Why Your Ketogenic Diet Isn’t Working Part One: Underfueling and Overtraining

April 13, 2017

Written by Megan Roberts, MSc, and Tommy Wood MD, PhD

“My training, racing, and health were all great… until I crashed.”

For athletes, it’s not uncommon for the transition to a ketogenic diet from a standard high-carbohydrate diet to look something like this:

  1. Take all the carbs out of your diet, cold-turkey - feel awful…

  2. Build the metabolic machinery to burn fat more efficiently - feel great!

  3. Suddenly, out of nowhere - crash.

Like a rollercoaster, you went from feeling terrible to feeling on top of the world, and then back to feeling terrible. The question is “why the crash??”

You think: maybe I just need to do a few more fasted training sessions each week. Or, maybe I need to drop my carbs from 30 grams per day to 20 grams per day (broccoli just has too many carbs)...

Nope. You might just need to train less and eat more.

Still here? Good.

This is part one of a series of articles examining potential reasons why a ketogenic diet may fail to produce the expected benefits. Regardless of whether things are just now starting to go downhill, or you never saw results in the first place, the most important step is recognizing that something isn’t right. Getting into nutritional ketosis is one thing, but just because you’re registering 2.0mmol/L on the blood ketone meter doesn’t mean the diet is working for you. Ultimately, performance and health are the goals, and they may or may not coincide with high blood ketones. There are many aspects of life as an endurance athlete that must be accounted for in the equation of optimal health and performance. The most important one that we regularly see is people struggling on a ketogenic diet because they’re underfueling and overtraining. So that’s where we’ll begin!

Ultimately, performance and health are the goals, and they may or may not coincide with high blood ketones.

Why underfueling and overtraining may occur in the IRONMAN athlete

Lack of awareness

Often times, the culprit in the under-fueled athlete is simply a lack of awareness of energy needs relative to training volume. The increased satiety associated with a ketogenic diet can be both an advantage and a disadvantage, depending on the context [1]. For weight loss, decreased hunger can be beneficial, but by adding reduced hunger cues on top of hours and hours of training each week, you may inadvertently find yourself in a state of low energy availability (due to under-eating). There is a critical difference between energy availability and energy balance, which is especially important for the endurance athlete [2]. Exercise physiologists define energy availability as:

Energy Availability = Dietary Energy Intake - Exercise Energy Expenditure

Whereas energy balance (usually used in the realm of dietetics) is defined as:

Energy Balance = Dietary Energy Intake - Total Energy Expenditure.

(Total energy expenditure includes energy expenditure during both exercise and rest.)

Knowing your energy expenditure or balance tells you nothing about how much energy is left over to fuel the body’s day-to-day physiological processes (resting energy expenditure). As an athlete, expending large amounts of energy during training and failing to increase energy intake can unintentionally cause low energy availability, which will activate your stress responses, and negatively impact metabolism and sex hormones.

This phenomenon is not uncommon - even the International Olympic Committee has officially coined the term “Relative Energy Deficiency in Sport” (RED-S) [3]. To clarify, we’re not saying you should never ever be in a caloric deficit. In specific situations, such as trying to increase your power:weight ratio, periods of acute calorie restriction may be in order. Instead, this conversation is directed at the endurance athletes who are trying and failing to improve body composition, health, and performance due to a state of chronically low energy availability.


With some introspection, you might find that the reason you’re undereating and/or overtraining is psychologically-motivated. Some athletes may fear getting fat if they don’t train a certain number of hours each week. For others, the pursuit of optimizing one’s diet may turn into orthorexia - an unhealthy obsession with being healthy and eating “healthy” food. Moralizing particular foods or macronutrients can not only create unnecessary dietary restrictions, but dietary restraint is also associated with increased cortisol [4]. This increase in cortisol suggests that the body is registering cognitive dietary restraint as a stressor - on top of the physiological stress from low energy availability and a large training load.

Years ago, we were all fat-phobic. Now, with the increasing popularity of low carbohydrate and ketogenic diets, the tables have turned and everyone seems to be afraid of carbs. But we must keep in mind that no macronutrient is inherently bad. Consider the context of your situation. Who are you and what are your goals (in sport and beyond)? What’s holding you back from eating carbs, calories, or specific foods? For instance, as we mentioned in the first article, being a keto-adapted athlete does not mean completely removing carbohydrates from the diet.

