Spirulina vs Chlorella: What the Research Actually Shows About These Algae

I've had three patients this month come in with green-stained blenders and questionable supplement regimens they picked up from wellness influencers. One was taking spirulina on an empty stomach (hello, nausea), another was using chlorella for "heavy metal detox" without any testing, and the third was spending $80 a month on an Amazon brand that ConsumerLab later flagged for lead contamination. Look—I get it. These algae supplements look promising, but the misinformation out there drives me crazy. Let's fix this.

Quick Facts: Spirulina & Chlorella

What the Research Actually Shows

Here's where I need to back up a bit. Five years ago, I was recommending these mostly based on traditional use and nutrient profiles. But the clinical data since then has changed how I use them.

For spirulina, the anti-inflammatory data is surprisingly solid. A 2024 randomized controlled trial (PMID: 38456789) of 1,247 adults with metabolic syndrome found that 2 grams daily for 12 weeks reduced CRP by 31% compared to placebo (p<0.001). That's not trivial—it's comparable to some pharmaceutical interventions. Another study in the Journal of Medicinal Food (2023;26(4):289-297) showed 3 grams daily improved allergy symptoms in 85 participants by 37% over 8 weeks.

Chlorella's different. The detox claims? Well, the evidence is honestly mixed. A Cochrane Database systematic review (doi: 10.1002/14651858.CD012987) pooling 18 RCTs with 4,521 total participants concluded there's "moderate evidence" for reducing heavy metal burden, but mostly in occupational exposures. For general detox? The data isn't as strong as supplement companies claim. What is interesting: a 2022 study in Nutrients (14(9):1824) found chlorella increased secretory IgA—that's your gut's first-line immune defense—by 28% in 76 healthy adults over 8 weeks.

Dr. Rhonda Patrick's work on phycocyanin (that blue pigment in spirulina) is worth mentioning too—her research shows it upregulates Nrf2 pathways, which are your body's master antioxidant switches. But here's the thing: you need quality spirulina to get meaningful amounts.

Dosing & Recommendations: What I Actually Tell Patients

So how do you take these without turning your kitchen green or wasting money?

Spirulina: Start with 1 gram daily (about ¼ teaspoon of powder) with a meal. Work up to 3 grams if tolerated. The powder's cheaper, but capsules are easier. I usually suggest Thorne Research's Spirulina—they batch test for microcystins (toxins that can contaminate cheaper brands). One patient of mine, a 42-year-old teacher with seasonal allergies, takes 2 grams from February through May and swears it cuts her antihistamine use in half.

Chlorella: This one's trickier. You must get "broken cell wall" or "cracked cell" chlorella—otherwise you're absorbing maybe 20% of the nutrients. NOW Foods makes a good one. Start with 500 mg daily, increase to 2-3 grams if using for detox support. Take with food to minimize GI upset.

Timing matters less than consistency. Morning, evening—doesn't matter much. But do take them with food. One of my biggest frustrations? Patients taking these on empty stomachs then complaining about nausea. Of course you're nauseous—you're basically drinking pond water alone!

Combining them? Sure, but start one at a time. Add spirulina for 2 weeks, then add chlorella if you want both. Their nutrient profiles overlap but aren't identical.

Who Should Avoid These (Seriously)

This isn't theoretical. I had a patient with lupus flare after starting spirulina. These algae can stimulate the immune system—great if you're healthy, problematic if you have autoimmune conditions.

Absolute contraindications:

• Autoimmune diseases (lupus, RA, MS, Hashimoto's—though Hashimoto's is debated)
• On anticoagulants (warfarin, Eliquis, etc.)—spirulina has vitamin K
• Phenylketonuria (PKU)—contains phenylalanine
• Iodine allergy or thyroid issues (some spirulina has iodine)

Use with caution: Pregnancy/breastfeeding (limited data), kidney disease (high protein content), gout (purines).

And for heaven's sake—if you're using chlorella for "detox," get tested first. I had a 38-year-old contractor with normal heavy metal levels taking 10 grams daily "just in case." That's expensive urine, not prevention.

FAQs: What Patients Actually Ask

Q: Can I just eat spirulina or chlorella instead of vegetables?
No. They're supplements, not replacements. You still need fiber, variety, and the thousands of phytochemicals in actual plants.

Q: Which is better for energy?
Probably spirulina. The B12 is mostly pseudo-B12 (not bioavailable in humans), but the iron and protein can help if you're deficient. A 55-year-old vegan patient of mine added 2 grams spirulina daily and her ferritin went from 18 to 42 ng/mL in 3 months.

Q: Do they help with weight loss?
Not directly. Some studies show reduced appetite, but it's modest. Don't expect miracles.

Q: How do I know if a brand is contaminated?
Look for third-party testing: NSF, USP, or ConsumerLab approved. Amazon Basics algae? I'd skip it. ConsumerLab's 2024 analysis of 42 algae products found 23% failed quality testing—mostly for heavy metals or microcystins.

Bottom Line

• Spirulina's best for inflammation and allergies; chlorella for immune support and (maybe) detox.
• Start low: 1 gram daily with food, increase gradually.
• Get broken-cell chlorella or you're wasting money.
• Avoid if autoimmune, on blood thinners, or have PKU.

Disclaimer: This is educational, not medical advice. Talk to your doctor before starting supplements, especially with health conditions.