Carb Cycling Guide for Athletes

Originally published on HVMN by Nate Martins.

10,080–that’s how many minutes are in a week. Maintaining a diet through all those minutes, for weeks or months, requires supreme, almost unwavering willpower.

Even The Rock doesn’t do it; his Sunday night cheat meals are stuff of legend, consisting of thousands of calories of his favorite food.

The social side of dieting is tough. It takes dedication to remain unmoved on a diet; happy hour invites, dinners out, work-sponsored lunches–saying “no” to all these are small wins on the battlefield of dieting. For a diet like the ketogenic diet, avoiding carbohydrates can feel like tip-toeing through a minefield of Western, carb-centric eating.

For athletes, it can be difficult because we rely so heavily on carbohydrates for fuel. Of course, there’s growing research about how to use bodily fat as a fuel source,1 but carbohydrates have been the gold standard exercise nutrition for years.

Carb cycling is planned consumption of different amounts of carbohydrates, usually throughout the week. Everyone can develop their own carb cycle based on need; for example, keto athletes might work in carb days during especially hard training blocks.

While carb cycling isn’t for everyone, it can be a great way to optimize a diet based on your personal needs.

What’s a Carb, Anyway?

There are three different types of macronutrient fuel sources in our food: fats, proteins and carbohydrates.

The main function of dietary carbs is to be a source of energy. Some even argue they aren’t essential, and can be made from dietary protein and fat.2 This process is called gluconeogenesis, a metabolic pathway generating glucose from non-carbohydrate substrates.

Carbs (especially refined carbs) raise blood sugar, resulting in the body producing extra insulin to bring that blood sugar down. Insulin is a hormone that triggers fat storage–so more carbs means more insulin which means more conversion of carbs to fat stores.

As a fuel source, carbohydrates replenish glycogen stores in the muscle and liver. They also maintain blood glucose concentrations as fuel for the body, but also for the brain. That’s the spike in energy you experience after an afternoon stack, as blood glucose fluctuates throughout the day when we consume carbs.

Simply put, carbohydrates are the body’s most readily available fuel. But when we don’t use that fuel, carbohydrate manifest as fat.

When following a keto diet, lower carb intake is necessary (like 25g of carbs per day–the amount in a single banana). This encourages the body to burn fat and also to convert fat to ketones. Consuming carbohydrates causes insulin release, which inhibits ketone production in the liver.

Science Behind Carb Cycling

What is carb cycling, and why is it beneficial? Looking at the science can provide some clarity. Maybe a more accurate definition of carb cycling is carb manipulation.

The goal is to match the body’s need for glucose depending on activity or activity level overall.

High-Carb Days

High-carb days are usually matched with workouts when you might need more glucose–like high-intensity interval sessions or a long day in the weight room.

When you exercise at a high intensity, the body makes most of its energy from carbohydrates, either breaking it down aerobically (with oxygen), or anaerobically (without oxygen), forming lactic acid. This would be the optimal time to introduce a higher amount of carbohydrates into the diet because the body uses more carbohydrate during the workout itself, and then after the workout to make glycogen to refuel and decrease muscle breakdown.3

When looking for your highest possible power or speed output, carbs are often necessary for the body to produce its best results during intense training sessions.

Low-Carb Days

In traditional carb-cycling, low-carb days are meant for days on which you do not train–the idea is the body doesn’t need carbs because its demand for fuel is far less than on workout days.

But further investigation by scientists have shown some of the advantages of training on these low carb days, which has two main benefits: it helps to speed up general adaptations to aerobic training, and it increases fat burning and thus improves endurance.

One of the key, groundbreaking experiments in this field was conducted using single-legged cycling exercise. Athletes had to cycle using just one leg at a time; the left leg cycled one hour straight, and the right leg did two half hours with a few hours in between where no recovery fuel was given. This means that the right leg was training in a carb depleted state during the second session. Muscle biopsy samples revealed that the twice-trained leg saw bigger gains in the enzymes that are key for aerobic respiration. This led to the conclusion that low-carb training could accelerate aerobic gains.4

Strategic low-carb days focus on switching the body back to using fat as energy and increase aerobic capacity. Research is continuing on this topic, but athletes are looking to boost the ability of the body to tap into fat as a fuel source, since we store more fat than carbohydrates.

Training in a low-carb state has been shown to increase the ability of the body to burn fat over the long haul, improving metabolic flexibility.5 There have even been studies noting keto-adapted athletes can use fat in preference to carbohydrates for moderate intensity endurance exercises, in which carbohydrates would usually be used as fuel.6

But it takes time. Robert Sikes is a professional bodybuilder and founder/owner of Keto Savage. He’s a bodybuilder on the keto diet; backstage at events, he receives inquisitive looks from competitors when they find out he’s keto. But the results speak for themselves and after events, he’ll even get asked about he’s able to train with such little carb intake. He says it can takes years to full fat-adapt, and that it’s something that doesn’t happen in the short term.

