The Low Carb Athlete

There are good reasons why you should investigate becoming a low carb athlete. These reasons include long-term health as well as improved performance.


Since the 1980s, athletes have been told repeatedly that, in order to perform at our best, we need to eat a high carbohydrate diet. It’s been pushed so hard for so long that it’s simply become accepted that we need “energy” in the form of carbohydrate food in our diet.

What’s worse is that this belief has spurned a huge number of companies selling energy foods, energy gels and energy drinks. This is simply insane because people had more energy when I was a kid in the 1970s, when none of these things existed.

I was an athlete before these products were ubiquitous. On a race day in 1989, I might have taped a Powerbar to the top tube of my bike, but even that was probably unnecessary.

Improvements in performances over recent years have almost certainly not been due to to better fuelling but better equipment.

I was heavily influenced as an athlete by Tim Noakes and his massive volume, “The Lore of Running”. He was very clear that carbohydrates were essential. In 2009, Tim Noakes changed his mind and declared publicly that he had been wrong.

I’m convinced, both by my reading, my personal experience as an athlete and my observations as a coach, all over more than 30 years that there is a better way.

Reasons to Become a Low Carb Athlete

There are a lot of reasons why becoming a low carb athlete might be a good idea. I feel that most of those reasons can be broadly separated into two main categories... 

Health and Performance

Long-Term Health

If you become a low carb athlete for no other reason, this is the best reason by far.

The result of the decades long experiment that is the USDA Dietary Guidelines, adopted across almost the whole world, is an epidemic of obesity and type 2 diabetes.

What is the key feature of those guidelines? Lots of starchy carbohydrates, primarily in the form of grains, and seed oils (vegetable oils) in place of animal fats.

Those guidelines have spawned all kinds of ultra-processed foods that weren’t available in the 1970s. The key feature of all those foods - I call them obesity precursor chemicals - is refined grains, sugar and seed oils.

The best thing you can do for your health is to get these items out of your diet completely. There are few things on which I’m an absolutist, but this is one of them.

Athletes are often led to believe that they can eat what they want, just because they are athletes. Wrong!

For example: Sir Steve Redgrave was a 5-time Olympic gold medallist as a rower, Bruce Fordyce won the Comrades Marathon 9 times, Sami Inkinen was a world-class age-group triathlete and Tim Noakes (as mentioned above) was a lifelong runner. All developed pre-diabetes and diabetes.

Far more athletes than we would like to believe suffer from the very same conditions.

If you have three of the following: excess abdominal fat, high blood pressure, elevated insulin, high triglycerides, low HDL cholesterol and type 2 diabetes, you’d be diagnosed with metabolic syndrome. If you have just one or two, you’d probably benefit dramatically from becoming a low carb athlete.

Unfortunately, even being lean doesn’t remove you from risk. Although the odds are far better that you’re metabolically healthy, it’s perfectly possible to have metabolic syndrome. This has come to be known as TOFI - “Thin on the Outside Fat on the Inside”.

Improved Performance

This is what initially got me to look at being a low carb athlete.

In every Ironman race I did in which I used energy drinks and energy gels in the belief that athletes need carbs, I suffered significant digestive distress. I was simply unable to absorb the amount of carbs my coach and I had calculated I would need to do well.

Some days I managed to overcome the problems and finished well, others they simply destroyed my race.

I had the same kind of problems on almost every long run in my training, but just accepted this as normal.

Towards the end of that time, I started training fasted with just water. And even without undertaking a low carb adaptation process, I found that I could ride for 6 hours or run for 3 hours at a good speed without any food.

In 2013, I changed to a low carb diet and I haven’t looked back. I’m effortlessly lean, have immense energy and have no problems in workouts, be they long and steady or short and intense.

The athletes I work with who choose this route find the same. For some, it’s easy to transition, for others there are challenges along the way and the adaptation takes longer.

The longer the event, the more effective being a low carb athlete seems to be but that’s not to say that it’s not effective for athletes in power sports. For example, any athlete who competes in a sport with weight classes can train closer to their competition weight because low carb athletes tend to be able to remain leaner year-round: drastic weight cuts are always risky.

