Is Your Low-Carb Diet Ruining Your Athletic Performance?

woman-liftingWhen I first started getting interested in Paleolithic nutrition close to a decade ago, the impression I got from reading ancestral health blogs was that many, if not most, Paleo dieters believed that a very low-carb diet was the optimal human diet. Some bloggers even went as far as to say that you could eat as much fat as you wanted as long as you restricted your carbohydrate intake, that insulin was the devil, that eating a strict ketogenic diet was the way to go for those seeking to increase their healthy lifespan, and that everyone, including those people who perform a lot of prolonged, high-intensity exercise, should severely restrict their carbohydrate intake and seek to become properly “fat adapted”.

So, naturally, I made a conscious attempt to lower my carbohydrate intake. To make up for this reduction I boosted my fat intake by adding more butter, olive oil, avocados, and other high-fat foods to my plate.

For a long time, I was getting upwards of 60% of my calories from fat; and since I was taking in fairly high levels of protein, my carb intake typically hovered around 15-20% (of total daily calories). At the time, this macronutrient ratio seemed to be fairly common among Paleo dieters; and within the low-carb community, many went even higher in fat…

Optimal carbohydrate intake and fat adaptation

As you know if you’ve been reading this blog for some time, my perspective on these things have changed quite a bit since I first started fiddling with the whole Paleo thing many years ago. I still advocate a diet that most people would describe as low-carb, as it contains much less carbohydrate than the typical Western diet. However, it’s important to note that the carbohydrate intake I recommend (about 20-40% of total daily calories) actually could be classified as the evolutionary norm for our species, while the average carbohydrate intake in contemporary industrialized societies (about 45-60% of daily calories consumed) is – from an evolutionary perspective – absurdly high.

Getting grains (particularly the refined types), sugar-rich desserts, and highly processed foods out of the diet may be the single most important thing people can do to improve their health. However, that doesn’t mean that going very low in carbohydrate is necessarily optimal, particularly for those who perform a lot of anaerobic exercise…

The average Joe who spends most of his waking hours in front of a computer and rarely exercises doesn’t need a lot of carbohydrate. This person will do best on a Paleo-style diet that is fairly low in carbohydrate, particularly if he’s insulin resistant and/or severely overweight. A bit of fruit here and there, some starchy tubers for dinner now and then, and the occasional treat are all the carbs he need.

But what about those people who are very physically active? Personally, I’ve found that if I go very low carb, my exercise performance suffers. For a long time, I tried to support my training with a very low carb diet (about 15-20% of total daily calories from carbohydrate), but I eventually had to realise that this approach didn’t work for me.

That doesn’t mean that a very low-carb diet never works for athletes though. It all depends on your genetics and current health condition, and even more importantly, what types of activities you perform.

I do quite a bit of anaerobic training such as heavy strength training and sprinting, something that can be difficult to do optimally on a very low-carb diet – even if you spend weeks trying to get better and better at using fat as fuel. However, those who primarily perform light-moderate intensity aerobic exercise often do better on a high-fat diet, as long as they realise it’s going to take some time to become good at burning fat.

Where should you get your carbs from?

One of the reasons the Paleo Diet is so healthy is that it excludes high-carb, highly insulinogenic foods. I certainly don’t recommend that people who do a lot of strength training, sprinting, or other anaerobic activities should eat a lot of breakfast cereals, sugary desserts, and other foods that are very high in carbohydrate. There is a better way...

Fruits such as bananas and apples and “safe starches” like sweet potatoes, potatoes, and yams are the perfect source of carbohydrate for those who are physically active. Those who are very physically active may also benefit from including foods that have a higher carbohydrate density, such as white rice and quinoa.

When I first started boosting my intake of root vegetables and tubers (particularly sweet potatoes), my athletic performance improved noticeably. I was doing okay on a very low-carb Paleo diet, but not great. It took a stack of sweet potatoes to really boost my performance.

That’s not to say that I binge on starchy foods – or recommend that anyone should eat a high-carb diet. All I’m saying is that if you’re one of those people who’ve been duped into believing that the less carbohydrate you eat, the better of you are, then you should probably reevaluate your perspective on things – particularly if you’re very physically active.