“You need to allow yourself to be completely adapted to life without carbs. Play the long game. Be diligent with hitting macros and eating wholesome foods.”
Robert Sikes

By controlling carbs, and the types of carbs consumed, there also may be a benefit in manipulating insulin and insulin responses.7,8 This would likely help with improving metabolic health.

It is becoming widely accepted that athletes should adopt carb cycling or periodization of carbs based on training needs. This ensures fuel for the work required (so training intensity isn’t compromised), while also empowering the body to metabolically trapease between carbohydrates and fats as fuel sources as available.9

Benefits of Carb Cycling

The benefits are carb cycling are measured against personal goals. Do you want to improve body composition? How about improve training or recovery?

Ask yourself what you want to achieve with carb cycling to best understand its benefits.

Body Composition

As with most diets, a major goal is usually weight loss. Because we consume such a high amount of calories as carbohydrates in Western diets, limiting those calories and carbs will ultimately lead to fat loss. The process aligns with most other diets: consume less calories than the body burns, enter a calorie deficit and promote weight loss.10

Though specific research on carb cycling is limited, generally studies show that limiting carb intake works well for weight loss. One study analyzed overweight women who had a family history of breast cancer. Three groups were randomly assigned different diets: calorie-restricted and low-carb diet, low-carb but unlimited protein and healthy fat, and a standard, calorie-restricted diet. Women in both low-carbohydrate groups showed better results for weight loss.11

Performance and Recovery
Training in a low-carb state can help with weight loss, boost fat burning capacity, and can speed up aerobic adaptation to training. However, athletes face a compromise when employing low-carb diets; they need the carbohydrates to perform at the highest intensity (especially in a race), and want to keep that energy system working well, but still want the benefits of carb restriction.

Making sure the body has carbs for tough training can help performance. The body needs fuel for the most difficult exercise days. Since carbohydrates are the body’s most readily available fuel source, consuming carbs before a workout enables the body to train harder for high-intensity, short-duration exercise.12 Interestingly, even the presence of carbohydrates in the mouth (meaning, not actually ingested) can lead to increased performance, because they activated brain regions believed to be involved in reward and motor control.13

Carbs can also help accelerate recovery. After exercise, consuming carbohydrates can lead to glycogen resynthesis and protein synthesis (after resistance training).14,3 So, it’s easier to perform and recover if you have enough carbohydrate in your diet. Carb cycling means those big training days can be high quality.

Other Benefits

By cycling carbohydrate consumption, you may be afforded some of the benefits of both higher-carb and lower-carb diets–and avoid some of the common negative side-effects.

Metabolic Health: The combination of two types of diets may help you become metabolically flexible.5

The days with low-carbs may have a positive impact on insulin sensitivity; this study showed the benefits of a low-carb, high-fat diet on glucose metabolism, lowering fasting glucose and insulin values.8 And when compared to a low-fat diet, a low-carb diet led to greater weight loss, which in turn led to a decrease in triglyceride levels15–high levels of triglycerides have been associated with cardiovascular disease.16

Hormone Health: There are some concerns that hormones might be negatively affected by a badly put together low-carb diet, but this could be mitigated by strategic carb feeding.

High-carb feeding periods can potentially boost the levels of some vital hormones, like cortisol. There are some concerns that cortisol can decline when following a low-carbohydrate or ketogenic diet (although not much research supports this fear). To combat this possibility, either make sure your keto diet is well-formulated with enough calories and nutrients,17 or cycle periods of carbohydrate feeding to give your body a break.

In men, testosterone concentrations were higher after a ten-day high-carbohydrate diet, while cortisol concentrations were consistently lower on the same diet, suggesting the power of diet (specifically the ratio of carbohydrate to protein) as a factor in hormone regulation.16

Thyroid hormones are essential to regulating metabolism,18 being crucial determinants of resting metabolic rate. But they themselves are in turn regulated by diet and metabolism because glucose fuels the production of those thyroid hormones. The thyroid produces a large amount of T4 hormones, which are then converted into T3 hormones (T3 is the active thyroid hormone influencing many body processes). When carb intake is reduced, conversion of T4 to T3 reduces.19 People worry that this might lead to a lower metabolic rate and thus slow down weight loss with a low-carb diet

Longevity: The ketogenic diet may help to increase lifespan and healthspan.

This might be increased further by taking a cyclical approach to the diet: alternating high-carb and low-carb weeks. One study fed a ketogenic diet to mice every other week. Results showed avoidance of obesity, reducing midlife mortality, and prevented memory decline.20

How to Carb Cycle

Anyone from ametuer dieter to serious athlete can carb cycle. There are different options for how carefully you implement carb cycling, depending on training and recovery needs as well as your overall goals.

Creating a schedule, tracking your progress and targeting carbohydrate intake can help develop a well-formulated plan to succeed cycling carbs.

Create a Schedule

Before a single carb touches your lips, think about your goals. These will formulate your carb cycling plan.

Do you want to lose weight, or maintain weight? Do you want to boost aerobic fat burning capacity or target a lean body composition?

Then consider your typical training week. Which days are your most intense workouts? Which days can you recover, even without carbs? Do you meal prep to make sure you get enough quality, low-carb foods?

