Similar to IIFYM, carb-cycling is a hot topic in the fitness industry these days. From followers of IIFYM to people who follow strict meal plans, it seems that carb-cycling as a nutritional strategy has spread its way into most sub-groups of dieters. It’s a pretty simple concept as the name says it all. Carb-cycling involves changing your macro distributions around, mainly fat and carbs, for various periods of time. Technically, the definition of carb-cycling could be extended quite wide as there are many forms. For example, someone could have a few high carb days a week followed by low and moderate carbs for the rest of the week, while another person could have high carbs for a full week followed by a week of low carbs. These are both considered forms of carb-cycling. For the purpose of this article, everything will be focused on the carb-cycling strategy of 2-3 high carb days a week and the rest of the days as low/moderate carbs.
What Exactly is Carb-Cycling?
A typical carb-cycling protocol involves switching up the macro distribution with a mix of high/moderate/low carb days incorporated throughout the week. Usually it will involve three high carb days, two moderate carb days and two low carb days, but that’s not a universal rule. The specific macro ratio of those days just depends on whatever the individual decides to follow. Carb-cycling can be implemented into any form of dieting, from IIFYM and flexible dieting to rigid meal plans. The sources don’t necessarily have to change as one would normally do with IIFYM though, although they can. The only variables that have to change are the amounts of each macro, primarily carbohydrates and fat.
There are a lot of proposed benefits to carb-cycling. Some claim that it leads to more calories burned or increased weight loss at the end of the week. Some say that extra carbs timed around exercise helps performance so cycling carbs is good for said reason. Let’s take a look at what’s legitimate and what’s not.
The Benefits of Carb-Cycling
In theory, it makes sense as to why carb-cycling could be an effective nutritional method. There are benefits that both increased carbs and increased fat can provide and carb-cycling aims to take advantage of each macro. Timing carbohydrate intake around exercise is frequently recommended for the performance benefits that it provides.
Research has shown that roughly 1-2g CHO/kg taken 3-4 hours before physical activity can improve performance, and it has also shown that ingesting a combination of protein and carbs before exercise can increase muscle protein synthesis (1). The effects carbohydrates can have post-exercise are even better. Taking in ample carbs right after a workout has been shown to stimulate glycogen re-synthesis at a greater rate and to further increase muscle protein synthesis (1).
This essentially means that your body is fueling up for its next workout and utilizing protein more efficiently. If your diet was consistently low in carbs, it’s unlikely you would have enough of them to spread out between pre and post workout to reap the max benefits. It’s easy to see why ingesting a greater carbohydrate intake before and after exercise is a popular strategy to increase performance.
However, even though sufficient carbs timed around workouts can have positive effects, what about the days that you’re not working out and therefore not having the same amount of calories burned? If you’re not training on a given day, then why have the extra carbs for performance benefits that will just be rendered futile? It seems like it would make sense to have less carbs on the days that you’re not training and more carbs on the days that you are training. Or maybe moderate carbs on your lighter workout days, and higher carbs timed around your more intense workouts.
The Effects of Differing Macro Ratios
One study took 40 individuals on the same number of calories and divided them into a low carb and a low fat group with varying macro ratios (2). The low carb group reported to have reduced glucose/insulin concentration and insulin sensitivity in comparison to the lower fat group. The low carb group even experienced greater weight loss by a factor of 10%, indicating a greater number of calories burned. Another study reported similar findings with the low carb diet’s beneficial effects on body composition and insulin/glucose levels (3). Diets higher in fat have also been linked to greater testosterone concentrations when compared to lower fat diets(4). High test levels leaves more room for potential muscle growth so this is obviously a good thing. Although the data on higher fat intake is certainly positive, whether its benefits outweigh the pros of higher carbs is still up to debate.
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All of the research comparing various macro distributions isn’t exactly consistent across the boards either. Another study assigned 411 overweight individuals to four different diets with varying macro ratios and had them track their food for two years to determine if there was a difference in calories burned or fat loss (5). Caloric intake was the same for all groups. It was found that the specific macro ratios had no significant effect on weight loss or calories burned, illustrating the point that overall caloric intake over macro distribution is the most important factor when determining weight balance and the amount of calories burned.
