Carb cycling is a dietary strategy that involves alternating high-carbohydrate days with medium and low-carbohydrate days. It is often used as a weight loss, fat loss or bodybuilding tool.
The idea is that on high-carbohydrate days, your body will have enough carbohydrates to fuel your workouts and support muscle growth, while on low-carbohydrate days, your body will be forced to burn body fat and dietary intake of protein and fat for energy.
Carb cycling can be beneficial for fat loss because it can help regulate insulin levels and improve insulin sensitivity, which can reduce body fat. Additionally, cycling carbohydrates can help prevent metabolic adaptation and plateaus in weight loss by keeping the body guessing and preventing it from getting used to a particular diet.
Carb cycling can also be helpful for athletes who need to increase their carbohydrate intake for performance on certain days while still maintaining a calorie deficit for weight loss.
It is important to know it will not be suitable for everyone and should be undertaken with guidance from a qualified practitioner.
What’s going on?
The glycolytic pathway and gluconeogenesis are both metabolic pathways involved in the production of glucose, but they have opposite functions.
The glycolytic pathway is a catabolic pathway that breaks down glucose to produce energy, while gluconeogenesis is an anabolic pathway that synthesises glucose from non-carbohydrate sources.
Shown below we can see the pro- and preceding functions of these two pathways.
Simply put, our bodies use sugar, if we don't eat it, we make it by breaking down our own fatty acids and protein (body fat, circulating fat or muscle protein) or from dietary sources.
Therefore, it is an expensive pathway in the body to use fat and protein, it costs you to fuel you.
*image found at: https://step1.medbullets.com/biochemistry/102052/gluconeogenesis
Differences between the glycolytic pathway and gluconeogenesis:
The glycolytic pathway proceeds in the direction of glucose breakdown, while gluconeogenesis proceeds in the opposite direction to produce glucose.
The glycolytic pathway generates energy (ATP) by breaking down glucose, while gluconeogenesis requires energy (ATP) to synthesise glucose.
The glycolytic pathway uses glucose as its substrate, while gluconeogenesis uses non-carbohydrate sources like pyruvate, lactate, and amino acids.
The enzymes involved in the glycolytic pathway and gluconeogenesis are different, although some enzymes are shared between the two pathways. For example, pyruvate kinase is used in the glycolytic pathway to convert phosphoenolpyruvate to pyruvate, while during gluconeogenesis, the reaction is catalysed by pyruvate carboxylase and phosphoenolpyruvate carboxykinase.
The glycolytic pathway is regulated by the availability of glucose and the energy needs of the cell, while gluconeogenesis is regulated by hormones like glucagon and insulin.
In summary:
The glycolytic pathway is a catabolic process that breaks down glucose to produce energy, while gluconeogenesis is an anabolic process that synthesises glucose from non-carbohydrate sources.
Water Balance
Protein and carbohydrates can have different effects on water balance in the body due to their differences in chemical structure and metabolism.
Protein:
Protein is made up of amino acids, which contain nitrogen.
When protein is metabolised, nitrogen is excreted through the kidneys in the form of urea. Urea requires water to be excreted from the body, so the more protein consumed, the more water is needed to excrete the urea.
This can lead to increased urine output and water loss, which can contribute to dehydration if fluid and salt intake is not increased to compensate for the extra water loss.
Carbohydrates:
Carbohydrates are broken down into glucose, which is used by the body for energy or stored as glycogen in the liver and muscles.
Glycogen is stored with water, so when glycogen is broken down to release glucose, the water is also released.
This can lead to an increase in water retention and hydration in the body.
Overall, both protein and carbohydrates can have an impact on water balance in the body, but the effects are different.
We can see a great shift in body weight when utilising carb-cycling but also this means we need different levels of hydration.
Hormones
Carb cycling can have different effects on hormones depending on the specific details of the protocol and individual factors. Carb cycling is generally designed to manipulate insulin levels, which can in turn affect other hormones and promote fat loss.
The impact of carb cycling on hormones such as testosterone, estrogen, cortisol, thyroid, and insulin can vary depending on the specific details of the carb cycling protocol, as well as individual factors such as age, sex, and health status.
Testosterone:
Testosterone is an important hormone for muscle growth and development.
Some studies suggest that a diet high in carbohydrates may reduce testosterone levels, while a low-carbohydrate diet may increase testosterone levels.