Personally, I eat about 100-200 grams of carbohydrate each day, the exact amount depending on how physically active I am. This may not sound like a lot, but the fact is that to get 200 grams of carbohydrate, you have to eat a lot more fruits and vegetables than you would think.

I find that I “need” some starch to perform optimally in the gym, so I typically consume quite a bit of sweet potatoes every day. I’m also considering adding some quinoa into my diet, but as it’s so damn expensive – and contains some potentially problematic anti-nutrients – I’ve put it on hold for now.

Now I want to hear your thoughts: What type of physical activity program do you adhere to? How much carbohydrate do you take in every day? Have you tried eating a very low-carb diet; if yes, how did it affect your athletic performance?

Picture: Creative Commons picture by Arctic Warrior. Some rights reserved.


  1. Years ago a doctor decided I was diabetic. He wanted me to do a second blood test 6 weeks later to confirm his diagnosis. In that 6-week period I eliminated sweets and almost all grain products. Lo and behold, the second blood test showed a very healthy blood sugar level at the low end of normal. The first blood test may have been in error, but it was nevertheless a wake-up call for me to change my eating habits.

    My son was on a medically supervised ketogenic diet for a seizure disorder when he was young. I don’t know what the percentage of carbs was, but he was allowed very little in the way of low-glycemic vegetables and no fruit at all. Obviously he couldn’t have any grain products whatsoever. He was given homemade “ice cream” three times a day to keep him from losing too much weight. (This consisted of carefully measured portions of oil, heavy cream, and artificial sweetener.)

    My son was constipated a lot while he was on this year-long diet, and he was often tired and out of sorts. My personal feeling is that a VLC diet consisting of mostly protein and fat can eventually become unhealthy. Although grains really are unnecessary, the human body does need the fiber and various nutrients found in moderate amounts of fruit and all kinds of vegetables in order to function optimally.

    • Yes, a VLC diet low in fermentable substrates can wreak havoc on the gut microbiome and general health.

      Hope your son is doing better now!

  2. Many of us have changed our views since the early years. WelI done article.
    I do HIIT and strength training, in the fasted state, and I find a great post workout meal is oatmeal (steel cut and the bran), mixed with whey protein powder and fruit. That will refill my glycogen stores, provide the aa for muscle synthesis, and give my microbiome their MACs – we all win! I do not believe that oats are incompatible with a paleolithic approach
    to nutrition. The other CHOs in the day come from veggies (mostly nonstarchy) and fermented dairy- very little CHO, since the bugs have used the lactose as an energy substrate.

    • Sounds like you’ve landed on a plan that works well for you. I don’t recommend oats and whey protein, but by all means, if it works for you, stick with it.

      How is fasted training working for you?

  3. I totally love the fasted workouts – I do those 4 times per week- been doing those for about 2 years – whether its weights or HIIT, and I find it so interesting that MY APPETITE IS SUPPRESSED for hours after – I could do a 9 am workout and not feel hunger until noon – I know that because I used to do a leangains style IF protocol, with a 7-8 hour eating window. I’m not sure about how healthy that is, so I eat right after the workout now. I have theories about the metabolic dysfunction that can occur in some people doing extensive IF, but cannot prove it other than n=1.
    On the days that I’m at the office, no morning workout, I’m hungry by 8am!
    I never did any grains for 3 years, strict Cordain eating pattern. I still avoid grains other than oats – their MAC content changed my mind, also their positive impact on lipid profiles. They are not plagued by gluten or by Monsanto’s long reach (yet), and buying organic helps.

    • I know what you mean. I rarely feel hungry directly after a fasted training session, so if I do a fasted morning workout I typically won’t eat until a couple of hours after the workout is done.

      Thanks for sharing your thoughts/experience.