Although, it’s important to note that this study was conducted over a two year period, whereas the other two previously referenced studies that gave favor to low carb diets were only performed over 12 weeks and 16 weeks. A two year study utilizing a greater number of people holds more merit in my book than studies done in a few months with less people.
The Mental Advantage
These are just the potential physical benefits associated with each macro, but is there any type of mental advantage to carb-cycling? Well, that’s going to depend on the person. Some people love the feeling of having a high carb day and get really excited whenever those days arrive. That excitement could help increase adherence since it gives them something to look forward to multiple times throughout the week. Not only for the aspect of being able to eat more delicious carbs that day, but also because the extra carbs should help fuel that day’s workout and allow them to really push themselves.
Also, even though it’s not cheating on your diet, those high carb days could make some people ‘feel’ as though they’re having a break in their diet. In actuality they’re staying perfectly on track with their goals, so it’s a win-win scenario. This just depends on the individual though. Some people may not see the benefit and therefore it wouldn’t help them stay on track anymore than the usual approach would, but to others it could provide a nice mental edge that assists with adherence.
The Effects of Leptin and Cortisol
Another important factor to consider with carb-cycling is its effects on various hormones such as leptin and cortisol, both of which can play a significant role in weight loss. Let’s take a look at leptin first.
What is leptin first of all? Leptin is a hormone that is responsible for controlling fat cell size and regulating hunger levels. The less fat you have, the less leptin you have. The opposite also holds true. When leptin levels are above a certain threshold, they are released from fat cells which helps suppress your appetite and signals your body that it is full. At the beginning of a diet when people are holding more fat, leptin concentration is sufficient enough that this usually isn’t an issue.
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Yet, as one loses more and more fat, leptin concentration is also decreasing which means your body has a harder time telling when it’s full and therefore is always hungry. When your leptin levels fall below that certain threshold that tells your body everything is good to go, your body essentially enters starvation mode and will constantly remind you how hungry it is.
Clearly, this is not a good thing when calories are getting lower and you’re already hungry as is. This is where a lot of people can struggle to adhere to their diets since they’re hungry ALL the time.It doesn’t have to be all bad though. Even in a period of caloric deficit there are some strategies that can be utilized to control leptin levels to an extent.
Research has shown that meals high in carbohydrates can positively affect leptin concentration in comparison to meals higher in fat(6).
One study tested 10 females in 3 day periods of carbohydrate overfeeding and fat overfeeding. It was shown that plasma leptin concentrations increased as much as 28% in the carbohydrate overfeeding period when compared to the fat overfeeding(7). While this information is certainly relevant, it only covers the scenario of people having multiple high carb days in a row. What about the carb-cycling strategy of alternating daily between high/mid/low carb days?
Another study was done that tested the effects of plasma leptin concentration on 22 individuals after a single meal high in fat and again after a meal high in carbs. The calories were the same for each and measurements were recorded 9 hours afterwards. It turns out leptin levels were indeed higher in the high carb meal compared to the high fat meal(8). This supports the notion that carbohydrate overfeeding can have a positive effect on leptin concentration regardless of whether it comes from a single meal, single day or period of multiple days.
Yet, it’s important to note that there isn’t an immediate spike in leptin levels after a high carb meal but the effects are more delayed. If you are truly trying to optimize all the benefits that increased leptin can give you then I would recommend getting a lot of the carbs earlier in the day as opposed to later.
Cortisol is a steroid hormone that is produced in the adrenal glands, it’s been nicknamed the ‘stress hormone’ since it is directly related to stress levels. High cortisol is equal to high stress. Chronically elevated cortisol levels have been linked to increased abdominal fat and decreased muscle mass… Clearly features we want to avoid. Cortisol is actually an important hormone that is required for optimal health function, the issue is when it gets too high for too long negative effects start coming in. Fortunately, there are some ways in which we can help lower it that involves focusing on certain macros.
There is mixed research on carbohydrate feeding being linked to cortisol levels. Some studies have shown increased cortisol levels after a high carb meal where other studies haven’t reported any noticeable correlation between the two(9).