Another reason that you’re likely to perform better as a low carb athlete is that one of the ketone bodies produced when you metabolise fat - beta-hydroxybutyrate - is anti-inflammatory in nature. Athletes find that they recover more quickly. This is especially beneficial as we get older and recovery becomes a huge limiter for most people.

Let’s Talk About Ketosis

Low carb diets are often referred to as ketogenic diets.

Strictly speaking, this is incorrect because any diet that has less than 15% of calories from carbohydrates would be considered “low carb”. Although for the purposes of becoming a low carb athlete, we’re looking for carbohydrates below 50g per day.

Ketogenic diets often need to have the carbohydrates below 20g per day.

I’m not religious about the terminology. A diet that has 50g of carbohydrates per day and one that has 20g will both yield ketosis for most people.

What is ketosis?

Ketosis is a metabolic state in which your body is using fat for fuel and the liver produces ketones from the fat you eat or your body fat. These ketones are then used for energy in place of glucose, especially by the brain.

Glucose must be low for ketosis to occur. If you’re measuring ketones, you’re considered to be in ketosis when you have a level of 0.5mMol/L of Beta-Hydroxybutyrate in the blood.

Ketosis needs to be differentiated from keto-acidosis, a potentially fatal condition that occurs in type 1 diabetics where the whole process gets out of control. Your body has feedback mechanisms that prevent this occurring. These mechanisms don’t work properly in type 1 diabetics.

Is ketosis the goal? Or is it something else?

Ketosis is absolutely not the goal. In fact, it’s arguably not worth measuring because people tend to obsess about whether they are or are not in ketosis.

The goal for the low carb athlete is to achieve a state in which you are fat-adapted. This means you can train and race at the same intensity as the carb-fuelled athlete without ingesting any or anywhere near the same level of carbs.

For years, it has been accepted in sports science that the maximum level of fat that could be utilised by an athlete was 1g per minute. The average was in the region of 0.6g per minute. It’s mostly this number that gets used when coaches calculate how much carbohydrates you need to eat to sustain yourself during a long race.

In a very interesting piece of research called the FASTER study in which the researchers compared two very well-matched groups of athletes - one high carb, one long-term low carb - the researchers found the same for the high carb group. Remarkably, the worst performer in the low carb group was significantly above 1g per minute.

What's more, the high fat athletes were still burning mostly fat at 89% Max Heart Rate (MHR). Carb-fuelled athletes have made the switch and are burning predominantly carbs from 80% MHR if they're really well trained. It's more like 70% for most.

Let that sink in for a moment: Predominantly fat at threshold heart rate!

The goal isn't a number on a ketone analyser, it's not even an RQ of 0.7 at a higher heart rate (that's max fat burning) in a lab test.

The goal is the ability to burn predominantly fat at as high a pace as possible for as long as possible.

It's also to have the ability not to have to eat all the time, which means you'll be leaner. Because leaner is lighter, and lighter is faster if you're an endurance athlete or stronger for your weight if you're a weight class athlete.


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How Do You Become a Low Carb Athlete?

Knowing that you want to become a low carb athlete and why is all very well. The question is, "How do you do it?"

Unfortunately, your carb-fuelled lifestyle means that you have almost certainly down-regulated your body's ability to metabolise fat for energy. There are enzymes and pathways that are required if you're going to exercise using fat for fuel and these need a chance to switch back on properly.

Be patient

The process of getting your system to operate on fat takes time and seems to occur in steps.

The initial phase takes about 3 weeks for most people and during this time, a lot of athletes really struggle to do much training at all. This will probably depend on just how carb-dependent you are. Also, athletes who have been doing a lot of distance seem to have an easier time.

Then, there's the process of getting to a place where everything runs at its absolute best on fat. This can take as much as two years to achieve.

The reason so many people rabbit on about not being able to manage without carbs because they lack the patience to get to that point. Just because it's difficult to achieve, doesn't mean it's impossible.

Don't start in race season!

If you've read the paragraph above, you'll immediately realise that if you have big goals, the race season is NOT the time to make this switch.

