Exogenous ketones are a dietary supplement that people primarily use as a fat burner.

According to exogenous ketone advocates, taking exogenous ketone supplements puts you into a metabolic state where your body burns fat instead of carbohydrates for fuel. This, they say, boosts fat burning without you needing to follow a specialized diet.

Detractors argue that this is really just an attempt to profit on the upsurge in interest in the ketogenic diet, which is related but quite different than simply popping some exogenous ketones. 

Who should you believe? 

Can exogenous ketone supplements help you lose fat, or are they just another scam that should burn in the dumpster fire with most other fat loss supplements?

Learn the answer according to science in this article.

What Is Ketosis?

When you follow a regular diet, your body uses a combination of carbs and fat for fuel. This changes if you follow a low-carb diet such as the ketogenic diet, however, because your body has very few carbs to work with and thus depends almost entirely on fat for energy.

As your body breaks down fat, it produces ketone bodies, which are metabolites your body uses as an energy source. Although your body normally produces ketone bodies in small amounts, production increases as you rely more heavily on fat for fuel. And once ketones build up in your bloodstream, you enter a state called ketosis.

The three main ketone bodies that your body produces during ketosis are acetoacetate (AcAc), beta-hydroxybutyrate (BHB), and propanone (also known as acetone).

What Are Exogenous Ketones?

While you produce ketones endogenously (within the body), scientists can also synthesize them exogenously (outside the body).

Thus, exogenous ketones are simply ketones that have been manufactured that you consume as dietary supplements.

Exogenous ketone supplements primarily come in two forms:

  • Ketone salts, which are a powdered form of ketones that you mix with water. Supplement companies typically market ketone salts as exogenous ketones powder.
  • Ketone esters, which are a liquid form of ketones commonly sold as exogenous ketones drinks.

Do Exogenous Ketones Work?

The main reason people use exogenous ketone supplements is to induce ketosis without following a low-carb diet. They believe this boosts fat burning and athletic performance. 

Let’s look at what science says about each of these claims separately.

Exogenous Ketones and Fat Burning

Studies show that exogenous ketones mimic ketosis by increasing blood ketone levels and some research suggests that they raise the resting energy expenditure of obese mice and human cells in a test tube. However, it’s not clear whether this has any effect on body composition in living humans.

For instance, in one study conducted by scientists at Ohio State University, researchers put 28 obese men and women on a ketogenic diet that resulted in a 25% calorie deficit. During the study, half of the dieters took an exogenous ketone supplement and the other half took a placebo. 

After 6 weeks, both groups lost the same amount of fat and muscle, suggesting exogenous ketones don’t increase fat burning or help you preserve muscle while following a keto diet.

In another 90-day study published in the scientific journal Nutrients, researchers found that healthy adolescents who took a daily exogenous ketone supplement experienced no change in body composition during the study.

Despite these uninspiring results, one way that exogenous ketones may support weight loss is by suppressing your appetite

For example, one small study published in Obesity (Silver Spring) showed that people felt ~50% less hungry for 1.5-to-4 hours after they consumed an exogenous ketones drink. The researchers believed that this was most likely because exogenous ketones increase blood ketone levels and lower ghrelin, a hormone that stimulates your appetite. 

Bear in mind, though, that if the researchers are correct, exogenous ketones are unlikely to abate hunger if you’ve recently consumed food containing carbs. That’s because eating carb-rich food prevents exogenous ketones from raising blood ketone levels as high, which would lessen their ability to quell hunger.

Another reason people take exogenous ketones is to accelerate the onset of ketosis and diminish the fatigue that occurs as your brain transitions from primarily burning carbs to burning ketones instead (known as “keto flu”).

Unfortunately, there’s little evidence that they help in this regard.

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Exogenous Ketones and Athletic Performance

Many supplement companies claim exogenous ketones boost your endurance by allowing you to use your vast fat stores for fuel instead of your comparatively small carb stores and lowering blood lactate levels so you can exercise for longer without fatiguing. 

Some also claim exogenous ketones reduce inflammation, boost cognitive function, prevent muscle breakdown, and increase protein synthesis, all of which can aid performance and recovery.

While these claims sound compelling, three extensive reviews concluded that there’s no clear evidence that exogenous ketones improve athletic performance, and they may even reduce it if you experience negative side effects . . . 

Exogenous Ketones: Side Effects

Despite some research showing that exogenous ketones are safe and well-tolerated, several other studies show that taking exogenous ketone supplements can cause nausea, abdominal cramps, vomiting, dizziness, and diarrhea.

There’s currently a lack of research on the dangers of exogenous ketone supplements over the long term. That said, some researchers believe that maintaining high ketone levels may increase oxidative stress and inflammation, leading to brain, kidney, liver, and cardiovascular issues.

FAQ #1: What’s the best exogenous ketones supplement?

There’s little scientific evidence that exogenous ketones help you lose fat or perform better. As such, I can’t recommend any exogenous ketones supplements, let alone say which is best.

If you want fat loss supplements that are well-supported by peer-reviewed research, here’s what I recommend:

  • 3-to-6 mg of caffeine per kilogram of body weight per day. This will raise the number of calories you burn and also increases strength, muscle endurance, and anaerobic performance. If you want a clean, delicious source of caffeine that also contains five other ingredients that will boost your workout performance, try Pulse.
  • 0.1-to-0.2 milligrams of yohimbine per kilogram of body weight before fasted training. This increases fat loss when used in conjunction with fasted training, and is particularly helpful with losing “stubborn” fat. If you want a 100% natural source of yohimbine that also contains two other ingredients that will help you lose fat faster, preserve muscle, and maintain training intensity and mental sharpness, try Forge.
  • One serving of Phoenix per day. Phoenix is a 100% natural fat burner that speeds up your metabolism, enhances fat burning, and reduces hunger and cravings. You can also get Phoenix with caffeine or without.

Or if you’re interested in supplements that are proven to boost performance, check these out:

  • 0.8-to-1.2 grams of protein per pound of body weight per day. This provides your body with the “building blocks” it needs to build and repair muscle tissue and help you recover from your workouts. If you want a clean, convenient, and delicious source of protein, try Whey+ or Casein+.
  • 3-to-5 grams of creatine per day. This will boost muscle and strength gain, improve anaerobic endurance, and reduce muscle damage and soreness from your pull workouts. If you want a 100% natural source of creatine that also includes two other ingredients that will help boost muscle growth and improve recovery, try Recharge.
  • One serving of Pulse per day. Pulse is a 100% natural pre-workout drink that enhances energy, mood, and focus; increases strength and endurance; and reduces fatigue. You can also get Pulse with caffeine or without.

(And if you aren’t sure if the supplements discussed here are right for you or if other supplements might be a better fit for your budget, circumstances, and goals, then take the Legion Supplement Finder Quiz! In less than a minute, it’ll tell you exactly what supplements are right for you. Click here to check it out.)

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FAQ #2: Should I believe online exogenous ketones reviews?

Probably not.

There’s no evidence that ketone supplements boost fat burning or athletic performance. Anyone who writes a review stating otherwise is probably experiencing the placebo effect or has been paid by a supplement company to promote their product.

FAQ #3: How long do exogenous ketones stay in your system?

Evidence suggests that exogenous ketone supplements only exert their effects for a few hours, which means you have to take several doses of exogenous ketones throughout the day to stay in ketosis.

Keep in mind that exogenous ketones also only help you achieve ketosis if you’re already eating a very low-carb diet (generally less than ~50 grams of carbs per day). 

+ Scientific References