When dietary carbohydrates are low, protein and fat usage are elevated.
However, the impact of carb cycling on testosterone levels is not well-established, and more research is needed.
Estrogen:
Estrogen is a hormone that plays a key role in reproductive health, bone density, and cardiovascular health.
Some research suggests that a diet high in carbohydrates may increase estrogen levels, while a low-carbohydrate diet may reduce estrogen levels.
When dietary carbohydrate goes up, estrogen and insulin elevate, inversely as dietary carbohydrates come down.
However, the impact of carb cycling on estrogen levels is not well-established, and more research is needed.
Cortisol:
Cortisol is a catabolic hormone that is released in response to stress and can contribute to the breakdown of tissue.
Some studies suggest that a low-carbohydrate diet may increase cortisol levels, while a high-carbohydrate diet may reduce cortisol levels.
On low-carbohydrate days, cortisol levels may be elevated due to the stress of glycogen depletion and increased reliance on fat for fuel. However, over time, you adapt and become more efficient at using fat as fuel, which can reduce cortisol levels and promote fat loss.
However, the impact of carb cycling on cortisol levels is not well-established, and more research is needed.
Thyroid:
The thyroid gland produces hormones that regulate metabolism and energy expenditure.
Some research suggests that a low-carbohydrate diet may reduce thyroid hormone levels, while a high-carbohydrate diet may increase thyroid hormone levels.
On low-carbohydrate days, thyroid hormone levels may be reduced due to the stress of glycogen depletion and carbohydrate intake.
However, over time, the body will adapt and regulate itself.
Insulin:
Insulin is an anabolic hormone that regulates blood sugar levels and promotes blood sugar and nutrient storage.
This is the only hormone that you actually have any kind of control over, by movement and what you put into your mouth.
Carb cycling is designed to manipulate insulin levels by alternating between high-carbohydrate and low-carbohydrate days.
On high-carbohydrate days, insulin levels are expected to be higher, while on low-carbohydrate days, insulin levels are expected to be lower.
Insulin gets elevated, which can promote the uptake of glucose (and water) into cells and the storage of glycogen in the muscles and liver.
This replenishes energy stores and supports muscle growth and recovery. On low-carbohydrate days, insulin levels are expected to be reduced, which can promote the breakdown of stored glycogen and the use of fat as fuel.
This can potentially vary depending on individual factors such as your own current insulin sensitivity.
Overall, the impact of carb cycling on hormones such as testosterone, estrogen, cortisol, thyroid, and insulin is complex and not well-understood.
More research is needed to determine the optimal approach to carb cycling for different health and fitness goals, as well as individual differences in hormone levels and metabolism.
Calories
Carb cycling involves alternating between high-carbohydrate days and low-carbohydrate days, impacting overall calorie intake.
Caloric intake can affect sex hormone levels, particularly in women. When caloric intake is too low, the body may reduce the production of sex hormones such as estrogen and progesterone. Sex hormones are synthesised from cholesterol, and when the body is in a state of energy deprivation, it may prioritise the production of other hormones that are necessary for survival, such as cortisol and thyroid.
Low levels of sex hormones can lead to irregular menstrual cycles, fertility problems, and decreased bone density.
In extreme cases, it can lead to amenorrhea, the absence of menstrual periods for three or more months.
Low levels of estrogen can also contribute to symptoms such as hot flashes, mood changes, and vaginal dryness during menopause.
On the other hand, when caloric intake is too high, it can increase body fat, contributing to the production of sex hormones such as estrogen.
Fat cells produce an enzyme called aromatase, which converts testosterone into estrogen.
In men, excess body fat can lead to an increase in estrogen levels and a decrease in testosterone levels, which can contribute to conditions such as gynecomastia (enlarged breast tissue) and erectile dysfunction.
It is important to ascertain the correct caloric intake that supports overall health and hormonal balance before embarking on interventions such as carb cycling.
Calorie Balance
On high-carbohydrate days - the goal is to consume more carbohydrates to fuel workouts and support muscle growth. This often means that overall calorie intake will be higher on these days to accommodate the increased carbohydrate intake.
On medium-carbohydrate days - the goal is to consume a moderate amount of carbohydrates to achieve dietary balance without compromising fat-loss efforts. This leads to a moderate calorie intake.
