The ketogenic or keto diet is a very low-carb, high-fat diet.
Being on the diet for several days puts your body into ketosis, a nutritional state characterized by raised blood ketones and weight loss (1).
While the diet may provide benefits, it can also be difficult to follow consistently.
Some suggest that ketone supplements can mimic ketosis and raise blood ketone levels without changing your diet.
However, that’s not exactly how your body interprets it.
This article tells you whether exogenous ketone supplements can help you shed extra pounds.
What Happens in the Body During Ketosis?
If you follow a standard high-carb diet, your body’s cells typically rely on glucose for fuel.
Glucose comes from the carbs in your diet, including sugars and starchy foods like bread, pasta and some vegetables.
If you restrict those foods, as with a ketogenic diet, you force your body to look for alternative fuel sources.
Your body then turns to fat for fuel, which produces ketone bodies when broken down in excess.
This shift in metabolism puts your body in a state of ketosis.
Most people naturally experience a mild state of ketosis during periods of fasting or strenuous exercise (2, 3).
The two main ketone bodies produced during ketosis are acetoacetate and beta-hydroxybutyrate. Acetone is a third, less abundant, ketone body (4).
These ketone bodies replace glucose as fuel and provide your brain, heart and muscles with energy.
It’s thought that the ketone bodies themselves may be responsible for the weight loss associated with a ketogenic diet (5).
SUMMARY
Ketosis is a process in which your body produces high numbers of ketones and uses them for energy instead of glucose from carbs.
What Are Exogenous Ketone Supplements?
Ketone bodies can be produced in your body (endogenously) or come from a synthetic source outside your body (exogenously).
Thus, ketones found in supplements are exogenous ketones.
These supplements contain only the beta-hydroxybutyrate ketone. The other primary ketone body, acetoacetate, is not chemically stable as a supplement.
There are two main forms of ketone supplements:
Ketone salts: These are ketones bound to a salt, typically sodium, potassium, calcium or magnesium. They’re most often found in powder form and mixed with liquid.
Ketone esters: These are ketones linked to another compound called an ester and packaged in liquid form. Ketone esters are used primarily in research and aren't as readily available for purchase as ketone salts (6).
Both forms of ketone supplements have been shown to increase blood ketone levels, mimicking what happens in ketosis when you follow a ketogenic diet (7, 8, 9, 10).
In one study, supplementing with approximately 12 grams (12,000 mg) of ketone salts increased participants’ blood ketone levels by over 300% (8).
For reference, most available ketone supplements contain 8–12 grams of ketones per serving.
This elevation in blood ketone levels following supplementation is beneficial for people who want to transition into ketosis without necessarily having to follow the diet (11).
That said, supplementing with ketones is thought to have many of the same health benefits as a ketogenic diet, including weight loss.
People also take ketone supplements along with a ketogenic diet, especially when first beginning the diet.
This reduces the time it takes to reach ketosis and lessens the unpleasant effects that may come from transitioning from a standard, higher-carb diet to a ketogenic one.
The symptoms that often accompany the transition to a ketogenic diet, more commonly known as the “keto flu,” include constipation, headache, bad breath, muscle cramps and diarrhea.
There’s limited research to suggest that ketone supplements can reduce these symptoms (12).
SUMMARY
Taking exogenous ketone supplements increase ketone levels in your body, imitating the state of ketosis achieved through a ketogenic diet.
Exogenous Ketones May Decrease Appetite
Ketone supplements have been shown to decrease appetite, which may help you lose weight by eating less.
In one study in 15 people of normal weight, those drinking a beverage containing ketone esters experienced 50% less hunger after an overnight fast than those drinking a sugary beverage (13).
This appetite-suppressing effect was attributed to lower levels of the hunger hormone ghrelin between two and four hours after drinking the ketone ester drink (13).
However, ketone supplements may not affect appetite as much in people who have had a meal beforehand.
Studies have observed higher blood ketone levels in those who didn’t eat a meal before taking a ketone supplement compared to those who did (14, 15, 16).
And since it’s the elevated ketones that are associated with reduced appetite and lower ghrelin levels, ketone supplements may only be beneficial during a fast, such as upon rising in the morning, rather than after a meal that contains carbs (13).
In other words, taking a ketone supplement after a carb-containing meal will still raise blood ketone levels but not as high as if you fasted, suggesting that your body is using fewer ketones as fuel since there is more available glucose from the carbs (15).
SUMMARY
One small study found that exogenous ketone supplements reduced appetite for over four hours, which may be promising for weight loss. However, additional studies are needed before ketone supplements can be recommended for appetite control.
The Case Against Exogenous Ketones for Weight Loss
Despite the potential appetite-curbing effects of ketone supplements, their potential weight loss benefits are unknown.
Therefore, ketone supplements cannot be recommended for weight loss at this time. In fact, some evidence suggests that they may even hinder it.
Ketones Inhibit Fat Breakdown
The purpose of the ketogenic diet for weight loss is to produce ketones from stored fat as an alternative fuel source.
But if your ketone blood levels become too high, your blood can become dangerously acidic.
To prevent this, healthy people have a feedback mechanism that slows down production of ketones if they become excessively high (12, 15, 17, 18).
In other words, the higher your blood ketone levels are, the less your body produces. As a result, taking ketone supplements may prevent body fat from being used as fuel, at least in the short term (19, 20).
Ketones Contain Calories
Your body can use ketones as a fuel source, meaning they have calories.
They contain about four calories per gram, the same number of calories as carbs or protein.
A single serving of exogenous ketone salts typically contains less than 100 calories, but to maintain a state of ketosis, you’ll need several servings each day.
That’s because the effect of ketone supplements lasts only a few hours and thus requires repeated doses throughout the day to maintain a state of ketosis (17, 21).
Not to mention, at upwards of $3 per serving, they can become costly, too (22).
SUMMARY
Ketone supplements themselves are not ketogenic because they prevent your body from producing its own ketones. They’re also a source of calories, which, depending on how many servings you have, may not be worthwhile for weight loss.
Side Effects
Exogenous ketone supplements are generally considered to be a safe and effective way to increase ketone body concentrations, but the long-term effects are unknown (9).
Reported side effects are more common with ketone salts than ketone esters and include nausea, diarrhea and stomach discomfort (7, 17, 23).
Ketone supplements reportedly have a poor aftertaste as well (24).
Moreover, achieving ketosis with ketone salts is not recommended due to the high amounts of minerals you’d ingest (11).
One serving of ketone salts provides (22):
680 mg of sodium (27% of the DV)
320 mg magnesium (85% of the DV)
590 mg of calcium (57% of the DV)
However, to maintain ketosis, you’ll need to take a dose every two to three hours, doubling or tripling these numbers.
Manufacturers of ketone supplements recommend taking up to three servings per day.
But while ketone supplements can still help you maintain ketosis even after a meal, the rise in levels of blood ketones is much less than if you were in a fast or didn’t consume a carb-containing meal (15).
SUMMARY
The side effects associated with ketone supplements range from stomach discomfort to diarrhea. Because these supplements are also bound to salts, consuming too much is not recommended.