Without a doubt the most common question I get asked about is the requirement to use carbs as a ketogenic athlete. It normally goes something like this:
Hey Ella, I notice you sometimes talk about running a TKD. Are carbohydrates required to build muscle? If so, how much? When? Why? Should I CKD or TKD? Which sources should I use? How often? TELL ME!
Whoa. Okay, lets slow down here, turbo.
There is a lot of questions here that are very easy to answer once we understand whats going on under the hood and the problem you're trying to solve by introducing carbs at all.
Now, I shouldn’t HAVE to make this disclaimer, but I inevitably get keyboard warriors riding in on their white horses firing half read PUB-MED summaries at me demanding I admit I am wrong.
So here it is; DISCLAIMER:
Although this is based on the currently available literature, this is still just my opinion. Feel free to come to a different conclusion based on the research yourself.
So, why do we cycle in carbohydrates on a ketogenic diet?
There are two broad categories why people want to use carbohydrates on a ketogenic diet. They are:
Physiological reasons, which include:
Increasing muscle growth
Increasing muscle glycogen stores
Increasing circulating leptin levels
Cycling carbs may cause a “whoosh” leading to losing water weight that was hiding fat loss
Cycling Carbs MAY improve your metabolism.
Psychological reasons, which include:
Carbohydrate cycling MAY improve long term dietary adherence in some populations (and be extremely detrimental in others)
Carb ups can be fun/enjoyable
Carbs can improve mood through increasing serotonin
Carbs before bed may improve sleep
Not all of these reasons are entirely accurate. In order to answer which of the above reasons are valid and which are not, we will explore the purpose and utility of each of the reasons above individually.
For today's post, I will only be addressing the physiological reasons for increasing carbohydrates.
Reason 1: Carbohydrates increase muscle growth
It is a common misconception that consuming carbohydrates causes anabolism (meaning increasing muscle protein synthesis). The belief is that because insulin drives nutrients into storage (more accurately, insulin is more like a gatekeeper than a driver, but I digress), you should combine protein and carbohydrates in your meals to maximize muscle protein synthesis.
To test this idea, this study compared the MPS between consuming 20gms of protein vs consuming 20gms of protein +60 grams of carbohydrates and found no effect on net muscle protein synthesis. This is because contrary to popular belief, insulin is not anabolic per se, rather it is anti-catabolic.
In another study, researchers compared total net nitrogen balance by administering an amino acid solution by itself (control) or with the addition of insulin. What was great about this study was that they administered the insulin directly, instead of relying on carbohydrates. This allowed the researchers to isolate the effects of insulin on nitrogen balance with out the confounding factor of increasing carbohydrates and calories.
Whilst total nitrogen balance was greater in the insulin group, the actual amount of muscle protein did not increase when compared to the control. This means that insulin did not result in more muscle protein being formed but DID suppress whole body protein breakdown.
So to maximise lean body mass, we should be consuming carbohydrates then? Again, slow down ace.
Whilst the study demonstrated that insulin suppressed MPB, that effect was caused independently of carbohydrates. This means that it was not the energy availability of glucose which suppressed MPB but the nutrient partitioning effects caused by insulin.
As we have discussed previously, protein is also a strong stimulator of insulin release, with the area under the curve of the insulin response linked to the digestion speed of the food. Study Here.
This then raises the question, which is more effective for promoting total muscle protein balance? Spiking insulin via glucose, or spiking insulin via protein with the added effect of also increasing total amino acid availability?
Given that to achieve the same insulin response from protein compared to carbohydrates would require substantially more calories to achieve, it is likely that consuming glucose is more effective on a per calorie basis at improving insulin mediated protein balance.
However, this would also require chronically elevated insulin levels which can result in several other metabolic health issues and is incompatible with a ketogenic diet.
Similarly, whilst the affect of increased amino acid availability to the blood stream doesnt reduce amino acid oxidation the same way consuming carbohydrates does, the amino acids burnt for energy are much more likely to have come from dietary sources than from stored body protein.
