New study: Isn’t low carb superior for weight loss?


Another study is out in the endless fight between low-carb and low-fat diets for weight loss. First some quick background: The total standing so far, according to the Public Health Collaboration’s overview of studies, is at 29 victories for low carb (meaning a statistically significantly larger weight loss).1

The number of victories for low fat? A big fat zero.

However, there are also 28 studies that show no statistically significant differences between the study groups, meaning they are draws.

The big picture is thus 29 wins for low carb, (the same) 29 losses for low fat, and then a big bunch of draws.

However, when the media reports on a new study they are not too interested in painting the full picture. That’s boring and the full picture does not change with every new study. No, the media always wants something new, exciting and worthy of a click. So they tend to mostly ignore what came before.

This allows them to report something exciting and new every time. In the case of low-carb vs. low fat diets, this can sometimes translate to 50% of headlines saying ”Low carb is superior for weight loss” and 50% of the headlines saying ”Low carb is NOT superior for weight loss” (i.e. it was a draw).

Notice what is missing? The ”low fat is superior for weight loss” study result. It has never happened, and likely it never will. Low-fat diets have been a failure forever.

The current Stanford study

The new study from Stanford and Professor Christopher Gardner, out yesterday, is pretty interesting. It’s part of the media’s second category (”low carb is not superior”) even though it ended with a non-significant advantage for the low carb group (6 kg lost vs. 5.3 kg):2

The study was 12 months long and tested a ”healthy” low-fat diet vs. a ”healthy” low-carb diet. So what is ”healthy”? It turns out both groups were advised to avoid sugar and refined carbohydrates! How’s that for progress! We’ve come a long way.

Unfortunately this (healthy) piece of advice ended up making the differences between the study groups fairly modest. In fact, the low-fat diet group ended up eating fewer carbs too (compared to before), significantly less sugar and a lowered glycemic load.3

The low-carb group was initially, for the first 8 weeks, targeting below 20 grams of carbs per day (usually highly effective). However, after that limited period participants were then asked to just keep the carbs as low as they felt was easy to do. This resulted in the group reported eating 100 grams of carbs per day at 3 months, and at the end of the study they were on average eating 130 grams of carbs per day. Pretty far from a keto diet, and thus the results do not say much, if anything, about the long-term weight effects of a stricter low-carb diet.

Here’s the data for carb intakes in the low-fat (left) and low-carb (right) groups. Notice that the low-fat group is reducing their carb intake too, and the “low-carb” group ends up with a barely-low average carb intake of 130 grams per day.


Anyway, the bottom line is that the groups both got some good advice: avoid sugar, avoid refined carbs (like flour), avoid processed foods, eat plenty of vegetables and focus on whole foods. It’s also notable that the final results (-6 kg for low carb and -5.3 for low fat) is a pretty good 12-month average, compared to other weight loss studies.

Note that the average includes everyone, whether they managed to follow the advice or not, so the results for people who did everything perfectly according to instructions were likely much higher on average.

If I’m allowed to speculate, the reason that we did not see any major additional benefit from low carb in this study is that the groups ended up so similar when it came to bad carbs. The low fat group ended up eating fewer carbs too (!) and significantly less sugar, while the low-carb group ended with a somewhat weak low-carb diet, reporting 130 grams of carbs per day.

Insulin levels and gene tests

The study also aimed to see if they could predict who would do best on low carb or low fat by testing their insulin levels and gene profile before the start of the study.

The result, somewhat disappointingly, was no. There was no clear difference in results, based on these measurements. This negative result may have been influenced by the fact that the diets in the two groups ended up relatively similar. But it’s still a blow to the idea that it’s possible to predict who’ll do best on a specific diet based on blood tests or genes.

What happened at 3 and 6 months?

In other studies comparing low carb and low fat, the largest differences (pretty much always favoring low carb) can be seen early in the study, during the first 6 months, while the participants eat the fewest carbs. As more people return to their regular diets over time (very human) the differences usually shrink and we often end up with a non-significant result.

