Weighing In
On the Low Carb Diet Controversy
Evan David Rosen, M.D., Ph.D.
Assistant Professor of Medicine,
Harvard Medical School
For
those of you who follow the medical literature on obesity and
diabetes, the big news of the past week centered on two papers
in the New England Journal of Medicine discussing the relative
merits of low-fat versus low-carbohydrate diets. As is true
of most topics where people hold strong and widely differing
opinions, the reports about these two diet trends have been
all over the map. If you read the general press, you could conclude
just about anything you like, depending on who you listen to.
“Atkins Diet is Superior to Low Fat!” crow some
articles, while others caution that “Benefits of Low Carb
Diet Remain Unproven!”
For those of you who may have
recently emerged from a cave and know nothing about this controversy,
let's take a step back (and welcome to the internet!). Based
on the discovery of a link between cholesterol and heart disease,
it seemed reasonable to promote a diet with reduced consumption
of fat. Such a diet, it was felt, would help folks lose weight
(or maintain lower weights) while exerting beneficial effects
on serum lipid levels. In fact, a number of reports showed some
such benefits, although in all honesty, the standard low-fat
diets promoted by many physicians were never truly shown to
be very good at helping people lose weight.
For years, however, there have
been “voices in the wilderness” claiming that the
increased amounts of carbohydrates we consume in place of fat
in these diets lead to exactly the sort of problems we were
trying to avoid: increased obesity and relate problems, such
as type 2 diabetes, heart disease, and stroke. These voices,
including that of the late Dr. Robert Atkins, explained this
phenomenon by pointing out that carbohydrate intake causes the
body to produce more insulin, which leads to the deposition
of fat, which leads to insulin resistance, which leads to higher
insulin levels—a vicious, fattening cycle. Furthermore,
it is claimed, it takes people much longer to feel “full”
after eating carbohydrates than they do with a diet based on
fat and protein. This leads to more calories being ingested,
leading to more insulin, more fat, more insulin…. you
get the picture. Books like “The Atkins Diet”, “Sugar
Busters”, and “The Zone” flew off the shelves,
pushing diets rich in fat and protein and eschewing carbohydrates
even to the point of ketosis (“Ketosis feels better than
sex!” was one of Dr. Atkins’ more famous quotes).
The medical mainstream never
warmed up to the low-carb movement, however, and low-fat diets
have remained the staple of dietary therapy for obesity and
diabetes. Why? Well, there are sound biological principles behind
the low-fat concept, for one. Moreover, the body’s response
to carbohydrate intake is well established. Critics of low-carb
diets have never been able to refute these principles. There
were other issues at stake as well, most notably arrogance,
pride, and stubbornness on both sides of the controversy. Although
this will certainly earn me a fair number of angry e-mails from
my colleagues, I’ll go on record as stating that physicians
as a group can be very unwilling to challenge dogma, and will
angrily denounce new ideas without putting them to the test,
despite the fact that we have seen cherished notions go by the
wayside time and time again.
Thus, it is absolutely unconscionable,
in my opinion, that in the twenty-odd years that low-carb diets
have been out there, during which time the prevalence of obesity
and type 2 diabetes was skyrocketing, there has not been a single
decent long-term, randomized, controlled study to compare the
risks and benefits of this approach to traditional low-fat diets.
It is, frankly, shameful.
There have been a bunch of small trials of short duration (typically
less than three months, and performed without control groups)
that showed that low-carb diets produced a fair amount of weight
loss in obese patients, and over that short stretch of time
the plan seemed safe. Now, the two new studies in the NEJM directly
compare low-carb diets to a traditional low-fat diet in obese
patients over a longer period of time (six months in one study
and a year in the other). The conclusions were that: (a) about
a third of patients on both diets quit early on, proving that
as much as we like to talk about diets, we don’t like
to stick to them; (b) people who stayed on the low-carb diet
lost more weight than the folks on the low-fat diet; (c) regardless
of which diet you were on, the longer you stayed on the diet,
the less well it seemed to work; and (d) scary predictions of
bad things happening to people’s cholesterol levels on
a low-carb diet turned out, in this time frame at least, not
to come true.
Here are my feelings about these
results:
1) It’s about time.
2) Diet, by itself, isn’t
going to do it for most people. Even if you can stick with the
diet, our bodies have developed mechanisms to resist weight
loss that are hard to overcome. Both diet and exercise have
to be incorporated into the plan, and even then most people
will likely require additional help from drugs or other forms
of therapy.
3) I don’t believe in demonizing
individual food groups. Cutting calories from ALL sources is
the key. In the one study that kept track of total calories
ingested, people tended to eat fewer calories on the low-carb
diet than did those on the low-fat diet. This has been seen
in other low-carb studies as well. It is highly likely that
eating a low-carb diet makes it easier to eat fewer total calories
(you just can’t pile up eggs and meat the way you can
French fries), and this is why people lose more weight on these
diets. If you can control your portion size, it probably doesn’t
matter overly much if you have a bagel for breakfast or a sausage.
4) Longer studies need to be
performed. There are lingering concerns about things like kidney
stones and blood lipids (although as I mentioned, the early
returns are promising). These need to be more fully addressed
before low-carb diets will be accepted by the medical mainstream.
It will also be important to show that patients with diabetes,
in particular, are not put in harm’s way by the induction
of ketosis called for by many low-carb adherents.
In the meantime, prepare yourself
for a cacophony of recommendations from the learned societies.
The American Diabetes Association still recommends a balanced
diet with reduced calories for people with type 2 diabetes,
and it’s hard to argue with that. I do know that some
highly trained dieticians in famous teaching hospitals are still
telling folks with type 2 diabetes to increase their carbohydrate
intake in exchange for lower fat intake, which I think is questionable
advice at best. And I know of several prominent endocrinologists
and diabetes researchers who have quietly told me that they
are themselves following a low-carb diet, with happy results.
References:
New England Journal of Medicine 348:2074 (2003).
New England Journal of Medicine 348:2082 (2003).
Written by Evan D. Rosen, M.D., Ph.D.
Content created 6/10/03
Content last reviewed June 10, 2003
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Rosens Archives