Bottom line; Carbohydrate cycling, whether it is a TKD or CKD is unlikely to meaningfully contribute to muscle protein balance provided adequate protein consumption, given its short term cyclical nature.
Conclusion: A TKD or CKD is NOT effective at promoting increased muscle protein balance on its own, though its effect on training intensity may.
Reason 2: Carbohydrates Increase Muscle glycogen stores.
There is really no debate that chronically depleted muscle glycogen results in reduced athletic performance, which limits progressive overload during training. The question then is do you need to consume carbohydrates to ensure adequate muscle glycogen and if so, should you do a Cyclic Ketogenic Diet (CKD) or a Timed Ketogenic Diet (TKD)?
As you are likely already aware, your liver is completely capable of producing all required glucose for homeostasis via gluconeogenesis. This is a demand-driven, but also enzymatically rate-limited process which increases to meet demand.
This provides all required fuel to feed cells which exclusively require glucose, such as red blood cells and certain brain tissues. Your liver can also convert any remaining glucose to glycogen which is then stored in muscle cells in preparation for your next training session. This means that provided your training volume and frequency are kept within your maximum recoverable volume (MRV) (which for the majority of trainee’s it should) you do not need to consume carbohydrates to support intense exercise.
It is also worth noting that there are many many factors which affect your MRV, not all of them dietary related. With regards to whether carbohydrates are required, we are defining your MRV as the maximum amount of volume you can complete in a training session, and still be able to perform at your maximum by your next training session.
The issue arises when the glycogen demands of your training, exceed your bodies ability to produce enough glycogen prior to the next training session. This will generally only occur when training volume and frequency exceeds your MRV.
Whilst the MRV for everyone differs based on training age, hormonal profile, sleep, cardio conducted, protein intake and total caloric intake, for the majority of trainees eating close to maintenance, the MRV will be around 22 sets to failure per body part per week, trained twice per week. Anything greater than this is likely to result in an inability to adequately recover prior to your next training session, and so you will need to consume carbohydrates to support your training requirements.
Let’s say that you are training beyond your MRV, should you conduct a CKD or a TKD?
The major performance benefit of a CKD is that you are able to “super compensate” muscle glycogen by carbohydrate overfeeding, which you then utilize throughout the week during training. The problem with this is two-fold.
Despite what you think, your very likely NOT training with enough intensity during the depletion to adequately deplete muscle glycogen to cause a super compensation.
Despite what you think, your very likely NOT training with enough intensity to gain the marginal performance benefits of super compensating glycogen storage throughout the week.
This means that in the average trainee, a CKD is unlikely to produce any significant performance benefit over a TKD. Does that mean a TKD is superior to a CKD? No, only that a TKD achieves the same performance benefits of a CKD at substantially lower calories, which brings us neatly to our next reason for consuming carbohydrates.
Reason, the Third: Carbs, and particularly over consuming carbs, Increase circulating Leptin levels.
As a quick primer, Leptin is a long term regulator of food intake. It is released by fat cells constantly, and its purpose is to signal to your brain what your current amount of body fat is. When you are at a higher BF%, there is a greater amount of circulating Leptin which your brain interprets to assess its current body fat percentage.
When Leptin levels change, your brain interprets the rate of that change as an indicator of the rate of fat loss and then increases downstream hormones such as Ghrelin, Thyroid T3/T4 and many others in an attempt to maintain homeostasis, by increasing appetite and decreasing expenditure.
There is a large body of evidence that Leptin can be increased through short periods of overfeeding, even when fat stores have not changed. This effect is greatest when the overfeeding is conducted with carbs, moderate to low effect with fat and almost no effect from protein. Study Here.
There is also strong evidence that very high doses of exogenous (i.e. Injected) Leptin can reverse the metabolic adaptions to dieting, at least in the short term.
The obvious conclusion then is that short periods of calorie and carbohydrate overfeeding, or a “refeed”, will increase circulating Leptin and thus both increase your metabolism and reduces your hunger.