Choose a time when you can safely limit training volume and intensity, a time when you can be patient.

Limit your carbs

If you're going to be a low carb athlete, you need to start by severely limiting carbs. That means all carbs. I know that you'll read about net carbs and "some carbs are just fibre so you can ignore those". For ease of implementation, just limit all carbs.

Your initial target is to get your daily carbs below 50g and keep them there day after day. Some people - probably those who are more metabolically damaged - find they need to eat even less.

This means that all sugar, all grains and all root veg is off the table for this period of time. In fact, most of that is off the table forever if you want to get the most from being a low carb athlete.

Recognise that you don't need dietary carbs

At this point I want to address two of the main objections that almost everyone will raise, some of them with numbers, when you tell them that you're a low carb athlete.

People will tell you that you NEED to eat carbs. 

In fact, some will tell you that you need 130g of carbs per day. They're right, your body does use about 130g of carbs per day.

But here is the truth: there is no such thing as an essential carbohydrate. There are such things as essential fats and essential amino acids (which you get from protein). "Essential" in this context means that your body cannot make them, you have to get them from your diet.

Your body is more than capable of making all the glucose you need from the glycerol backbones of metabolised fat or from dietary amino acids by a perfectly normal, natural process called gluconeogenesis. You do not need to eat them.

And then, people will tell you that you'll run low on glycogen, so you won't have energy for high intensity exercise.

This is pure nonsense. Your muscles need to have glycogen stores, it's a survival priority, and your body will use that same gluconeogenesis process to create the glucose needed to refill those stores.

Remember those FASTER study athletes? The fat-fuelled guys refilled their glycogen after the long run in their test at the same rate as the carb guys.

As a low carb athlete, you have as much glycogen available for intense work as do high carb athletes. People who have tried low carb and said they couldn't do it: (a) didn't do it long enough to adapt properly and (b) I'd go so far as to suggest that much of those perceived limits are in their heads.

Get enough protein

As mentioned above, there are such things essential amino acids, found in protein.

Adequate protein is vital for tissue repair, immune function and lots of other systems. Especially as an athlete, you must get enough protein.

Shoot for 1g of protein per pound of ideal body weight per day.

I'd strongly suggest you get this from animal sources. Why? Well, animal protein is more bioavailable than protein found in plants and comes bundled with lot of other nutrients that you absolutely need (vitamin B12 is one example of something you cannot get from plants).

Also, if you try to get enough protein from plant sources, you will struggle to stay below your 50g of carbs per day.

Don't fear fat

You have to get energy from somewhere and if you're a low carb athlete, fat is that energy fuel.

We've spent almost 50 years being told that saturated fat is bad and will give us heart disease. That is complete nonsense, driven by people with vested interests and propped up by the processed food industry; an industry that relies on processed carbs and seed oils.

Fats from animal products are probably the healthiest fats that you can eat. They're stable when heated, they don't easily go rancid and they come with nutrients that are tied up with the protein and fat in that animal product.

What's more, fat is involved in a host of essential body functions.

Eating lean meat and low-fat foods mean you will be hungry. In the early days of becoming a low carb athlete, you should avoid being hungry. If that means you eat a little more, that is absolutely OK. Over time, most people find their appetites decline.

First, make sure you get your protein, then eat enough fat to be satisfied.

Finally, DO NOT eat seed oils, marketed as vegetable oils. There is some thinking that the obesity epidemic has been driven more by the effects of seed oils than sugar. The stuff started life as industrial lubricants!

Keep your exercise intensity down initially

In the early days of becoming a low carb athlete, you need to keep your training intensity down. You're likely to find intensity difficult as your body does all it can to conserve glycogen stores in the absence of the uprated mechanisms to (a) metabolise fat for fuel at high enough rates and (b) run gluconeogenesis efficiently enough to refill glycogen stores.

The weights you lift will probably be down. This is normal and OK.

Your running, cycling or swimming speed will be down. This is normal and OK.

Being patient with a body that is trying to work out what you're doing to it will allow you to succeed. Driving yourself hard and getting sick as a result can be summed up in one word: stupid. 

