Should you refeed carbs when in keto?


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If you are ready this, perhaps you are already following a ketogenic diet, or contemplate doing so. Perhaps your goals are to ease your fat loss, fight your sugar cravings or improve your athletic performances. In either case, you may be wondering if you should ever eat carbohydrates again and may also have heard different points of view on the matter. This article is intended to answer this question, and much more…

What is a ketogenic diet?

Many believe that the definition of a ketogenic diet is a diet where one eats lots of fats. Although this may be true, this is not technically the condition to define a ketogenic diet. A ketogenic diet is in fact any diet where the individual builds up ketone bodies.

What are ketone bodies?

Ketone bodies (or molecules) are organic compounds containing a ketone group (that is an oxygen atom connected to a carbon atom by a double covalent bond. The naturally occurring ketone bodies are acetoacetate, beta-hydroxybutyrate, and their metabolite, acetone.

How are ketones produced?

Ketone bodies are produced from the breakdown of fatty acid in the mitochondria during fasting, prolonged carbohydrates restriction, and intense physical activities. Carnitine participates in the transport of long-chain acyl-CoA into the mitochondria.

Enzymatic conversion of fatty acids to ketone bodies (in mitochondria)

  • “N” carbon fatty acid -> Acetyl CoA + “N-2” carbon fatty acid
  • 2 Acetyl CoA -> 2 Acetoacetyl CoA + CoA
  • Aceto-acetyl CoA +Acetyl CoA -> Hydoxymethyl Glutaryl CoA
  • Hyrdoxymethyl Glutaryl Co A -> Acetoacetate + Acetyl Co A
  • Acetoacetate + NADH = H2 -> 3-Hydroxy Butyrate


How are they used by the body?

Ketone bodies are energy sources that can be used by the liver, brain and heart, but not muscles. Muscles, on their end, can use fatty acids and sugars, but not ketones. It is also noteworthy to mention that the brain, an energy demanding organ, can use both sugar and ketones as fuel.

Ketone bodies are used to create usable energy through conversion into acetyl CoA, which enters the Krebs cycle, and is oxidized in the mitochondria to create ATP, the energy currency of all cells.

Why does ingestion of carbs or high quantities of protein stop ketogenesis?

As we know now, Acetyl CoA resulting from the metabolism of fatty acid is essential to produce ketogenic bodies. However, such Acetyl CoA produced in mitochondria associates with oxaloacetate produced from glucose (when ingesting carbohydrates, or high amounts of protein) or citrate (when ingesting citric acid) in the Krebs cycle and transported (by the tricarboxylate anion carrier system – or Acetyl CoA shuttle) away from the mitochondria and into the cytosol where it may be used to create new fat. In other words, both carbs and citric acid remove the fuel needed by the mitochondria to produce ketone bodies.

Additionally, CPTI (Carnitine Palmitoyl Transferase I) is a key mitochondrial enzyme controlling FA oxidation and Ketogenesis. Malonyl Co A is derived from. High levels of Malonyl CoA (produced from Acetyl CoA) in the hepatocyte inhibits the activity of CPTI, and damps down ketogenesis. Because insulin stops lipolysis (source of free fatty acids used to produce ketone bodies) and increases the production of Malonyl CoA from Acetyl CoA, we understand why ketogenesis is stopped in its track when ingesting sugars.

Furthermore, because proteins also trigger release of insulin in addition to be transformed to sugar via a processed called neoglucogenesis, ingestion of high amounts of protein can also stop ketogenesis.

How much protein and carbohydrates should you eat?

The amount of carbohydrate and protein one can eat and still initiate or maintain a state of ketosis depends on various factors such as bodyweight, metabolism and the activity level.

Generally, an inactive individual should maintain his net carbs level below approximately 30g daily, while athletes may increase carbohydrate consumption around the workout.

It has long been believed that individuals needed roughly 0.8g of protein per kg (current US RDA) of lean body mass, and that this need was higher for athletes – especially weight lifters where it could be as high as 1g per pound of lean body mass.

Also, based on a 1996 study by Lemon P., Lyle McDougal, the author of “The Ketogenic Diet” has speculated that sedentary individuals on ketogenic diets should consume 0.8g per pound of lean body mass, while athletes should consume 0.9g per pound of lean body mass, and that those requirements should be increased to 150g during the 3 first weeks since the brain needs roughly 400 Calories per day, and does not have yet the ability (necessary enzyme levels) to fuel itself using the available ketone bodies during the few first weeks of a ketogenic diet.

However, more recent studies have shown that the body recycles amino acids, and that the true requirement is often around 56g daily for a 70kg individual, and that this need was only slightly higher for athletes. In fact, one study demonstrated endurance athletes (oxidizing amino acids during aerobic training) needed more protein than weight lifters, while another study demonstrated that the ingestion 20g of protein post workout was optimal for muscle protein anabolism, and that any additional protein did not lead to any significant improvement in lean body mass.

Because individuals following a ketogenic do not break down muscle protein to create sugar between meals as individuals on a standard diet do, their need for protein should typically be lower than individuals on a standard diet.

I personally have observed excellent results on myself and on hundreds of athletes using 1g per kg of lean body mass. This means 70g (far from the 180g we are used to see in the bodybuilding industry) of protein for a 70kg LBM individual.

