I Think The Results Of This Moderate Carb vs. Low Carb Study Are Pretty Meaningless. How About You?

A Randomized Pilot Trial of a Moderate Carbohydrate Diet Compared to a Very Low Carbohydrate Diet in Overweight or Obese Individuals with Type 2 Diabetes Mellitus or Prediabetes

Laura R. Saslow, Sarah Kim, Jennifer J. Daubenmier, Judith T. Moskowitz, Stephen D. Phinney, Veronica Goldman, Elizabeth J. Murphy, Rachel M. Cox, Patricia Moran, Fredrick M. Hecht

Published: April 09, 2014, Plos One

From the Abstract:

We compared the effects of two diets on glycated hemoglobin (HbA1c) and other health-related outcomes in overweight or obese adults with type 2 diabetes or prediabetes (HbA1c>6%). We randomized participants to either a medium carbohydrate, low fat, calorie-restricted, carbohydrate counting diet (MCCR) consistent with guidelines from the American Diabetes Association (n = 18) or a very low carbohydrate, high fat, non calorie-restricted diet whose goal was to induce nutritional ketosis (LCK, n = 16). We excluded participants receiving insulin; 74% were taking oral diabetes medications. Groups met for 13 sessions over 3 months and were taught diet information and psychological skills to promote behavior change and maintenance.

From Changes in Clinical and Laboratory Outcomes (Results Section):

The mean HbA1c did not change during the trial in the MCCR group, but decreased by −0.6% in the LCK group (p = 0.04, Table 3). The Cohen’s d for HbA1c change in the LCK group was −1.8, a very large effect size. No one in the MCCR group achieved a normal HbA1c of <5.7%, compared to 13% percent (n = 2) of the LCK group. All individuals in the LCK group showed a drop in HbA1c, whereas 72% (n = 13) of the participants in the MCCR group showed an improved HbA1c (χ2 = 5.2, p = 0.02). More specifically, 56% (n = 9) of participants in the LCK group showed a clinically significant drop of 0.5% or greater in HbA1c, whereas only 22% (n = 4) of participants in the MCCR group showed a drop of 0.5% or greater of HbA1c (χ2 = 4.2, p = 0.04).

OK, slight advantage to the lower carb group. Or, is it the higher protein group? See, if you look at Table 2, you’ll see that over the [self reported] 3-month intake, protein was 106g daily for the LC group, but only 68g for the MC group.

Table 2
Table 2 (click to enlarge)

If you look at the dietary instructions given in the Methods section, you see that the LC group did a reasonable job (self reported) of following the guidelines. They kept protein about the same, lowered carbohydrate by nearly 75% (!), and fat remained the same—though they were instructed to make up any additional food consumption with fat—which means that they dropped 700 calories from daily intake under ad libitum conditions. Of course, as we’re accustomed to seeing, all improvements in weight loss and health markers are always attributed to low carbohydrate, not a daily 30% decrease in energy intake.

On the other hand, here’s what the dietary instructions say for the MC group:

Participants in the MCCR group were encouraged to derive 45% to 50% of their calories from carbohydrates and were taught to count carbohydrates using 15 grams of carbohydrates as a unit. We provided specific suggestions for the amount of carbohydrate units participants should eat at each of 3 meals and 2 snacks. Most participants were asked to eat 3 carbohydrate units per meal and 1 per snack, or roughly 165 grams of carbohydrates a day. They were also instructed to keep their protein levels about the same as before they started the study and to lower their fat consumption. We further recommended that participants eat 500 fewer kilocalories (kcal) per day than their calculated maintenance needs based on their age, weight, height, and physical activity level (ranging from sedentary to very active), using the formula from the Institute of Medicine Dietary Reference Guidelines. [emphasis added]

A summary of how instructions weren’t followed very well:

  1. Protein decreased from 97g to 68g (30% decrease!).
  2. While they did lower fat from 100g to 56g in absolute terms, it only amounted to a small drop in percentage dietary intake, from 39% to 35% of daily energy (b/c way fewer calories).
  3. They went 60% beyond calorie restriction guidelines of 500, reducing by about 800.

