The largest criticism of low-carb diets seems to be that people are all
lying about eating more veggies and are in reality eating bacon
cheeseburgers and therefore upping their fat intake significantly.
I ran across the Yudkin study on Dr. Eades blog:
http://www.proteinpower.com/drmike/2007/09/11/is-a-calorie-always-a-calorie/
In the Yudkin study, the low-carb instructions were "Essentially, the
subjects were asked to take between 10 and 20 oz milk daily (about
300-600 ml), and as much meat, fish, eggs, cheese, butter, margarine,
cream and leafy vegetables as they wished. The amount of carbohydrate in
other food was listed in “units” with each unit consisting of 5 g
carbohydrate; the subjects were told to limit these foods to not more
than 10 units (or 50 g) carbohydrate daily."
So it's not a very low-carb study or anything, as the 50g carb limit
applied to "other" foods; the participants got a free pass on carbs in
milk, cheese, cream and leafy veggies. When they looked at what people
were actually eating on this diet, carbohydrate changed most, with study
participants going from an average of 216g per day to 67g per day. Not
terribly low carb, double what Bernstein recommends and triple what is
allowed on Atkins induciton phase, but certainly a lot lower than a
"normal" diet or the diet recommended by the ADA.
Protein barely changed going from an average of 84g before the diet to
83g on the diet - so much for the myth of a high-protein diet. If you
manage to cause yourself damage from "all that protein" on a low-carb
diet, you'd be just as damaged on the normal pre-study diet.
Fat *decreased* from 124g to only 105g per day. While eating "as much
meat, fish, eggs, cheese, butter, margarine, cream and leafy vegetables
as they wished," their fat intake went *down*. Apparently, the
increased fat from meat and dairy was more than offset by the fat not
used with carbs.
Apparently, when you tell people they can eat all the bacon
cheeseburgers they want, they eat a lot less fat as long as they aren't
having french fries along with it. So much for the criticism of the
diet having "too much fat."
Obviously, with both a decrease in carbs and fat, the calories went
down. The average dropped from 2330 to 1560 spontaneously. I say it
was "spontaneous" because these folks were instructed to eat as much as
they wished. No one was trying to limit calories, just carbs.
The "problem" people have with this type of diet is it looks high-fat.
It is over 60% of the calories from fat *even* though people cut their
fat intake by an average of 19g per day! To me, this is a good
example of why the whole notion of measuring foods in percentages is
bogus.
My own favorite example is a large salad with cheese and ranch dressing
on top, which is a "high-fat" meal since almost all the calories are
from fat, but becomes "low-fat" as soon as you add a couple cans of Coke
and a dessert of candy to the meal. Obviously, the fat content doesn't
change and the cans of Coke don't add anything good to the meal, so the
whole notion of "high fat" vs. "low fat" isn't a useful distinction.
How did people feel on the Yudkin diet? "In conformity with our
experience with this diet during the last 15 years, none of our subjects
complained of hunger or any other ill effects; on the other hand,
several volunteered statements to the effect that they had increased
feeling of well-being and decreased lassitude.”
The Yudkin study is compared to the Keys study at the link to the Eades
blog.
The Keys study was not a diet study in terms of weight loss, but a
starvation study to determine what would happen to people in
concentraiton camps during the war. It had a similar level of calories
- 1570/day. But in the Keys study, fat was at 17% of daily intake
instead of over 60%.
The people in the Keys study were locked-in to enforce the diet for 24
weeks, and went from a normal diet to the low-fat diet halfway through.
So they were only on the low-fat diet for only 12 weeks.
In the Keys study, protein was higher at 100g/day, carb was much higher
at 225g/day and fat was very restricted at 30g/day. So we know the
protein wasn't inadequate since it was higher than on the Yudkin study,
the primary difference is lots of carb and little fat for the same total
calories.
The effect? "As the time wore on the men thought ceaselessly about
food, they became lethargic, they were cold all the time, they became
depressed, they developed bleeding disorders, their ankles became
edematous, and some developed more serious psychological disorders."
Lots more discussion at the Eades blog... and these studies are also
discussed in Taubes book.