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Carb Cycling

Carb Cycling

Tiffani Bachus, R.D.N., and Erin Macdonald, R.D.N

What is a carb-cycling diet?

Carbs are one of three macronutrients, along with protein and fat. When carbs are digested, they break down into glucose, which is the preferred fuel for your body and brain. As glucose enters the blood stream, your pancreas is signaled to produce insulin, a hormone that shuttles the glucose from the blood and into the cell, where it is converted to energy, stored as glycogen or stored in fat cells.

A carb-cycling diet is a dietary strategy used among body builders, fitness competitors and certain athletes that are looking to increase muscle mass and shed body fat. It can also be used by those who need to bust through a weight-loss plateau. As it is a very rigorous diet, it’s only used for a short time and not appropriate for everybody.

Carb cycling involves planned increases and decreases in carbohydrate intake depending on the day. While a high-carb day calls for eating 2 to 2.5 grams of carbs per pound of body weight, a low-carb day includes approximately 0.5 grams of carbs per pound of body weight. There is also a no-carb day that usually calls for less than 30 grams of carbohydrates. Carb cycling allows you to still eat carbs from clean sources, and cycling enables you to better utilize fat for burning as fuel, as opposed to burning carbs and muscle tissue for fuel.

How does it work?

Your metabolism increases or decreases based on your calorie consumption and macronutrient intake. Eating enough carbohydrates at the right time resets metabolism and signals the body to produce enough hormones, such as thyroid and leptin, which help keep you at a healthy weight. Consuming too many carbs, as in a standard American diet, can have the opposite effect and cause weight gain by stimulating insulin to be released too often.

Lower-carbohydrate days, when done in succession for three days, encourages the body to use up its stored carbohydrates (glycogen) and switch over to burning body fat (ketones) for fuel. Burning stored body fat will lead to weight loss (from both body fat and water).

Every carb-cycling plan is different, depending on your goals. A typical plan keeps carbohydrate intake low or very low for two to three days and then increases carbohydrate intake for one day, usually on a day that includes heavy training. On low-carb days, carbohydrate intake is usually 50-150 grams and comes from non-starchy vegetables and some dairy. Higher-carbohydrate days typically feature 20-400 grams of carbohydrate from starchy carbs, whole grains, fruit and non-starchy vegetables, as well as dairy.

Are there any benefits to carb cycling?

People who are insulin resistant, prediabetic, have type 2 diabetes, or are weight-loss resistant can benefit from carb cycling, as the decrease in carbohydrate intake and insulin release allows the body to burn through its stores of carbohydrates and switch to using fat (in the form of ketones) for fuel.

What about protein and fat? 

When carb cycling, protein intake usually stays the same each day, while fat intake varies in opposition to carb intake. When carb intake is reduced, fat intake goes up to provide the necessary calories and fuel for the body. On higher-carb days, fat intake is lowered to keep total calories in check.

Why is carb cycling becoming more popular?

Carb cycling is a type of low-carbohydrate diet, such as Atkins and ketogenic diets. These diets promise quick weight loss in the short term, even though the lost weight is primarily coming from water. Once people are able to function on using ketones for fuel instead of glucose, they feel fewer cravings for carbohydrate foods, feel fuller for longer and have more sustained energy levels. Low-carbohydrate intake can help keep blood sugar levels steadier, decrease insulin resistance and reduce blood pressure.

What are some possible dangers or pitfalls with this diet?

Low-carb days, when done for more than two to three days, can lead to fatigue, carb cravings, constipation, bloating, sleep disturbances, moodiness and irritability, as the body is using up available carbs and switching to fat for fuel. This “carb flu” is temporary and can pass by maintaining hydration levels and taking in adequate electrolytes.

Not everyone does well with carb cycling. For certain people, it can actually be counter-productive. People with adrenal fatigue or Hashimoto’s (autoimmune hypothyroidism) can experience a decrease in thyroid hormone production and metabolism. Also, people who are pregnant, lactating, underweight, have an eating disorder (current or history of), or have disordered eating habits should not try carb cycling.

The Bottom line

Manipulating macronutrient intake to lower carbohydrates on certain days of the week and to correspond with specific workouts can help people increase muscle mass and shed body fat. Carb cycling is a carefully planned dietary strategy that can be used for a short duration to achieve both body-composition goals and improve health markers, such as blood sugar and blood pressure. It is not good for everybody and be sure to check with your healthcare provider before embarking on any dietary and lifestyle changes. A registered dietitian nutritionist (RDN) can create a well-balanced, individualized dietary plan that will help you achieve your goals.