On low-carbohydrate days - the goal is restricting carbohydrate intake and relying on fat and protein for energy.
This can lead to a reduction in overall calorie intake since carbohydrates tend to be a significant source of calories in most diets.
Overall, carb cycling can be an effective way to manipulate calorie intake for weight loss or bodybuilding goals, but it is important to maintain an overall calorie deficit if weight loss is the goal. It is also important to ensure that adequate protein and fat intake is maintained throughout carb cycling to support muscle growth and overall health.
Protein
High protein diets provide twin benefits of improving satiety and decreasing fat mass.
Eating more protein can make you feel fuller, which can help you eat less overall. It can also help regulate your blood sugar levels, which is important for managing metabolic conditions such as diabetes.
However, there are some things to consider before you start eating a lot of protein.
Eating too much protein can be hard on your kidneys, and it can also contribute to weight gain if calorie balance isn’t addressed.
Additionally, some studies suggest that a high-protein diet might not be great if you're already at risk for metabolic diseases. Explore the pros and cons of a high-protein diet so you can decide if it's right for you.
Who is Carb-Cycling For?
Carb cycling can also be a useful tool for women and men looking to promote fat loss.
During the menstrual cycle, hormone levels fluctuate, and some women may experience increased cravings and changes in their energy levels up to two weeks prior (after ovulation) and a few days into a bleed in their cycle.
Carb cycling can help regulate blood sugar levels and provide the body with adequate energy during times of higher demand.
Who it is Not For
Carb cycling may not be suitable for everyone, and there are certain groups of people who should approach carb cycling with caution or avoid it altogether.
1. People with eating disorders:
Carb cycling may be triggering for individuals with disordered eating or eating disorders. It is important to therefore use methods such as intuitive eating to regain an association with the body, thoughts and feelings associated around food and seek qualified specialists.
In Nottinghamshire, Freed Beaches is an incredible service offering high-quality counselling, nutrition advice and 1-2-1 and group support.
Nationally, BEAT are a wonderful provider to assist with disordered eating.
2. People with certain medical conditions:
Carb cycling may not be appropriate for individuals with certain medical conditions such as diabetes, hypoglycemia, or kidney disease. It is important to consult with a healthcare professional before starting carb cycling if you have any medical conditions.
3. Pregnant or breastfeeding women:
Carb cycling is not recommended for pregnant or breastfeeding women since it can impact the nutrient intake of both the mother and the baby.
4. People who are underweight:
Carb cycling is not appropriate for people who are underweight or have a low body mass index (BMI) since it can lead to inadequate calorie and nutrient intake.
5. People who are not physically active:
Carb cycling is not that useful if you are sedentary or have low levels of physical activity.
There are other methods that are easier.
This can be achieved through a variety of protocols, high protein, low fat, low carb, calorie counting, fasting and more but you find the protocol that suits you and your needs.
The Protocol
The most effective carb-cycling approach (but also the hardest) looks like this:
Day 1: High
Day 2: Medium
Day 3: Low
Day 4: Low
Day 5: Medium
Repeat.
The back-to-back low days are challenging and are best suited to days where stress levels are low and activity is less intense or shorter.
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You could also look at a 28-day cycle:
Week 1: High CHO | Moderate k/Cal
Week 2: Medium CHO | Moderate k/Cal
Week 3: Low CHO | Higher k/Cal
Week 4: Low CHO | Higher k/Cal
** CHO refers to carbohydrates, the three elements, carbon (C), Hydrogen (qH) and Oxygen (O).
Periodised over a 6-week block to support de-loading:
Week 1: Medium
Week 2: Medium
Week 3: Intensity pushes | High
Week 4: Intensity pushes | High
Week 5: Deload | Low
Week 6: New Baseline | Medium
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Setting Baselines
For most people, finding the calorie balance that actually maintains their weight may take some time.
It is important to do this: do not skip this step.
If you don’t know this: there are tonnes of resources in my blog The Coaches Cheat Sheet
Let me give you (only) an example:
The Person
A 6ft, 96kg male, aged 30, lightly active (desk job but does an evening 25-minute run twice a week and a home weights gym session once, with a daily 15-minute lunchtime walk) and has maintenance calories around 2720 calories.
They want to lose body fat and build muscle before going away on holiday in four weeks.
