The Dangers of Calorie Cycling During Your Bulk

A theoretical analysis might suggest calorie cycling is a viable nutrition strategy during any weight loss or weight gain endeavour. After all, there is compelling research to suggest that it is not our net caloric intake over 24 hours that dictates long-term weight loss or gain, but in fact our cumulative calorie position across the week or even month. As a practical example, to lose 500 g of mixed human tissue over one week requires a cumulative energy deficit of ~3500 kcal, under the assumption that 1 g of mixed tissue liberates approximately 7 kcal of energy. This energy deficit could be achieved with an even daily distribution of 500 kcal per day (500 kcal x 7 days = 3500 kcal) or a cycling model, whereby one could undergo a 700 kcal energy deficit across 5 days (700 kcal x 5 days = 3500 kcal) followed by 2 days in energy balance (eating for weight maintenance requirements). This was supported by a recent trial by Campbell et al which demonstrated equal weight loss with a continuous deficit for 7 weeks, versus a matched weekly deficit using an intermittent cycling model, whereby 5 days of a more aggressive energy deficit was alternated with a 2 day ‘refeed’.

In a weight loss phase, as suggested above, it is pragmatic to assume that fat loss is the primary outcome of interest. In that case, a calorie cycling model is likely a feasible dietary strategy to adopt, considering there are no notable downsides or impairments to the magnitude of weight/fat lost, and may present numerous psychological benefits, namely, less irritability, improved hunger management, greater enjoyment, and the opportunity for planned social meals with friends and family. Overall, these benefits contribute to a less disturbed psychological state during energy restriction/weight loss, and likely facilitate improved adherence when the intervention is more doable and enjoyable. With this rationale considered, I am not surprised that many have extrapolated these potential benefits to the weight gain or muscle bulk phase. In contrast to using calorie cycling during a weight loss intervention, I believe there are notable downsides to cycling calories during your bulking phase that are worthy of discussion.

Setting the scene

It is generally accepted that muscle gain takes far longer to accumulate (on a per gram basis) than fat takes to be lost. This is no surprise, as research tells us that the approximate lean component of weight gain during a bulking phase is ~20-30%, whereas the proportion of fat lost in a weight loss phase is ~60-80%. To state this otherwise, gaining 1 kg of weight during a bulking phase might yield 200 – 300 g of lean weight, whereby losing 1 kg of weight during a cutting phase might yield 600 – 800 g of body fat.  So, muscle gain is quite slow, in comparison to fat loss, thus it is understandable that bulking phases should last longer than cutting phases (2 – 4 times as long in fact), if notable progress is desired. Now one might say, “well why don’t we just bulk more aggressively, and do it in less time?”. We would be ill-advised to adopt this guidance, as muscle gain on a per week basis has quite a low ceiling. Meaning, once we hit a certain threshold of energy surplus/weight gain (approximately 0.5 % of your body weight per week), the excess energy is mostly directed towards fat storage, not extra muscle gain. So, going too fast with your weight gain, actually makes muscle gain less efficient, on a muscle to fat gain basis. This is in stark contrast to fat loss, which appears to have a much higher per week ceiling. Not only does fat loss occur faster than muscle gain, but a larger energy deficit almost always contributes to a greater amount of fat loss, particularly if you are above 10% body fat for a male or above 20% body fat for a female. This is evidenced by the pronounced success people with overweight have on very low energy diets ‘VLEDs’, whereby they undergo severe energy deficits (usually ~1200 kcal intake per day, equating to a >60% energy deficit), losing a number of kilograms per week, with almost no loss from lean compartments.

