Carb cycling is a dietary strategy that involves intentionally varying your carbohydrate intake on different days, weeks, or months. Followers of this plan may choose to alternate between high-carb, moderate-carb, and low-carb periods, or just high and low-carb phases. The diet's objective is to try and optimise metabolic efficiency, energy availability, and potentially encourage weight and fat loss.

Why are carbs important?

Before we get into the nitty-gritty of the carb-cycling diet, it's useful to learn more about carbohydrates, and their role in the body.

Carbohydrates, or carbs, are the primary source of energy used in the body. There are two types of carbohydrates: simple carbs with up to two sugar molecules, and complex carbs which contain at least three molecules. Simple carbs are easily metabolised and so can provide a quick spike of energy. In contrast, complex carbs take longer to digest and typically are full of healthy fibre which slows down digestion. Although simple carbs can sometimes be utilised in training when instant energy is required, overall when carb cycling, it is preferable to consume more of these nutrient-dense complex carbohydrates, especially on high-carb days.

Complex carbs provide more sustained energy sources and keep blood sugar levels stable, which helps to curb sugar cravings and maintain a healthy metabolism. Kerry Beeson BSc (Nut. Med), Metabolic Balance Coach

Does carb cycling work? The science behind carb cycling

It takes a lot of planning and commitment, so a key question that most people ask before starting this diet is, does carb cycling work? Is all the effort going to be worth it? Before embarking on any diet, it's definitely sensible to do a little research to see what the science says.

The concept of a diet based on carb manipulation and intermittent energy restriction is built around our body's physiological responses to carbohydrate consumption and availability. It is believed to have been originally developed by six times 'Mr. World Fitness' winner, Franco Carlotto, back in the 1980s, who shared the principles of the diet in his book, The Carb Cycle.

Since then, there haven't been too many scientific studies which have looked specifically at the effects of a carb-cycling diet programme, and much of the supporting evidence has been derived from studies which look at either carbohydrate restriction or loading. Carb cycling aims to provide carbs when your body most requires them and restricts them when not required - this helps to match your body's needs more efficiently:

• Glycogen storage: during intense workouts, glycogen stores can become depleted, which is why replenishing glycogen after exercise is important for recovery, but manipulating glycogen levels through carb cycling can have various benefits for training and performance. On high-carb days, building glycogen stores in the liver and muscles means that these are readily available as a fuel source for intense exercise. [1,2]
• Fat oxidation: on low-carb days, the body can adapt by shifting to metabolising fat for energy, a process known as fat oxidation. [3,4]
• Metabolic adaptability: carb cycling can potentially improve metabolism and make it more flexible, by enhancing the body's ability to efficiently switch between utilising either carbohydrates or fats for energy. [5,6]

How to do carb cycling

Before you embark on a carb cycling diet, you need to make sure that this approach is right for you, your body, your health goals, and your lifestyle.

• Consult a professional: ideally, you should consult your doctor and a qualified nutrition professional before starting any restricted diet, especially if you have specific health goals and underlying health conditions.

• Define your goals: determine whether your primary objective is fat loss, muscle gain, or enhanced athletic performance.

• Make a plan: don't just wing it! Ideally to get the best out of the strategy, Plan around your training: Schedule high-carb days around intense training sessions and low-carb days on rest days or days with lighter activity.

Carb cycling and macronutrient distribution

When following a carb cycling diet, you'll also need to vary your intake of other macronutrients, depending on whether you're having a high, moderate, or low carb day.

Individual needs will vary depending on personal goals, age, sex etc. Protein intake is crucial across both phases, and intake should remain constant at around 40% of daily calories. Aim for 1.6-2.2 grams of protein per kilogram of body weight daily to support muscle protein synthesis and recovery. Find out more about protein intake on our blog: How much protein do I need? Fat intake varies significantly between phases, with higher fat intake on low-carb days.

• High-carb days: typically consist of 50-60% of calories from carbohydrates, 25-30% from protein, and 15-20% from fat. This provides ample fuel for intense training sessions.
• Moderate carb days: on a moderate carb day, you'd want to split your macros across your calorie intake with 30% of calories from carbs, 30% of calories from fat and 40% of calories from protein.
• Low-carb days: Involve significantly reduced carbohydrate intake, typically around 10-20% of calories, while increasing protein intake to 40-50% and healthy fat intake to 30-40%.