Many athletes who experience symptoms of overtraining are so burned out that the only time they feel good is while training

On the training front, many athletes who experience symptoms of overtraining are so burned out that the only time they feel good is while training. Some are chasing the exercise high because nothing else can provide it, while others are using exercise to avoid a bigger problem in life. Realize that using exercise as a mental crutch can only proved a short-lived benefit. The longer the underlying issue is covered up with training, the more severe the later consequences tend to be.

Training stress

Many athletes use the notion of overreaching followed by supercompensation to improve performance (i.e. they intentionally push themselves past the point of fatigue in hopes of recovering and bouncing back stronger and faster than before). However, most exercise physiologists agree that the line between overreaching and overtraining (or underperforming) is blurry at best [5, 6]. Many people often argue that under-recovering rather than overtraining is the real problem. Call it what you’d like, but training too hard or too often relative to the amount of recovery you are able to achieve is an all-too-common issue in the world of triathlon and endurance sports in general. It becomes complicated because each athlete has his or her own tolerance for the amount of training “stress” that can be handled healthfully, depending on the athlete’s physical fitness and the level of other stressors in daily life.

Problematic training stress includes, but is certainly not limited to:

  • Too few rest days
  • Too much volume (volume = frequency x intensity)
  • Too many fasted morning workouts, especially those that occur at the expense of sleep, which is essential for recovery and adaptation.

If one of the above resonates with you, remember that awareness of the problem is the first critical step in making positive change. But do you do next? Let’s talk action steps.

How to dig yourself out of the overtraining and underfueling trap

Nutrition strategies

Eat more calories (and/or nutrients)

This may be stating the obvious, but the easiest way to deal with underfueling is to eat more. As an athlete who wants to optimize health and performance, you should think about energy availability, rather than energy balance, as discussed above. While you might not be consciously restricting calories, appetite is often not a reliable indicator of energy needs in athletes. In fact, prolonged endurance exercise has a significant effect on decreasing food intake and consequently, energy availability [7]. It has been suggested that changes in hunger and satiety hormones may explain this decrease in food intake after exercise [8]. Therefore, relying solely on intuitive eating as an athlete expending large amounts of energy during training may put you into an unintentional calorie deficit.

Nutrient density vs caloric density

Bulletproof coffee is great for some people, but as far as nutrient density goes, it just doesn’t come close to an omelette with veggies, and an avocado and a cup of bone broth on the side. It’s important to make sure your Bulletproof intermittent fasting doesn’t come at the expense of eating enough nutrient-dense food.

Most health-conscious athletes are aware that nutrient density is important for achieving optimal health. Foods such as organ meats, shellfish, eggs, vegetables, and berries are amongst the most nutrient-dense options, and we encourage people to eat more of these on a daily basis. But just as you don’t want nutrient density to suffer at the expense of calorie density, the opposite is also true: you don’t want calorie density to fall because you’re focusing too much on nutrient density.

Eat some carbs

The ketogenic diet is not a zero carb diet, and strategic timing of carbohydrates can work in the fat-adapted athlete’s favor. Consuming the majority of your carbs in the post-workout window will allow you to take advantage of enhanced insulin sensitivity and insulin-independent glucose uptake into muscles. If your workout happens to be in the evening, even better - having a source of healthy carbohydrate with dinner can positively affect neurotransmitter production and improve sleep quality [9]. And no, we’re not talking about spaghetti squash. Examples of dense sources of carbohydrate include white potatoes, sweet potatoes, plantains, rice, and fruit.

If you struggle with lack of appetite, adding in some carbohydrates can actually help stimulate the desire to eat more food. This will ultimately support performance, recovery, and health. Also, keep in mind that the diet that’s right for you today might not (and likely won’t) be the diet that’s right for you in five years time.

Note that if carbohydrates have been absent from your diet for a long time, reintroduce them slowly to minimize any negative gut symptoms and blood sugar issues.


Increasing your carb intake doesn’t mean you get to skimp on the fat. Healthy, unprocessed fat sources are important for calories in the context of underfueling. Think of foods with a good amount of naturally-occurring fat such as meat, fish, eggs, nuts, and avocados. While carbohydrates can help stimulate appetite, the amount of calories and fiber coming from whole food sources of carbs such as starchy vegetables isn’t enough to meet your energy needs. Macronutrient ratios at the extremes appear to decrease food intake, as very high carbohydrate diets can (similar to the ketogenic diet) decrease energy availability and consequently, endurance performance [10]. So, for the athlete struggling to eat enough calories to support training and performance, both carbs and fat are important parts of the equation.

