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Do chlorella and spirulina break a fast?


Intermittent fasting has become an increasingly popular health and fitness trend in recent years. Many people use it as a way to lose weight, improve metabolic health, and simplify their diet. During fasting periods, people restrict their calorie intake to a very low level or avoid food altogether for set periods of time. This gives the body a chance to burn through its glucose stores and switch to a metabolic state called ketosis where it burns fat for energy.

Some people choose to consume certain low-calorie or non-caloric drinks and supplements during their fasting periods. Two popular supplements used during fasting are chlorella and spirulina. But do these algae supplements break your fast or are they safe to consume?

What are Chlorella and Spirulina?

Chlorella and spirulina are two types of freshwater algae that are renowned for their high nutrient content. Here’s a quick overview of each:


– Single-celled green algae
– Rich source of protein, vitamins, minerals, antioxidants
– Contains chlorophyll, omega-3s, iron, zinc, vitamin A, vitamin C
– Contains chlorella growth factor (CGF), a compound believed to promote healing
– Comes as a powder, tablets, or capsules


– Blue-green algae that grows in warm alkaline waters
– Rich source of protein, B vitamins, iron, and antioxidants
– Contains phycocyanin, a compound with antioxidant effects
– Has gamma-linolenic acid (GLA), an omega-6 fat with anti-inflammatory effects
– Comes as a powder, tablets, or capsules

Both chlorella and spirulina have an impressive nutritional profile and have been associated with health benefits like improved immunity, lower blood pressure and cholesterol levels, and enhanced antioxidant status. Many people add these superfood algae to smoothies or mix the powders into water. But can they be consumed while following intermittent fasting regimens?

Key Factors that Break a Fast

To determine if supplements like chlorella and spirulina are allowed during fasting windows, it helps to understand what actually breaks a fast. There are two key factors:


Consuming calories from any macro or micronutrient (carbs, protein, fat, vitamins, minerals) during the fasting period will break the fast. Even a small amount of calories can trigger metabolic processes in the body that disrupt the fasting state. Most experts advise consuming 0-25 calories maximum per hour to remain in a fasted state.

Insulin Secretion

Insulin is the hormone released by the pancreas in response to rising blood sugar levels. It signals the cells to take up glucose from the bloodstream and store it as glycogen. Consuming anything that stimulates insulin secretion can break the fast, even if it does not contain calories. For example, some artificial sweeteners and flavorings can provoke an insulin response.

Do Chlorella and Spirulina Have Calories or Spike Insulin?

Now let’s examine chlorella and spirulina specifically and see if they contain calories or increase insulin levels:


– Very low in calories with about 3-4 calories per gram of powder. A one teaspoon (2 gram) serving would provide 6-8 calories.

– Does not spike insulin levels. Studies show it does not impact blood glucose or insulin secretion.


– Also very low in calories with about 4 calories per gram of powder. A one teaspoon (2 gram) serving would have about 8 calories.

– Does not spike insulin or blood sugars. One study gave participants spirulina and saw no increase in insulin levels.

So based on their very low calorie content and lack of effect on insulin, both chlorella and spirulina are generally considered safe and allowed for consumption during intermittent fasting periods. A small amount can be consumed without disrupting the fasted state.

Recommended Intake While Fasting

Most experts recommend limiting chlorella and spirulina intake to about 1-2 teaspoons (2-4 grams) per day during fasting windows. This small serving size provides about 10-20 calories total.

Consuming too much could provide a more significant amount of calories that could technically break the fast. Some sources recommend keeping intake under 100 calories and 25 grams of protein to remain in a fasted state. Going beyond that may negate some of the benefits of intermittent fasting for metabolic health and weight loss.