Carb cycling and exercise

For maximum benefit, your high and low-carb days should be arranged around your training schedule:

• Strength training: high-carb days provide fuel for intense weightlifting sessions, supporting muscle protein synthesis and maximising training output.
• Endurance training: adequate carbohydrate intake is crucial for optimal performance in endurance sports like running and cycling.
• High-intensity training: high carb days help you to load up on energy before an intense training session, and can replenish glycogen stores post-workout. Conversely, if you train when in a glycogen-depleted state this may even improve aerobic efficiency and help your body to use its glycogen stores more efficiently.[3]
• Rest days: low-carb days can be beneficial on rest days to promote fat oxidation and recovery.

Carb cycling and body composition

Research suggests that carb cycling may help to promote positive changes in body composition by promoting fat loss while still preserving lean muscle mass.[4] However, individual results may vary, and it might be necessary to stick to the diet for an extended period, which might be difficult for many people in the long term. To achieve these results, it's also important to do the carb cycling plan in combination with a supporting exercise regime.

If you're trying to lose fat to achieve more defined muscles, you may be interested to read our article about bulking and cutting.

Can carb cycling help you lose weight?

Most followers of this diet want to know how to use carb cycling for fat loss or weight loss. Many people consider a carb cycling diet for weight loss, especially if they have previously been following another diet plan and their weight loss has plateaued, or they may be looking to lose fat after a period of bulking. By encouraging the body to utilise fat for fuel on low-carb days, carb cycling may encourage fat loss [4,5,6,7] which can contribute to overall weight loss, though this would still need to be in conjunction with a calorie deficit.

For more information about calculating an appropriate calorie deficit, read our article: How to lose, gain, or maintain with Prep Kitchen.

Take a look at our range of calorie-balanced, weight-loss meals.

Benefits of carb cycling

Both low and high-carb phases can have unique benefits[3]:

• Can be tailored for both weight loss or bulking programmes depending on whether you're working to a calorie surplus or deficit. Adding a few higher carb days to your fat loss programme can help to aid muscle recovery after exercise and prevent you from losing muscle. Adding low-carb days to your bulking programme can help to ensure you build muscle not fat.[1]
• Enhanced metabolic flexibility: regularly switching between carbohydrate and fat utilisation can improve the body's metabolic efficiency.[7,8]
• Regulating appetite: low carb days might help to positively regulate hormones associated with appetite, like leptin and grehlin [9]
• Muscle gain: high-carb days provide the necessary energy for intense workouts, aiding muscle protein synthesis and recovery. [10]
• Enhanced insulin sensitivity: Low-carb days may help to increase insulin sensitivity [11]

Challenges of carb cycling

Whilst there are numerous potential benefits to undertaking this dietary protocol, it also presents some challenges. It's good to be aware of these before starting the diet, so you can anticipate and address any difficulties or concerns beforehand:

• Adherence: consistently tracking macronutrient intake and adhering to a cyclical pattern can be challenging to do on a long-term basis.
• Calorie control: achieving a calorie deficit for fat loss requires careful monitoring of overall energy intake.
• Meal planning: carb cycling requires careful meal planning to ensure adequate nutrition on high and low-carb days.
• Lack of specific research: there are only a few studies to date which have specifically looked at the effects of carb cycling
• Many dietary variations: opinion on how to implement the diet may vary, and it can also be used for widely varying goals which can become confusing.

Practical tips for successful carb cycling

Successful carb-cycling takes a lot of research and commitment. Before you start, it can be helpful to make sure that you have a good structure for success in place:

• Get advice and support: If you want to follow a complex diet of this type, it can help to get some professional advice before you start and also during the programme. This will ensure that you are following the correct diet for your individual body and health goals, and can also provide the motivation that you need to adhere to it.
• Start slowly: gradually adjust carbohydrate intake to minimise potential side effects like fatigue or irritability.
• Prioritise protein: ensure adequate protein intake throughout the day, especially on low-carb days.
• Incorporate healthy fats: include sources of healthy fats like avocados, nuts, seeds, and olive oil in your diet.
• Choose complex carbs: Restricting food groups like carbs can dramatically reduce your nutrient and fibre intake, so make every carb count, especially on low-carb days, and make sure you're eating plenty of complex carbs over refined carbs. These contain fibre which will also help to fill you up and support a healthy gut environment.
• Plan your meals: don't just focus on carbs! It's important that you eat a healthy balanced diet - choose whole, unprocessed foods whenever possible, such as fruits, vegetables, whole grains, lean protein sources, and healthy fats.