  4. Good article! Definitely a key topic.
    I didn’t *intentionally* go on a low-carb diet, I just figured more vegetables and leafy greens would be good for me. I already didn’t eat a lot of carbs before making the switch to begin with. And things were going great on my new eating plan; felt fantastic, no digestion issues… until… BOOM == definitely hit a wall in my workouts and I felt/feel tired more often. Also, suddenly the digestive problems happened (again).
    So now I figure I should start at least eating at least some sweet potatoes or more pasta or white rice more often to solve the energy/workout problem. The doctor told me to eat more fiber or take fiber supplements without even asking me how much fiber I already consume — say what you ask?! No kidding. I’ll try more water before consuming more fiber or fiber supplements. Recently I’ve been reading that too much fiber (from plants) causes problems — that’s more likely the case with me.
    I know it’s all about balance and what works for each individual; I just want to be happy and healthy 🙂 More carbs it is!

    • I definitely recommend giving potatoes (sweet or regular) a try if you’re looking for a good carb source.

      Haha, I guess your doc told you to eat more “heart healthy” whole grains, right?

      My recommendation: Steer clear of fiber supplements. Instead, eat plenty of fiber-rich vegetables (and some fruit here and there) and work on improving your gut biome.

      • I’ve been doing *everything* right for the last year, including making bone broth and consuming almost no dairy at all. In fact I don’t even need any of the 3 allergy medicines I used to take.

      • Surely one should differentiate between natural fiber supps and manmade fiber supps. I cannot imagine that to grind up a root and put it in a capsule with nothing else in it can be bad for you. Also, it is important if the supp is fermentable or not. If it’s a MAC, you are improving your microbiome. Please expand on your thoughts. Thank you.

        • Of course, some fiber supplements are better than others. My main point is that the primary focus should be on consuming natural, whole foods.

          If there’s one thing I’ve learned from keeping up on the scientific literature in this area, it’s that most supplements come with some potential adverse effects. E.g., whey protein is highly insulinogenic, can exacerbate acne vulgaris, and negatively impact adult gut flora. Multivitamins can interfere with quorom sensing in gut biofilms, among many other potential issues. I could go on.

          This quote from a recent paper summarizes my perspective on this issue.

          Our diet is composed of millions of substances that are part of a biological network. In fact, we eat “biological systems” like a banana, a fish or a piece of meat. There is a connection between the various nutrients in these systems. In other words, there is a balance and an interaction that is part of a living organism. This balance can be found in the reconstruction of our Paleolithic diet

          To make it clear, not all supplements are a waste of money. If you for some reason aren’t able to eat much fibrous whole foods, supplementing is worth considering.

          • Please share the studies that show that whey protein isolate is disruptive to adult microbiota. This information would have significant impact on my eating pattern, and I would love to read it. Certainly any protein is highly insulinogenic, more so than carbs actually.

            I have read – “Thus, human milk is good for babies, but bad for adult gut flora because most of the protein, fat and carbs are digested and no soluble fiber remains for colon gut flora.”

            But, if the protein is present in the gut at the same time that significant fermentable fiber is also present , I am not clear at all that the presence of the whey protein would have a negative impact. That is certainly not the gist of the above quote.
            Thank you in advance for spending this time to share the information.

          • To my knowledge, there are no studies out there that have specifically looked at the impact whey protein has on the gut microbiota.

            So, let’s instead apply an evolutionary perspective and some logical sense.

            Protein powder is an evolutionarily novel, processed food item that has a nutrient composition that doesn’t resemble anything you’ll find in natural, whole foods. In itself, this suggests that consumption of whey protein shakes may be problematic.

            As you know, our primal ancestors didn’t drink milk (from any species) as adults. Milk contains a wide range of hormones, bio-active peptides, and other compounds that are specifically “designed” by natural selection to support the growth and development of an infant. Some of these substances have potent antibacterial action, which is one of the reasons why breastfed babies have a gut microbiota that only consists of a limitied number of lactic acid bacteria (Breastmilk selects for the growth of a specific set of bacteria).

            This suggests that milk consumption (particularly concentrated sources of certain components found in milk, such as whey shakes) may be problematic for adult gut flora. Whey protein contains many antibacterial compounds (e.g., lactoferrin), which is likely one of the main reasons some people experience gastrointestinal upset from drinking whey shakes.

            Dr. Art Ayers had this to say about whey shakes:

            Adult gut flora probably adjusts to the milk components that reach the colon, so only large amounts of milk, such as whey shakes, will impact the gut flora.

            Whey shakes, by the way, can disrupt the gut flora and facilitate weight gain or loss, since gut flora are involved in weight stability.

