Oat milk soared to popularity during the plant-based wellness movement of the 2010s, but the milk alternative is now facing criticism from nutritionists and influencers, including food activist, integrative nutritionist and podcaster Courtney Swan.
Known online as @realfoodology, Swan has spoken out many times about oat milk on social media.
She told Newsweek that this was because many people "are being told that oat milk is healthy and environmentally friendly—which is a lie." Swan said that there were "a lot" of problems with the drink.
"It's carbohydrate rich and when you break it down into a liquid, it loses its beneficial fiber that helps slow down the sugar surge," said Swan.
"Oats are also heavily sprayed with glyphosate—a carcinogenic herbicide—unless they are organic, but glyphosate is showing up even in organic oats. So, it's essentially glyphosate starch juice."
When we eat or drink carbohydrates, the body breaks it down into glucose—sugar—and the responds with the hormone insulin, to remove the glucose from the bloodstream to be used as energy elsewhere.
But when we consume a lot of carbohydrates, in refined, sugary or liquid forms, without fiber, fats or protein, it is quickly turned into glucose, and then the body has to send out a lot of insulin in response.
This can cause energy fluctuations, with a big glucose spike followed by a crash when the insulin kicks in—and in the long term, these fluctuations can lead to insulin resistance and diseases such as type 2 diabetes and obesity.
"Many people are starting out their morning with an oat milk latte, surging their blood sugar, then crashing," said Swan. "It leaves your body wanting more sugar throughout the day."
She also takes issue with oat milk's image as a more environmentally friendly alternative to dairy or other plant-based alternatives.
"The glyphosate sprayed on the oats is destroying our soil, a leading cause of climate change, and oats are a part of the monocrop agriculture system that's destroying our environment," said Swan.
Many wellness influencers have spoken out against drinking oat milk after previously enjoying it, but this is not the case for Swan.
"I have never been a fan of drinking it," she said. "I never understood why I would be drinking my carbohydrates. I don't vilify carbohydrates, but I eat them."
This is because, she explained, when oats are turned into liquid, they lose their fiber—and fiber slows down oats' effect on blood glucose levels, leading to a slower release of energy.
A similar effect happens when oranges are turned into orange juice; a healthy, high-fiber fruit becomes a high-sugar drink that may have a dramatic impact on blood sugar.
Swan said that oat milk is an important issue "because the majority of Americans are dealing with some sort of metabolic dysfunction."
Metabolic dysfunction is an umbrella term for people with obesity, inflammation, poor heart health, or problems dealing with sugar such as insulin resistance or type 2 diabetes.
"The root of metabolic dysfunction is sugar dysregulation," said Swan. "Many [Americans] are diabetic or prediabetic. You can prevent this by reducing intake, and not eating your carbs 'naked'—meaning, always consume them with protein and fat to mitigate large fluctuations in blood sugar surges."
A spokesperson from oat milk brand Oatly previously told Newsweek: "Fortified plant-based milks such as Oatly are a nutritious choice and are included in government dietary guidelines around the world.
"Oatly's fortified, unflavored oat milks benefit from the inherent goodness of oats and contain vitamins and minerals including calcium, riboflavin and vitamins B12, A and D."
The spokesperson also said that oat milk had a lower climate impact than cow's milk and that the blood sugar effect of oat milk was "low."
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