In this study, too, participants in the low-carb group ate a bit fewer carbs in the beginning, at 3 and 6 months, and more over time.

According to the study they also measured all factors (presumably including weight) at 3,6 and 12 months. However they only report the weight at 12 months.

I find this curious. Why not report 3 and 6 month results on weight, if they measured them? Likely, based on earlier studies, the advantage for low carb would have been more noticeable at those times. But we don’t know, because the study authors apparently decided to not disclose those numbers. Too bad, I’m quite curious at what they showed.

Addition: These weight measurements are actually available in the online supplementary material, outside of the main published study. eTable 1 (below) shows that the advantage for low carb was slightly bigger at 3 months (6.9 kilos lost vs. 5.8 in low-fat group) and at 6 months (9.1 kg lost vs. 7.5 kilos in the low-fat group). The advantages for low carb at 3 and 6 months appear to be close to statistically significant:


Note above that the average total weight lost after 12 months in the finishing part of the low-carb group is 7.6 kilos4, compared to 6 as reported in the main study publication. This later number includes dropouts.5

Putting it all together

On the whole, this study adds to the 57 earlier studies (RCTs) comparing low carb and low fat for weight loss.

From a standing of 29 wins for low carb, zero for low fat and 28 draws, we now have 29 wins for low carb and 29 draws. The wins for low fat stay at zero.

This study adds, however, that a low-fat diet can work pretty well too, as long as you avoid added sugar, refined carbs and processed foods while instead focussing on vegetables and whole foods. That’s probably good advice, no matter what diet you’re on.

Finally, there is some progress going on in the diet debate, as Gary Taubes pointed out on Twitter:


JAMA: Effect of Low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion

Public Health Collaboration: Randomised Controlled Trials Comparing Low-Carb Diets Of Less Than 130g Carbohydrate Per Day To Low-Fat Diets Of Less Than 35% Fat Of Total Calories

Low carb basics



Low carb for beginners

Why carbs and exercise are not the answers to reverse type 2 diabetes

  1. Randomized controlled trials.

  2. 13.2 pounds vs. 11.7 pounds.

  3. Total carbs multiplied by the glycemic index (how quickly carbs raise blood sugar)

  4. 17 pounds

  5. The latter number includes people who stopped participating in the study. The study then uses their weight from earlier, before they dropped out, for the final calculation. In some cases from before the study even started if they dropped out early, lowering the average of the whole group. This is another way that the result of studies can underestimate the effect of a dietary intervention.


  1. Barbara Manard
    Thanks so much for the analysis...very helpful!
  2. Don Morgan
    One of the reasons for our type 2 diabetes epidemic is the confusion the media stirs up in reporting these kind of results! I appreciate your determination and expertise coming from the Diet Doctor. I recommend your newsletter to all my clients. Great job! Thanks again Carbwatchers Utah Don Morgan Check out my website
  3. Maureen O’Rorke
    I agree, this is a helpful analysis. I heard an interview yesterday with the study’s author and it sounded like he was just an advocate for eating vegetables and eliminating refined carbs and processed foods. His view did somewhat erode my confidence in low carb. But! Now I understand more with DD analysis.
    This very fast response from Diet Dr makes the monthly fee worthwhile.
  4. Jennifer
    Thank you. I read a news article about this yesterday and even though I know LC is the only dietary intervention that has ever worked for me, still I felt quite discouraged. Somehow the media always manages to make a questionable "not better," seem equivalent to "unsafe & won't work." Thank you so much for doing these examinations of studies. It is so very encouraging. Thank you!
  5. Mi
    Thank you for this analysis! I first encountered Dr. Gardner and his research back in 2015 when his team conducted a study of all "named" diets (ie Atkins, DASH, Ornish, etc). In that study, Atkins not only produced the best weight loss, but also the most improvements in all biomarkers associated with CVD & CHD. There is an interesting lecture on youtube by Dr. Gardner, who is himself a vegan, where he admits quite conclusively that the Atkins diet was the best performer of all named diets by all measures. In this new study, although the weight loss results were only slightly better with LCHF, there were again significant improvements in CVD/CHD related biomarkers in the LCHF group compared to the LFHC group. The actual complete text of the study is still behind a paywall, but here is an excerpt I found on a site quoting from the original paper:

