Why do low-carb dieters fail in the long-term?

This video is pretty convincing that they do fail to reach or maintain adequate fitness:

However, I don't quite understand the causes. Why do they fail where high-carb dieters do not?

(Is this the right subforum to post this question?)


  • @maxb

    I've been working in the field of weight management for about 8 years now and what I can say on the topic is that the best diet is the one that you can follow for the rest of your life.

    When it comes down to it, weight loss happens because we are burning more calories than we are consuming. At some point, we plateau because we can no longer cut-back/burn more calories (plus, metabolism tends to decrease with weight loss).

    What I've noticed in practice is that low-carb followers lose +++ weight off the start (a combination of weight and water). However, following this initial weight loss, things start to plateau and many people get frustrated that the effort isn't worth the outcome.

    In addition, it can be difficult to attend social events as a low-carb eater, since it triggers feelings of deprivation.

    Hope this provides some additional insight!

    Susan Macfarlane, MScA, RD
    Registered Dietitian Nutritionist
    As always, any and all postings here are covered by our T&Cs:

  • @maxb

    I'm not a low carb advocate. In fact, I think low carb diets can be uniquely dangerous for a number of reasons. However, low carb diets are not really obesogenic diets. In the literature, carbohydrate-restriction generally produces more reliable reductions in calorie intake in free-living humans when compared to most other diets. This video is basically just propaganda, and it's no way to conduct any sort of proper comparative analysis.

    If people don't want to track their calories, they have to eat according to heuristics in order to lose weight. Carbohydrate-restriction is a powerful heuristic because of just how profoundly restrictive it is. However, fat-restriction is also a very powerful heuristic, but much harder to implement in practice. Fat-restriction is just much more complicated and hard to manage. As a result, low fat diets don't tend to do as well in the literature. However, in a recent study called DIETFITS, low carb diets and low fat diets produced the same amount of weight loss. The only difference was that participants were allowed to self-select and customize their diet to best suit their personal preferences.

    So, the real question for personal weight loss is what heuristic can you adhere to the best and most reliably over time. Preferably something you can do indefinitely. For me, a low carb diet didn't make me gain weight, but it certainly impeded my weight loss progress. The diet I'm on right now, which is relatively fat-restricted, allows me to maintain a caloric deficit more easily. In order to lose weight, you almost need a dietary villain to work against. People seem to need a boogeyman, even if you know deep down that it is irrational. Whether it's carbs, fat, calories, animal flesh, gluten, grains, ethics, cholesterol, saturated fat, PUFA, you name it. Being spooked out by your food tends to induce weight loss. Just pick your boogeyman and call it a day.

  • @BRBWaffles

    I find the video very convincing (Seeing is believing and all that. Anyone can CLAIM that their method is effective)

    Can you cite any study that tracked low-carb vs low-fat dieters for more than 5 years?

  • @maxb

    If you're convinced by a video like that then I think any research that could be cited, even if it existed, wouldn't be likely to persuade you. Your standards for what constitutes credible evidence are unreasonably low, and your standards for what constitutes credible counter-evidence is unreasonably high.

  • @BRBWaffles

    Why? That's ad hominem.

    You said "in the literature", but failed to actually link any relevant long-term study.

    DIETFITS was just 12 months. The title of this thread has "long-term" in it. If you have no evidence for your claims, you shouldn't make them.

  • @BRBWaffles

    The forum isn't letting me post direct links, it seems, but here's what Harvard's Medical School wrote about the Keto diet this year:

    We also do not know much about its long-term effects, probably because it’s so hard to stick with that people can’t eat this way for a long time.

    So maybe it's not my standards of evidence that are poorly adjusted.

  • @maxb

    Why? That's ad hominem.

    No it's not. I'm not attacking you personally. I'm criticizing your standards because they don't make any sense.

    You said "in the literature", but failed to actually link any relevant long-term study.