Using the MAF workout as the vast majority of what you do at this stage makes an enormous amount of sense.

Build your exercise volume slowly

Similar to exercise intensity, early on, you need to not be too ambitious with your exercise volume.

One of the things that sells being a low carb athlete to many people is a desire for the ability to exercise for 4, 5 or 6 hours without needing to eat. This is something you should get time.

Initially, short workouts at low intensity give your body the best opportunity to adapt.

Get enough water and salt

When you first cut carbs, your body will dramatically drop water and, with it, sodium. This can result in something often called "keto flu". Feeling low on energy, light-headed and generally off-colour can usually be solved by liberally salting your food and drinking enough. In fact, for a while, I added salt to all my water.

It appears that, after that initial loss of water, the need for water is actually reduced. Drinking too much once you’re fat-adapted simply results in the excretion of - and subsequent need to consume more - sodium. Once more, it comes down to drinking in line with your thirst.

Relax - Stress is a glycolytic state

Finally, relax, don't stress out!

Stress is a glycolytic state. When you're stressed, you burn glucose. If you're not eating it, it's got to come from glycogen. Worse still, you're more likely to reach for the cookies when you're stressed.

In the early days, if your body is using glucose, it's not using fat. If it's not using fat, it's not getting good at using fat.

All you need to "worry" about is that you keep your carbs below 50g per day, your protein above 1g per pound of ideal body weight and your fat intake at a level that means you're not hungry.


There are definite benefits to becoming a low carb athlete, both for your long-term health and in enhanced performance. 

Getting there isn't always easy but it is worth making a concerted effort to do so.

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Will Newton

In over twenty years of coaching, I have coached everyone from absolute beginners to world champions. My interest in getting the best results for people who train for health and fitness or the love of sport, rather than as professionals, drives me to find the most effective ways to get results. My mission is simple: Be in better shape at 70 than most people are at 20, and to help you do the same.

  • Hi Will. As a newcomer to your site and a successful fat-adapted runner for the last 5 1/2 years, I found that almost every aspect of this article chimed with my own experiences and philosophy. This lifestyle helped me qualify for the England Masters 65+ marathon team last year, although sadly a heel injury prevented me from competing. In late 2014 I cut out the carbs to see what impact it would make on my performance, and the difference was dramatic: a 20+ minute improvement in marathon to 3:20, 20 lb reduction in weight, 2 in off waist, better energy, sleep and mood, etc, etc. Last year I was ranked UK #2 at 20 miles for my age. I run my training and races fasted, although I have experimented with some strategic carbs for racing as suggested by Grant Schofield, Zach Bitter et al. Not sure how much difference that makes!
    I’m also in complete agreement about omega-6 seed oils. I’m sure they are inflammatory: I worked many days bare-chested on my patio the scorching summer before last and needed no sun protection. I’d have been badly burned if I’d done that before. Butter and coconut for me. Salt too. Redmond is my favourite with its lovely sweet flavour. I have a steak marinading with it at the moment. Lots of animal protein to ward off the sarcopenia!
    Running-wise I’m a Lydiard disciple, though at the moment I’m using MAF heartrate limits for my aerobic base training before starting faster anaerobic sessions.
    Many thanks for the article, which I will find very useful in explaining to others the many benefits of our shared approach.

    • Hi Tim,

      You’re a fantastic example of just what is possible as a low carb athlete. Much of what you report is common among athletes who have been willing to take the plunge and go low carb.

      There is little question that a little CHO during a tough event will help, but it’s just that: a little. No the constant stuffing of oneself with gels and sugary drinks throughout the event. We don’t know why it works but I suspect it’s a central governor effect (i.e nervous system) because the effect is the same if you simply swill sugar water around your mouth and spit it out.

      Keep up the good work!

      P.S. If it helps with your education mission, the post will soon be available in both audio and PDF.

      • Absolutely, Will. All I’ve ever done in-race is trickle a fruit gum held in the mouth in the second half of a race. I think you could be right about the central governor. #Noakes!

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