below maintenance. Better, as
this at least scales the deficit relative to maintenance. A big a.s
guy with a 4000 calorie maintenance gets a larger deficit (800 cal/
day) than a small female with a 1700 calorie maintenance (340 cal/
day). Of course, weekly fat/weight loss will be significantly
different for the two, which seems to pass the reality check. Bigger
males do lose more fat than smaller females. I regularly advocate this
approach.

In the Ketogenic Diet book, I suggested setting a deficit based on
current total bodyweight, since most people have trouble figuring out
their true maintenance intake. Assuming an average maintenance intake
of 14-16 cal/lb (you can use 15 cal/lb and split the middle), a 20%
deficit yields ~11-13 cal/lb (and 10-12 cal/lb for dieting has been
around in the bodybuilding world for at least a decade), which will
then have to be adjusted based on real world results. Some people, for
example, with low daily activity and shitty genetics, may have to go
to 8 cal/lb AND do aerobics to lose fat effectively. Back when I was
lifting twice/week and doing fuckall else activity, I had to do that.
Now that I’m training 16-20 hours/week, I get to eat more when I diet.
Hooray. In the two new books (The Rapid Fat Loss Handbook and A Guide
to Flexible Dieting (you should BUY THEM NOW), I offer my personal
scheme for adjusting intake based on what’s happening to bodyweight
and strength levels in the gym.

Now, empirically and based on research, it’s well established that…

a. fatter individuals lose more fat and less lean body mass (LBM) than
leaner individuals; and
b. bigger individuals lose weight more quickly

By corollary, smaller/leaner individuals not only lose total weight/
fat at a slower rate, they lose a greater proportion of LBM. The whole
issue of calorie partitioning has been discussed to death in my
various books, especially The Ultimate Diet 2.0.

It’s why those fat a.ses on “The Biggest Loser” can drop 8-10 lbs. a
week, well at least for the first week (and some of that is certainly
water, glycogen and clearing the sh.t out of their bowels), and
someone at 12% bodyfat may struggle to drop one pound per week without
sacrificing muscle.

And anybody who read the Rapid Fat Loss book notes that I sort of
worked the above into the schema: based on starting bodyfat, fatter
individuals end up with a larger deficit than leaner individuals.
Leaner folks ended up maybe 40% below maintenance but fatter folks
might have been as much as 75% below maintenance. But it was a rough
back of the hand kind of calculation; it was more that I wanted
protein intake set at a certain level and daily caloric intake sort of
fell out of that. As it turns out, the feedback I’ve received tells me
I was at least in the right ballpark: leaner folks aren’t losing LBM
(as long as they set it up correctly) and fatter folks are dropping
fat like crazy.

Now, some work on fasting had suggested a maximal rate of fat
oxidation (you’d expect this value to be largest during total fasting,
but the numbers never quite worked out how I wanted to express them.
So I gave up on the question for a bit.

The basic question in my mind, and the one I’m going to address here
is, “Based on an individuals’ current bodyfat/bodyweight level, do we
know what their maximum rate of weekly fat loss can or will be?”
Phrased differently, what’s the maximum deficit that they can run and
spare lean body mass?

The Answer
So imagine my surprise when this little theoretical paper (note the
journal title) showed up on my Pubcrawler last year (1). Titled, “A
limit on the energy transfer rate from the human fat store in
hypophagia”, it examined (from a somewhat simplified and theoretical
way) exactly the question I gave above: what is the maximum rate at
which the body can derive energy from fat stores to cover a diet
induced deficit while sparing lean body mass.

It’s a nasty little paper, filled primarily with equations,
explanations of those equations and some more equations to boot.
Headache inducing to be sure. I’ll spare you the details. Based on a
somewhat simplified analysis of what data exists (including the
seminal Minnesota semi-starvation experiment), they conclude that the
maximal rate at which fat stores can provide energy to the body is 290
+- 25 kj/kg which is approximately 31 kcal/lb of fat per day.

So, if you are carrying a mere 10 lbs. of fat, you can sustain a 310
cal/day deficit.
20 lbs. = 620 calories.
30 lbs. = 930 calories

You get the idea and this is not difficult math. Multiply your total
fat mass in pounds by 31, that’s how much of a caloric deficit that
fat mass can support on a daily basis.