    "At the 12-month mark, low-density lipoprotein cholesterol (LDL-C) had significantly decreased in the low-fat group (-2.12 mg/dL), while it had increased in the low-carb group (+3.62 mg/dL). However, the low-carb group also saw a significant increase in high-density lipoprotein cholesterol (HDL-C) (+2.64, vs +0.40 mg/dL in the low-fat group) and greater reductions in triglycerides (-28.20, vs -9.95 mg/dL in the low-fat group).

    The change in the total Triglycerides and Triglyceride/HDL ratio in the LCHF vs. LFHC is in my opinion the most significant aspect of this story, as total Triglycerides and Triglyceride/HDL ratio is generally a much better indicator of overall risk for CVD/CHD.

    It's interesting that this revealing bit of data appears to be completely drowned out by the singular focus of reporting total weight loss.

  6. BenG
    I have been on the LCHF diet since Dec 16. The results are interesting:

    1. I have lost ~30 lbs on the LCHF diet and am now underweight, which caused heart problems (blood pressure would drop during exercise, had heart beating backwards) (electrical). I got passed it by eating more, but gaining no weight. BMI = 18.5.
    2. I have been unable to gain weight back to a more healthy level. So far, eating more has not worked. I eat a middle carb diet (estimated).
    3. My LDL didn’t change, but my HDL went up significantly, and my Triglycerides dropped significantly. i.e. the ratio improved by ~ 3x
    4. I am prediabetic. Fasting blood glucose levels hover around 120-135. LCFH hasn’t changed that at all. I have just started taking the herb fenugreek at meals, which is indicated in lowering blood glucose. I have tried sugar shock treatment - eating a little pure sugar in the middle of the day to kick start the insulin production. Seems to have worked "a little”. Maybe there is better timing.
    5. I now have chronic constipation. I have taken Psyllium(Metamucil), Miralax and other stool softeners. Their effect has not been normal bowels and uncomortable. I add Psyllium to my bread recipe.

    So far, the benefits of weight reduction and better lipid profile have kept me on the diet, but I have to be very cautious about the other problems it has caused. Still searching for answers.

  7. Cherise
    They tested so much in this study. I'm curious if they tested fat mass and lean mass. I feel this makes a big difference in a person's health and ability to maintain weight loss and just counting the number on a scale doesn't say as much as people think.
  8. Roy Gilley
    Why do so many articles have headlines in the form of a question? Gets a little tedious...
  9. 1 comment removed
  10. Richard Feinman
    Once you put the word "healthy" in your paper, it stops being science and becomes an informercial.
  11. 2 comments removed
  12. Ed
    Straight from the study - ->" the mean 12-month macronutrient distributions were 48% vs 30% for carbohydrates, 29% vs 45% for fat, and 21% vs 23% for protein."

    Think very carefully here. Avoid the trap!

    How can you say it was a true low-fat when it was still 29% calories from fat. How can you say this was true low-carb when 30% cal. came from carbs.

    After all their so called low fat diet is 48% carb / 29% fat. That's the macronutrient breakdown of cake!!

    All we can draw from this study is that in the face of a mixed macronutrient diet, the lower the carb the better because we know carbs cause insulin to rise and this causes dietary fat to be immediately shuttled into fat cells, not burned.

    Like Denise Minger in her posts point out, either you're in Ultra-low fat land or Ultra-Low carb land. Both are ok (and ideal), just don't be in the middle macronutrient swampland where metabolic disease starts occurring.