Reconsider intermittent fasting

Intermittent fasting can be a valuable tool for helping an athlete switch their metabolic fuel preference from carbohydrates to fat. Fasting can also be beneficial for a variety of chronic health conditions [11]. However, skipping meals or eating in a condensed window isn’t right for everyone. If you are able to eat enough calories while implementing some kind of fasting into your daily life and you feel great, then that’s fantastic! But if you find that eating a sufficient amount of calories is near impossible while also trying to eat in an eight to ten hour window, then reconsider your priorities and expand your eating window. Also, realize that women may be particularly susceptible to the negative effects of fasting on hormonal balance [12].


Nutrition can, and should, be periodized in sync with training. For example, on training days with large amounts of volume or intensity, it will be easier to slip into a state of low (or even negative) energy availability. On such days, make sure to mindfully refuel with sufficient calories and carbs. Rest days or low-volume days, on the other hand, won’t require as much energy or carbohydrate intake.

Training strategies

While tools such as heart rate variability can be useful in the beginning, the goal is to become in tune with your physiology so that you don’t need a device to tell you whether or not you’re recovered.

Rest days

If you’re thinking, “what is a rest day?” then chances are you need one! And in the future, you probably need to schedule them into your week. It has been suggested that the central nervous system does not always recover at the same rate as your muscles  [13]. Thus, relying on how your muscles are feeling might not be an accurate measurement of true recovery - you may still have some fatigue even if your muscles aren’t sore. While tools such as heart rate variability can be useful in the beginning, the goal is to become in tune with your physiology so that you don’t need a device to tell you whether or not you’re recovered. Just like intuitive eating, intuitive training might be difficult for some athletes. If you find this to be the case, schedule rest days in and make sure you stick to them. Put them on the calendar if needed, because that’s how important they are. Rest days don’t have to be boring - they can include active recovery such as hikes with friends and family. Or maybe even better - schedule in a full rest day and swap one of your runs for hiking with the family!

Separate endurance and strength training

While it’s important to compliment your endurance training with some strength training, there can be an interference effect. Fortunately there are some basic strategies to optimize adaptations on both ends. Try to separate endurance and strength sessions by hours or (even better) days. If you’re training twice in the same day, make your fasted morning session focused on endurance and your evening session focused on strength [14].

Cultivate mindfulness

Objective measures of training stress such as heart rate variability, resting heart rate, and blood biomarkers definitely have their place. However, as mentioned above, the ultimate goal is to cultivate mindfulness around your training and recovery. For example, if you wake up feeling crushed from yesterday’s interval workout on the track, then go for an easy recovery ride instead of pushing through some difficult hill climbs. If you were up late and slept poorly, then allow yourself to sleep in, eat a nourishing breakfast, and go for a quick walk rather than sticking to your obligatory 6am swim. Subjective measures such as mood and perceived stress can be just as, if not more, important in determining when to rest and when to go hard [15]. This process of mindfulness in and around training and recovery may take some trial and error, but will be well-worth the effort when it comes to your athletic longevity.

Signs you might be overtraining and/or underfueling

All of the following are signs and symptoms of overall stress. Keep in mind that the body doesn’t differentiate between a hard training session, an annoying boss at work, or a lack of sleep. All of these can elicit a similar stress response. It’s your job to play detective and determine the culprit(s).

Hypothyroid symptoms

Symptoms of poor thyroid function include feeling cold, dry skin, brain fog, fatigue, constipation, thinning hair, brittle nails, and high cholesterol.

Sleep disturbances

Sleep disturbances can fall anywhere on the spectrum, from trouble falling or staying asleep, to never waking up feeling rested, to falling asleep the moment your head hits the pillow.

Dysregulated cortisol metabolism

Using the DUTCH test, most of the athletes we see have hypocortisolism (low available cortisol). Orthostatic hypotension (getting dizzy upon standing up) and changes in blood sugar control are common results of low cortisol. However, symptoms of dysregulated cortisol are not black and white, which is why testing is so important.

Poor immune function

If you’re always getting sick, it could be the result of poor immune function. The best way to test this would be a complete blood count (CBC) - which is part of our routine functional blood chemistry analysis at Nourish Balance Thrive. Chronically low immune function can lead to (gut) infections which can be a source of systemic inflammation - something everyone wants to avoid.