Unfortunately, the Leptin increase from carbohydrate refeeding is much smaller compared to that of injecting Leptin. In the previously linked study, circulating leptin after the injection increased by 8 nano-grams/ml whereas after carbohydrate refeeding there was only a 0.6 nano-grams/ml, or about 7.5% of the increase seen using exogenous Leptin.
In another study, they found that overfeeding did not restore Leptin levels to baseline. The authors stated “We find that the altered Leptin levels resulting from overfeeding and underfeeding were not restored to baseline when the participants were returned to a eucaloric diet.” and “Leptin levels returned to baseline only after the participants crossed over to the complementary dietary treatment and repaid the deficit or surplus in cumulative energy balance.
This means that the only way to return Leptin levels to baseline is to regain the lost body fat.
In another study, they found that extended periods of maintenance (in this case 17 weeks!) did not return leptin levels to baseline provided that body fat was not regained.
Further, the brain’s response to changes in Leptin is highly asymmetric. Whilst decreasing Leptin results in a sharp increase in Ghrelin and perceived hunger, increasing Leptin does not seem to reverse those effects to any significant degree. In one study, overfeeding carbs by 670 calories above maintenance only boosted energy expenditure by 139 calories per day, which was entirely explained by the increase in TEF and NEAT of the participants. This resulted in a net surplus of 531 calories above baseline, and so was not beneficial to the dieter at all!
Similarly, short term increases in Leptin have not been shown to have a statistically significant reduction on appetite, with any decrease in appetite experienced largely explained by the increase in energy substrate availability. Study Here.
Given the weight of evidence, it is highly likely short refeeds, regardless of macronutrient profile, has only minor effects on leptin endogenously, and are unlikely to result in any statistically significant decrease in appetite or other counter-regulatory effects to calorie restriction.
Reason 4: Cycling Carbs may result in a “whoosh” effect
There is evidence, largely based on the work of Ansel Keys from the Minnesota starvation experiment that prolonged dieting raises cortisol, causing edema, and refeeding then reduces cortisol causing a whoosh as water is expelled.
Unfortunately, over the years, this has simply become an “accepted truth” that dieting causes cortisol increases and thus water retention, which may not actually be the case.
In this study comparing female physique competitors during a contest prep (if there is any demographic who is going to suffer from high cortisol, that’s it). They found there were no significant changes in cortisol before, during or after contest prep nor compared to the control group.
In a meta-analysis of 15 studies comparing the cortisol response to dieting, they found no change to cortisol compared to baseline in either Low calorie or Very Low calorie (less than 800 calories/day) dieting, however there was a significant increase in cortisol whilst fasting.
These demonstrate that there is no significant increase of cortisol with dieting, nor does overfeeding or returning to maintenance intakes result in a decrease in cortisol.
It is likely any visual effect observed by carbohydrate refeeding is likely caused by the uptake of fluid with glucose into muscle cells and the subsequent expulsion of that fluid as glycogen is burnt.
So after all that Evidence, what are the key lessons learnt?
Carbohydrates DO NOT increase muscle protein synthesis, though they are muscle protein sparing by reducing GNG requirements from protein.
High insulin levels suppress muscle protein breakdown, but only whilst insulin remains elevated.
High protein intakes are likely sufficient to adequately suppress MPB through insulin and provide enough amino acids to offset any whole body protein breakdown through diet rather than lean body mass.
f your goal is ABSOLUTE maximum lean body mass, a ketogenic diet is suboptimal.
You only need to integrate carbs into your diet if your total training volume or frequency exceeds your ability to adequately recover before the next training session.
Most people will be better served by conducting a TKD to replenish muscle glycogen than a CKD.
A CKD was not effective at producing a statistically significant increasing leptin.
The effect of leptin following a CKD did not effectively increase energy expenditure nor did it result in decreased appetite.
A CKD was not effective at reducing cortisol.
Visual changes resulting from a carb refeed are likely the result of muscle glycogen changes, not changes in cortisol, and are unlikely to aid in long term body composition changes.