  5. I am in no way trying to be confrontational, just trying to find my own optimal nutrition. I want to link to a piece that Mark Sisson recently wrote – extolling the virtues of said lactoferrin, among other components… ….11/2014.
    AND also from Dr Ayers – …”Lactoferrin is prebiotic and supports the growth of probiotic gut flora.”
    Dr Ayers even wrote a post specifically supporting whey shakes –

    Would you mind linking to Dr. Ayers post that contains your quote? – I tried to find it in his search engine, not successful. Thank you. I am simply trying to reconcile this contradictory information.
    My IBS antedates the addition of whey protein to my diet. However, it persists to some extent (althugh significantly better since I read and implemented Cordain’s material 4 years ago), and I will take your information and eliminate whey protein powder to see if there is symptomatic improvement. I know that you’re in favor of fermented products, so I’ll continue with my homemade kefir.
    I’m glad to have a place to be able to discuss this. Thanks for your blog.

    • No problem. I like that you question things – but still keep an open mind. I also have to say that I think your name is poorly chosen, as you definitely doesn’t seem like a newbie when it comes to health & nutrition 🙂

      The quote in my last reply is from a comment Dr. Ayers made in this thread.

      • NO, I am no longer a newbie, that name was chose 4 years ago, and I haven’t bothered to change it. Thank you for the compliment.
        I’ll contact Dr. Ayers and print his exact response in this post if you’d like.

        • Would be great to hear what Dr. Ayers has to say, so please post the response.

          • Here is his reply- he is always clear and educational.
            Dr. Art Ayers said…
            I see milk and whey as feeding dairy probiotics (lactobacilli) and inhibiting the growth of everything else, i.e. adult gut microbiota. In the context of the Drs. Eades quick weight loss diet, I see the use of whey shakes as being different from other protein shakes. Protein shakes and whey shakes both lack prebiotic fiber to feed gut microbiota, but whey shakes also have proteins that are partially digested to produce antimicrobial peptides and other factors that disrupt adult gut flora. I think that the whey shakes work temporarily, because they destabilize the gut microbiota that are providing part of the metabolic set point that helps the body to resist weight change from excess or insufficient dietary calories.

            I consider liquid milk to just have a more mild impact on gut microbiota than whey shakes. Milk products like plant products have natural antibiotics, e.g. lactoferricin or essential oils, that alter the composition of gut bacterial and fungal communities. Your gut adapts and its no big deal in most cases. It is easy to overcome lactose intolerance, for example, just by eating live yogurt.

            I don’t see the point of fiddling with whey powder instead of whole foods. Milk products are adapted for support of dairy (newborn) probiotics. They are not natural foods for adults, but if you enjoy them, then your gut will adapt.

            Thanks for your comments/questions.

            AUGUST 30, 2015 AT 12:22 PM

          • Thanks for sharing!

  6. I’ve done a lot of tweeking to my diet over the last couple years. Now I did have a routine that was close to carb cycling. I would eat high carbs in the morning and low carb lunch and dinner. I was also running in the mornings or in the afternoon which I would have a banana as a snack before my run. Then I started working during the day and could only workout in the evenings but kept my diet the same. It was terrible my run time was slower and I was getting tired half way through. So I looked how I was eating and changed my high carb meal to dinner or before I workout that day and noticed a huge difference, my run time was improving and I had a lot more energy. Now when I day high carb I’ll have oatmeal for breakfast before I workout or a sandwhich for lunch or protein and rice bowl with veggies for dinner.

  7. Just an add on about the whey protein, I tried shakes with small amounts and found they didn’t fill me up after a while. It turns out I can only handle small amounts otherwise it is terrible on my digestive system and leaves me curled up on the couch for hours. No protein Bars or shakes for me, I’d rather eat whole foods anyway….much more filling.

    • You’re not alone… My impression is that a lot of people experience digestive issues from consuming whey protein. This makes complete sense to me, as concentrated/isolated whey protein is an evolutionarily novel food item with a “strange”/abnormal nutrient composition.

      I’ve wanted to make a post on whey protein for a long time, but haven’t gotten around to it yet. Hopefully I’ll get it done soon.