One quick note: the above values are for dieting only and one of the
simplifying assumptions in the paper was relatively ‘normal/moderate’
activity levels. The paper mentions specifically that the values above
might be varied through pharmaceutical means (which target the rate
limiting steps of fat energy transfer), or through high levels of
activity. It even mentions bodybuilders specifically as a group that
might exceed this value with a lot of training. For now, I’ll just
focus on the diet end, I’ll come back to drugs and exercise
afterwards.

So, the basic assertion of the paper is that, so long as the net daily
deficit does not exceed what your fat stores can provide, you should
spare lean body mass. And based on the small amount of research that
they found, this seemed to be generally true (many studies find an
initial rapid LBM loss but this is most likely glycogen and water and
stuff, not muscle mass). By extension, if your daily caloric deficit
exceeds the above, your body will have to mobilize LBM to cover the
difference. So let’s look at an example.

Say we have a 180 lb male at 15% bodyfat. He has 27 lbs. of fat, and
his maintenance calorie intake is 15 cal/lb or 2700 calories. With 27
lbs. of fat, he should be able to sustain a caloric deficit, from diet
alone, of 27 lbs. fat * 31 cal/lb = 837 calories/day. So he could
reduce his calories to 1863 (ha! 10 cal/lb) and shouldn’t lose any LBM
at that level of intake. He should get a weekly fat loss of just over
1.5 lbs./week.

If the same 180 lb guy was at 10% bodyfat, only 18 lbs. of fat, he
could only sustain a 558 calorie/day deficit (2150 cal/day or 12 cal/
lb), he’s down to 1 pound per week. By the time he’s at 8%, he’s down
to 14.5 lbs. of fat and a total deficit of 446 calories/day and about
2/3 a pound of fat loss/week. Oh yeah, if he were a fat sh.t at 30%
bodyfat, that’s 54 lbs. of fat, he could sustain a deficit of over
1500 cal/day and lose over 3 pounds per week of pure lard; of course
he’d only be eating 1300 cal/day. Again, the above all seem to roughly
pass the reality check in terms of what we see in human dieters.

Now, one implication of the above is that, as a diet proceeds and your
fat stores shrink, your net deficit has to decrease. Ok, step back,
take a breath and read that again. More importantly, note my use of
the word ‘net’ in the first sentence of that paragraph.

Now it’s going to get confusing.

At first glance, the above seems to be indicating that, as you get
leaner, you’ll need to raise calories to compensate, so that the
deficit isn’t as extreme. But that’s incorrect; it is saying that fat
loss will need to slow (because the net deficit you can sustain will
be smaller). By ‘net’ deficit, I mean the difference between your
current maintenance requirements and your intake. This is important
because, as you diet, your maintenance requirements go down due to the
loss of bodymass along with the adaptive component of metabolic rate
(due to insulin, leptin, ghrelin, peptide YY, etc). Let’s simplify
this by looking at the math.

Our 180 lb man at 15% starts his diet. He has 27 lbs. of fat and can
sustain a maximum deficit of 27 lbs. * 31 cal/lb = 837 calories.
Assuming a maintenance of 15 cal/lb (2700), his starting calorie level
will be 2700 cal - 837 calories = 1863 calories/day. He’ll be losing
around 1.5 lb fat/week.

So now we check in 8 weeks later, he’s down 12 lbs., almost purely of
fat (we’ll ignore any small LBM losses). His new numbers are 168 lbs.
with 15 lbs. of fat = 9% bodyfat. Maximal sustainable deficit = 15 *
31 = 465 cal

Assuming his maintenance is still 15 cal/lb (not automatically a safe
assumption), his maintenance requirements should now be 2520 calories.
But the adaptive part of metabolic rate reduction has probably dropped
him a good 10% below that. So let’s say his maintenance is 2250 cal/
day or so. 2250 cal/day - 465 calories = 1785 calories. So, not much
of a reduction from his previous 1863 calorie/day diet. Basically, the
drop in his maintenance levels over the course of 8 weeks offsets the
fact that he can’t sustain as much of a deficit and is now leaner. Of
course, his fat loss has also slowed to just under a pound/week.

