What is cyclical ketogenic diet (CKD)?
Cyclical keto (CKD) is a modified ketogenic protocol that adds planned high-carbohydrate days (called carb-ups or carb refeeds) to a standard ketogenic diet. The structure is typically 5–6 strict keto days followed by 1–2 high-carb days timed around the most demanding training sessions of the week. The purpose is to replenish muscle glycogen stores that become depleted during high-intensity training on a ketogenic diet.
The CKD approach was formalized by Dr. Lyle McDonald in "The Ketogenic Diet" (1998) and has been used by bodybuilders and strength athletes who found that pure ketosis limited their training intensity and muscle-building capacity. CKD is not a shortcut to eat carbs periodically — it is a structured protocol designed specifically for athletes with high glycogen demand.
CKD keto days vs carb-up days
Keto days (70/25/5)
Standard keto days maintain the classic ketogenic macro split: 70% fat, 25% protein, 5% carbohydrates (approximately 20–30g net carbs for most people). During keto days, you are in nutritional ketosis, burning fat and ketones as primary fuel. The goal is to maximize fat oxidation and deplete any glycogen loaded during the previous carb-up.
Carb-up days (50/30/20)
Carb-up days invert the macro split: 50% carbohydrates, 30% protein, 20% fat. The high carbohydrate intake triggers an insulin response that drives glucose into muscle cells, rapidly resynthesizing glycogen. Carb-up days are intentionally positioned 24–48 hours before the most demanding training sessions — usually the same day as or the day after your longest workout. You will exit ketosis on carb-up days; this is by design, not a failure.
Weekly structure
A common CKD structure for someone training 5 days per week: train Monday–Friday, carb-up Saturday–Sunday, return to strict keto Monday. More minimalist: 5 keto days + 2 carb-up days per week. The specific placement depends on your training schedule — carb-up days should precede your highest-intensity training days.
Who is CKD for?
CKD is designed for athletes who perform high-intensity training and need glycogen to fuel it — strength athletes, CrossFit athletes, HIIT practitioners, and endurance athletes doing interval work. The critical requirement: you must train hard enough to actually deplete the glycogen you load on carb-up days. If you do 3 sets of curls twice a week, CKD will not work as intended — the glycogen won't be depleted, ketosis re-entry will be slow, and you'll simply add calories without the intended metabolic benefit.
For general weight loss without athletic performance goals, standard keto is simpler and often more effective. CKD's advantage is specifically the preservation of training performance, muscle glycogen, and anabolic capacity in people doing high-intensity, high-volume resistance training.
Carb-up day nutrition strategy
On carb-up days, prioritize high-glycemic, easily digestible carbohydrates: white rice, white potatoes, sweet potatoes, white bread, fruits, rice cakes, and sports drinks. These are the opposite of what you typically eat on keto — and deliberately so. The goal is to trigger maximum insulin response for maximum glycogen resynthesis rate, not to eat "healthy" carbs.
Critically: keep fat very low on carb-up days. The combination of high insulin (from carbs) and dietary fat is the scenario most favorable to fat storage. Protein should be kept at 30% to support muscle protein synthesis in the training recovery window. This means avoiding butter, nuts, oils, and fatty meats on carb-up days — lean protein sources (chicken breast, white fish, egg whites) pair better with the high-carb strategy.
CKD vs targeted keto (TKD)
Both CKD and TKD are performance-focused modifications of standard keto. The key difference: TKD adds a small amount of carbohydrates (25–50g) immediately before or during workouts on every training day, without ever fully exiting ketosis. CKD has full high-carb refeed days that intentionally exit ketosis followed by a return to strict keto. TKD is better for lower-intensity training and people who want to stay consistently in ketosis; CKD is better for very high-intensity training with significant glycogen demand.