The divided results don’t give a lot of support to carbs having much to do with the hormone, nothing that can be 100% confirmed at least. Research done on fat intake and cortisol is certainly more promising and consistent across the boards though as multiple studies have shown cortisol levels to significantly decrease when measured after a meal high in fat (9). This definitely merits the benefits of a high fat diet on cortisol levels over a high carb diet. If you have a problem with consistently high cortisol levels, then a diet higher in fat could be a solid solution to help offset that.
Breaking Down the Research
To sum it up in simple terms; high leptin levels are good and high cortisol levels are bad. In breaking down the research it seems that high carbs can increase leptin with no real effect on cortisol, and high fat can decrease cortisol with no real effect on leptin… Irony at is finest.
Of course the body just had to make things as complex as possible such as it does with everything else. This essentially makes it a toss-up in choosing between high carbs and high fat in a weight loss phase, as it’s very hard to simultaneously increase leptin while decreasing cortisol when your body fat % is low and you only have so little calories to work with. This is exactly where carb-cycling comes into play since it aims to reap the benefits of both a high carb and high fat diet. Based on the above research, it seems that carb-cycling could be an excellent strategy to favorably control leptin and cortisol levels when calories are getting lower. ‘Seems’ is the key word here. Until there’s a study conducted in this exact fashion which can confirm this, it just remains an educated hypothesis.
Is Carb-Cycling Actually Effective or Not?
You may be more confused than ever now after the conflicting data that I’ve presented you with. Despite there being some mixed research out there, the vast majority suggests that specific macro ratios do not have an effect on weight loss or calories burned. At the end of the day, overall caloric intake will be the most significant factor.
Unfortunately to my knowledge, there haven’t been any studies to this date that have directly compared the effects of carb-cycling while keeping the same caloric intake throughout the week so this is what we mainly have to go by. Based on the research that is available though, I’m inclined to believe that the two methods would lead to the same amount of weight loss/gain over time assuming caloric intake was the same at the end of the day or week.
For example, let’s take someone who eats 1,400 grams of carbs a week. Assuming their overall caloric intake is the same at the end of the week, it technically doesn’t matter how they split up those carbs when it comes to weight loss or calories burned. They could split it evenly into 200 grams per day, or they could have 300 grams on three days, 150 grams on two days and 100 grams on the last two days. From the standpoint of weight fluctuation and the number of calories burned, these macro distributions wouldn’t matter at all.
For this reason, to someone who strictly cares about weight loss with no focus on performance, then carb-cycling may be largely unnecessary and complicate a simple process that doesn’t need to be complicated. There are a lot of other factors that can affect variables such as performance and body composition, but weight loss is purely a matter of eating less calories than the number of calories burned.
Despite the Research Presented
Even though macro ratios don’t have an effect on the number of calories burned or weight balance, I do think there are some individuals who could still see benefits from carb-cycling though. If someone is only working out three times a week, carb-cycling could be a great method to incorporate to really optimize those workouts.
For example, they could time three high carb days around the three workouts where they will need the extra carbs for performance benefits, then consume low and moderate carbs on the other four days. The number of calories burned at the end of the week would be the same, but there are some potential benefits that could be seen with timing a lot of their weekly carbohydrate intake around their workouts.
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A similar strategy of carb-cycling could even be done with someone who is working out 5 days a week. They could plan their high carb days around their most intense workouts or around a lagging body part, moderate carb days around their less intense work outs, then finally low carbs on their two off days when extra carbs won’t be needed as much. Theoretically, it makes sense that this could be an effective strategy to optimize workouts with adequate carbohydrate intake strategically timed while still having the potential to see the benefits that a higher fat diet can provide. It’s like it’s the best of both worlds… In theory, that is. While it does seem like it would make sense, as previously stated there are unfortunately no studies directly done on this that can confirm it yet.
Ultimately, everything comes down to adherence. Whether or not carb-cycling will truly be effective depends on your personal preferences and if you can actually stay consistent with it. Some people like to keep things simple and maintain a steady intake throughout the week. Changing up the macro ratio in their IIFYM plan on a daily basis might be too stressful for some or too much of a hassle to keep up with as it could be easy to mix up certain days up if they live a hectic lifestyle. For these people, I would recommend a steady carb intake throughout the week as that will more than likely allow them to stay on track more. On the flip side, there are other people who get bored eating the same foods and same amounts every day.