Applying this information to calorie cycling

Now that we have set the scene, we will discuss how this information provides us with a rationale for or against calorie cycling during weight loss and weight gain phases. During a weight loss phase, a more severe energy deficit across 4-6 days followed by a higher calorie period for 1-3 days (calorie cycling) seems viable, considering that the evidence suggests greater amounts of fat loss will occur on those severe restriction days, which would equate to the same amount of fat loss (on a per week basis) in comparison to a less severe, but even distribution of the energy deficit across the week. The same cannot be said for muscle gain phases. Prescribing low/moderate calorie days during the week, alternated with 1-3 days of super-high energy intake to achieve your weekly energy surplus for muscle gain is a problem, as minimal muscle growth is likely to occur during your low/moderate days (particularly if you are close to maintenance calories on these days), and the super-high days are unlikely to pack massive amounts of muscle on in just 24-72 hours. As we discussed, muscle growth takes time and has a low ceiling, which means a short-term, severe energy surplus just won’t equate to that much better muscle growth than a moderate energy surplus in the same period of time, as the extra energy is destined for fat storage once the ceiling has been reached.

Let’s work through a practical example to provide some clarity. Let’s say we had an aspiring bodybuilder looking to gain muscle. He weighs 90kg, with a maintenance calorie level of 3000, and is looking to gain roughly 270 g per week on the scale, equating to 0.3% body weight gains per week. Assuming 1 g of mixed human tissue liberates 7 kcal, a weekly energy surplus of ~1890 kcal (270 g x 7 kcal) would be required to reach his target rate of gain. With an even distribution across the week, this would mean he would consume 3270 kcal per day (3000 kcal maintenance + 270 kcal surplus). Now, let’s propose that he intends to adopt a calorie cycling model, so that he can have a burger and Ben & Jerry’s on Saturday night, and a Big Breakfast from his favourite café, and a large pizza on Sunday. Our theoretical bodybuilder might choose to then consume 3000 kcal Monday to Friday, but then allocate the 1890 kcal weekly surplus over Saturday and Sunday, so that his energy intake on those days is 3945 kcal. Now remember, absolute energy intake is not the only predictor of muscle gain, there is also a TIME component. So, our bodybuilder is in one respect satisfying the requirement of eating in a weekly energy surplus BUT he is not satisfying the time requirement. In all likelihood, net muscle gain during Monday to Friday will be nil (as he is eating at maintenance requirements), with muscle growth only likely to occur during the time in an energy surplus which is Saturday and Sunday (48 hours). Our bodybuilder is only in positive energy balance for 28% of his week! How can he expect to grow the same amount of muscle as someone using an even distribution of the energy surplus, remaining in positive energy balance for every day during the week? Remember, muscle growth has a low ceiling, so even though during the weekend he has established a significant energy surplus, muscle growth will not increase linearly, in fact the majority of the excess calories of those days will go towards body fat. Now, our bodybuilder might assume that he is progressing at the desired rate if his week to week average body weights are increasing ~270 g each week, BUT that weight gain is likely to only be occurring during the weekend, with a low proportion of that gain going to lean compartments. Someone distributing the same energy surplus evenly across the week will gain the same amount of weight on the scale (remember energy balance rules weight gain, not muscle gain per se), but with a higher proportion going to lean compartments, and less towards fat.

I know the proposition of fitting in super-high calorie meals in during the weekend is enticing but be aware that cycling your calorie allocation in such a way is likely to sell yourself short of muscle gain progress. If eating your favourite meals each week is more important to you than muscle gain, then by all means play with your calorie distribution. However, if muscle gain is your primary objective, and you intend to carry it out in the most efficient fashion, then evenly distribute your energy surplus during your bulking phase.

References

Campbell, B. I. A., D.; Colenso-Semple, L.M.; Hartke, K.; Fleming, A.R.; Fox, C.D.; Longstrom, J.M.; Rogers, G.E.; Mathas, D.B.; Wong, V.; Ford, S.; Gorman, J. (2020). Intermittent Energy Restriction Attenuates the Loss of Fat Free Mass in Resistance Trained Individuals. A Randomized Controlled Trial. J. Funct. Morphol. Kinesiol., 5(19).

Dulloo, A., Jacquet, J., Miles-Chan, J. et al. Passive and active roles of fat-free mass in the control of energy intake and body composition regulation. Eur J Clin Nutr 71, 353–357 (2017).

Harper, C.,  Maher, J.,  Grunseit, A.,  Seimon, R. V., and  Sainsbury, A. ( 2018)  Experiences of using very low energy diets for weight loss by people with overweight or obesity: a review of qualitative research. Obesity Reviews,  19:  1412– 1423.