Debunking Yet Another Low-carb Claim

IMG_0177 If you pay any attention to nutrition headlines, you’ve most likely come across numerous articles this week that, once again, proclaim low-carb the king of weight loss diets. The low-carb vs. low-fat debate has been going on for nearly two decades now–you’d think the media would be tired of this topic by now, right?

Don’t we all wish.

Not surprisingly, most journalists did what they normally do when they see any sort of diet-related headline. They skimmed the abstract and got writing.

After taking a closer look at the study myself, it was obvious they missed several important pieces of information–the most obvious ones I’ve highlighted below.

Before we get to those, here’s a little background on the study:

The purpose of the experiment was to compare the effects of a low-carbohydrate diet with a low-fat diet both on body weight and heart health.

The 150 racially-diverse participants, all of whom were obese, were randomly divided into 2 groups: a low-carb group and a low-fat group. The low-carb group was directed to eat 40 grams or less of carbohydrates per day (I almost certainly would have died by dinnertime on Day 1) while the low-fat group was told to take in less than 30% of their calories from fat, which aligns with the current Dietary Guidelines. The participants were not given calorie goals to adhere to however the two groups had comparable average calorie intake at the end of the trial.

If you just scan the abstract (as most journalists did) the weight loss results seem pretty clear. After 12 months, participants following the low-carb diet saw significant decreases in weight loss, body fat, and certain markers associated with cardiovascular risk compared to those on the low-fat diet.

Don’t start counting out your 40 grams of daily carbs just yet though.

Check out what wasn’t included in the abstract:

1. The low-carb diets weren’t nearly as low-carb as you think.

The low-carb dieters were instructed to eat less than 40 grams of carbs per day; however, the average carb intake for the entire group ranged from 93 grams per day at the six month mark to 127 grams at 12 months, over 300% more carbs than the target amount assigned at the beginning of the study. Not only does 127 grams per day barely classify as a low-carb diet, it also leaves me wondering about the sustainability of a 40 gram carbohydrate diet.

2. The study participants had an unfair advantage.

Both groups received either meal replacement bars or shakes and routine counseling from a nutritionist for the duration of the study. Awesome for the participants but not everyone trying to lose weight has access to these same benefits. Because of this, the applicability of this study to the general population is automatically lessened.

3. Participants in the low-carb group ate significantly more protein.

Not surprisingly, something had to take the place of all those carbs, and protein seemed to fill the void. Protein has been shown to have a positive impact on fat loss by increasing satiety and maintaining calorie-burning muscle… thus, it’s impossible to tell whether the greater fat loss in the low-carb group was due to cutting carbs, eating more protein, or some other factor that wasn’t accounted for.

4. The trial didn’t use the best method for measuring fat loss.

Researchers essentially used a fancy bathroom scale that measures body fat using bioelectrical impedance, which works by measuring total body water. Accuracy issues aside, low-carb diets notoriously reduce water weight quickly which, in this case, was likely misinterpreted as additional fat loss.

Researchers also tracked changes in waist circumference, the next best measurement of fat loss in this situation, however the ultimate differences between the two groups in this area were negligible. The low-carb group had smaller waists than the low-fat group for the first half of the study but both groups had similar decreases in waist circumference at the conclusion of the trial. Based on waist circumference measurements, it’s hard to support the claim that low-carb diets are superior for longer-term fat loss.

So WTH does this all mean?

As it turns out, the study doesn’t actually prove that low-carb diets lead to greater weight loss compared to low-fat diets. Instead, it shows consuming fewer carbohydrates may increase protein consumption, and something about that combination seems to enhance weight loss—however, the cause is not yet clear.

What is clear is that adhering to a diet of 40 grams of carbohydrate per day for any amount of time is pretty damn hard, even with low-carb meal supplements and nutrition counseling.

On the upside, the results from this study hint that a lower carb intake paired with higher protein consumption may lead to greater weight loss over time—which seems infinitely more sustainable (and enjoyable) for most than a true low- or no-carb lifestyle, especially for us pasta, bread and cupcake lovers.

Ever tried going low-carb for weight loss? I did in college… to get Britney abs for a Hawaiian luau I was dancing in. True story. (Did I seriously just admit that to you guys?) Well, it worked… kind of… until I caved and went completely carb crazy. NOT COOL.

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  • There are about 200 more studies to glean from and you were biased from the start of this article (would have died by dinnertime on day 1). It’s not for everyone but it does work for many of us. I have adhered to a low carb lifestyle for about 15 yrs (I’m almost 60 & entered menopause at 38). It is the only thing that I can seem to stick to, not get hungry and stay in better health. After a few months on low carb (not NO carb)my doc took me off of all cholesterol meds that I was on. My lipid profile comes out as “optimal” and has remained so. The same did NOT happen with me when I tried a stint on weight watchers. For the most part, I’m cutting out sugars and refined flours. Why do people have a problem with that? So many get the wrong idea of what a low carb diet is (including some low carb neophytes who erroneously think they can just eat copious amts of bacon & cheese and lose weight and remain healthy). I started out initially on pretty low carbs and then as you get to your goal weight you add in healthy carbs (veggies & fruits) along the way until you reach the amount that your body requires to maintain a healthy weight. My skin is clear with constant compliments, I went from a size 12 to size 4/6, great lipid profile and no hunger. Why does that make so many people angry?