  8. What you say about whey protein makes sense, Eirik. I’ve tried different brands of whey protein off and on over the years, including the isolate version. All of them have invariably upset my stomach. I chalked it up to a lactose intolerance, but the isolate supposedly contains little to no lactose, so undoubtedly there are other factors that cause problems. For me, at least, the take-home message is “Eat Real Food.” There’s nothing real about whey protein. It’s probably one of the most heavily processed food substitutes out there.

    • Couldn’t agree more, Shary. The scientific literature clearly shows that we’re best of placing our bets on “real food”. That’s not to say that supplements are never useful, but in general, I’m very cautious about recommending that people take fiber supplements, whey protein, mineral and vitamin supplements, etc.

  9. Been consistent with IF for 2yrs. 16-8 protocol, train fasted at 430am, then 50 grams of whey post workout. At 54 yrs. never been easier to maintain consistent 7-8% BF, and strength and conditioning has never been better!

  10. hello, great article!
    Ive been on a diet called fast tract for about a year. Its high protein &fat, low carb. It was designed to treat heartburn and is similar to paleo. The difference is it limits high starch and high fructose fruits &vegetables with a point scoring system called fermentation potential. It really works for heartburn but i found, like you that i needed to increase my carb intake depending on my activity level.

  11. Hi Eirik,

    How do you get the 70g-150g fiber a day? What are your thoughts on eating legumes since they’re the fiber richest foods?


    • Hi Sam!

      Welcome to the blog.

      First off, I’m not saying that 70, 100, or 150 grams (or any other number for that matter) of fiber is the “optimal” amount to take in every day. There really isn’t any magic number. All I’m saying in the article is that our hunter-gatherer forebears ate a lot more fiber than we do today, and that there are a wide range of health benefits associated with the consumption of “high-fiber diets”.

      Getting 100-150 grams of fiber every day is probably unrealistic for most people. Moreover, if there are any additional benefits of going from 70 or 100 grams of fiber to 150 grams, they are probably small.

      If you eat a Paleo-style diet rich in fiber-rich fruits and vegetables (e.g., onions, leeks, jerusalem artichoke, green bananas, root vegetables) you get a wide range of fermentable fibers into your body every day. I wouldn’t worry so much about exactly how many grams you consume.
      I think certain types of legumes are an okay addition to your diet if you prepare them properly and tolerate them well.

      Hope this helps.


  1. […] Is Your Low-Carb Diet Ruining Your Athletic Performance? — Eirik Garnas […]

  2. […] things I’ve learned from my own training career and my years as a personal trainer is that it can be difficult to achieve peak athletic performance on a very low carbohydrate diet, particular…. I’ve read many of the papers on ketogenic diets and athletic performance, and I’m open […]

  3. […] Is Your Low-Carb Diet Ruining Your Performance? via Eirik Garnas […]

  4. […] A big part of becoming physically fit is your nutrition. How many carbohydrates should you consume and what kind? Part of our personal training programs sets up your macros (carbs/fat/protein) and helps you set up meals according to your level of fitness and goals. In this article they break down why carbohydrates are good for you and what kinds to eat. Low carb or high carb? […]

  5. […] a carbohydrate intake that is more in line with the carbohydrate intake of our primal ancestors, going very low-carb isn’t necessarily optimal, particularly for those who perform a lot of ana…. When people go Paleo, they typically replace cereal grains with non-starchy vegetables and more […]

  6. […] A carbohydrate intake of 20-40% (of total daily calories) is a good fit for most people. The exact value depends on activity levels, goals, and health situation. E,g., those who are metabolically deranged and/or insulin resistant may benefit from a very restricted intake of starch and simple carbohydrates, while those who are physically fit and perform a lot of anaerobic training often benefit from a somewhat higher carbohydrate intake. […]

  7. […] I mentioned in my recent article on low-carb diets and athletic performance, when I first got interested in evolutionary nutrition almost a decade ago, I too was led to […]

  8. […] When I first started getting interested in Paleolithic nutrition close to a decade ago, the impression I got from reading ancestral health blogs was that many, if not most, Paleo dieters believed that a very low-carb diet was the optimal human diet. [36] […]

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