Conclusion

Hopefully, you now have a good overview of the basic principles of carb cycling. Here's a quick recap of the key points:

• What is carb cycling? Carb cycling is a flexible dietary strategy that aligns carbohydrate intake with your body's energy needs, offering potential benefits for weight management, performance, and metabolic health. It alternates between high- and low-carb days to optimise energy and metabolism.
• Benefits: may enhance fat oxidation, improve insulin sensitivity, and support muscle recovery.
• Practical tips: plan meals carefully, prioritise protein, choose complex carbs, and consult a professional.
• Challenges: requires adherence, careful calorie control, and a solid understanding of your goals.

When combined with a balanced diet and tailored exercise, carb cycling can be an effective tool for helping to achieve your health and fitness objectives. Good luck!

If you enjoyed this article, take a look at these other related articles on the blog:

How to lose weight and keep it off

Protein and weight loss

What is bulking and how does it work?

Are you eating too much sugar?

References:

1. Coyle, E. F. (1995). Substrate utilization during exercise in active individuals. American Journal of Clinical Nutrition, 61(4), 840S-848S.
2. Correia-Oliveira CR, Bertuzzi R, Dal'Molin Kiss MAP, Lima-Silva AE. Strategies of dietary carbohydrate manipulation and their effects on performance in cycling time trials. Sports Med. 2013;43(8):707-719.
3. Kresta JY, Byrd M, Oliver JM, Canon C, Mardock M, Simbo S, Jung Y, Koozehchian M, Khanna D, Lockard B, Dalton R, Kim HK, Rasmussen C, Kreider RB. Effects of diet cycling on weight loss, fat loss and resting energy expenditure in women. J Int Soc Sports Nutr. 2010 Sep 15;7(Suppl 1):P21. doi: 10.1186/1550-2783-7-S1-P21. PMCID: PMC2951044.
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6. Lou, Z. (2024). A Comparative Analysis of Different Fat Loss Methods: Carb Cycling, Intermittent Fasting, and Ketogenic Diet. E3S Web of Conferences, 553, 05016-05016. https://doi.org/10.1051/e3sconf/202455305016
7. Paoli et al. (2017). Beyond Weight Loss: A Review of the Therapeutic Uses of Very-Low-Carbohydrate (Ketogenic) Diets. European Journal of Clinical Nutrition.
8. Greene et al. (2018). Fueling the Fire: Low-Carbohydrate Diets and Exercise Performance. Current Sports Medicine Reports.
9. Hearris MA, Hammond KM, Fell JM, Morton JP. Regulation of Muscle Glycogen Metabolism during Exercise: Implications for Endurance Performance and Training Adaptations. Nutrients. 2018 Mar 2;10(3):298. doi: 10.3390/nu10030298. PMID: 29498691; PMCID: PMC5872716.
10. Wachsmuth, N. B., Aberer, F., Haupt, S., Schierbauer, J. R., Zimmer, R. T., Eckstein, M. L., Zunner, B., Schmidt, W., Niedrist, T., Sourij, H., & Moser, O. (2022). The Impact of a High-Carbohydrate/Low Fat vs. Low-Carbohydrate Diet on Performance and Body Composition in Physically Active Adults: A Cross-Over Controlled Trial. Nutrients, 14(3), 423.
11. Gower BA, Goss AM. A lower-carbohydrate, higher-fat diet reduces abdominal and intermuscular fat and increases insulin sensitivity in adults at risk of type 2 diabetes. J Nutr. 2015 Jan;145(1):177S-83S. doi: 10.3945/jn.114.195065. Epub 2014 Dec 3. PMID: 25527677; PMCID: PMC4264021.