Subpar recovery

The athlete who isn’t recovering properly may experience constant soreness and/or lack of energy and motivation for training. Other indications of poor recovery include a higher rating of perceived exertion at a given intensity, a lower maximum heart rate during exercise, and a higher resting heart rate.

Sex hormone deficiencies

Low testosterone in men and low estrogen and progesterone in women are often seen with overtraining and undereating. Men may experience erectile dysfunction and women may develop an irregular cycle or lose their periods completely, since the body requires signals of adequate energy status to cycle regularly [16]. Low libido is also a common consequence of sex hormone deficiency in both men and women.

Additional signs and symptoms of underfueling and overtraining:

  • Poor (or ravenous) appetite
  • Mood disturbances and depression
  • Unintentional weight loss or inability to gain lean muscle mass
  • Excess body fat despite a strict diet and training plan
  • No longer looking forward to training

The typical protests

Here are two protests we hear when trying to convince an athlete they need to eat a little more and train a little less.

1) “I’ll get fat [eating carbs]!”

The conversion of carbohydrate to fat in the body (called de novo lipogenesis) is not a major pathway in humans, even when carbohydrates make up a large percentage of calories.

While low carb gurus speak ad nauseam about how carbs will make you fat, often the context is left out of the conversation. Excessive refined carbohydrate intake on top of excess calories is undoubtedly problematic for an individual with insulin resistance. However, in the context of a metabolically healthy athlete, strategically adding in some carbohydrate after hard training sessions can be a game-changer for both health and performance. It’s also not uncommon that people find an improvement in body composition after reintroducing some carbs back into their otherwise high-fat diet. Plus, the conversion of carbohydrate to fat in the body (called de novo lipogenesis) is not a major pathway in humans, even when carbohydrates make up a large percentage of calories [17,18]. Once you’ve made sure you’re eating enough total calories, treat carbs and fat like a seesaw. That is, when you’re having a higher carb meal, just drop the added fat and vice versa.

2) “I have to train x hours a week!”

There’s no prize for putting in a certain amount of training hours each week. Convincing a passionate athlete to train smarter, not harder, is difficult to say the least. Most athletes train in a metabolic gray zone (between the aerobic and anaerobic thresholds), where progress can be harder to come by. Anecdotally, when we can get our athletes to slow down and drop the training volume, they end up performing and feeling better all around. Embracing minimalist training will not only aid in recovery but will also make time for other activities in life, such as spending time with loved ones or discovering a new hobby. We’re not advocating you turn into a couch potato, but rather incorporate as much movement into your day as possible. This low-level activity should be the background of your day and will only serve to augment your training and health.

Case study

Obstacle course racer and Nourish Balance Thrive client, Ryan Baxter is a prime example of how eating too low-carb for too long can cause major problems in the context of a high training volume. Not long after Ryan began eating a ketogenic diet, he started experiencing many of the symptoms mentioned above including poor sleep, mood swings, food cravings, and low libido. While some underlying gut infections and hormonal imbalances were certainly not helping Ryan’s situation, the most important changes he made were adding carbs back into his diet and backing off on the training. Ultimately, eating 100-150 grams of carbs per day and temporarily replacing some intense training with restorative movement did wonders for Ryan’s health and performance.


  • If you’ve failed to reap the benefits of a ketogenic diet or your health and training are suffering, you may be underfueling and/or overtraining
  • Strategies to combat underfueling:
    • Bump up the calories, nutrients, and carbs
    • Reconsider intermittent fasting
  • Strategies to combat overtraining:
    • Take rest days
    • Separate endurance and strength training
    • Cultivate mindfulness
  • Symptoms of overtraining and underfueling are all indicative of general stress

Get 1-on-1 Help Customizing Your Diet and Training

If you’re experiencing the roller coaster effect of feeling great on a ketogenic diet only to crash and burn in the months following, then, a few diet and training modifications may be in order.

At Nourish Balance Thrive, we’ve helped many athletes climb out of the overtraining and underfueling hole only to become faster, stronger, and more mindful individuals in the process.

If you need more help customizing your diet and training, you can book a free “Elite Performance Program Starter Session” consultation where we’ll take a look at your history and identify possible root causes that are holding you back and share how we’d approach working on your case as part of our “Elite Performance Program.”

→  Click here to book your free Elite Performance Program Starter Session


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