    "Long term" is relative. Virta has decent two-year weight loss data on people using ketogenic diets. DIETFITS followed people for 12 months. The A to Z Study followed people for 12 months. DIRECT's trial lasted two years as well. This study also saw sustained weight loss after two years. To date there are no five-year trials that I'm aware of, but the direction of the literature leans heavily toward the trend that sustained weight loss is a matter of dietary compliance. Compliance among low-carb diets seems to be fine over time, and not uniquely worse.

    So maybe it's not my standards of evidence that are poorly adjusted.

    When I read your comments, all I read was this: "This random YouTube video that presents no actual data at all is persuasive to me. You're unlikely to persuade me otherwise unless you can provide me with five-year prospective or trial data".

    Sorry, but that's not a reasonable perspective to have. You'd be hard-pressed to find a study duration of that length with any diet. However, the bulk of the most highly powered literature suggests that low-carb diets lead to weight loss that is durable throughout the duration of the study period in free-living humans. At the very least, on balance, the literature does not suggest that adherence uniquely wanes with low-carb diets.

    Again, I'm not a fan of low-carb diets and I'm highly skeptical of their long-term safety. However, it's absolutely undeniable that they're an effective tool for weight loss.

  • Be cool mate...You can explain in much calm way..So just stay calm.Peace!

  • Another thing I noticed at my grocery store: people who buy avocados are typically fatter than those who buy tomatoes.

  • @maxb

    Cool story. Maybe you could publish it on PubMed.

  • I’m low carb Paleo and fit and my aunt is low carb plant based and fit. Both of us have been low carb for around 10 years. And Btw you can be low carb and plant based. I know a bunch of fat high carb vegans. And skinny ones. Whatever works bruh. I’m skeptical of the long term safety of low carb diets too, but the video wasn’t really compelling to me...

  • @BRBWaffle

    FYI PubMed is just a search engine, like Google Scholar, not a publication venue.

    If you try to be snarky, try to sound like you know what you are talking about.

  • @maxb

    Dear god, the sarcasm went right over your head. 🤣

  • Dear god, the sarcasm went right over your head.

    It didn't. Re-read what I wrote. I'm just pointing out that your term usage is nonsensical.

  • edited October 2020


    That video is from John A. McDougall, a thoroughly biased source with a long history of citing statistics out of context (among other things). I mean, the guy opposes conventional cancer treatment, for crying out loud!

    Seriously though, all diets can be effective, the laws of thermodynamics are immutable. Calories in, calories out. There is no such thing as a one-size-fits-all diet either, the best diet is the one that is the easiest for you personally to follow. Long term adherence and building good health habits with your food is the most important thing.

  • @Dante80

    I agree, actually. As I wrote in another thread, I think McDougall's organization is very cult-like. He might be right about Steve Jobs's cancer though.

  • I did the ketogenic diet for over two years (for the original reason it was invented - decreasing or getting rid of seizures. Temporary weight loss was just a side effect). One of the reasons is doesn’t work for the long term in my experience, and I’ve heard from others, is that it is very stressful for your body to maintain. A large part of this stress is because high intakes of protein decrease blood sugar which force the body to get energy from its own fat and - unless perhaps one is obese - very soon also muscle stores. This will cause a spike in blood sugar. Unbalanced blood sugar is a large cause of hypothyroidism and one of its worse symptoms - a slow metabolism. Basically, if one ever returns to a regular diet they will gain weight and in my opinion it should only be used if one is quite overweight or obese but even then they should transition to a more balanced diet so the body isn’t malnourished (there are some high carb foods such as milk, root vegetables, blueberries, and other fruits which would be banned on Keto but have powerful nutritional benefits).

  • @vwang

    Thanks for sharing your experience! While I think a keto diet can change how your body metabolizes nutrients for energy, I'm not sure to what degree it puts the body under stress.

    I just wanted to clarify that a keto diet typically doesn't include high intakes of protein, as protein can also be converted into sugar, thus defeating the purpose of the keto diet (so protein doesn't drop blood sugar).

