Carbohydrate cycling involves consuming different amounts of carbohydrates on different days.
There can be many ways this approach can be implemented. It can be considered an advanced strategy in some cases. In other cases, it can be implemented in a simple way.
It is often promoted to help with body composition and performance.
In this post, I will go through some of the evidence on the topic. I will also discuss how and when it could be worth implementing.
Variations of Carbohydrate Cycling
There are many variations of carb cycling.
Touching briefly on one aspect though is that it technically only involves adjusting carbohydrate intake.
This could lead to two outcomes:
- Adding more carbohydrates on a certain day could lead to more total calories.
- Adding more carbohydrates on a certain day could be accounted for by reducing calories elsewhere. Usually, this will involve a reduction in dietary fat.
Each of these approaches is valid. I just wanted to highlight that both exist and will be used in the discussions below.
Effect of Carbohydrate Cycling on Body Composition
Carb cycling is more often implemented during fat loss phases than muscle gain phases.
Sometimes it is implemented during muscle gain phases. Since the number of carbohydrates included in a calorie surplus is usually higher, it is arguably less relevant during these phases.
In a fat loss phase, there is usually less total carbohydrate comparatively.
There are a lot of theoretical reasons proposed as to how carb cycling can help fat loss.
Some of these are hormonal. Some of them are performance related. Some of them are adherence related.
When total calorie and macronutrient intake for the week is matched, there is not much clear research highlighting differences in fat loss outcomes.
There can be people who disagree with that statement. But I encourage reading further since I am going to add a lot more nuance. There are a lot of exceptions and situations where I would be looking at this from a different perspective.
I wanted to start with this part of this discussion to highlight that for most people, the decision to carb cycle is related to personal preference.
One Easy Way to Implement Carbohydrate Cycling: Training Days vs Rest Days
One approach I consistently use with my clients is to have slightly more calories and carbohydrates on training days.
This is easily achieved through adding a pre-workout meal or snack or adding intra-workout carbohydrates.
This ticks two boxes:
- It helps people feel better during their training sessions.
- It adds slightly more calories on training days than on rest days. This is adding more calories on the days they are burning more calories.
That first point is obviously a good thing. And it is more relevant to athletes in more glycogen-intensive sports.
The second point is a more debatable point. I do it since theoretically, it makes sense that it could help improve body composition. But we also do not have any compelling research to suggest that it matters.
While I often use this approach with clients, there are people who prefer simplicity who I do not do it with. Since it does not have evidence for improving muscle gain or fat loss, it is unnecessary for those who prefer not to do it.
Hard Training Days vs Easier Training Days
It can make sense to add more carbohydrates and calories on harder training days than on easier ones.
This makes a lot of sense for endurance athletes. But it also can have a place in cases such as bodybuilding too.
Let’s say you are a bodybuilder who is in a calorie deficit and has been for a while. Your performance might be dropping a bit, particularly during tougher sessions. Often the sessions that are the hardest are leg sessions, particularly long leg sessions.
If you trained legs 2x per week, you could make a case for having a “refeed day” on those days. This would involve having significantly more carbs on those days. This could help performance.
Potentially this improved performance could carry over to improved muscle growth too.
Then on the other days when training is easier, carbohydrate intake could be lower.
Glycogen Replenishment
Glucose is our body’s best fuel source for performance. Glycogen is our storage form of glucose.
If glycogen gets depleted, performance typically decreases.
While in a phase where you have a good intake of carbohydrates all the time, this likely does not matter much. Typically, you will almost always have good stores of glycogen while you are in a calorie surplus.
During a deficit, often these stores are lower. So theoretically you could cycle carbohydrates so that you have higher glycogen stores when it matters more.
This is a large part of why refeed days the day before or the day of hard sessions can make sense.
The downside of this approach is that you have less carbohydrates and glycogen available at other times of the week. It is a balancing act that is based on the individual situation.
Hormones
High-carb days have a clear impact on hormones in the short term. Particularly if they contain more calories.
Leptin increase. Ghrelin decreases.
The increase in leptin can increase energy expenditure. It is also a satiety hormone.
Ghrelin is a hormone that tells us to eat more. Leptin tells us to eat less.
A decrease in ghrelin and an increase in leptin should mean less hunger.
This sounds great. If you only looked at this, it would make carb cycling sound like it can help manage hunger and energy expenditure. This would make it easier to stay in a deficit.
Unfortunately, there are two issues:
- The effect of refeeds on hormones is too acute. It does not actually translate to lasting impacts that have a meaningful effect on longer-term progress.
- If you add additional calories in the refeed, these calories must be reduced elsewhere for things to balance out. Adding these calories could potentially slow down fat loss.
Insulin
Another hormone people are interested in is insulin.
If you focus solely on insulin and carbohydrates, this aspect could make logical sense.
Theoretically, the low carbohydrate days would keep insulin low.
Insulin decreases lipolysis (fat breakdown) and increases lipogenesis (fat storage). Keeping insulin low could help overall fat loss based on that logic.
Then the high carbohydrate days would spike insulin. But if they had the benefits previously mentioned in relation to hormones and performance, it could be a worthwhile trade-off. It would be the best of both worlds.
There are a few things undermining this thought process though:
- Insulin is not the main determinant of fat loss. Research has found plenty of cases comparing calorie and protein-matched high carbohydrate vs low carbohydrate diets. Fat loss almost always comes out similarly. This occurs despite insulin levels being higher in the higher carbohydrate groups.
- Protein also raises insulin. Overly focusing on the carbohydrate aspect can ignore that insulin would still be present even on the lower carbohydrate days.
- Insulin does not work in isolation. Other hormones play a role. And it is not like insulin is either in your system or completely out of your system. Think of it like a dimmer switch instead of an on/off switch.
While insulin plays a role, it is not the only thing that matters. If it mattered a lot, we would see consistent evidence of lower insulin levels leading to more fat loss when calories are matched over the course of a week. But that is not what we see.
Personal Preference – Weekends
The average person who does not track their calorie intake typically does not eat the same number of calories each day.
In everyday life, most people eat significantly more calories on weekends. Or on days when they have more social commitments.
The information that carbohydrate and calorie cycling does not improve body composition can also be looked at from another perspective. It also does not worsen body composition.
You could get great results having 7 days with the same calorie/carb intake each day. Or you can get similar results having slightly less during the week and more on the weekend.
For some people, adding this flexibility can make it easier to stick to the plan and get great results.
Practical Summary
Carbohydrate cycling is not necessary. But it is also not detrimental.
For most people, it does not matter much beyond personal preference.
For some people, particularly in a calorie deficit, it can be a tool that helps with training performance on certain days.
Some people prefer the simplicity of having the same number of calories and carbohydrates every day. Others could find calorie cycling to be a convenient way to stick to the plan and get great results.