Protein
We set protein at 1g per lb of body weight in line with many standards set by sports scientists and the Olympic committee, which is more than they currently get, meaning straight away they will see improvements in muscle and body composition.
96kg = 212lbs
212g protein (ok let’s round it up) 215g
860 calories in protein
2720 calories - 860 = 1860
We set an even split of the remainder calories 50/50.
930 calories in fat = 103g fat
930 calories in carbohydrate = 233g carbohydrate
Let’s not be bastards so round it up.
2745 calories
Protein: 215g
Carb: 235g
Fat: 105g
That is the balanced maintenance diet with emphasised protein.
Understandably depending on unique preferences for fat or carb based foods your balance can differ.
To lose body fat and promote insulin sensitivity for anabolism (muscle building) later on. We shift into a deficit.
Everyone responds differently to deficits of calories.
Some of us need a big deficit - this depends on our current levels of body fat, calorie tracking and behaviours. A large deficit has more room for these people to get things wrong but still get a result. It doesn't mean it's easily done, however.
Some of us need a smaller deficit - this depends on the ability of precision and repetition with dietary and caloric expenditure behaviours and is typically better for more advanced/experienced trainees.
Days with a smaller deficit of calories are more approachable and with carb-cycling gives you high days to look forward to.
An example:
Day 1: High | Maintenance
Day 2: Medium | -200
Day 3: Low | -800
Day 4: Low | -800
Day 5: Medium | -200
Day 6: High | Maintenance
Day 7: Medium | -200
This reduces 2200 calories per week: that's a whole day's BMR of calories.
In 2 weeks 4400 calories, 3 weeks, 6600, in 4 weeks, 8800 calories, it adds up.
A lot of body weight will get lost from the reduction of food volume, bowel contents, water glycogen and salts.
They look much tighter make a strong aesthetic change and with a solid protein intake and positive hormonal changes, we influence physique.
The maintenance calories in the diet are now the high day.
The medium day takes a moderate 200k/cal deficit.
The low fat takes a large 800k/cal deficit.
Never take from protein - this means the weight you do lose comes from a higher percentage of fat and minimally from protein (muscle/organs).
Moderate Carb Approach
High Day
2745 calories
Protein: 215g
Carb: 235g
Fat: 105g
Medium Day
-200 cals from carbohydrate = 50g carbohydrate.
2545 calories
Protein: 215g
Carb: 185g
Fat: 105g
Low Day
800 cals from carbohydrate = 200g carbohydrate
1945 calories
Protein: 215g
Carb: 35g
Fat: 105g
This type of diet could emphasise whole eggs, red meat cuts, salmon, skin-on poultry, nuts and their butter, plant-based oils and fats with some carbohydrates such as honey, squash, sweet and white potatoes, lentils and chickpeas.
High(er) Carb Approach
For more highly active people partaking in athletics, CrossFit and long duration very intense lifting - we prefer a higher carbohydrate starting point.
High Day
2745 calories
Protein: 215g
Carb: 335g
Fat: 60g
Medium Day
-200 cals from carbohydrate = 50g carbohydrate.
2545 calories
Protein: 215g
Carb: 285g
Fat: 60g
Low Day
800 cals from carbohydrate = 200g carbohydrate
1945 calories
Protein: 215g
Carb: 135g
Fat: 60g
This type of diet would need to emphasise low-fat sources of protein such as turkey, chicken, egg whites, low-fat dairy items, lentils and whey protein to assist with the balance of dietary fat. It would emphasise more starchy carbohydrates such as oats, pasta, potatoes, rice, cereals, grains, breads, lentils, honey, fruit and dairy.
How to Track Macros
Use a food tracking app: There are many apps available, such as MyFitnessPal or Nutracheck Calorie Counter that allow you to log your meals and track your macros. These apps have extensive food databases that can help you estimate the macronutrient content of your meals.
Weigh and measure your food: To accurately track your macros, it's important to know the exact portions you're eating. Use a food scale and measuring cups to ensure accuracy.
Monitor your intake: Log each meal and snack in your tracking app, and make adjustments as needed to ensure you're hitting your macro goals.
Read nutrition labels: Look for the macronutrient content on nutrition labels when grocery shopping or eating out to make informed choices.
Remember to also prioritise consuming nutrient-dense, whole foods to support overall health and well-being.