I follow a CKD and been for decades, I combine it with IF and I carb up evert 7-14 days, not because I "need' to but because it is fun and a reward if I go strict and never stray from my macros.
Carbing up is frowned upon in many keto groups because most people cannot handle the carbs and end up binging but that does not mean it is not a great protocol.
The general consensus on the benefits of a carb up (those of us who follow a Cyclical Ketogenic Diet CKD) if one is following a ketogenic diet (it is NOT a cheat day) fall under the following categories.
1)Physiological
2)Psychological
3)Pyschoneuroendocrinological
4)Affective
It resets hunger hormones Leptin and Grehlin levels which are crucial for continuous fat-loss, stabilize to normal T4-T3 conversion, (which slows on keto) which make the thyroid work at the normal. Increase anabolism (muscle glycogen) to increase muscle mass.
Carbohydrates boost leptin levels far more than protein fat. In fact, fat has almost zero effect on leptin levels.
Leptin is highly responsive to glucose metabolism so when doing a refeed, you will benefit much more if the majority of your additional calories are coming from good sources of carbohydrates that will turn into glucose (potatoes, pasta, rice, bread, oats and grains). When done this way, leptin levels will show a significant rise over if you had eaten a surplus of calories coming from more protein, fat, or fructose.
You may hear others say that an increase in calories will have the same effect, while that is technically a true statement they're not telling you the whole story. As long as the increasing calories comes from CARBS then yes it will work but it all comes down to the carbs. Another example of a play on words..here's another misleading statement, "you can be in ketosis on a 100% carbohydrate based diet"....this is a true statement..BUT.( If and only) if you're restricting your carbs to say around 20 grams or so, that's 80 calories total and you're not having any protein or fat so yes that statement is "true".
Carbs are also not converted as easily to fat as dietary fat, which means you can overfeed on carbs for short periods of time and gain slightly less body fat. However, this is assuming you keep your fat intake low. If you eat a bunch of carbs and fat while refeeding, the extra fat is generally going to be stored. This is because your body is primarily burning carbohydrate while refeeding and thus doesn’t need to burn the fat you’re consuming, so it will/can store it as body fat instead.
https://www.ncbi.nlm.nih.gov/pubmed/11126336
- Carb overfeeding increased plasma leptin concentrations by 28%, and 24 hour Energy Expenditure by 7%. Basal metabolic rate and the energy expended during physical activity were not affected. FAT overfeeding did NOT significantly change plasma leptin concentrations or energy expenditure. There was NO relationship between changes in leptin concentrations and changes in energy expenditure, suggesting that leptin is not involved in the stimulation of energy metabolism during overfeeding.
CONCLUSIONS:
CARB overfeeding, but NOT fat overfeeding, increases energy expenditure and leptin concentration.
https://www.ncbi.nlm.nih.gov/pubmed/10334310
- High-fat, low-carbohydrate (HF/LC) meals, which induce smaller insulin and glucose responses, would produce lower leptin concentrations than low-fat, high-carbohydrate (LF/HC) meals.
During LF/HC feeding, there were larger increases of leptin 4-6 h after breakfast (38 +/- 7%, P < 0.001) and lunch (78 +/- 14%, P < 0.001) than after HF/LC meals (both P < 0.02).
During LF/HC feeding, leptin increased from a morning baseline of 10.7 +/- 1.6 ng/ml to a nocturnal peak of 21.3 +/- 1.3 ng/ml (change, 10.6 +/- 1.3 ng/ml; percent change, 123 +/- 16%; P < 0.0001). The amplitudes of the nocturnal rise of leptin and the 24-h leptin AUC were 21 +/- 8% (P < 0.005) and 38 +/- 12% (P < 0.0025) larger, respectively, on the LF/HC day. In summary, consumption of HF/LC meals results in lowered 24-h circulating leptin concentrations. This result may be a consequence of decreased adipocyte glucose metabolism. Decreases of 24-h circulating leptin could contribute to the weight gain during consumption of high-fat diets.
Another reason some people do CARB refeeds:
Some of us use it as more of a reward system for adhering to the diet strictly the prior week or two. For instance if I wasn't strict leading up to the carb up and did not drop body fat then I did not earn my carbs and I don't get to have a carb day. It forces that need to be super strict in order to be able to give myself that carb day. So in fact it's a lot harder in my opinion to do a cyclical ketogenic diet then it is a standard ketogenic diet especially trying to control yourself on the carb day which can go crazy and out of control once your insulin levels get out of whack and you want to eat everything in sight.
And the main reason I do a carb up..is..well fruity pebbles!
For those who do not want to carb up that is fine but I recommend cycling calories here and there or have one big huge keto meal here and there, lots of fat/sodium.