Now four weeks later, he’s dropped about 4 more pounds of fat. His new
numbers are
164 lbs. with 11 lb of fat = 6.7% bodyfat. Maximal sustainable deficit
= 11 * 31 = 341 cal

His maintenance will have dropped further, let’s say 14 cal/lb
(people’s daily activity tends to go down due to the hormonal changes
from extreme dieting) and a 15% adaptive reduction which brings him to
1951 calories/day. Reduce by 341 to get 1610 calories/day. He will
need to reduce daily calories by a couple of hundred (from 1785/day to
1610/day) to achieve the maximum deficit but his fat loss will be down
to 2/3rds pound per week.

Ok, step back for a second: the above calculations aren’t meant to be
the holy word of god, there are a lot of estimates upon estimates
being made, especially my guesses as to the changes in maintenance
level and how big of an impact the adaptive component is having. The
adaptive component is a big question mark with not enough data for my
liking. Tracking morning body temperature gives a rough guideline: for
every 1 degree drop in morning temperature below 97.8 degrees, your
metabolism is suppressed by about 10%. This was more to illustrate
what I meant by ‘net deficit’ with changes in both fat mass and
maintenance requirements.

But, again, the above seems to scale roughly with reality. As people
get leaner and leaner, fat loss slows drastically. To keep it moving,
they have to either cut calories further or increase activity, both
can cause muscle loss. Every bodybuilder who has had to move to 2
hours/day of aerobics to keep the fat coming off knows what I’m
talking about. Drugs become more and more attractive as the myriad
other systems start to fight back against you as well (on which note:
will someone please get the folks working on intranasal leptin to
hurry it up).

Drugs and exercise
As mentioned above, the paper I’m basing all of this nonsense on was
looking at non-exercising dieting or fasting men, not folks who were
training or taking drugs. And it mentioned specifically that both of
those could potentially increase the maximum rate of fat mobilization
value (above 31 cal/lb) without sacrificing lean body mass. Certainly,
once again, this idea passes the reality check. Even the addition of
the ephedrine/caffeine stack elevates fat loss while sparing muscle
mass. Clenbuterol is more potent, GH is great and DNP is like f.cking
magic.

Clearly, exercise also has an impact. Even back in Bodyopus, Dan
mentioned that only part of the total deficit (he used 20%) should
come from diet, the other part should come from increased activity.
This usually means aerobics, but some prefer to use high rep/short
rest period weight training or interval training and there is some
logic to picking one of the latter options. He suggested that men do
better with 15% calorie deficit and 5% aerobics and women at 10%
apiece. Given the issues women have with lower bodyfat blood flow, and
that aerobic activity can overcome some of the limitations that make
lower bodyfat so stubborn, that makes a lot of sense. As well, women
(because of their lower maintenance requirements), end up eating a
tiny amount of food if they cut too much out of their diet. Increasing
their net daily deficit via activity allows them to eat more and not
starve to death on a daily basis. I’ve been working on the stubborn
bodyfat issue for years now; my next book outlines not only the
problem but multiple solutions to that problem.

Conclusion
In this article, I’ve been able to give dieters a starting point for
the maximum sustainable deficit which can come from calorie
restriction. To summarize: simply determine how many pounds of fat
you’re carrying. Then multiply that value by 31 calories. That’s how
much you can potentially decrease your daily food intake. If you want
to try to increase fat loss, any further increase in the deficit
should either come from increased activity or compounds that either
increase the mobilization or burning of fatty acids for fuel. As well,
as you get leaner/lighter, you will need to periodically recalculate
your daily calories to take into account your diminishing fat mass and
decreased maintenance requirements due to both decreased bodymass and
the adaptive component of metabolic rate. An argument can also be made
for saving increases in activity for later in the diet when your diet
deficit has to be lower.

Please keep in mind, however, all of these theoretical calculations
sort of pale to real world results. If you’re losing strength in the
weight room like crazy, your deficit is too big regardless of what the
math works out too, increase them until you stop hemorrhaging strength
(and probably muscle). And even if you have to trial and error it a
bit, the above should at least give you a starting point.

References
1. Alpert SS. A limit on the energy transfer rate from the human fat
store in hypophagia. J Theor Biol. 2005 Mar 7;233(1):1-13.

Lyle McDonald is an all around physiology nerd with far too much time
on his hands who apparently enjoys doing math for his readers. You can
read more of his work or join his new weekly (no, really) newsletter
at www.bodyrecomposition.com. You should buy all of his books from his
store at store.lylemcdonald.com. You know you want to.
__________________

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