(5 things you should know before trusting that supplement.)

“Correlation is not causation. Yet [supplement companies] are allowed to make claims suggestive of causation, like ‘supports heart health’ or ‘supports brain health,’ based on observational research,” explains David Seres, director of medical nutrition and professor of medicine in the Institute of Human Nutrition at Columbia University Medical Center. “People don’t always realize that wording is not indicative of hard evidence from randomized control trials”—studies that randomly assign people to an intervention group (taking a supplement) or a control group (taking a placebo). “A randomized trial is the only way you can get to cause and effect,” he says.

Plenty of companies extrapolate the benefits from whole fruits and vegetables in a similar way, says Sara Campbell, an associate professor of kinesiology and health at the Rutgers-New Brunswick Institute for Food, Nutrition, and Health. Take apples: “Is the whole apple ground up into the powder, or did they just add the flesh or peels? Both have bioactive compounds that promote health, so eliminating one or the other eliminates that aspect of the fruit’s health-promoting properties,” she explains. 

Credible science on the health effects of greens powders, in general, is extremely limited. When Campbell dug into the existing literature, she only turned up 12 papers after searching “green powder” paired with broad terms like “gut” and “health” in PubMed, a reliable database of scientific studies. Most of the papers focused on green tea powder specifically or didn’t examine a supplement powder in its entirety. “From a research perspective, it’s a giant understudied area,” she says.

The potential risks of greens powders

Supplement companies don’t have to prove that what they say is in their powders is actually in their powders, unless they choose to have their product independently tested by a third-party lab, which can verify its listed ingredients and also check for stuff that shouldn’t be in there, like heavy metals, common allergens, or harmful toxins. This issue is well-documented: One 2023 paper found that 89 percent of the 57 supplements studied, including powders, had inaccurate ingredient labels; 12 percent were contaminated with at least one ingredient banned by the FDA.