I’m not sure in what world a diet that’s still 35% of energy as fat is “low fat,” as described in the very first paragraph of the paper, but isn’t this the same sort of complaint LCers raise when papers have the “LC group” eating 35% carbohydrate? Sure, this is in the context of calorie restriction anyway, but so often are LC groups, yet that complaint still persists—so, what’s good for geese… In essence, most of the caloric restriction here came via a substantial reduction in protein in real terms, when it ought to have been the fat being reduced way more than it was—assuming we wanted a true comparison here.

All that said, LC intervention for diabetics and prediabetics seems pretty well established as beneficial to me, in both the literature and anecdotally (though I now believe there are better long-term solutions for a lot of people, like the Perfect Health Diet).

So what, exactly, is the point of this study? And where in the discussion (admittedly, I only skimmed it) does it say that one group really didn’t follow the guidelines so what they set out to compare wasn’t really compared as designed?

Richard Nikoley

I'm Richard Nikoley. Free The Animal began in 2003 and as of 2021, contains 5,000 posts. I blog what I wish...from health, diet, and food to travel and lifestyle; to politics, social antagonism, expat-living location and time independent—while you sleep—income. I celebrate the audacity and hubris to live by your own exclusive authority and take your own chances. Read More


  1. Goodstuff on July 3, 2014 at 15:40

    Yawn. Not one comment. Ok, just this one.

    Wooo on the other hand is nailing the traffic to her blog (I think).

    • Richard Nikoley on July 3, 2014 at 16:06

      You might want to check out Alexa on that. 🙂

  2. CharlesQ on July 3, 2014 at 16:26

    The only studies that matters are “medical ward” studies where the individual never leaves the medical facility and the input and outputs of energy are calculated.

    • matt on July 3, 2014 at 18:33

      CharlesQ, the authors reference a met ward study in the discussion – Boden 2005. Short term study but calorie reduction accounts for weight loss on 21g CHO/day diet for two weeks.

    • CharlesQ on July 3, 2014 at 20:34

      My comment was about all health studies in general. Only metabolic ward studies are scientific.

      Surveys are useless whether they confirm or refute a metabolic ward study.

      The only thing a survey can prove is whether the group of people chosen can follow the diet given to them.

    • Bret on July 4, 2014 at 04:52

      Agreed to a point. The problem is such a study is unrealistic, and issues stemming from living in a ward (no sun, no work, little family exposure–not living a life) may confound the results.

      I remember Tom Naughton made an interesting and poignant remark on one of his recent Fat Head Blog posts about RS, which is that anecdotes are not as worthless as most of us have convinced ourselves they are. Especially when they may be the only realistic solution.

      Put anecdotes in the context of the wisdom of the crowd, and that is really how this RS cat broke out of the bag.

  3. matt on July 3, 2014 at 18:28


    There was a short blurb about noncompliance in the discussion. Sort of.
    “While we and our participants made an earnest effort to collect data, there is a rich literature indicating that there are important inaccuracies this data that limit our ability to relate specific changes in self reported diet content to outcomes.”
    They go on to mention that 20% of energy intake is “missing” at baseline.

    I didn’t understand the point of this study either, especially considering the poor design.

  4. Raz Vox on July 5, 2014 at 07:11

    The hell does it matter if the weight loss was from low carb or low cal. Basically, as long as low carb is shutting my appetite down ‘naturally’ and I’m losing /maintaining weight I’m ecstatic about that. As far as studies go they’re for some reason always off in some way and well ANY study can be manipulated to give the desired outcome. It’s all bogus!

    • Richard Nikoley on July 5, 2014 at 07:21

      Both were reduced calorie diets. The LC group reduced by 700kcal and the MC group by 800kcal. Both groups lost weight.

      But this is the eternal silliness with the Shiite LC crowd. Study after study shows spontaneous calorie reduction on LC diets, but the weight loss is forever touted as some sort of magical metabolic advantage rather than a simple reduction in intake.

      And of course, so many people stall eventually. There’s an easy explanation for that, too, though always ignored.

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