Serious athletes might want to take it one step further and consider carb cycling over a longer period, to keep up with training or competition cycle. Instead of breaking up a single week into high-carb and low-carb days, each week would have a different carbohydrate goal. Weeks with a heavy training load would be carb-heavy, while weeks with a lower training load or coming into a weigh-in could be more low/moderate-carb.

Your answers to these questions will determine how you go about cycling carbs. Don’t be afraid to change the schedule and be a bit flexible once you get started.

Log calories and macros

Establishing a calorie goal could prove helpful (especially if you’re trying to lose weight). Multiply your bodyweight by ten, and that’s the amount of calories to work toward if you want to lose weight. To gain weight, you can multiply your bodyweight by 15 to garner a ballpark daily calorie target.

Tracking your macros in a food journal or an app will help keep you accountable. Taking note of everything you eat will let you make sure you get enough calories from the right type of macronutrients while giving you a better understanding of how diet impacts your training output.

Target for a High-Carb Day

High-carb days should accompany your toughest training sessions of the week, such as intense intervals or prolonged weight training. These days call for about 2g of carbs per pound of bodyweight, and they’ll be your highest calories days. If you’re working out four times a week, and weight training once or twice a week, then you should have about one or two high-carb days each week.

Note that you might want to eat high-carb the night before a heavy morning workout to make sure that you are fueled up and ready to go, even if the training on that day was not that intense.

Target for a Medium or Low-Carb Day

Low-carb or medium-carb days can be used to fuel less-intense workouts or recovery days. Depending on training volume, low/medium carb days can be anywhere from 50g – 150g of carbs.

Training low doesn’t mean training on zero carbohydrates. On low-carb days, be sure to prioritize other macronutrients such as good quality protein and fat. High protein intake is important for post-workout recovery and the development of muscle mass. When cutting back on carbs, make sure you get enough calories, and the bulk of these should come from fat.

There are a few strategies that you can use to control your carb intake around your training sessions.

Training low: start your training having limited your carb intake beforehand. Implementing this strategy is simple. You may wake up and workout in the morning without eating before. You may even increase the effect by limiting carb intake the night before. If you workout during the evening, you may limit carbs from morning until that evening training session.

Sleeping low: don’t refuel using carbs after a workout, and stretch out the period before you refuel by sleeping overnight before refuelling with carbs at breakfast. This has shown promise, with a recent review in elite cyclists describing how the “sleep low, train low” method (where morning exercise commences with less than 200 mM of glycogen), improved results for cycling efficiency.20

On low-carb days, be clever to ensure quality training and recovery. Performing on a low-carb day can be difficult, so consider taking a low-carb or keto energy source, such as HVMN Ketone. Elite athletes have used HVMN Ketone to give them BHB as a fuel during high intensity time trials, showing that if you really want to avoid carbs, swapping in ketones can be a great energy alternative.

Another way to get a boost is to mouth rinse with carbs; this can improve performance without needing to actually eat carbs. You can also use caffeine before your workout, which is another reliable, carb-free way to get your body ready to perform.

What about recovery? BHB from HVMN Ketone is a carb-free alternative for recovery on low-carb days. Studies have shown that not only is less glycogen broken down in training with HVMN Ketone,21 but glycogen22 and protein resynthesis23 are also increased by 60% and 2x respectively. BHB could be a great way to help protect your recovery but also keep carb intake low.

Foods to Remember

With all this talk of carbs, you need to know where to find them so you can either stock up or steer clear.

A carb cycling diet requires high quality, healthy carbs and whole foods. Every once in a while it’s fine to treat yourself in epic, The Rock-like proportions, but from day-to-day, it’s all about maintaining balance. Good carbs include whole grains (like brown rice and oats), legumes (like beans, a good slow-digesting carb) and tubers (sweet potatoes).

Foods low in carbs include meat (beef, chicken, fish), eggs, vegetables (like bell peppers, broccoli and mushrooms), nuts (almonds, walnuts) and dairy (cheese, yogurt). Building a meal plan to incorporate all these types of food should help with each phase of the carb cycling. Even better? Meal prepping, so the stress of cooking depending on the day goes out the window.

But don’t forget about fiber; it plays an important role in weight loss, energy maintenance, regulating blood sugar and controlling hunger. Though fiber is a carb, it doesn’t raise blood sugar like other carbs and plays an important metabolic role because it doesn’t convert to glucose.

Is Carb Cycling Right For You?

It depends on your goals. It also requires some experimentation–based on your lifestyle and fitness routine, finding the right balance of high-carb and low-carb days can take some time and will probably change over the long-term.

What’s nice about carb cycling is the flexibility. It empowers a dieter some choice, while also providing the ability to fuel on days where it’s required, like ahead of intense training sessions. Benefiting from each could help an athlete reach goals for exercise, as well as goals for body composition. But remember to check with your doctor before implementing such wholesale changes to the way you eat.

If you’ve tried carb cycling, let us know the results in the comments.

Scientific Citations