    I also don't think there is evidence to support irregular blood sugars being the cause of hypothyroidism. That said, we do see high rates of hypothyroidism among Type 1 Diabetics since autoimmune conditions often co-occur.

    The real reason low-carb diets "fail" over time is that the body is designed to fight against weight loss. Eventually, an individual's metabolism will slow to compensate for the weight loss, thereby reaching a plateau. This effect is seen on all diets that result in weight loss.

    Kind regards,

    Susan Macfarlane, MScA, RD
    Registered Dietitian Nutritionist
    As always, any and all postings here are covered by our T&Cs:

  • Thanks for catching my errors! You're right, keto is moderate fat and high protein. I admit when I did the diet my body didn't react so well to the amount of fat the diet required so I instead ate more protein than usually keto dieters do. You're right, irregular blood sugar I don't think is a cause of hypothyroidism; it seems to be more like one of the symptoms of hypothyroidism. As for stress, my case was perhaps a more atypical one. The keto diet was originally created for young children who were unable to control seizures with medication, as you may know. Young children luckily are generally not exposed to as much temptation, stress in life, and don't have to cook for themselves. I'm not sure the carb limit of, I'll's call it "weight loss keto", but for "medical keto" it is 20g net carbs (sugar alcohols are counted as carbs). I had to weigh my food, be VERY careful, already was going through a hell lot of stress and it made socializing very challenging too. Especially if you had friends like mine who were normal weight and fine with it (as I think they should be)! Anyway, that's my two cents - again haha.

  • Unprocessed high carbs are life....for me.

  • edited January 15

    I dispute the premise of this discussion, which is equivalent to "when did you stop beating your wife? "

    I think low carb works. Dr David Unwin has been putting his diabetic and pre-diabetic patients on low carb for 7 years, and is finding continued success. I easily reached and passed my goal weight 8 months ago, and have been effortlessly keeping it off since then.

    When I stuck to the high carb food-pyramid recommended eating, dieting was a struggle and the weight piled back on as soon as I relaxed my constant vigilance, or grew tired of being hungry all the time.

    Ironically, it was cronometer that taught me that calories in/calories out is nonsense; that simply reducing calories was going to fail in the long term. It drove me to find an alternative approach.

    Lockdown had helped, too. It would be much harder to have gone low carb if it meant turning down crisps and beer at the pub.

    The picture on the left was me on a high carb diet, the day after cycling 100km. That is the body that plenty of cardio and the food pyramid built. On the right, I am 57 and menopausal. I have not put the weight back on at all since then.

    (ugh, reuploaded for clarity)

  • edited January 19

    I'm not going to comment on the keto diet but I can tell you why high carb low fat works for weight loss. It's because you can eat larger amounts of food and still be in a healthy calorie range. It's calorie density. For example I make a lot of soups, casseroles, rice dishes, potato based dishes, tacos, lasagnas, pasta etc and they are usually between 300 and 400 calories per pound. That means I can eat 5 pounds of (yummy) food all day and only have 2000 calories. I don't, I eat about 4 pounds. Every person eats between 3 to 5 pounds of food every day. I have lost 65 pounds over two years. I have about 20 more pounds I want to lose. It took me a lot of time to get to this point where I have an arsenal of meals and I can plan ahead and make sure I have what I need. That's part of why it took so long. Here on Cronometer I can see that I am getting all my nutrients. I have gotten my blood levels checked and everything is within normal range, except vitamin D. I live in the Midwest, and I work nights. So I don't get enough sun. Edit: I forgot to mention that I eat only plant foods, no meat dairy or eggs. I do struggle a little with Vitamin E. It's the only nutrient I struggle to get because I don't like to eat a lot of nuts and seeds. But if I eat a lot of leafy greens, I get plenty of E. I have a Vitamix on its way to me, and I will start having green smoothies for this reason.

  • @jefmcg

    Would you mind sharing how many carbs per day is considered low for you? How much protein and fat you eat per day and what sorts of meat and dairy do you eat (assuming you eat them)? Are you particular about oils you use? ex. coconut oil, olive oil or not really?

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