Low-carb diet trumps low-fat diet, yet again
A study published in the current edition of the New England Journal of Medicine demonstrates once again that the low-carbohydrate diet is better than the low-fat diet in bringing about both weight loss and an improvement in lipid profiles. This study, as published, is not without its flaws, which we will get to in a due course. What I find amazing – or maybe I don’t – has been the press reaction.
First came the television reports (here, here and here), all of which reported the study as the Atkins diet triumphing over the low-fat diet and the beloved Mediterranean diet. TV was made for sound bites and sensationalism, so this report fits right in. Although numerous studies have shown the same superiority of the low-carb diet, the TV media seems to treat these studies in one of two ways: it ignores them or it treats them as a man-bites-dog kind of story. The print media has had a little time to reflect on the situation and is reporting the study in a different way.
Two of the primary press sources that many newspapers rely on for press releases are HealthDay and Reuters. Both of these reported this study incorrectly. The headline of the Reuters report is:
Similar weight loss on 3 different, popular diets
HealthDay weighs in with
Diet Plans Produce Similar Results
And follows up with the subtitle
Study finds Mediterranean and low-carb diets work just as well as low-fat ones
If you ever harbored illusions that the print media never lies, these two reports should cure you. And if these aren’t enough to persuade you, take a look at this dog’s breakfast of a coverage by Tara Parker Pope of the New York Times.
You can read the full-text of the actual study yourself and come to your own conclusions. And you can wonder why HealthDay and Reuters decided to run the story the way they did. Most newspapers that subscribe to these services will tend to report the study the same way. In fact, most will print the story verbatim from whichever agency they get it from. And many readers will simply glance at these headlines and figure they know the contents of the story. Or the headline will set their expectations for the story and will give them the take-home lesson.
As you can read, the study shows that the subjects in the group following the low-carb diet had a statistically significantly greater weight loss and improvement in lipid profiles as compared to those subjects following the low-fat diet and the Mediterranean diet. A number of other health parameters changed for the better with all the diets, but did not reach statistical significance between the diets.
I have a few comments to make on this study, but I want to let everyone know up front to take everything I say with a grain of salt. When it comes to reading medical studies I am severely handicapped if I have to read them online. I like to make notes, underline, and otherwise write all over the hard copies of studies that I review. I can’t do this online and so always don’t feel that I’ve really read the thing thoroughly if I read it online only. And I’m still here in Jackson Hole, where I have no access to a printer.
Having covered myself with the above caveat, I have found a couple of problems with this study. First, it would have been nice to have known the caloric intake of the subjects at the beginning of the study. Table 2 lists the caloric change from baseline from the beginning of the study, but not the actual baseline caloric intake, which makes it impossible with the data presented to tell what the actual caloric intake of the three groups were at the various points of the study. Consequently, it’s impossible to tell if the weight-loss changes came about simply because those on the low-carb arm consumed fewer calories or if something else is a foot.
Second, I would liked to have seen the data points for all the subjects, which is pretty easy to represent in a couple of different ways. This would allow is to see if the changes came about in pretty much the same way across the group of subjects or if it came about because there was a large weight loss in a few subjects that skewed the averages. It’s always nice to see all the data.
Third, I haven’t a clue why the researchers who ran this study decided to encourage those on the low-carb arm to
choose vegetarian sources of fat and protein and to avoid trans fat.
Say what? The avoiding trans fat I can understand, but if it’s the Atkins diet (or Protein Power, for that matter) that’s being tested, why on earth would the subjects be counseled to go vegetarian for their fat and protein? It beggars belief. One of the results of this bizarre recommendation is that the anti-low-carb-diet crowd can disavow the results of this study by claiming that the diet isn’t really an Atkins-style diet. You don’t think they would do that? Think again. Read all about it in today’s New York Times. Why didn’t the researchers just give the subjects the instruction to restrict carbs and be done with it? Your guess is as good as mine.
Finally, I can’t understand why the instructions to the low-carb group were to increase carbs to 120 grams per day after the initial two month induction. We don’t know how many carbs the subjects in this study were actually consuming because the data shows carbohydrate intake only as the percent of total energy intake, but without showing what total energy intake is. If we assume that the subjects were eating about 120 grams per day, we know that they were right on the cusp of having any advantage from the low-carbohydrate diet other than the spontaneous caloric restriction it brings about. Our bodies need about 200 grams of glucose per day for all the tissues requiring sugar for proper function. Under conditions of zero carb intake, the body replaces about 70 grams of this glucose with ketone bodies, leaving about 130 grams that the liver must produce, which it does via the process called gluconeogenesis. Consuming zero carbs puts the body into the metabolic status that drives gluconeogenesis. If we are consuming 120 grams per day of carb, as the subjects in this study apparently were, then we are riding on the edge in terms of driving gluconeogenesis. We probably are making a little sugar to bridge the gap, but probably aren’t in the metabolic status most of the day that gives the low-carb diet its real advantage. It’s interesting to note that the data from this study show that only about 8 percent of those in the low-carb diet arm were spilling ketones in their urine, which leads me to believe that most were probably not gaining the full metabolic advantage that a low-carb diet offers.
Despite the instruction to increase carbs to 120 grams per day, I believe these subjects had a long-term benefit from the two months of rigid low-carb dieting (20 grams per day) with which they started the study. Why do I believe that? There is a terrific study in Nutrition & Metabolism showing that subjects with diabetes who underwent a strictly supervised low-carb diet for six months, and who lost weight, improved blood sugar control and lipid parameters, were still showing the positive effects of this intervention 44 months later. These impressive findings seem to indicate that there is some sort of rejuvenation that takes place in people after they have spent a period of time on an honest-to-God low-carb diet that carries over for several years. Maybe this is the phenomenon we’re seeing in the subjects in this NEJM study. The two months of rigid low-carb carries over for the rest of the study despite the subjects cranking their carbs up to non-low-carb levels.
It’s really too bad that the researchers didn’t check all the lab parameters and measure weight loss after the two month induction period. And it’s too bad they made the silly recommendation to go vegetarian low-carb. And it’s too bad they encouraged the subjects in the low-carb arm to increase their carbs to 120 grams per day. But despite all these missteps, the low-carb dieters were still triumphant over the other diets. It just goes to show what a powerful metabolic strategy restricting carbs is.