Here is a quick table summarizing the calorie content of different serving sizes of chlorella and spirulina:

Supplement Serving Size Calories
Chlorella powder 1 teaspoon (2 grams) 6-8
Chlorella tablets 6 tablets (3 grams) 10-12
Spirulina powder 1 teaspoon (2 grams) 8
Spirulina tablets 6 tablets (3 grams) 12

Benefits of Taking Chlorella or Spirulina While Fasting

Adding a small amount of chlorella or spirulina powder or tablets to your water or other allowed beverages can provide some advantages during fasting periods:


These algae supplements supply an array of vitamins, minerals, and antioxidants to help sustain micronutrient status when calorie intake is very low. In particular, they provide iron, B vitamins, vitamin A, and vitamin C.


Protein intake helps preserve lean muscle mass when calorie restriction is low. The protein in just a teaspoon serving of chlorella or spirulina provides 2-4 grams protein to support muscle retention.


The combination of antioxidants like chlorophyll, phycocyanin, vitamin C, and carotenoids helps combat oxidative stress and inflammation during fasting.


Some research indicates chlorella and spirulina increase satiety and feelings of fullness when consumed with water, which may support adherence to the fasting regimen.


The nutrients in chlorella and spirulina may enhance the body’s ability to detoxify during fasting. The chlorophyll in chlorella in particular may support liver detoxification.

Other Supplements That Don’t Break a Fast

In addition to chlorella and spirulina, some other supplements that don’t provide significant calories or increase insulin are generally considered appropriate for use during intermittent fasting windows. These include:


Adding a pinch of salt to your water helps replace sodium and minerals lost through increased urine output during fasting. This prevents low sodium that can lead to headaches, fatigue and dizziness.

Apple cider vinegar

1-2 tablespoons apple cider vinegar mixed into a glass of water may aid metabolism and fat burning. The acetic acid in vinegar appears to increase circulation and glucose uptake by muscles.


Caffeine from coffee, tea or energy drinks can help suppress appetite and boost metabolism. It may also enhance ketone production. Limit intake to avoid dehydration or sleep disruption.

Exogenous ketones

Ketone supplements like ketone salts and MCT oil powder provide the body with ketones directly. This can facilitate the transition into ketosis during fasting.

Branch chain amino acids (BCAAs)

BCAA supplements like leucine, isoleucine and valine support muscle protein synthesis and help minimize loss of muscle during fasting periods.

Herbal teas

Sipping on herbal teas can make fasting more pleasant without adding calories. Green tea, chamomile, peppermint and ginger teas have appetite suppressing and calming benefits.

Putting It All Together

In summary, consuming a small amount of chlorella or spirulina during intermittent fasting is unlikely to break your fasted state due to the very low calorie content and minimal impact on insulin levels. Many people find taking 1-2 teaspoons per day helps provide nutrients and protein to support energy, fight oxidative stress, and preserve muscle while fasting.

Exceeding more than 2-4 grams of chlorella or spirulina may provide excessive calories that could counteract some of the intended benefits of fasting. For optimal results, stay within recommended serving sizes. When in doubt, check with your doctor or dietitian about the best fasting regimen and allowed supplements for your health goals.

The Bottom Line

– Chlorella and spirulina are very low in calories and will not spike insulin levels when consumed.

– Limit intake to 1-2 teaspoons (2-4 grams) per day to stay within fasting guidelines.

– These algae supplements can provide protein, vitamins, minerals, and antioxidants when calorie intake is restricted during intermittent fasting.

– Other supplements that don’t break a fast include salt, apple cider vinegar, caffeine, exogenous ketones, BCAAs and herbal tea.

– Check with your healthcare provider before starting any fasting regimen or taking new supplements.


[1] Bailey, Stephanie. “16 Foods That Won’t Break Your Intermittent Fast.” Healthline, 14 Nov. 2018, [2] Gunnars, Kris. “Does Spirulina Have Side Effects?” Healthline, 12 Aug. 2018, [3] “All About Intermittent Fasting.” Johns Hopkins Medicine, [4] Ngo, Robin. “The Benefits of Chlorella and Spirulina.” Healthline, 28 Jan. 2020,