    What if there is no dietary fat to store, in a HCLF diet? Your body is processing pure carb, with no dietary fat in the way --> high insulin --> burn carb, no fat to get in the way. Situation is good.

    What if there is no dietary carb to store, in a LCHF diet? Your body is processing pure fat, with no dietary carbs in the way --> low insulin --> burn fat, no carbs to get in the way. Situation is good.

    Think how ridiculous it would be to say this: "Butter is good, so throw butter at flour and sugar and eat cake." It's the combining of the 2 energy sources that's the problem. Take a cue from nature - nothing from nature comes with both carb+fat together. Only exception is milk.

  13. Ed
    If you were to see a study with 80%carb+20%protein vs 80%fat+20%protein, the results would be very very similar.

    All macronutrients need to be considered for it to truly be your way of eating for the rest of your life. Will you truly avoid another carb for the rest of your life? Hmm..

    We need all macronutrients. Just not all at the same time.

    What this translates into practically speaking is LCHF/HCLF cycling.

    Dending on your lifestyle, health, and goals;
    1 meal HCLF, 1 meal LCHF, and fast
    2 meals LCHF, 1meal HCLF, and fast
    3 days LCHF, 1 day HCLF, and fast
    6 days LCHF, 1 day HCLF, and fast

  14. Gentiann
    It may work with someone with a normal metabolism but it's not for me.
    First, it's too complicated.,. I like the simplicity of lchf: I just don't buy the high carbs foods as I don't think we need them
    Second I don't see the advantage of switching back and forth between the 2 diets.
    Third eating carbs without fat is not very tempting on my opinion....I would rather skip the meal.
  15. Ed
    Hi Gentiann, you can do that for the short term and encourage you to do so to heal yourself. At some point in your future, just keep it in mind that carbs are going to come into your life. There will be a decision to be made how you are going to incorporate them. The question is, how will you do that? Also, there is plenty of evidences that true low-fat is healing too.

    We had to learn how to eat LCHF right? You say butter is good and LCHF is good. People say that does not sound tempting. But to me and you who are doing it, we say it is very tasty and satisfying. Exact same for HCLF. There are those foods.

    I encourage you in your journey.

    Best wishes!

  16. Pat
    After reading the discussion regarding the latest study comparing low-fat to low-carb diets, I am compelled to share my story.

    In October 2017 my doctor informed me: blood sugar level - 7.6 (7.7 = diabetes), fatty liver, blood pressure skyrocketed to 165/95 on 20m of blood pressure reducing meds and weight at 104kg. One foot firmly in the grave!

    By chance, I met a young woman who had lost 40kg in 9mths on a low carb high fat diet and decided it was time to give up my bread/pasta/rice addiction. I call it an addiction as I physically craved these things. Despite this, it was relatively easy to give them up along side all sugar.

    To my doctors surprise at the end of January 2018 my blood sugar level has dropped to 5.2, no fatty liver - functioning perfectly, blood pressure 130/80 and on 5m blood pressure med (hoping to come off completely soon) and weight today, 86.2kg ( loss of 19.8 kg). After only 4 months on a Keto diet (strict 20g carbs), both feet firmly out of the grave.

    I cannot thank you enough Dr Enefeldt for the wonderful work you and others like are doing.

  17. Marty Kendall
    So nutrient dense minimally processed foods FTW?

    I would still lower carbs to stabilise blood sugar if diabetic.

  18. John Stewart
    Good analysis Andreas and rapidly!
  19. Helen
    The study that still needs to be done is comparing a low carb diet with a mixed diet (not necessarily low fat), BUT KNOWING THE CALORIE LEVEL OF EACH DIET.

    LCHF cannot be proven better FOR WEIGHT LOSS until it shows that it can provide better weight loss with the same number (or more) calories than a mixed diet.

    If LCHF simply causes reduced calorie ingestion, and thereby weight loss, then “calories in, calories out” remains the bottom line for weight loss, and people can just choose their macro ratios but keep calories in check to lose weight.

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