A simple way to find if you have too much protein in your diet is to look (and smell) your urine. Yellowish, bubbly and smelly (ammonia odor) urine is a good indicator that your body had too much protein, and converted the excess in glucose, releasing ammonia, which was then converted in urea for excretion.

A little note, remember to ingest some salt when following a ketogenic diet, since sodium is not as well reabsorbed when in ketosis, and since sodium is essential for many bodily functions, including the reabsorption and recycling of amino acids, constituents of protein.

Why typical Paleo and Atkins diets are not necessarily ketogenic?

You may have heard that Paleo and Atkins were ketogenic diets. However, Paleo simply means the individual has removed grains and processed foods, while Atkins diet removed all carbs, but not necessarily processed food. However, Paleo diets are not necessarily always sufficiently low in carbohydrate to initiate and sustain ketosis. Furthermore, consumption of meat and other sources of protein are not limited, so it is easy to exit (or not even ever enter in) ketosis when following those two diets. In a nutshell, food choices of those diets are similar to ketogenic diets, but they are not true ketogenic diets. A Ketogenic diet is by definition a diet which leads to the production of ketone bodies, and to do so, one needs to ensure that both his carbohydrates and protein intake are monitored and maintained under the limits.

I personally do not advocate the use of processed food as is often the case in Atkins diet, and only recommend paleo manuals to find tasteful recipe ideas.

Why does fasting jump starts ketogenesis?

In addition to remove the breaks by reducing insulin levels, fasting jumps starts ketogenesis by triggering the release of glucagon, which activates fatty acid oxidation. Therefore, several ketogenic diet adepts will often start their regimen by a 1-3 day fast.

Factors influencing ketogenesis

  1. Availability of medium and long chain fatty acids (substrate of ketogenesis reactions)
  2. Glucagon/insulin ratios, which are affected by sugar and protein levels

Do we ever need carbs when on a ketogenic diet?

There are three reasons why you may need to occasionally refeed with carbohydrates:

  1. When glycogen is unavailable, the body wastes BCAA and ATP: When glycogen is unavailable, the body breaks ATP into ammonia (and IMP), and the body converts valuable BCAAs (especially leucine) into glutamine to carry the ammonia to the liver for conversion into urea for excretion.
  2. At training intensity higher than 75% of VO2MAX, the body cannot get all the needed energy solely from fat, since the decrease in pH caused by release of lactic acid prevents the release of free fatty acid, and the blood flow restriction prevents their circulation.
  3. When stores of glycogen are exhausted, glycolysis (needed for high intensity exercise) is impaired, even if blood sugar levels are normal.
  4. Prolonged ketogenic diet may lead to hypoglycemia (especially if fat consumption is too low, forcing the body to use its available glucose) and chronic high cortisol levels. Such high levels of cortisol prevent thyroid hormone to be converted to T3 hormone. Finally, low T3 levels reduces the metabolism of fatty acids in Acetyl CoA (fuel to produce ketones), as well as the clearance of cortisol, creating a vicious loop.
  5. Furthermore, chronic hypoglycemia has been shown to cause several health issues, including low testosterone levels, which leads to both reduced muscle mass, and increased body fat.

How much carbs to ingest when refeeding?

When on ketosis for a prolonged period, the liver and muscles get depleted of their glycogen. Since liver does not convert much of the ingested sugar before it (and the muscles) starts producing fat, it is possible to refeed without increasing bodyfat (spilling), if the amount of sugar ingested does not exceed the storage capacity of the muscles.

Based on the Textbook of Biochemistry with Clinical Correlations 4th ed. written by Ed. Thomas M. Devlin Wiley-Liss in 1997, an average individual has approximately 3g of glycogen per pound of lean body mass. Also, based on the maximum glycogen storage capacity of the liver and muscles tissues, as well as on the energy required to convert glucose into glycogen, we can estimate the upper limit of carbohydrate ingestion without producing significant body fat to be 7g per pound of LBM, spreaded in two days (4.5g on the first day, and 2.5 on the second day).

It is however important to note that, on refeed days:

  • Insulin will be released, stopping the ketosis
  • Fats consumption should be limited, since insulin is a non-specific messenger, and will signal the fat cells to store any circulating fat
  • Refeed should be initiated with ingestion of 25-50g of fructose to ensure that the liver produces glycogen, exit catabolism, and allow muscle anabolism
  • Remaining of refeed should be made with a mix of glucose and starches on day 1, and only complex carbohydrates on day 2. Fructose should be avoided, since it favors production of fat by liver

Pierre Vinet, BSc. Biochemistry, Master Studies Biomechanics

Health & Fitness Professional

About the Author

Pierre Vinet is a Master Trainer who graduated in Biochemistry at Quebec University, and continued post graduate studies in Biomechanics. His fields of expertise include biomechanics, nutrition, exercise physiology, strength training, muscular hypertrophy, fat loss and longevity. to Over the last 40 years, he has trained thousands of individuals, including Professional athletes, as well as personally won the State Championships and was finalist at the National Championships at several occasions in both Bodybuilding and Olympic Taekwondo. For more information, you may visit, or reach him at


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