If switching up the food sources weren’t enough for them already with IIFYM, then switching up the macro distributions multiple times throughout the week might further help prevent things from getting stale. I know some people who really look forward to planning out their high carb days, so being able to do that a few times a week could be exciting and something to look forward to, increasing adherence. However, it is a double-edged sword at the end of the day because then that means there’s a couple days where they have to grind out on lower carbs. Maybe not an issue for some, but for other people it can be.
Why to Consider It…
Another important to factor to consider with carb-cycling is that because the macro ratios are varying so greatly throughout the week, the sources can as well. If someone was consistently low in fat, then there would be a lot of foods that would be hard for them to fit in like peanut butter, red meats, etc. Likewise, if someone else was consistently low in carbs, then they would have a hard time fitting in foods like bread, pasta, etc. By switching up the macro distribution on a day-to-day basis, you’re also allowing yourself the chance to eat foods you couldn’t normally eat as well. Obviously this has no real effect on anything performance related, but it could actually be a really big factor in making people adhere to their diet.
At the end of the day, the best diet is the one you can stick to. Whether you choose to cycle carbs vs. keeping a steady intake throughout the week, the most important things are consistency and adherence. Stay consistent in tracking your numbers with whatever method you prefer, and the results will come with time.
1. Kerksick, Chad, Travis Harvey, Jeff Stout, Bill Campbell, Colin Wilborn, Richard Kreider, Doug Kalman, Tim Ziegenfuss, Hector Lopez, Jamie Landis, John L. Ivy, and Jose Antonio. “International Society of Sports Nutrition Position Stand: Nutrient Timing.” Journal of the International Society of Sports Nutrition. BioMed Central, 3 Oct. 2008. Web.
2. Volek, JS, SD Phinney, CE Forsythe, EE Quann, RJ Wood, MJ Puglisi, WJ Kraemer, DM Bibus, ML Fernandez, and RD Feinman. “Carbohydrate Restriction Has a More Favorable Impact on the Metabolic Syndrome than a Low Fat Diet.” US National Library of Medicine. PubMed, 12 Dec. 2008. Web.
3. Gower, BA, and AM Goss. “A Lower-carbohydrate, Higher-fat Diet Reduces Abdominal and Intermuscular Fat and Increases Insulin Sensitivity in Adults at Risk of Type 2 Diabetes.” US National Library of Medicine. PubMed, 3 Dec. 2014. Web.
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6. Izadi, Vajiheh, Sahar Saraf-Bank, and Leila Azadbakht. “Dietery Intakes and Leptin Concentration.” US National Library of Medicine. NCBI, 10 Sept. 2014. Web.
7. Dirlewanger, M., V. Di Vetta, E. Guenat, P. Battilana, G. Seematter, P. Schneiter, E. Jequier, and L. Tappy. “Effects of Short-term Carbohydrate or Fat Overfeeding on Energy Expenditure and Plasma Leptin Concentrations in Healthy Female Subjects.” US National Library of Medicine. PubMed, 24 Nov. 2000. Web.
8. Romon, M., P. Lebel, C. Velly, N. Marecaux, JC Fruchart, and J. Dallongeville. “Leptin Response to Carbohydrate or Fat Meal and Association with Subsequent Satiety and Energy Intake.” US National Library of Medicine. PubMed, 27 Nov. 1997. Web.
9. Alleman, Rick J., Jr., and Richard Bloomer J. “Hormonal Response to Lipid and Carbohydrate Meals During the Acute Postprandial Period.” Journal of the International Society of Sports Nutrition. BioMed Central, 11 Nov. 2011. Web.
About the Author
Corbin Pierson is an IFPA Professional Bodybuilder, a Certified Sports Nutritionist from the International Society of Sports Nutrition (CISSN) and an ACE Personal Trainer. He graduated from the University of Kansas with a BS in Exercise Science. He works as a nutritionist and contest prep coach through Team Pierson Fitness. Corbin has been competing in natural bodybuilding contests since 2010 and has been a follower of IIFYM for about 5 years, he recently won his pro card while utilizing IIFYM and flexible dieting.
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