  • I spent January on a very low carb diet and I did lose some weight. I felt pretty weak and low energy by the end though and, of course, the minute I tried to return to a carbs-in-moderation diet I regained the weight I lost–and then some. I appreciate the nuanced look you take at this hard issue. I do think you are right when you suggest that a combination of lower carb (especially refined carbs) combined with more protein is the ticket to a healthy diet and sustainable weight loss. At least, that’s what I’m going for these days. Thanks for the sane analysis!

    • Hi Joy,
      Couldnt help commenting, low carb diet in eutarian sense just means slowly reducing carbs from your existing level to a level that you can sustain. I am not a dietician,but i think the whole thing of measuring and eating is just sick and impossible to adhere to.

      What a person needs is to eat just right which you can define easily by looking into it, all by yourself. Weight loss is easy,idea is to find what your brain says is workable and heart says you can stick to it forever.

  • A great post on the debate! As far as my thinking goes, it’s less how many carbs you’re eating, and more where are they coming from? Sweet potatoes are far better than, say, wonder bread. Low carb leaves you feeling deprived, but sticking to “good carbs” for a lack of better term, like fruits and starchy vegetables, with a treat every now and then, that works for me!

  • As an RD with many years experience, I could get on my low-carb-diet-soapbox, but you covered it well and I agree! The bigger take-away for me is the issue of research. You hit the nail on the head! No one cares to know the specifics about the actual research. Or heaven forbid, go another step and – dare I say it?!- RESEARCH the RESEARCH. Such a logical approach is certainly not headline-worthy. Yet supposedly journalists and reporters have a reputation of digging to the bottom and not stopping till they get the truth. I guess it depends on whose truth they like the best. I have worked in a variety of settings, clinical, community, with aged, with very young, with healthy, and with medically complex patients. I’ve worked with a variety of healthcare professionals and had the privilege of working with Interns. I think no matter what the circumstance, whether it be for my own knowledge base or other’s, the importance of evaluating the research cannot be stressed enough. Even well educated people can be misled, or worse misleading!

  • What the study showed was that with advice and support a group of obese women told to limit their “net carbs” to 40 grams achieved a much better weight loss and cardiovascular marker outcome at 3 months than a near-identical group told to limit fat to 30% of diet.

    Neither group lost weight after 3 months, so had 9 months eating 25% less than their baseline with ZERO weight loss, or worse.

  • I’ve tried the no-carb diet, also in college, but now I follow a paleo lifestyle which is probably considered lower-carb. I think it’s important to just find something that is sustainable, long-term. Thanks for sharing a more detailed description of the study! Love the Brittany story!!!

  • Interesting post! I’m doing a comparatively low-carb diet right now, but that’s just because I’m eating a ton of protein. Still getting in 120g of carbs each day! I need it for the energy.

  • Thank you thank you for breaking this down. I am learning (slowly) that cutting entire food groups out is detrimental to me and this certainly helped reinforce that :)

  • Thank you Elle for being one to actually read the research. The media drives me nuts when they sensationalize all the time on vague abstracts. I know I’ve tried low-carb before and after 3 days I’m ready to eat all the bread in sight. I do limit it to reasonable amounts now. I know myself better than to try it hardcore ever again. I just want to yell “People please stop trying to eliminate entire food groups.”

  • I remember hearing Britney say she did 500 crunches a day. Well, now we know that a handful of properly done planks and hovers is much more effective at core training than crunches. Thanks for looking at this study and pulling out some thing I didn’t notice as I read the articles about it. I’d say eat in moderation, eat healthy things, and sweat. You’ll be fine! Have a great weekend!

  • Britney abs! (Circa “I’m a Slave 4 U”? Me too…) I can’t do low-carb. I’m in the midst of Whole30 and even though it’s technically paleo, I have a serving of fruit with every meal and for snacks and a sweet potato once a day. I think I’d have a massive meltdown without it!

  • I to did the whole “low carb” South Beach diet my first year of working full time. Except I thought it would be cute to extend the initial 2 week low carb to a month and a half and once I started eating carbs again – well it wasn’t pretty lol! Balanced diets are where its at!! Hopefully you have some good pictures from that HI trip!

  • Ah, the Britney abs! I remember doing 100 crunches a night trying to get those abs… so thankful to be older and wiser now! Haha! Love this post – it’s very well-written and explains the bigger picture of the study, not just what’s in the headlines.