By now, you’ve probably heard of the ketogenic diet — often called “keto” by its devoted followers, many of whom are celebrities. The main promise of the popular form of this eating approach is fast weight loss.
“What happens when you deprive your body of carbohydrates is that your body uses fat as energy,” says Abby Langer, RD, the Toronto-based founder of Abby Langer Nutrition. When the body digests this much fat, it produces by-products called ketone bodies and enters a state called ketosis, which means the body looks to fat rather than carbohydrates to fuel its functions.
“Generally, [the keto diet] ends up being low-calorie,” Langer says. “You’re eating 80 percent of your calories in fat, but it’s very filling.”
Dina Griffin, RDN, the owner of the Nutrition Mechanic in Boulder, Colorado, says people are also drawn to the diet for potential cognitive and anti-inflammatory benefits, as well as enhanced athletic performance and recovery.
The problem is, it’s hard to maintain ketosis, and one snack is all it takes to slip up. “Anytime you go over [about] 50 grams (g) of carbohydrates, you’re going to kick yourself out of ketosis and the weight is going to come back,” Langer says.
That’s where exogenous ketones come in.
What Are Exogenous Ketones?
The idea is that if you eat something that’s not keto-friendly, you can reach for exogenous ketones to keep your body in ketosis. The word “exogenous” means created externally, and these supplements are forms of the ketone beta-hydroxybutyrate (BHB), which your body normally creates on its own, per a study in the September 2022 Advances in Nutrition.
“The purpose is to, in a timely fashion regardless of your dietary pattern, raise your blood level of ketone bodies,” Griffin says. Of course, your body can get back into ketosis on its own through your diet, but that can take a few days, so exogenous ketones are designed to speed up the process.
Usually, exogenous ketones take the form of powdered ketone salts. Less common are ketone esters, which are the purest form of ketones and the most effective, per a review in the February 2023 Experimental Physiology. Griffin says ketone esters work quickly (in 15 to 30 minutes, as opposed to an hour for the salts), and while they’re more expensive and have a “challenging” flavor profile, they are far more potent and effective (DeltaG is the pioneer in ketone ester product formulations). People also use medium-chain triglyceride (MCT) oil or powders to increase their blood levels of ketones. MCT is absorbed differently from longer-chain fatty acids, making them more readily used as energy rather than stored as body fat, per a review in the March 2022 Comprehensive Reviews in Food Science and Food Safety. That said, not all MCT products are effective, because of differences in form and composition, Griffin says.
Do Exogenous Ketones Bring Your Body Back Into Ketosis?
Griffin says it depends on your expectations and the reasons you’re using them. You can’t just take them, eat a carb-heavy diet, and expect magic to happen. “The problem is a lot of people associate [exogenous ketones] with, ‘That means I’m going to burn fat and lose fat,’ and those don’t actually go together,” she says. “The ketones themselves don’t cause fat loss.”
Instead, they should be viewed as supplements to support a keto diet or to reap the benefits of ketosis without strict adherence to a keto diet or prolonged fasting periods. “Provided you experiment with the right ketone formulation and test your blood level of BHB, you certainly can experience many benefits once you figure out your personalized dose and timing strategy,” Griffin says. But, yes, you do have to put in the work.
Though research on ketone supplements is still in the early stages, it seems promising. One small study of 15 participants with a normal weight found that exogenous ketone esters lowered hunger hormones and acted as appetite suppressors. That can lead to weight loss because “if we don’t feel hungry, gosh, we probably aren’t going to eat as if we were,” Griffin says.
Another study found that participants who drank a ketone ester supplement lowered their blood sugar. The study was done on 20 healthy individuals ages 18 to 35; ketone esters could be helpful if similar results are found among people with type 2 diabetes.
A review in the December 2018 Current Sports Medicine Reports found that exogenous ketones were helpful in fueling endurance exercise, but other research came to the opposite conclusion, so more research is needed in this area.
Finally, the aforementioned Experimental Physiology review noted that exogenous ketones were shown to lower glucose levels and improve cognitive function, which may make them helpful in treating diabetes and neurological diseases. There’s also future research looking into whether exogenous ketones can be used to treat psychiatric diseases because of their metabolic changes and anti-inflammatory effect, according to a review published in Frontiers in Psychiatry in 2019.
Downsides of Exogenous Ketones
A serving of exogenous ketones will set you back only 100 calories or less, based on a general internet search, but most people who’ve tried them — including Langer — say they taste awful. And there’s the cost: A two-week supply could run you $50 or more. Langer says that money is better spent on whole foods.
Griffin says that because ketone salts are usually made up of ketones bound to sodium, they can be dangerous for people with high blood pressure. “There could be an issue there with heart health and heart function — that is one concern I have,” she says.
She also cautions that the ketone salts may cause stomach distress. “Some products can really tear up our guts,” she says, adding that downing an entire serving may send you running for the bathroom. To reduce that risk, she suggests starting small — maybe one-third of a serving or one-half of a serving until your body adjusts.
How to Pick a Good Exogenous Ketone Supplement
Griffin and Langer say to ignore the companies that make these supplements sound too good to be true. As with any supplement, Griffin says it’s important to look at what’s in it. Beware of products with lots of fillers and instead go for one with a short, straightforward list of ingredients that is also backed by clinical studies (Griffin likes the options from DeltaG).
Bottom Line on Exogenous Ketones for Ketosis
Some evidence supports the idea that exogenous ketones can be helpful for people already dutifully following the keto diet — but research has been limited. One thing we know for sure: These aren’t a get-thin-fast solution. “I think people are drawn to a quick, easy fix, kind of a magic bullet supplement, and it’s not that this won’t contribute to weight loss, but it’s not that magic bullet,” Griffin says.
Langer sums it up this way: “You have to put the effort in,” she says. “If you want to be in ketosis, do the ketogenic diet. You cannot just relax and eat whatever you want and automatically lose weight with this or any other product.”