Low-Carbohydrate Diet for Workouts and Fat Loss

One of the doubts many people have about low-carbohydrate diets is how they affect athletic performance. Sure, you want to lose fat, but what if they make your athletic performance suffer? If you can’t maintain a weight lifting routine at the same level, for example, perhaps you’ll lose some muscle. Fortunately, there’s ample evidence that you can use a low-carbohydrate diet for workouts and fat loss.

Glycogen and performance

Glycogen is carbohydrate stored in the liver and muscles that’s used for energy, and broken down into glucose when necessary. The amount of glycogen stored is around 2,000 calories worth, although in some cases it could be double that, “during massive carbohydrate overfeeding“.

Glycogen is preferentially burned during high-intensity exercise, a fact which has led many to say that you “need” carbs in your diet to fuel athletic performance. However, glycogen and glucose are made in process called glycogenesis and gluconeogenesis, respectively. In gluconeogenesis, lactate, amino acids, or glycerol (from fat) are used to make glucose, and subsequently glycogen.

Personally, I’ve never noticed any difference in my weight lifting performance whether I’ve been eating carbs or not. Science bears out the fact that you don’t need them to perform well.

And even if glycogen is necessary — which it is — you don’t need carbohydrates to get it.

You don’t need a “full tank” of glycogen either; if you burn 500 calories in a one-hour workout, that’s still far less than total glycogen stores.

When someone omits carbohydrates for any length of time, they become fat-adapted, and burn more fat as a fraction of total energy.

Fat-burning ultra-endurance runners

Dogma in distance running has long held that carbohydrates are necessary. Is this true?

No, you don’t need carbohydrates for distance running, a fact many runners have discovered.

When elite ultra-marathon runners who had been eating a low-carbohydrate diet for an average 20 months were compared to those on a high-carb diet, the low-carb runners burned more than double the fat at peak, and on average it was 59% higher. There were no differences in total glycogen or its depletion between the two groups.

Compared to highly trained ultra-endurance athletes consuming an HC [high carbohydrate] diet, long-term keto-adaptation results in extraordinarily high rates of fat oxidation, whereas muscle glycogen utilization and repletion patterns during and after a 3 hour run are similar.

Fat-burning in high-intensity interval exercise

Increased rates of fat-burning may account for the better performance of well-trained athletes, as compared to recreational athletes.

When a group of well-trained runners and a group of recreationally trained runners were put through the paces of a high-intensity interval workout, the well-trained runners burned more than three times the fat. The researchers who conducted the study wrote, “The greater capacity to perform high-intensity intermittent work is mostly explained by the higher fat oxidation rates in well-trained runners.”

These athletes were not on low-carbohydrate diets, but the better training of the well-trained athletes appears to derive from a better ability to burn fat.

Low-carbohydrate diets effects on strength and power

Low-carbohydrate diets do not appear to diminish strength and power among athletes, such as weightlifters, who depend on them.

A group of elite gymnasts were put on a very low carbohydrate ketogenic diet (VLCKD) for 30 days, and then put through their paces.

There were no differences in strength in all tests between the low-carb ketogenic diet and the Western (high-carb) diet.

However, they lost an average 2 kg of fat.

What about lifting weights?

A group of trained weight lifters, men and women with >2 years of training experience, average age mid-20s, were put on a low-carbohydrate diet for 7 days. The diet was 5% carbohydrate. They were then tested in

  • handgrip
  • vertical jump
  • bench press max (1RM)
  • squat
  • 30-second all-out cycling

Strength and power outputs were all maintained after 7 days of low-carb eating.


Low-carbohydrate, high-fat diets have been shown to be superior for fat loss and metabolic risk compared to high-carbohydrate, low-fat diets.

My own low-carb, high-fat, paleo diet keeps me lean and gives me great lipid numbers.

So in addition to fat loss and better metabolic markers, you don’t need to worry about workout performance on a low-carb diet.

PS: For why and how to get in great shape, read my book, Muscle Up.

PPS: You can support this site by purchasing through my Supplements Buying Guide for Men. No extra cost to you.


Leave a Comment:

Low-Carbohydrate Diet for Workouts and Fat Loss says December 14, 2016

[…] Original Article: Low-Carbohydrate Diet for Workouts and Fat Loss […]

AJ says December 14, 2016

Hi PD,

Thanks again for the concise summaries of the studies.

Before I say anything else, I will admit that I am a believer in keeping a low carb, low insulin approach to enhancing longevity and quality of life.

However, I must point out that a distinction has to be made between paleo, low carb and keto. While i know that you are aware of the subtle differences, this may not be obvious to the casual reader.

You can be paleo without being low carb. Just eat enough carrots or tubers and you are easily over 100 g of carbs daily. This is not necessarily a bad thing (natural, paleo diet), especially if you are insulin sensitive, but certainly not super low carb.

Then comes distinction between low carb and keto. Low carb is a very grey area and can be anything from 0-150 grams of carbs a day, depending whose book you read, compared to standard american diet of 300 g carbs a day. Again, multiple advantages, but not ketogenic. Keto as you have stated implies roughly 5% of macros coming from carbs, usually less than 50 g a day, but often needing to be less than 20 g a day for a lot of folks before hitting ketosis.

So not everyone who is low carb or paleo is necessarily in ketosis. Do you actually need to be in ketosis to lose weight and maintain healthy biomarkers or not? Or is low (ish) carb adequate to do both of the above.

I think that debate is still out there

    P. D. Mangan says December 14, 2016

    I wouldn’t disagree with anything you said. Low-carb has benefits even without ketosis. If someone cut carbs from 300 to 150, I think they’d see real benefits.

Diogo says December 15, 2016

Hi P.D,

In the leangains method is adviced to cosume a high carb meal post workout.

I think Martin Berkhan states the carbs post workout help replenish the glycogen stores, helps build muscle and helps diet adherence.

I believe it’s benefecial to consume carbs only after a intense workout. What do you think about it? Of course the carbs sources should be from unprocessed foods.

    P. D. Mangan says December 15, 2016

    Carbohydrates are fine if you’re in shape and don’t need to lose weight. They do replenish glycogen, but, as we see in the study above on ultramarathon runners, there was no difference in glycogen between the 2 groups. Thing about glycogen is that you don’t need a full tank. If you have stores of ~2,000 calories, and you burn 500 during lifting, there doesn’t seem to be a huge need to eat carbs to replenish. That being said, if you want to eat carbs after lifting and it works for you, then that’s fine.

Roland says December 15, 2016

Hey P.D.
Curious about what’s your take on the theory of low carb equals low testosterone?

    AJ says December 16, 2016

    where is this from? I wasn’t aware there was a correlation.

    although I will admit that there is correlation between folks going low carb and seeing a significant decline in libido and sex drive, sometimes leading to ED on paleo and keto.

    number of theories on this, but not due to low testosterone.

    above phenomenon is thought to be possibly due to link between insulin and serotonin levels in your brain. or possibly insulin and VTA region of the brain. essentially insulin affecting your ability to feel “good”

Eimantas says December 29, 2016

great article!

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